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Sheahan Diamond Literature Technical Reference Compilation 2016


The Sheahan Diamond Literature Reference Compilation
The Sheahan Diamond Literature Reference Compilation is compiled by Patricia Sheahan who publishes on a monthly basis a list of new scientific articles related to diamonds as well as media coverage and corporate announcementscalled the Sheahan Diamond Literature Service that is distributed as a free pdf to a list of followers. Pat has kindly agreed to allow her work to be made available as an online digital resource at Kaiser Research Online so that a broader community interested in diamonds and related geology can benefit. The references are for personal use information purposes only; when available a link is provided to an online location where the full article can be accessed or purchased directly. Reproduction of this compilation in part or in whole without permission from the Sheahan Diamond Literature Service is strictly prohibited. Return to Diamond Resource Center
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
A B-Bq Br+ C D E F G-Gq Gr+ H I J K-Km Kn+ L M-Md Me+ N O P Q R S-Sg Sh+ T U V W X Y Z
Sheahan Diamond Literature Reference Compilation - Media/Corporate References by Name for all years
A B C D-Di Di+ E F G H I J K L M N O P Q R S T U V W X Y Z
Tips for Users
Posted/Published Reference CodesThe SDLRC provides 3 types of references identified in the reference code. DS for scientific article, DM for a media article, and DC for a corporate announcement. Consider DS0512-0001. The DS stands for "diamond scientific". 05 stands for 2005, the year the reference was posted. 12 represents the month the reference was posted. For all years prior to 2015 the default month is 12. -0001 is the reference's identifier and it does not mean anything. The number below the refence code, ie 2015, is the year the article was published. Note that the posted year may sometimes be later than the published year.
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Monthly Sheahan Diamond Newsletters for 2016
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February 2016 June 2016 October 2016
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April 2016 August 2016 December 2016
2016 Technical Reference Compilation
Posted/
Published
AuthorTitleSourceRegionKeywords
DS1610-1838
2016
Abersteiner, A., Giuliani, A., Kamenetsky, V.S., Phillips, D.Petrographic and melt inclusion constraints on the petrogenesis of a magmaclast from the Venetia kimberlite cluster, South Africa.Chemical Geology, in press available 11p.Africa, South AfricaDeposit - Venetia

Abstract: Kimberlitic magmaclasts are discrete ovoid magmatic fragments that formed prior to emplacement from disrupted kimberlite magma. To provide new constraints on the origin and evolution of the kimberlite melts, we document the mineralogy and petrography of a magmaclast recovered from one of the ca. 520 Ma Venetia kimberlites, South Africa. The sample (BI9883) has a sub-spherical shape and consists of a ~ 10 mm diameter central olivine macrocryst, surrounded by porphyritic kimberlite. The kimberlitic material consists of concentrically aligned, altered olivine phenocrysts, set in a crystalline groundmass of calcite, chromite, perovskite, phlogopite, apatite, ilmenite, titanite, sulphides, rutile and magnetite along with abundant alteration phases (i.e. serpentine, talc and secondary calcite). These features are typical of archetypal hypabyssal kimberlites. We examined primary fluid/melt inclusions in chromite, perovskite and apatite containing a diversity of daughter phases. Chromite and perovskite host polycrystalline inclusions containing abundant alkali-carbonates (i.e. enriched in K, Na, Ba, Sr), phosphates, Na-K chlorides, sulphides and equal to lesser quantities of olivine, phlogopite and pleonaste. In contrast, apatite hosts polycrystalline assemblages with abundant alkali-carbonates and Na-K chlorides and lesser amounts of olivine, monticellite and phlogopite. Numerous solid inclusions of shortite (Na2Ca2(CO3)3), Na-Sr-carbonates and apatite occur in groundmass calcite along with fluid inclusions containing daughter crystals of Na-carbonates and Na-chlorides. The primary inclusions in chromite, perovskite and apatite are considered to represent remnants of fluid(s)/melt(s) trapped during crystallisation of the host minerals, whereas the fluid inclusions in calcite are probably secondary in origin. The component proportions of these primary fluid/melt inclusions were estimated in an effort to constrain the composition of the evolving kimberlite melt. These estimates suggest melt evolution from a silicate-carbonate kimberlite melt that became increasingly enriched in carbonates, phosphates, alkalis and chlorides, in response to the fractional crystallisation of constituent minerals (i.e. olivine to apatite). The concentric alignment of crystals around the olivine kernel and ovoid shape of the magmaclast can be ascribed to the low viscosity of the kimberlite melt and rapid rotation whilst in a liquid or partial crystalline state, or to progressive layer-by-layer growth of the magmaclast. Although the mineralogy of our sample is similar to hypabyssal kimberlites worldwide, it differs from hypabyssal kimberlite units in the main Venetia pipes, which contain monticellite-phlogopite rich assemblages and segregationary matrix textures. Therefore magmaclast BI9883 probably originated from a batch of magma distinct from those that produced known hypabyssal units within the Venetia kimberlite cluster.-
DS1606-1076
2016
Ackerman, L., Bizimis, M., Haluzova, E., Slama, J., Svojtka, M.Re-Os and Lu-Hf isotopic constraints on the formation and age of mantle pyroxenites from the Bohemian Massif.Lithos, Vol. 256-257, pp. 197-210.Europe, Czech Republic, AustriaPyroxenite

Abstract: We report on the Lu-Hf and Re-Os isotope systematics of a well-characterized suite of spinel and garnet pyroxenites from the Gföhl Unit of the Bohemian Massif (Czech Republic, Austria). Lu-Hf mineral isochrons of three pyroxenites yield undistinguishable values in the range of 336-338 Ma. Similarly, the slope of Re-Os regression for most samples yields an age of 327 ± 31 Ma. These values overlap previously reported Sm-Nd ages on pyroxenites, eclogites and associated peridotites from the Gföhl Unit, suggesting contemporaneous evolution of all these HT-HP rocks. The whole-rock Hf isotopic compositions are highly variable with initial eHf values ranging from - 6.4 to + 66. Most samples show a negative correlation between bulk rock Sm/Hf and eHf and, when taking into account other characteristics (e.g., high 87Sr/86Sr), this may be explained by the presence of recycled oceanic sediments in the source of the pyroxenite parental melts. A pyroxenite from Horní Kounice has decoupled Hf-Nd systematics with highly radiogenic initial eHf of + 66 for a given eNd of + 7.8. This decoupling is consistent with the presence of a melt derived from a depleted mantle component with high Lu/Hf. Finally, one sample from Becváry plots close to the MORB field in Hf-Nd isotope space consistent with its previously proposed origin as metamorphosed oceanic gabbro. Some of the websterites and thin-layered pyroxenites have variable, but high Os concentrations paralleled by low initial ?Os. This reflects the interaction of the parental pyroxenitic melts with a depleted peridotite wall rock. In turn, the radiogenic Os isotope compositions observed in most pyroxenite samples is best explained by mixing between unradiogenic Os derived from peridotites and a low-Os sedimentary precursor with highly radiogenic 187Os/188Os. Steep increase of 187Os/188Os at nearly uniform 187Re/188Os found in a few pyroxenites may be connected with the absence of primary sulfides, but the presence of minor late stage sulfide-bearing veinlets likely associated with HT-HP metamorphism at crustal conditions.
DS1605-0808
2016
Adam, J., Turner, M., Hauri, E.H., Turner, S.Crystal/melt partitioning of water and other volatiles during the near-solidus melting of mantle peridotite: comparisons with non-volatile incompatible elements and implications for the generation of intraplate magmatism.American Mineralogist, Vol. 101, pp. 876-888.MantleMagmatism - basanite, melting

Abstract: Concentrations of H2O, F, Cl, C, P, and S have been measured by secondary ion mass spectrometry (SIMS) in experimentally produced peridotite phases (including clinopyroxene, orthopyroxene, olivine, garnet, amphibole, and mica) and coexisting basanitic glasses. Because only two experiments produced glasses on quenching (with the melt phase in others reverting to felt-like crystallite masses) H2O concentrations in melts were also separately determined from mass-balance relationships and by assuming constant H2O/La in melts and starting materials. The resulting values were used to calculate mineral/melt partition coefficients (D values) for H2O [where DH2Ocrystal/melt = (mass fraction of H2O in crystal)/(mass fraction of H2O in melt)] for conditions of 1025-1190 °C and 1.0-3.5 GPa. These gave 0.0064-0.0164 for clinopyroxene, 0.0046-0.0142 for orthopyroxene, 0.0015-0.0016 for olivine, and 0.0016-0.0022 for garnet. Although less information was obtained for the other volatiles, F was found to be significantly more compatible than H2O during peridotite melting, whereas Cl is significantly less compatible. S also has small but appreciable solubilities in amphiboles and micas, but not in pyroxenes or olivine. The solubility of C in silicate minerals appears to be negligible, although C was present in coexisting melts (~0.5 wt% as CO2) and as residual graphite during experiments. The D values for H2O in clinopyroxene and orthopyroxene are positively correlated with ivAl but negatively correlated with the H2O concentrations of melts (when considered as wt%). These relationships are consistent with the broad trends of previously published partitioning data. Although some of the concentration dependence can be related to cross-correlation between ivAl in pyroxenes and H2O concentrations in melts (via the latter’s control of liquidus temperatures) this relationship is too inconsistent to be a complete explanation. A concentration dependence for DH2Omineral/melt can also be independently predicted from speciation models for H2O in silicate melts. Thus it is likely that DH2Opyx/melt is influenced by both ivAl and the absolute concentration of H2O in melts. DH2O/DCe for clinopyroxene is inversely correlated with M2 site radii. Because the latter decrease with increasing pressure and temperature, relatively hot and/or deeply derived melts should be enriched in Ce relative to H2O when compared to melts from cooler and shallower mantle sources. Conversely, melts from H2O-rich settings (e.g., subduction zones) should have higher H2O/Ce than their source rocks. When combined with previously obtained partitioning data for non-volatile elements (from the same experiments), our data are consistent with the enrichment of intraplate basalt sources in both volatile and non-volatile incompatible elements by small-degree melts derived from local mid-ocean ridge basalt sources. In this way, volatiles can be seen to play an active role (via their promotion of partial-melting and metasomatic processes) in the auto-regulation of incompatible element concentrations in the depleted upper mantle.
DS1612-2272
2016
Afanasev, A., Belyaeva, E.Linear stability analysis for hydrothermal alteration of kimberlitic rocks.Geophysical Journal International, Vol. 205, 3, pp. 1874-1885.TechnologyAlteration

Abstract: The influx of groundwater into hot kimberlite deposits results in the reaction of water with olivine-rich rocks. The products of the reaction are serpentine and release of latent heat. The rise of temperature due to the heat release increases the rate of the reaction. Under certain conditions, this self-speeding up of the reaction can result in instabilities associated with a significantly higher final serpentinisation in slightly warmer regions of the kimberlite deposit. We conduct linear stability analysis of serpentinisation in an isolated volume of porous kimberlitic rocks saturated with water and an inert gas. There is a counteracting interplay between the heat release tending to destabilise the uniform distribution of parameters and the heat conduction tending to stabilise it by smoothing out temperature perturbations. We determine the critical spatial scale separating the parameters where one phenomenon dominates over another. The perturbations of longer-than-critical length grow, whereas the perturbations of shorter-than-critical length fade. The analytical results of the linear stability analysis are supported by direct numerical simulations using a full nonlinear model.
DS1604-0589
2016
Agrosi, G., Nestola, F., Tempestra, G., Bruno, M., Scandale, E., Harris, J.X-ray topographic study of a diamond from Udachnaya: implications for the genetic nature of inclusions.Lithos, Vol. 248-251, pp. 153-159.RussiaDeposit - Udachnaya

Abstract: In recent years, several studies have focused on the growth conditions of the diamonds through the analysis of the mineral inclusions trapped in them. In these studies, it is crucial to distinguish between protogenetic, syngenetic and epigenetic inclusions. X-ray topography (XRDT) can be a helpful tool to verify, in a non-destructive way, the genetic nature of inclusions in diamond. With this aim, a diamond from the Udachnaya kimberlite, Siberia, was investigated. The diamond, previously studied by Nestola et al. (2011), has anomalous birefringence and the two largest olivines have typical “diamond-imposed” shapes. The study of the topographic images shows that the diamond exhibits significant deformation fields related to post growth plastic deformation. The absence of dislocations starting from the olivine inclusions, and the dark contrasts around them represent the main results obtained by XRDT, contributing to the elucidation of the relationships between the diamond and the olivines at the micron-meter scale. The dark halo surrounding the inclusions was likely caused by the effect of different thermo-elastic properties between the diamond and the inclusions. The absence of dislocations indicates that the diamond-imposed morphology did not produce the volume distortion commonly associated with the entrapment of the full-grown inclusions and, thus, only based on such evidence, a syngenetic origin could be proposed. In addition, stepped figures optically observed at the interface between diamond and one of the olivines suggest processes of selective partial dissolution that would contribute to a change in the final morphology of inclusions. These results show that a diamond morphology may be imposed to a full-grown (protogenetic) olivine during their encapsulation, suggesting that the bulk of the inclusion is protogenetic, whereas its more external regions, close to the diamond-inclusion interface, could be syngenetic.
DS1602-0187
2015
Agrusta, R., Tommasi, A., Arcay, D., Gonzalez, A., Gerya, T.How partial melting affects small-scale convection in a plume-fed sublithospheric layer beneath fast-moving plates.Geochemistry, Geophysics, Geosystems: G3, Vol. 16, 11, Nov. pp. 3924-3945.MantleConvection

Abstract: Numerical models show that small-scale convection (SSC) occurring atop a mantle plume is a plausible mechanism to rejuvenate the lithosphere. The triggering of SSC depends on the density contrast and on the rheology of the unstable layer underlying the stagnant upper part of the thermal boundary layer (TBL). Partial melting may change both properties. We analyze, using 2-D numerical simulations, how partial melting influences the dynamics of time-dependent SSC instabilities and the resulting thermo-mechanical rejuvenation of an oceanic plate moving atop of a plume. Our simulations show a complex behavior, with acceleration, no change, or delay of the SSC onset, due to competing effects of the latent heat of partial melting, which cools the plume material, and of the buoyancy increase associated with both melt retention and depletion of residue following melt extraction. The melt-induced viscosity reduction is too localized to affect significantly SSC dynamics. Faster SSC triggering is promoted for low melting degrees (low plume temperature anomalies, thick lithosphere, or fast moving plates), which limit both the temperature reduction due to latent heat of melting and the accumulation of depleted buoyant residue in the upper part of the unstable layer. In contrast, high partial melting degrees lead to a strong temperate decrease due to latent heat of melting and development of a thick depleted layer within the sublithospheric convecting layer, which delay the development of gravitational instabilities. Despite differences in SSC dynamics, the thinning of the lithosphere is not significantly enhanced relatively to simulations that neglect partial melting.
DS1601-0001
2016
Ahmed, A.H., Moghazi, A.K.D., Moufti, M.R., Dawood, Y.H., Ali, K.A.Nature of the lithospheric mantle beneath the Arabian shield and genesis of Al-spinel micropods: evidence from the mantle xenoliths of Harrat Kishb, western Saudi Arabia.Lithos, Vol. 240-243, pp. 119-139.Africa, Saudi ArabiaPeridotite

Abstract: The Harrat Kishb area of western Saudi Arabia is part of the Cenozoic volcanic fields in the western margin of the Arabian Shield. Numerous fresh ultramafic xenoliths are entrained in the basanite lava of Harrat Kishb, providing an opportunity to study the nature and petrogenetic processes involved in the evolution of the lithospheric mantle beneath the Arabian Shield. Based on the petrological characteristics and mineralogical compositions, the majority of the mantle xenoliths (~ 92%) are peridotites (lherzolites and pyroxene-bearing harzburgites); the remaining xenoliths (~ 8%) are unusual spinel-rich wehrlites containing black Al-spinel micropods. The two types of mantle xenoliths display magmatic protogranular texture. The peridotite xenoliths have high bulk-rock Mg#, high forsterite (Fo90-Fo92) and NiO (0.24-0.46 wt.%) contents of olivine, high clinopyroxene Mg# (0.91-0.93), variable spinel Cr# (0.10-0.49, atomic ratio), and approximately flat chondrite-normalized REE patterns. These features indicate that the peridotite xenoliths represent residues after variable degrees of melt extraction from fertile mantle. The estimated P (9-16 kbar) and T (877-1227 °C) as well as the oxidation state (?logfO2 = - 3.38 to - 0.22) under which these peridotite xenoliths originated are consistent with formation conditions similar to most sub-arc abyssal-type peridotites worldwide. The spinel-rich wehrlite xenoliths have an unusual amount (~ 30 vol.%) of Al-spinel as peculiar micropods with very minor Cr2O3 content (< 1 wt.%). Olivines of the spinel-rich wehrlites have low-average Fo (Fo81) and NiO (0.18 wt.%) contents, low-average cpx Mg# (0.79), high average cpx Al2O3 content (8.46 wt.%), and very low-average spinel Cr# (0.01). These features characterize early mantle cumulates from a picritic melt fraction produced by low degrees of partial melting of a garnet-bearing mantle source. The relatively high Na2O and Al2O3 contents of cpx suggest that the spinel-rich wehrlites are formed under high P (11-14 kbar), T (1090-1130 °C), and oxidation state (?logfO2 FMQ = + 0.14 to + 0.37), which occurred slightly below the crust-mantle boundary. The REE patterns of spinel-rich wehrlites are almost similar to those of the associated peridotite xenoliths, which confirm at least a spatial genetic linkage between them. Regarding the formation of Al-spinel micropods in spinel-rich wehrlite cumulates, it is suggested that the melt-rock reaction mechanism is not the only process by which podiform chromitite is formed. Early fractionation of picritic melts produced by partial melting of a mantle source under high P-T conditions could be another mechanism. The cpx composition, not opx, as it was assumed, seems to be the main control of the size and composition of spinel concentrations.
DS1604-0590
2015
Alexakhin, V.Yu., Bystritsky, V.M., Zamyatin, N.I., Zubarev, E.V., Krasnoperov, A.V., Rapatsky, V.L., Rogov, Yu.N., Sadovsky, A.B., Salamatin, A.V., Salmin, R.A., Sapozhnikov, M.G., Slepnev, V.M., Khabarov, S.V., Razinkov,E.A., Tarasov, O.G., Nikitin,G.M.Detection of diamonds in kimberlite by the tagged neutron method.Nuclear Instruments and Methods in Physics Research Section A., A785, pp. 9-13.TechnologyMethodology

Abstract: A new technology for diamond detection in kimberlite based on the tagged neutron method is proposed. The results of experimental researches on irradiation of kimberlite samples with 14.1-MeV tagged neutrons are discussed. The source of the tagged neutron flux is a portable neutron generator with a built-in 64-pixel silicon alpha-detector with double-sided stripped readout. Characteristic gamma rays resulting from inelastic neutron scattering on nuclei of elements included in the composition of kimberlite are registered by six gamma-detectors based on BGO crystals. The criterion for diamond presence in kimberlite is an increased carbon concentration within a certain volume of the kimberlite sample.
DS1603-0363
2016
Alexeev, S.V., Alexeeva, L.P., Kononov, A.M.Trace elements and rare earth elements in ground ice in kimberlites and sedimentary rocks of western Yakutia.Cold Regions Science and Technology, Vol. 123, pp. 140-148.RussiaGeomorphology

Abstract: The paper presents unique results of studying the composition of the ground ice (major components, trace elements, and rare earth elements — REEs) encountered at a depth of 200-250 m in sedimentary and magmatic rocks in the Western Yakutia diamond-bearing regions. In addition to those established earlier, three new geochemical types of ground ice have been defined: (i) sulfate-hydrocarbonate, (ii) chloride-hydrocarbonate, and (iii) sulfate-chloride types with mixed cation composition. The ground ice geochemical features are caused by evolutionary processes of interaction in the water-rock system during permafrost formation. The enclosed rocks were the source for the addition of sulfate and chlorine ions, as well as trace elements, to the ground waters of the active water exchange zone that had existed before freezing. The distribution pattern of REEs in ground ice has a special form distinct from that of sedimentary rocks, kimberlites, and ocean waters, but similar to the REE pattern in local river waters. This REE pattern features the positive europium (Eu) anomaly and approximate equality of light and heavy REEs. The obtained results essentially expand the insight into ice-formation processes in sedimentary and magmatic rocks.
DS1612-2273
2016
Alexeev, S.V., Alexeeva, L.P., Kononov, A.M.Trace elements and rare earth elements in ground ice in kimberlites and sedimentary rocks of western Yakutia.Cold Regions Science and Technology, Vol. 123, pp. 140-148.Russia, YakutiaGeomorphology

Abstract: The paper presents unique results of studying the composition of the ground ice (major components, trace elements, and rare earth elements - REEs) encountered at a depth of 200-250 m in sedimentary and magmatic rocks in the Western Yakutia diamond-bearing regions. In addition to those established earlier, three new geochemical types of ground ice have been defined: (i) sulfate-hydrocarbonate, (ii) chloride-hydrocarbonate, and (iii) sulfate-chloride types with mixed cation composition. The ground ice geochemical features are caused by evolutionary processes of interaction in the water-rock system during permafrost formation. The enclosed rocks were the source for the addition of sulfate and chlorine ions, as well as trace elements, to the ground waters of the active water exchange zone that had existed before freezing. The distribution pattern of REEs in ground ice has a special form distinct from that of sedimentary rocks, kimberlites, and ocean waters, but similar to the REE pattern in local river waters. This REE pattern features the positive europium (Eu) anomaly and approximate equality of light and heavy REEs. The obtained results essentially expand the insight into ice-formation processes in sedimentary and magmatic rocks.
DS1607-1325
2016
Ananda Reddy, R.Geophysical signatures over concealed kimberlite pipes from South Indian diamond province.IGC 35th., Session A Dynamic Earth 1p. AbstractIndiaGeophysics
DS1608-1388
2016
Andersen, A.K., Clar, J.G., Larson, P.B., Neill, O.K.Mineral chemistry and petrogenesis of a HFSE(+HREE) occurrence, peripheral to carbonatites of the Bear Lodge alkaline complex, Wyoming.American Mineralogist, Vol. 101, pp. 1604-1623.United States, Wyoming, Colorado PlateauBear Lodge

Abstract: Rare earth mineralization in the Bear Lodge alkaline complex (BLAC) is mainly associated with an anastomosing network of carbonatite dikes and veins, and their oxidized equivalents. Bear Lodge carbonatites are LREE-dominant, with some peripheral zones enriched in HREEs. We describe the unique chemistry and mineralogy one such peripheral zone, the Cole HFSE(+HREE) Occurrence (CHO), located ~2 km from the main carbonatite intrusions. The CHO consists of anatase, xenotime-(Y), brockite, fluorite, zircon, and K-feldspar, and contains up to 44.88% TiO2, 3.12% Nb2O5, 6.52% Y2O3, 0.80% Dy2O3, 2.63% ThO2, 6.0% P2O5, and 3.73% F. Electron microprobe analyses of xenotime-(Y) overgrowths on zircon show that oscillatory zoning is a result of variable Th and Ca content. Cheralite-type substitution, whereby Th and Ca are incorporated at the expense of REEs, is predominant over the more commonly observed thorite-type substitution in xenotime-(Y). Th/Ca-rich domains are highly beam sensitive and accompanied by high-F concentrations and low-microprobe oxide totals, suggesting cheralite-type substitution is more easily accommodated in fluorinated and hydrated/hydroxylated xenotime-(Y). Analyses of xenotime-(Y) and brockite show evidence of Embedded Image substitution for Embedded Image with patches of an undefined Ca-Th-Y-Ln phosphovanadate solid-solution composition within brockite clusters. Fluorite from the CHO is HREE-enriched with an average Y/Ho ratio of 33.2, while other generations of fluorite throughout the BLAC are LREE-enriched with Y/Ho ratios of 58.6-102.5. HFSE(+HREE) mineralization occurs at the interface between alkaline silicate intrusions and the first outward occurrence of calcareous Paleozoic sedimentary rocks, which may be local sources of P, Ti, V, Zr, and Y. U-Pb zircon ages determined by LA-ICP-MS reveal two definitive 207Pb/206Pb populations at 2.60-2.75 and 1.83-1.88 Ga, consistent with derivation from adjacent sandstones and Archean granite. Therefore, Zr and Hf are concentrated by a physical process independent of the Ti/Nb-enriched fluid composition responsible for anatase crystallization. The CHO exemplifies the extreme fluid compositions possible after protracted LREE-rich crystal fractionation and subsequent fluid exsolution in carbonatite-fluid systems. We suggest that the anatase+xenotime-(Y)+brockite+fluorite assemblage precipitated from highly fractionated, low-temperature (<200 °C), F-rich fluids temporally related to carbonatite emplacement, but after significant fractionation of ancylite and Ca-REE fluorocarbonates. Low-temperature aqueous conditions are supported by the presence of fine-grained anatase as the sole Ti-oxide mineral, concentrically banded botryoidal fluorite textures, and presumed hydration of phosphate minerals. Fluid interaction with Ca-rich lithologies is known to initiate fluorite crystallization which may cause destabilization of (HREE,Ti,Nb)-fluoride complexes and precipitation of REE+Th phosphates and Nb-anatase, a model valuable to the exploration for economic concentrations of HREEs, Ti, and Nb.
DS1610-1839
2016
Andersen, T., Elburg, M., Erambert, M.The miaskitic to agpaitic transition in peralkaline nepheline syenite ( white foyaite) from the Pilanesberg Complex, South Africa.Chemical Geology, in press available 16p.Africa, South AfricaPeralkaline rocks

Abstract: The Mesoproterozoic Pilanesberg Complex, South Africa, is built up by several distinct, ring-shaped intrusions of syenite and peralkaline nepheline syenite. A mildly peralkaline ((Na + K) / Al = 1.04–1.09), medium-to coarse grained nepheline syenite makes up the outermost ring in the southwestern part of the complex (“Matooster type white foyaite”). In this rock, mafic silicate minerals (amphibole, biotite, aegirine) and Ti-bearing minerals (ilmenite, astrophyllite, aenigmatite, lorenzenite, bafertisite, jinshajiangite) are interstitial to feldspar and nepheline, and define a series of mineral assemblages reflecting a change from a miaskitic crystallization regime (with Na-Ca amphibole, titanite and ilmenite) to increasingly agpaitic conditions (with arfvedsonite, aegirine, astrophyllite, aenigmatite, lorenzenite). The main driving force behind the evolution was an increase in peralkalinity of the trapped liquid, mainly by adcumulus growth of alkali feldspar and nepheline, which in the later stages of evolution was combined with increases in oxygen fugacity and water activity. Unlike in most other agpaitic rock complexes, Zr remained compatible in aegirine (and to some extent in amphibole) almost to the end of the process, when a hydrous zirconium silicate mineral (hilairite) crystallized as the only mineral in the rock having essential zirconium. The presence of minerals such as hilairite, bafertisite, jinshajiangite and a Na-REE-Sr rich apatite group mineral (fluorcaphite ?) in the latest assemblages suggests that the last remaining interstitial melt or fluid approached a hyperagpaitic composition. The isolated melt pockets in the Pilanesberg white foyaite follow a pattern of evolution that can be seen as a miniature analogue of the fractional crystallization processes controlling magma evolution in large, alkaline igneous rock complexes.-
DS1609-1697
2016
Andersen, T., Kristoffersen, M., Elburg, M.A.How far can we trust provenance and crustal evolution information from detrital zircons? A South African case study.Gondwana Research, Vol. 34, pp. 129-148.Africa, South AfricaGeochronology

Abstract: U-Pb and Lu-Hf data are routinely used to trace detrital zircon in clastic sediments to their original source in crystalline bedrock (the protosource), to map out paths of sediment transport, and characterize large-scale processes of crustal evolution. For such data to have a provenance significance, a simple transport route from the protosource in which the zircon formed to its final site of deposition is needed. However, detrital zircon data from Phanerozoic sedimentary cover sequences in South Africa suggest that this “source to sink” relationship has been obscured by repeated events of sedimentary recycling. Phanerozoic sandstones (Cape Supergroup, Karoo Supergroup, Natal Group, Msikaba Formation) and unconsolidated, Cenozoic sands in South Africa share major detrital zircon fractions of late Mesoproterozoic (940-1120 Ma, eHf ˜ 0 to + 15) and Neoproterozoic age (470-720 Ma, eHf ˜ - 10 to + 8). A Permian age fraction (240-280 Ma, eHf ˜ - 8 to + 5) is prominent in sandstones from the upper part of the Karoo Supergroup. All of these sequences are dominated by material derived by recycling of older sedimentary rocks, and only the youngest, late Palaeozoic fraction has a clear provenance significance (Gondwanide orogen). The virtual absence of Archaean zircon is a striking feature in nearly all suites of detrital zircon studied in the region. This indicates that significant events in the crustal evolution history of southern African and western Gondwana are not represented in the detrital zircon record. South Africa provides us with a record of recycling of cover sequences throughout the Phanerozoic, and probably back into the Neoproterozoic, in which the “sink” of one sedimentary cycle will act as the “source” in subsequent cycles. In such a setting, detrital zircon may give information on sedimentary processes rather than on provenance.
DS1603-0364
2011
Andrade, K.W., de Sa Carneiro Chaves, M.L.Geologia e mineralogia do kimberlito Grota do Cedro ( Coromandel, MG).Geonomos *** IN POR, Vol. 19, 1, pp. 39-45. *** In PortugueseSouth America, BrazilDeposit - Coromandel area

Abstract: Hundreds of kimberlite intrusions and related rocks are known in the Coromandel region (MG), in the "Alto Paranaiba Diamondiferous Province", although the knowledge of these rocks is still scarce. Among these intrusions, it emphasizes the Grota do Cedro kimberlite, which outcrops in the drainage of same name at south of Coromandel (MG), hosted in micaschists of the Araxá Group (Neoproterozoic). The body has a roughly elliptical surface shape with 350 and 300 m axis; its chemical composition is similar to others of the province, and mineral chemistry of Cr-pyrope shows a strong concentration in the "G9" and "G5" fields. These chemical fields generally characterize diamond-poor or infertile intrusions.
DS1607-1326
2016
Andriampenomanana, F.Crust and uppermost mantle structure of Madagascar.IGC 35th., Session The Deep Earth 1 p. abstractAfrica, MadagascarGeophysics - seismics
DS1611-2095
2016
Anzolini, C., Angel, R.J., Merlini, M., Derzsi, M., Tokar, K., Milani, S., Krebs, M.Y., Brenker, F.E., Nestola, F., Harris, J.W.Depth of formation of CaSi)3 - walstromite included in super -deep diamonds.Lithos, in press available 43p.South America, Brazil, Mato GrossoDeposit - Juina

Abstract: "Super-deep" diamonds are thought to crystallize between 300 and 800 km depth because some of the inclusions trapped within them are considered to be the products of retrograde transformation from lower mantle or transition zone precursors. In particular, single inclusion CaSiO3-walstromite is believed to derive from CaSiO3-perovskite, although its real depth of origin has never been proven. Our aim is therefore to determine for the first time the pressure of formation of the diamond-CaSiO3-walstromite pair by “single-inclusion elastic barometry” and to determine whether CaSiO3-walstromite derives from CaSiO3-perovskite or not. We investigated several single phases and assemblages of Ca-silicate inclusions still trapped in a diamond coming from Juina (Brazil) by in-situ analyses (single-crystal X-ray diffraction and micro-Raman spectroscopy) and we obtained a minimum entrapment pressure of ~ 5.7 GPa (~ 180 km) at 1500 K. However, the observed coexistence of CaSiO3-walstromite, larnite (ß-Ca2SiO4) and CaSi2O5-titanite in one multiphase inclusion within the same diamond indicates that the sample investigated is sub-lithospheric with entrapment pressure between ~ 9.5 and ~ 11.5 GPa at 1500 K, based on experimentally-determined phase equilibria. In addition, thermodynamic calculations suggested that, within a diamond, single inclusions of CaSiO3-walstromite cannot derive from CaSiO3-perovskite, unless the diamond around the inclusion expands by ~ 30% in volume.
DS1611-2096
2016
Arai, S., Miura, M.Formation and modification of chromitites in the mantle.Lithos, Vol. 264, pp. 277-295.MantlePodiform, UHP, melt

Abstract: Chromitites (aggregates of chromite or chromian spinel) inform us of various mantle processes, including magmatism, magma/peridotite reaction and mantle dynamics [1]. They typically form as magmatic cumulates from chromiteoversaturated melt within conduits in the mantle peridotite [2]. They are usually enveloped by replacive dunite [1]. In Oman, both concordant and discordant chromitites are of low-P (upper mantle) magmatic origin [3, 4]. Their chromite grains contain inclusions of pargasite, aspidolite and pyroxenes, which suggest low P. Mineral chemistry suggests involvement of MORB for the concordant chromitite, and of arc-related magma for the discrodant one. This is consistent with the switch of tectonic setting, from MOR to SSZ, for the Oman ophiolite magmatism. Only the concordant chromitite shows metamorphic characters, i.e. exsolution of diopside in chromite and outward diffusion of Ni (< 30 cm) in the dunite envelope [5], indicating its longer residence in the mantle. Ultra-high pressure (UHP) chromitites have been reported from the Tibetan and Polar Ural ophiolites [6, 7]. Most of their petrographic characteristics can be explained by UHP "metamorphism" of low-P magmatic chromitites above [8]. This may suggest recycling of low-P chromitite as deep as the transion-zone mantle [9]. The UHP chromitite is, however, still highly enigmatic: some characteristics, e.g., the amount and origin of carbon as diamond, are difficult to explain. High-T aqueous fluids containing Cl, S and C, can mobilize Cr and precipitate chromite in the mantle [10]. Chromite was dissolved and precipitated in/from high-T fluids which formed diopsidites in Oman. Chromite was concentrated to form thin "hydrothermal chromitite". Sub-arc metasomatized peridotites contain secondary chromite closely associated with fluid inclusions, indicating Cr mobility via fluids within the mantle wedge. Hydrothermal chromitites are expected in the mantle where fluid circulation is available.
DS1610-1840
2016
Aravanis, T., Chen, J., Fuechsle, M., Grujic, M., Johnston, P., Kok, Y., Magaraggia, R., Mann, A., Mann, L., McIntoshm S., Rheinberger, G., Saxey, D., Smalley, M., van Kann, F., Walker, G., Winterflood, J.VK1 tm - a next generation airborne gravity gradiometer.ASEG-PESA-AIG 2016 25th Geophysical Conference, Abstract 5p.TechnologyGradiometer

Abstract: The minerals exploration industry’s demand for a highly precise airborne gravity gradiometer has driven development of the VK1TM Airborne Gravity Gradiometer, a collaborative effort by Rio Tinto and the University of Western Australia. VK1TM aims to provide gravity gradient data with lower uncertainty and higher spatial resolution than current commercial systems. In the recent years of VK1TM development, there have been significant improvements in hardware, signal processing and data processing which have combined to result in a complete AGG system that is approaching competitive survey-ready status. This paper focuses on recent improvements. Milestone-achieving data from recent lab-based and moving-platform trials will be presented and discussed, along with details of some advanced data processing techniques that are required to make the most use of the data.
DS1608-1389
2016
Ardon, T., Eaton-Magana, S.High temperature annealing of hydrogen rich diamonds.GSA Annual Meeting, Abstract, Poster 1p.TechnologyType IIb diamonds

Abstract: This study gives an analysis of the effect of high temperature annealing on the infrared and photoluminescence (PL) features as well as the inclusions of two hydrogen-rich diamond plates from Zimbabwe that were cut from the same rough. The samples showed strong inclusion-related zoning known as hydrogen clouds which consist of micron-sized particles of as yet undetermined structure. This allowed hydrogen-rich and hydrogen-poor areas to be compared throughout the annealing study. The diamond plates were annealed to temperatures of 300oC, 600oC, 800oC, 1000oC, 1400oC, and 1700oC. The infrared and PL, and Raman maps were collected after every temperature step to study the effects of heat on the defects, and photomicrographs were collected to study the inclusions. Several photoluminescence features were seen to decrease in size including the 637 nm peak, which is the negatively charged nitrogen-vacancy center [NV-] and the 503.2 nm peak, known as the H3 and consists of two nitrogen atoms and vacancy in the neutral charge state and normally has a high thermal stability. The H2 defect at 986.2 nm, which is the negative form of the H3, was shown to increase after annealing. The hydrogen clouds underwent dramatic changes in apparent color and particle size, going from a light translucent gray appearance to an opaque black. The particle size grew from less than one micron to an average of fourteen microns, and the hexagonal outline of the particles became noticeable. Spatial raman spectroscopy was used to show that the color change and size change were due to graphitization of the included particles.
DS1610-1841
2016
Ardon, T., Eaton-Magana, S.High temperature annealing of hydrogen-rich diamonds.GSA Annual Meeting, 1/2p. AbstractAfrica, ZimbabwePhotoluminescence

Abstract: This study gives an analysis of the effect of high temperature annealing on the infrared and photoluminescence (PL) features as well as the inclusions of two hydrogen-rich diamond plates from Zimbabwe that were cut from the same rough. The samples showed strong inclusion-related zoning known as hydrogen clouds which consist of micron-sized particles of as yet undetermined structure. This allowed hydrogen-rich and hydrogen-poor areas to be compared throughout the annealing study. The diamond plates were annealed to temperatures of 300oC, 600oC, 800oC, 1000oC, 1400oC, and 1700oC. The infrared and PL, and Raman maps were collected after every temperature step to study the effects of heat on the defects, and photomicrographs were collected to study the inclusions. Several photoluminescence features were seen to decrease in size including the 637 nm peak, which is the negatively charged nitrogen-vacancy center [NV-] and the 503.2 nm peak, known as the H3 and consists of two nitrogen atoms and vacancy in the neutral charge state and normally has a high thermal stability. The H2 defect at 986.2 nm, which is the negative form of the H3, was shown to increase after annealing. The hydrogen clouds underwent dramatic changes in apparent color and particle size, going from a light translucent gray appearance to an opaque black. The particle size grew from less than one micron to an average of fourteen microns, and the hexagonal outline of the particles became noticeable. Spatial raman spectroscopy was used to show that the color change and size change were due to graphitization of the included particles.
DS1602-0188
2016
Armstrong, J.Karowe diamond mine: a world class source of exceptional diamonds.PDAC 2016, 1p. AbstractAfrica, BotswanaDeposit - Karowe
DS1607-1327
2016
Artemieva, I.Density structure of the cratonic mantle in southern Africa, kimberlite distribution, mantle velocities, MOHO sharpness, and dynamic topograhy.IGC 35th., Session A Dynamic Earth 1 p. abstractAfrica, South AfricaGeodynamics
DS1607-1328
2016
Artemieva, I.Density structure of the cratonic mantle in Siberia, correlations with mantle petrology and kimberlite distribution.IGC 35th., Session A Dynamic Earth 1p. AbstractRussiaKimberlite
DS1609-1698
2016
Artemieva, I.M., Thybo, H., Shulgin, A.Geophysical constraints on geodynamic processes at convergent margins: a global perspective.Gondwana Research, Vol. 33, pp. 4-23.MantleSubduction

Abstract: Convergent margins, being the boundaries between colliding lithospheric plates, form the most disastrous areas in the world due to intensive, strong seismicity and volcanism. We review global geophysical data in order to illustrate the effects of the plate tectonic processes at convergent margins on the crustal and upper mantle structure, seismicity, and geometry of subducting slab. We present global maps of free-air and Bouguer gravity anomalies, heat flow, seismicity, seismic Vs anomalies in the upper mantle, and plate convergence rate, as well as 20 profiles across different convergent margins. A global analysis of these data for three types of convergent margins, formed by ocean-ocean, ocean-continent, and continent-continent collisions, allows us to recognize the following patterns. (1) Plate convergence rate depends on the type of convergent margins and it is significantly larger when, at least, one of the plates is oceanic. However, the oldest oceanic plate in the Pacific ocean has the smallest convergence rate. (2) The presence of an oceanic plate is, in general, required for generation of high-magnitude (M > 8.0) earthquakes and for generating intermediate and deep seismicity along the convergent margins. When oceanic slabs subduct beneath a continent, a gap in the seismogenic zone exists at depths between ca. 250 km and 500 km. Given that the seismogenic zone terminates at ca. 200 km depth in case of continent-continent collision, we propose oceanic origin of subducting slabs beneath the Zagros, the Pamir, and the Vrancea zone. (3) Dip angle of the subducting slab in continent-ocean collision does not correlate neither with the age of subducting oceanic slab, nor with the convergence rate. For ocean-ocean subduction, clear trends are recognized: steeply dipping slabs are characteristic of young subducting plates and of oceanic plates with high convergence rate, with slab rotation towards a near-vertical dip angle at depths below ca. 500 km at very high convergence rate. (4) Local isostasy is not satisfied at the convergent margins as evidenced by strong free air gravity anomalies of positive and negative signs. However, near-isostatic equilibrium may exist in broad zones of distributed deformation such as Tibet. (5) No systematic patterns are recognized in heat flow data due to strong heterogeneity of measured values which are strongly affected by hydrothermal circulation, magmatic activity, crustal faulting, horizontal heat transfer, and also due to low number of heat flow measurements across many margins. (6) Low upper mantle Vs seismic velocities beneath the convergent margins are restricted to the upper 150 km and may be related to mantle wedge melting which is confined to shallow mantle levels.
DS1609-1699
2016
Artemieva, I.M., Vinnick, L.P.Density structure of the cratonic mantle in southern Africa: 1. Implications for dynamic topography.Gondwana Research, in press available 13p.Africa, South AfricaCratonic lithosphere

Abstract: The origin of high topography in southern Africa is enigmatic. By comparing topography in different cratons, we demonstrate that in southern Africa both the Archean and Proterozoic blocks have surface elevation 500-700 m higher than in any other craton worldwide, except for the Tanzanian Craton. An unusually high topography may be caused by a low density (high depletion) of the cratonic lithospheric mantle and/or by the dynamic support of the mantle with origin below the depth of isostatic compensation (assumed here to be at the lithosphere base). We use free-board constraints to examine the relative contributions of the both factors to surface topography in the cratons of southern Africa. Our analysis takes advantage of the SASE seismic experiment which provided high resolution regional models of the crustal thickness. We calculate the model of density structure of the lithospheric mantle in southern Africa and show that it has an overall agreement with xenolith-based data for lithospheric terranes of different ages. Density of lithospheric mantle has significant short-wavelength variations in all tectonic blocks of southern Africa and has typical SPT values of ca. 3.37-3.41 g/cm3 in the Cape Fold and Namaqua-Natal fold belts, ca. 3.34-3.35 g/cm3 in the Proterozoic Okwa block and the Bushveld Intrusion Complex, ca. 3.34-3.37 g/cm3 in the Limpopo Belt, and ca. 3.32-3.33 g/cm3 in the Kaapvaal and southern Zimbabwe cratons.The results indicate that 0.5-1.0 km of surface topography, with the most likely value of ca. 0.5 km, cannot be explained by the lithosphere structure within the petrologically permitted range of mantle densities and requires the dynamic (or static) contribution from the sublithospheric mantle. Given a low amplitude of regional free air gravity anomalies (ca. + 20 mGal on average), we propose that mantle residual (dynamic) topography may be associated with the low-density region below the depth of isostatic compensation. A possible candidate is the low velocity layer between the lithospheric base and the mantle transition zone, where a temperature anomaly of 100-200 °C in a ca. 100-150 km thick layer may explain the observed reduction in Vs velocity and may produce ca. 0.5-1.0 km to the regional topographic uplift.
DS1609-1700
2016
Artemieva, I.M., Vinnick, L.P.Density structure of the cratonic mantle in southern Africa: 2. Correlations with kimberlite distribution, seismic velocities, and Moho sharpness.Gondwana Research, Vol. 36, pp. 14-27.Africa, South AfricaKimberlite

Abstract: We present a new regional model for the depth-averaged density structure of the cratonic lithospheric mantle in southern Africa constrained on a 30' × 30' grid and discuss it in relation to regional seismic models for the crust and upper mantle, geochemical data on kimberlite-hosted mantle xenoliths, and data on kimberlite ages and distribution. Our calculations of mantle density are based on free-board constraints, account for mantle contribution to surface topography of ca. 0.5-1.0 km, and have uncertainty ranging from ca. 0.01 g/cm3 for the Archean terrains to ca. 0.03 g/cm3 for the adjacent fold belts. We demonstrate that in southern Africa, the lithospheric mantle has a general trend in mantle density increase from Archean to younger lithospheric terranes. Density of the Kaapvaal mantle is typically cratonic, with a subtle difference between the eastern, more depleted, (3.31-3.33 g/cm3) and the western (3.32-3.34 g/cm3) blocks. The Witwatersrand basin and the Bushveld Intrusion Complex appear as distinct blocks with an increased mantle density (3.34-3.35 g/cm3) with values typical of Proterozoic rather than Archean mantle. We attribute a significantly increased mantle density in these tectonic units and beneath the Archean Limpopo belt (3.34-3.37 g/cm3) to melt-metasomatism with an addition of a basaltic component. The Proterozoic Kheis, Okwa, and Namaqua-Natal belts and the Western Cape Fold Belt with the late Proterozoic basement have an overall fertile mantle (ca. 3.37 g/cm3) with local (100-300 km across) low-density (down to 3.34 g/cm3) and high-density (up to 3.41 g/cm3) anomalies. High (3.40-3.42 g/cm3) mantle densities beneath the Eastern Cape Fold belt require the presence of a significant amount of eclogite in the mantle, such as associated with subducted oceanic slabs. We find a strong correlation between the calculated density of the lithospheric mantle, the crustal structure, the spatial pattern of kimberlites, and their emplacement ages. (1) Blocks with the lowest values of mantle density (ca. 3.30 g/cm3) are not sampled by kimberlites and may represent the "pristine" Archean mantle. (2) Young (< 90 Ma) Group I kimberlites sample mantle with higher density (3.35 ± 0.03 g/cm3) than the older Group II kimberlites (3.33 ± 0.01 g/cm3), but the results may be biased by incomplete information on kimberlite ages. (3) Diamondiferous kimberlites are characteristic of regions with a low-density cratonic mantle (3.32-3.35 g/cm3), while non-diamondiferous kimberlites sample mantle with a broad range of density values. (4) Kimberlite-rich regions have a strong seismic velocity contrast at the Moho, thin crust (35-40 km) and low-density (3.32-3.33 g/cm3) mantle, while kimberlite-poor regions have a transitional Moho, thick crust (40-50 km), and denser mantle (3.34-3.36 g/cm3). We explain this pattern by a lithosphere-scale (presumably, pre-kimberlite) magmatic event in kimberlite-poor regions, which affected the Moho sharpness and the crustal thickness through magmatic underplating and modified the composition and rheology of the lithospheric mantle to make it unfavorable for consequent kimberlite eruptions. (5) Density anomalies in the lithospheric mantle show inverse correlation with seismic Vp, Vs velocities at 100-150 km depth. However, this correlation is weaker than reported in experimental studies and indicates that density-velocity relationship in the cratonic mantle is strongly non-unique.
DS1607-1283
2016
Asfaw, Z.G., More, H.Localized/shrinkage kriging indicators. * not specific to diamondsMathematical Geosciences, Vol. 48, 5, pp. 595-618.TechnologyKriging
DS1612-2274
2016
Ashchepkov, I.V., Logvinova, A.M., Ntaflos, T., Vladykin, N.V., Kostrovitsky, S.I., Spetsius, Z., Mityukhin, S.I., Prokopyev, S.A., Medvedev, N.S., Downe, H.Alakit and Daldyn kimberlite fields, Siberia, Russia: two types of mantle sub-terranes beneath central Yakutia?Geoscience Frontiers, in press availableRussia, SiberiaDeposit - Alakit, Daldyn

Abstract: Mineral data from Yakutian kimberlites allow reconstruction of the history of lithospheric mantle. Differences occur in compositions of mantle pyropes and clinopyroxenes from large kimberlite pipes in the Alakit and Daldyn fields. In the Alakit field, Cr-diopsides are alkaline, and Stykanskaya and some other pipes contain more sub-calcic pyropes and dunitic-type diamond inclusions, while in the Daldyn field harzburgitic pyropes are frequent. The eclogitic diamond inclusions in the Alakit field are sharply divided in types and conditions, while in the Daldyn field they show varying compositions and often continuous Pressure-Temperature (P-T) ranges with increasing Fe# with decreasing pressures. In Alakit, Cr-pargasites to richterites were found in all pipes, while in Daldyn, pargasites are rare Dalnyaya and Zarnitsa pipes. Cr-diopsides from the Alakit region show higher levels of light Rare Earth Elements (LREE) and stronger REE-slopes, and enrichment in light Rare Earth Elements (LREE), sometimes Th-U, and small troughs in Nb-Ta-Zr. In the Daldyn field, the High Field Strength Elements HFSE troughs are more common in clinopyroxenes with low REE abundances, while those from sheared and refertilized peridotites have smooth patterns. Garnets from Alakit show HREE minima, but those from Daldyn often have a trough at Y and high U and Pb. PTXfO2 diagrams from both regions show similarities, suggesting similar layering and structures. The degree of metasomatism is often higher for pipes which show dispersion in P-Fe# trends for garnets. In the mantle beneath Udachnaya and Aykhal, pipes show 6-7 linear arrays of P-Fe# in the lower part of the mantle section at 7.5-3.0 GPa, probably reflecting primary subduction horizons. Beneath the Sytykanskaya pipe, there are several horizons with opposite inclinations which reflect metasomatic processes. The high dispersion of the P-Fe# trend indicating widespread metasomatism is associated with decreased diamond grades. Possible explanation of the differences in mineralogy and geochemistry of the mantle sections may relate to their tectonic positions during growth of the lithospheric keel. Enrichment in volatiles and alkalis possibly corresponds to interaction with subduction-related fluids and melts in the craton margins. Incorporation of island arc peridotites from an eroded arc is a possible scenario.
DS1612-2275
2016
Ashchepkov, I.V., Ntaflos, T., Logvinova, A.M., Spetsius, Z.V., Downe, H., Vladykin, N.V.Monomineral universal clinopyroxene and garnet barometers for peridotitic, eclogitic and basaltic systems.Geoscience Frontiers, in press availableTechnologyMineralogy

Abstract: New versions of the universal Jd-Di exchange clinopyroxene barometer for peridotites, pyroxenites and eclogites, and also garnet barometer for eclogites and peridotites were developed. They were checked using large experimental data sets for eclogitic (~530) and peridotitic systems (>650). The precision of the universal Cpx barometer for peridotites based on Jd-Di exchange is close to Cr-Tschermakite method produced by Nimis and Taylor (2000). Cpx barometer was transformed by the substitution of major multiplier for KD by the equations dependent from Al-Na-Fe. Obtained equation in combination with the thermometer of Nimis and Taylor (2000) allow to reconstruct position of the magma feeder systems of the alkali basaltic magma within the mantle diapirs in modern platforms like in Vitim plateau and other Southern Siberia localities and several localities worldwide showing good agreement of pressure ranges for black and green suites. These equations allow construct PTX diagrams for the kimberlite localities in Siberia and worldwide calculating simultaneously the PT parameters for different groups of mantle rocks. They give very good results for the concentrates from kimberlite lamproites and placers with mantle minerals. They are useful for PT estimates for diamond inclusions. The positions of eclogite groups in mantle sections are similar to those determined with new Gar-Cpx barometer produced by C. Beyer et al. (2015). The Fe rich eclogites commonly trace the boundary between the lower upper parts of subcontinental lithospheric mantle (SCLM) at 3-4 GPa marking pyroxenite eclogites layer. Ca-rich eclogites and especially grospydites in SCLM beneath Precambrian kimberlites occurs near pyroxenite layer but in younger mantle sections they became common in the lower parts. The diamondiferous Mg Cr-less group eclogites referring to the ancient island arc complexes are also common in the middle part of mantle sections and near 5-6 GPa. Commonly eclogites in lower apart of mantle sections are remelted and trace the high temperature convective branch. The Mg- and Fe-rich pyroxenites also show the extending in pressure trends which suggest the anatexic melting under the influence of volatiles or under the interaction with plums.
DS1612-2276
2016
Ashchepkov, I.V., Ntaflos, T., Spetius, Z.V., Salikhov, R.F., Downes, H.Interaction between protokimberlite melts and mantle lithosphere: evidence from mantle xenoliths from the Dalnyaya kimberlite pipe, Yakutia, Russia.Geoscience Frontiers, in press availableRussia, YakutiaDeposit - Dalnyaya

Abstract: The Dalnyaya kimberlite pipe (Yakutia, Russia) contains mantle peridotite xenoliths (mostly lherzolites and harzburgites) that show both sheared porphyroclastic (deformed) and coarse granular textures, together with ilmenite and clinopyroxene megacrysts. Deformed peridotites contain high-temperature Fe-rich clinopyroxenes, sometimes associated with picroilmenites, which are products of interaction of the lithospheric mantle with protokimberlite related melts. The orthopyroxene-derived geotherm for the lithospheric mantle beneath Dalnyaya is stepped similar to that beneath the Udachnaya pipe. Coarse granular xenoliths fall on a geotherm of 35 mWm-2 whereas deformed varieties yield a 45 mWm-2 geotherm in the 2-7.5 GPa pressure interval. The chemistry of the constituent minerals including garnet, olivine and clinopyroxene shows trends of increasing Fe# (=Fe/(Fe + Mg)) with decreasing pressure. This may suggest that the interaction with fractionating protokimberlite melts occurred at different levels. Two major mantle lithologies are distinguished by the trace element patterns of their constituent minerals, determined by LA-ICP-MS. Orthopyroxenes, some clinopyroxenes and rare garnets are depleted in Ba, Sr, HFSE and MREE and represent relic lithospheric mantle. Re-fertilized garnet and clinopyroxene are more enriched. The distribution of trace elements between garnet and clinopyroxene shows that the garnets dissolved primary orthopyroxene and clinopyroxene. Later high temperature clinopyroxenes related to the protokimberlite melts partially dissolved these garnets. Olivines show decreases in Ni and increases in Al, Ca and Ti from Mg-rich varieties to the more Fe-rich, deformed and refertilized ones. Minerals showing higher Fe# (0.11-0.15) are found within intergrowths of low-Cr ilmenite-clinopyroxene-garnet related to the crystallization of protokimberlite melts in feeder channels. In P-f(O2) diagrams, garnets and Cr-rich clinopyroxenes indicate reduced conditions at the base of the lithosphere at -5 log units below a FMQ buffer. However, Cr-poor clinopyroxenes, together with ilmenite and some Fe-Ca-rich garnets, demonstrate a more oxidized trend in the lower part of lithosphere at -2 to 0 log units relative to FMQ. Clinopyroxenes from xenoliths in most cases show conditions transitional between those determined for garnets and megacrystalline Cr-poor suite. The relatively low diamond grade of Dalnyaya kimberlites is explained by a high degree of interaction with the oxidized protokimberlite melts, which is greater at the base of the lithosphere.
DS1611-2097
2016
Astic, T., Rosenkjaer, G.K.Where are the diamonds - using the northern lightsSimPEG Team, 1p. Poster pdfTechnologyGeophysics - magnetotellurics
DS1610-1842
2016
Aubach, S., Stagno, V.Evidence for a reducing Archean ambient mantle and its effects on the carbon cycle.Geology, Vol. 44, 9, pp. 751-754.MantleRedox

Abstract: Chemical reduction-oxidation mechanisms within mantle rocks link to the terrestrial carbon cycle by influencing the depth at which magmas can form, their composition, and ultimately the chemistry of gases released into the atmosphere. The oxidation state of the uppermost mantle has been widely accepted to be unchanged over the past 3800 m.y., based on the abundance of redox-sensitive elements in greenstone belt-associated samples of different ages. However, the redox signal in those rocks may have been obscured by their complex origins and emplacement on continental margins. In contrast, the source and processes occurring during decompression melting at spreading ridges are relatively well constrained. We retrieve primary redox conditions from metamorphosed mid-oceanic ridge basalts (MORBs) and picrites of various ages (ca. 3000-550 Ma), using V/Sc as a broad redox proxy. Average V/Sc values for Proterozoic suites (7.0 ± 1.4, 2s, n = 6) are similar to those of modern MORB (6.8 ± 1.6), whereas Archean suites have lower V/Sc (5.2 ± 0.4, n = 5). The lower Archean V/Sc is interpreted to reflect both deeper melt extraction from the uppermost mantle, which becomes more reduced with depth, and an intrinsically lower redox state. The pressure-corrected oxygen fugacity (expressed relative to the fayalite-magnetite-quartz buffer, ?FMQ, at 1 GPa) of Archean sample suites (?FMQ -1.19 ± 0.33, 2s) is significantly lower than that of post-Archean sample suites, including MORB (?FMQ -0.26 ± 0.44). Our results imply that the reducing Archean atmosphere was in equilibrium with Earth's mantle, and further suggest that magmatic gases crossed the threshold that allowed a build-up in atmospheric O2 levels ca. 3000 Ma, accompanied by the first "whiffs" of oxygen in sediments of that age.
DS1602-0189
2016
Augstsson, C., Wilner, A.P., Rusing, T., Niemeyer, H., Gerdes, A., Adams, C.J., Miller, H.The crustal evolution of South America from a zircon Hf-isotope perspective.Terra Nova, In press availableSouth AmericaGeochronology

Abstract: Hf-isotope data of greater than 1100 detrital zircon grains from the Palaeozoic, south-central Andean Gondwana margin record the complete crustal evolution of South America, which was the predominant source. The oldest grains, with crustal residence ages of 3.8-4.0 Ga, are consistent with complete recycling of existing continental crust around 4 Ga. We confirm three major Archaean, Palaeoproterozoic (Transamazonian) and late Mesoproterozoic to early Neoproterozoic crust-addition phases as well as six igneous phases during Proterozoic to Palaeozoic time involving mixing of juvenile and crustally reworked material. A late Mesoproterozoic to early Neoproterozoic, Grenville-age igneous belt can be postulated along the palaeo-margin of South America. This belt was the basement for later magmatic arcs and accreted allochthonous microcontinents as recorded by similar crustal residence ages. Crustal reworking likely dominated over juvenile addition during the Palaeozoic era, and Proterozoic and Archaean zircons were mainly crustally reworked from the eroding, thickened Ordovician Famatinian arc.
DS1604-0591
2016
Augustsson, C., Willner, A.P., Rusing, T., Niemeyer, H., Gerdes, A., Adams, C.J., Miller, H.The crustal evolution of South America from a zircon Hf-isotope perspective.Terra Nova, Vol. 28, 2, pp. 128-137.South AmericaTectonics

Abstract: Hf-isotope data of >1100 detrital zircon grains from the Palaeozoic, south-central Andean Gondwana margin record the complete crustal evolution of South America, which was the predominant source. The oldest grains, with crustal residence ages of 3.8-4.0 Ga, are consistent with complete recycling of existing continental crust around 4 Ga. We confirm three major Archaean, Palaeoproterozoic (Transamazonian) and late Mesoproterozoic to early Neoproterozoic crust-addition phases as well as six igneous phases during Proterozoic to Palaeozoic time involving mixing of juvenile and crustally reworked material. A late Mesoproterozoic to early Neoproterozoic, Grenville-age igneous belt can be postulated along the palaeo-margin of South America. This belt was the basement for later magmatic arcs and accreted allochthonous microcontinents as recorded by similar crustal residence ages. Crustal reworking likely dominated over juvenile addition during the Palaeozoic era, and Proterozoic and Archaean zircon was mainly crustally reworked from the eroding, thickened Ordovician Famatinian arc.
DS1604-0592
2016
Aulbach, S., Gerdes, A., Vijoen, K.S.Formation of diamondiferous kyanite eclogite in a subduction melange.Geochimica et Cosmochimica Acta, Vol. 179, pp. 156-176.Africa, South AfricaDeposit - Lace

Abstract: Diamond- and kyanite-bearing eclogites from the Lace kimberlite on the Kaapvaal craton have common picritic to gabbroic oceanic protoliths with bimineralic eclogites, lying on arrays of Eu* and ?REE that are consistent with accumulation and fractionation of plagioclase and olivine. However, they also show significant compositional differences, such as more grossular-rich garnet and aluminous clinopyroxene (cpx), which require the operation of additional processes. Their nature is elucidated using mineral major- and trace-element compositions, as well as Sr isotope ratios determined by in situ techniques.Highly variable major-element compositions across the co-genetic eclogite suites exert a strong effect on the trace-element distribution between garnet and cpx, whereby Sc, Ge, Sr, Y, Cd, REE, Th and U partition more strongly into garnet with increasing grossular-content. Thus, significant differences between the trace-element compositions of garnet can ensue from crystal-chemical effects alone, making their use as petrogenetic indicators potentially ambiguous. After correcting for these compositional effects, garnet in kyanite-/diamond eclogites, and in eclogites devoid of accessory minerals but with similar signatures, shows depletion (or dilution) in Sc, Ge, Y, In, Zr, Hf and the HREE, and enrichment in the LREE and Th compared to garnet in bimineralic eclogites. This is interpreted as the signature of a pelite-derived melt, which was transferred by addition of aluminous cpx that later exsolved kyanite and garnet, as observed in other aluminous eclogite suites. Continental input can explain initial (at 2.9 Ga) 87Sr/86Sr ? 0.714 measured in cpx in eleven samples with low 87Rb/86Sr (<0.01). The association of diamond with kyanite suggests that diamond formation is also linked to this event, possibly due to diamond formation by oxidation of reduced carbon, such as methane, and attendant reduction of Fe3+ in garnet. This model of sediment melt-oceanic crust interaction reconciles evidence for both low- and high-pressure igneous processes in some aluminous eclogites. We suggest that a subduction mélange is a favourable setting for the transfer of a sediment-derived signature into oceanic crust, leading to formation of diamondiferous kyanite-eclogites from bimineralic eclogites. Diapirism, fluxed by the presence of partial melt, may have facilitated dispersal of the eclogites in the lithosphere column, consistent with their widely varying equilibration pressures ranging from ~5 to 8 GPa.
DS1609-1701
2016
Aulbach, S., Jacob, D.E.Major and trace elements in cratonic mantle eclogites and pyroxenites reveal heterogeneous sources and metamorphic processing of low pressure protoliths.Lithos, Vol. 262, pp. 586-605.MantleEclogite

Abstract: There is a growing body of evidence for the origin of cratonic mantle eclogite xenoliths by low-pressure formation in now-recycled ocean floors. Because they have protoliths ultimately derived from the convecting mantle, their study can potentially yield unprecedented insights into as yet little-understood palaeo-geodynamic regimes, once primary (fractional crystallisation, accumulation, mixing) and secondary processes (kimberlite infiltration, metasomatism) affecting their compositions are understood. This is achieved using diagnostic concentrations or ratios of the analytically and geologically most robust elements (major and minor elements, transition metals, REE), and aided by comparison to natural and modelled analogues. Here, mineral compositions taken from the literature were used to reconstruct bulk rocks and assign the samples to eclogites (further divided into high-Mg, low-Mg and high-Ca types), pyroxenites and their gabbroic (Eu* > 1.05) counterparts. Various protolith types - formed predominantly by < 1 GPa crystallisation from broadly picritic magmas leaving garnet-poor mantle sources - are identified: (1) Many high-Mg eclogites lie on modelled crystallisation trends between 0.5 and < 1 GPa. Some have elevated FeO contents with lower SiO2 and CaO possibly requiring Fe-rich pyroxenite heterogeneities in their mantle source. (2) Many high-Ca eclogites may be the differentiated (higher Na2O, TiO2 and FeO at lower MgO) equivalents of high-Mg eclogites, following modelled crystallisation trends at somewhat lower pressure (0.05 to 0.5 GPa). Other high-Ca eclogites with low FeO were produced during interaction with fluids and melts in mélange-type settings. (3) Low-Mg eclogites, with intermediate MgO content, are too FeO-rich to be intermediary crystallisation products of the same parental melt and are ascribed to melting out of Fe-rich lithologies possibly related to recycling of eclogite and/or contamination with ferromanganese sediments. (4) The positive Eu anomalies in gabbroic eclogites require accumulation of substantial amounts of plagioclase, consistent with their low FeO and TiO2 contents, but their simultaneously low MgO contents suggest that they interacted with residual melts. (5) The elevated CaO and low Al2O3 in pyroxenite may indicate clinopyroxene-rich high- or low-pressure cumulate protoliths, but high Cr2O3 and MgO, combined with low HREE and high LREE in many of these samples, suggests formation by hybridisation of eclogite-derived melt with peridotite.
DS1612-2277
2016
Aulbach, S., Massuyeau, M., Gaillard, F.Origins of cratonic mantle discontinuities: a view from petrology, geochemistry and thermodynamic models.Lithos, in press available 74p.GlobalCraton

Abstract: Geophysically detectible mid-lithospheric discontinuities (MLD) and lithosphere-asthenosphere boundaries (LAB) beneath cratons have received much attention over recent years, but a consensus on their origin has not yet emerged. Cratonic lithosphere composition and origin is peculiar due to its ultra-depletion during plume or accretionary tectonics, cool present-day geothermal gradients, compositional and rheological stratification and multiple metasomatic overprints. Bearing this in mind, we integrate current knowledge on the physical properties, chemical composition, mineralogy and fabric of cratonic mantle with experimental and thermodynamic constraints on the formation and migration of melts, both below and within cratonic lithosphere, in order to find petrologically viable explanations for cratonic mantle discontinuities. LABs characterised by strong seismic velocity gradients and increased conductivity require the presence of melts, which can form beneath intact cratonic roots reaching to ~ 200-250 km depth only in exceptionally warm and/or volatile-rich mantle, thus explaining the paucity of seismical LAB observations beneath cratons. When present, pervasive interaction of these - typically carbonated - melts with the deep lithosphere leads to densification and thermochemical erosion, which generates topography at the LAB and results in intermittent seismic LAB signals or conflicting seismic, petrologic and thermal LAB depths. In rare cases (e.g. Tanzanian craton), the tops of live melt percolation fronts may appear as MLDs and, after complete lithosphere rejuvenation, may be sites of future, shallower LABs (e.g. North China craton). Since intact cratons are presently tectonomagmatically quiescent, and since MLDs produce both positive and negative velocity gradients, in some cases with anisotropy, most MLDs may be best explained by accumulations (metasomes) of seismically slow minerals (pyroxenes, phlogopite, amphibole, carbonates) deposited during past magmatic-metasomatic activity, or fabric inherited from cratonisation. They may accumulate as layers at, or as subvertical veins above, the depth at which melt flow transitions from pervasive to focussed flow at the mechanical boundary layer, causing azimuthal and radial anisotropy. Thermodynamic calculations investigating the depth range in which small-volume melts can be produced relative to the field of phlogopite stability and the presence of MLDs show that phlogopite precipitates at various pressures as a function of age-dependent thermal state of the cratonic mantle, thus explaining variable MLD depths. Even if not directly observed, such metasomes have been shown to be important ingredients in small-volume volatile-rich melts typically penetrating cratonic lithospheres. The apparent sparseness of evidence for phlogopite-rich assemblages in the mantle xenolith record at geophysically imaged MLD depths, if not due to preferential disaggregation in the kimberlite or alteration, may relate to vagaries of both kimberlite and human sampling.
DS1602-0190
2016
Aulbach, S., Mungall, J.E., Pearson, D.G.Distribution and processing of highly siderophile elements in cratonic mantle lithosphere.Reviews in Mineralogy and Geochemistry, Vol. 81, pp. 239-304.MantleMineralogy

Abstract: Cratonic lithospheric mantle is composed of predominantly refractory materials that formed at higher mantle potential temperatures (TP) than recorded in non-cratonic peridotites. It also shows stronger depletion and fractionation of Pd and Pt from Ru, Os and Ir than oceanic, supra-subduction zone or off-cratonic lithospheric mantle, as well as some of the lowest Se and Te contents. The varied response of the highly siderophile elements (HSE: Os, Ir, Ru, Rh, Pt, Pd, Re, Au), and their embedded radioactive decay systems, to changes in oxygen fugacity (fO2), sulfur fugacity (fS2) and pressure (P)-in particular through the impact of these parameters on the stability of the main HSE-bearing sulfide and alloy phases makes them potentially powerful tracers of their melting environment. Therefore, investigation of the HSE systematics of cratonic mantle peridotites, in combination with information from Re–Os isotopes on time-integrated enrichment or depletion, can help us to understand processes leading to mantle differentiation and continental lithosphere formation in the Archean, which are controversial subjects despite decades of research. The longevity of the cratonic lithosphere implies that there was ample opportunity for secondary overprint, obscuring our view of earlier processes. For example, destabilization of platinum-group element (PGE: Os, Ir, Ru, Rh, Pt, Pd) alloy leading to depletions in the compatible PGE, and perhaps Pt, in some cratonic mantle samples may occur in an oxidizing mantle wedge or through interaction with oxidizing small-volume, volatile-rich melts that typically invade cratonic roots. Such melts may eventually deposit S, Pd, Pt and Re and also capture remaining PGE alloys, consistent with the anomalous S-rich character of many kimberlite-borne xenoliths. Their basalt-borne counterparts show additional late effects of subaerial degassing that can deplete volatile elements (S, Re, Os). Basaltic melts can also scavenge PGE alloys at depth, while still sulfide-undersaturated. Such melts, may, on ascent, add sulfides when they become sulfur-saturated and, during the process, refertilize the mantle and modify major-element and modal compositions. The investigation of minor lithologies in the cratonic lithosphere, such as eclogites and pyroxenites, which are expressions of tectonothermal events ranging from subduction to melt infiltration, can enhance our understanding of the effects of these processes on HSE redistribution. Thus, three major topics will be discussed, using HSE systematics in cratonic mantle samples: (1) How did the HSE behave during the (in part) extreme degrees of partial melt extraction experienced by cratonic lithospheric mantle; (2) What were the effects of the secular metasomatic overprint of the cratonic mantle; (3) What was the composition of the Archean convecting mantle, for which cratonic mantle samples may afford better insight than modern samples, provided, of course, that we have an accurate grasp of how HSE are redistributed during partial melting and metasomatism. Models based on experiments done under controlled pressure (P), temperature (T), fO2 and fS2 conditions can help place the data in context and to distinguish between melt- and metasomatism-related processes. Disentangling the various primary and secondary effects is only possible when HSE are studied in combination with lithophile elements, with due attention to petrography and mineralogy. This adds many layers of complexity, but ultimately allows a more complete understanding of the variegated processes that have shaped the cratonic lithosphere through time. In this review, we commence by discussing the peculiarities and complexities of continental lithospheric mantle origin, evolution and current state. We then introduce the database used in this contribution, followed by a brief review of the mineral hosts of HSE in peridotite and of the diverse approaches to isolate the HSE for measurement. We examine the behavior of the HSE during the formation of cratonic lithospheric mantle under non-uniformitarian conditions, where the application of the Re–Os isotope system has afforded particularly useful information on the timing of initial melt depletion and the stabilization of cratonic roots. We then turn to the effects of mantle metasomatism, both during intra-plate and craton-margin processes (see also Gannoun et al. 2016, this volume), on HSE systematics in cratonic mantle. We also discuss the data in the context of melt extraction modelling that shed light on the primary versus secondary HSE signatures in cratonic mantle rocks. Finally, we evaluate the possibility that the HSE in cratonic mantle retain a memory of core formation and subsequent accretionary processes.
DS1609-1702
2016
Aulbach, S., Stagno, V.Evidence for a reducing Archean ambient mantle and its effects on the carbon cycle.Geology, Vol. 44, 9, pp. 751-754.MantleRedox state

Abstract: Chemical reduction-oxidation mechanisms within mantle rocks link to the terrestrial carbon cycle by influencing the depth at which magmas can form, their composition, and ultimately the chemistry of gases released into the atmosphere. The oxidation state of the uppermost mantle has been widely accepted to be unchanged over the past 3800 m.y., based on the abundance of redox-sensitive elements in greenstone belt-associated samples of different ages. However, the redox signal in those rocks may have been obscured by their complex origins and emplacement on continental margins. In contrast, the source and processes occurring during decompression melting at spreading ridges are relatively well constrained. We retrieve primary redox conditions from metamorphosed mid-oceanic ridge basalts (MORBs) and picrites of various ages (ca. 3000-550 Ma), using V/Sc as a broad redox proxy. Average V/Sc values for Proterozoic suites (7.0 ± 1.4, 2s, n = 6) are similar to those of modern MORB (6.8 ± 1.6), whereas Archean suites have lower V/Sc (5.2 ± 0.4, n = 5). The lower Archean V/Sc is interpreted to reflect both deeper melt extraction from the uppermost mantle, which becomes more reduced with depth, and an intrinsically lower redox state. The pressure-corrected oxygen fugacity (expressed relative to the fayalite-magnetite-quartz buffer, ?FMQ, at 1 GPa) of Archean sample suites (?FMQ -1.19 ± 0.33, 2s) is significantly lower than that of post-Archean sample suites, including MORB (?FMQ -0.26 ± 0.44). Our results imply that the reducing Archean atmosphere was in equilibrium with Earth's mantle, and further suggest that magmatic gases crossed the threshold that allowed a build-up in atmospheric O2 levels ca. 3000 Ma, accompanied by the first "whiffs" of oxygen in sediments of that age.
DS1604-0593
2016
Aulbach. S.Evidence from eclogite xenoliths for reducing and warm ( not hot) Archean ambient mantle.GAC MAC Meeting Special Session SS11: Cratons, kimberlites and diamonds., abstract 1/4p.MantleEclogite
DS1602-0191
2015
Azeez, A., Veraswarmy, K.K., Gupta, K., Babu, A.K.The electrical resistivity structure of lithosphere across the Dharwar craton nucleus and Coorg block of South Indian Shield: evidence of collision and modified and preserved lithosphere.Journal of Geophysical Research, Vol. 120, 10, pp. 6698-6721.IndiaGeophysics - craton

Abstract: Magnetotelluric-derived two-dimensional lithospheric resistivity structure of the western Dharwar craton (WDC) and adjoining Coorg block indicates isolated low-resistivity zones in the crust and three striking upper mantle conductive features within the highly resistive Archean lithosphere. The crustal conductors in the WDC show good spatial correlation with the exposed supracrustal rocks conformable with the relic schist belt channels having conductive mineral grains. Conductive zones within the Coorg crust might be related to the relatively young (933?Ma) metamorphic processes in the area and/or possible fluids derived from the Cretaceous passage of Reunion plume in the proximity of Coorg area. A near-vertical conductive structure extending from the lower crust into the upper mantle coincides with the transition zone between Coorg and WDC. This is interpreted as the suture zone between the two tectonic blocks and provides evidence for the individuality of the two Archean terrains. An anomalous upper mantle conductive zone found beneath the craton nucleus may indicate a modified cratonic lithosphere. This could have been derived due to the collision between Coorg and WDC and possibly survived by the subsequent multiple episodes of melt and fluid infiltration processes experienced in the region. Thick (~190?km) and preserved lithosphere is mapped at the eastern segment of WDC. Resistive lithosphere of ~125?km thickness is imaged for the Coorg block.
DS1612-2278
2016
Azuma, S., Yamamoto, S., Ichikawa, H., Maruyama, S.Why primordial continents were recycled to the deep: role of subduction erosion.Geoscience Frontiers, in press availableMantleSubduction

Abstract: Geological observations indicate that there are only a few rocks of Archean Earth and no Hadean rocks on the surface of the present-day Earth. From these facts, many scientists believe that the primordial continents never existed during Hadean Earth, and the continental volume has kept increasing. On the other hand, recent studies reported the importance of the primordial continents on the origin of life, implying their existence. In this paper, we discussed the possible process that could explain the loss of the primordial continents with the assumption that they existed in the Hadean. Although depending on the timing of the initiation of plate tectonics and its convection style, subduction erosion, which is observed on the present-day Earth, might have carried the primordial continents into the deep mantle.
DS1606-1077
2016
Baasner, A., Medard, E., Laporte, D., Hoffer, G.Partial melting of garnet lherzolite with water and carbon dioxide at 3 Gpa using a new melt extraction technique: implications for intraplate magmatism.Contributions to Mineralogy and Petrology, Vol. 171, 45p.MantleMagmatism

Abstract: The origin and source rocks of alkali-rich and SiO2-undersatured magmas in the Earth’s upper mantle are still under debate. The garnet signature in rare earth element patterns of such magmas suggests a garnet-bearing source rock, which could be garnet lherzolite or garnet pyroxenite. Partial melting experiments were performed at 2.8 GPa and 1345-1445 °C in a piston-cylinder using mixtures of natural lherzolite with either 0.4 wt% H2O and 0.4 wt% CO2 or 0.7 wt% H2O and 0.7 wt% CO2. Different designs of AuPd capsules were used for melt extraction. The most successful design included a pentagonally shaped disc placed in the top part of the capsule for sufficient melt extraction. The degrees of partial melting range from 0.2 to 0.04 and decrease with decreasing temperature and volatile content. All samples contain olivine and orthopyroxene. The amounts of garnet and clinopyroxene decrease with increasing degree of partial melting until both minerals disappear from the residue. Depending on the capsule design, the melts quenched to a mixture of quench crystals and residual glass or to glass, allowing measurement of the volatile concentrations by Raman spectroscopy. The compositions of the partial melts range from basalts through picrobasalts to foidites. Compared to literature data for melting of dry lherzolites, the presence of H2O and CO2 reduces the SiO2 concentration and increases the MgO concentration of partial melts, but it has no observable effect on the enrichment of Na2O in the partial melts. The partial melts have compositions similar to natural melilitites from intraplate settings, which shows that SiO2-undersaturated intraplate magmas can be generated by melting of garnet lherzolite in the Earth’s upper mantle in the presence of H2O and CO2.
DS1611-2098
2016
Babich, Yu.V., Feigelson, B.N., Chepurov, A.I.Manifestation of nitrogen interstitials in synthetic diamonds obtained usign a temperature gradient technqiue ( Fe-Ni-C system).Geochemistry International, Vol. 54, 10, pp. 992-927.TechnologySynthetics

Abstract: The IR-peak 1450 cm-1 (H1a-center) associated with nitrogen interstitials have been studied in nitrogen-bearing diamonds synthesized at high P-T parameters in the Fe-Ni-C system. FTIR study shows that manifestation of this nitrogen form is restricted to the regions of active transformation of C-defects into A-defects, which confirms the connection of its formation with C => A aggregation process. An examination of the dependence of the 1450 cm-1 peak on the degree of nitrogen aggregation indicates that H1a-centers are not only formed during C/A aggregation but also disappear simultaneously with the end of C => A transformation. Established facts suggest direct involving of nitrogen as interstitials in the C => A aggregation and serve as strong experimental argument in support of the "interstitial" mechanism of nitrogen migration during aggregation in diamonds containing transition metals.
DS1610-1843
2016
Badro, J., Siebert, J., Nimmo, F.An early geodynamo driven by exsolution of mantle components from Earth's core.Nature, Vol. 536, 7616, 4p.MantleMagnesium oxide

Abstract: Recent palaeomagnetic observations report the existence of a magnetic field on Earth that is at least 3.45 billion years old. Compositional buoyancy caused by inner-core growth is the primary driver of Earth's present-day geodynamo, but the inner core is too young to explain the existence of a magnetic field before about one billion years ago. Theoretical models propose that the exsolution of magnesium oxide--the major constituent of Earth's mantle--from the core provided a major source of the energy required to drive an early dynamo, but experimental evidence for the incorporation of mantle components into the core has been lacking. Indeed, terrestrial core formation occurred in the early molten Earth by gravitational segregation of immiscible metal and silicate melts, transporting iron-loving (siderophile) elements from the silicate mantle to the metallic core and leaving rock-loving (lithophile) mantle components behind. Here we present experiments showing that magnesium oxide dissolves in core-forming iron melt at very high temperatures. Using core-formation models, we show that extreme events during Earth's accretion (such as the Moon-forming giant impact) could have contributed large amounts of magnesium to the early core. As the core subsequently cooled, exsolution of buoyant magnesium oxide would have taken place at the core-mantle boundary, generating a substantial amount of gravitational energy as a result of compositional buoyancy. This amount of energy is comparable to, if not more than, that produced by inner-core growth, resolving the conundrum posed by the existence of an ancient magnetic field prior to the formation of the inner core.
DS1609-1703
2016
Badro, J., Siebert, J., Ninmo, F.An early geodynamo driven by exsolution of mantle components from Earth's core.Nature, Vol. 536, Aug. 18, pp. 326-328.MantleCore, mantle boundary

Abstract: Recent palaeomagnetic observations1 report the existence of a magnetic field on Earth that is at least 3.45 billion years old. Compositional buoyancy caused by inner-core growth2 is the primary driver of Earth’s present-day geodynamo3, 4, 5, but the inner core is too young6 to explain the existence of a magnetic field before about one billion years ago. Theoretical models7 propose that the exsolution of magnesium oxide—the major constituent of Earth’s mantle—from the core provided a major source of the energy required to drive an early dynamo, but experimental evidence for the incorporation of mantle components into the core has been lacking. Indeed, terrestrial core formation occurred in the early molten Earth by gravitational segregation of immiscible metal and silicate melts, transporting iron-loving (siderophile) elements from the silicate mantle to the metallic core8, 9, 10 and leaving rock-loving (lithophile) mantle components behind. Here we present experiments showing that magnesium oxide dissolves in core-forming iron melt at very high temperatures. Using core-formation models11, we show that extreme events during Earth’s accretion (such as the Moon-forming giant impact12) could have contributed large amounts of magnesium to the early core. As the core subsequently cooled, exsolution7 of buoyant magnesium oxide would have taken place at the core-mantle boundary, generating a substantial amount of gravitational energy as a result of compositional buoyancy. This amount of energy is comparable to, if not more than, that produced by inner-core growth, resolving the conundrum posed by the existence of an ancient magnetic field prior to the formation of the inner core.
DS1607-1329
2016
Baes, M.Can mantle suction flow trigger subduction initiation at passive margins?IGC 35th., Session The Deep Earth 1 p. abstractMantleSubduction
DS1601-0002
2016
Bailey, B.L., Blowes, D.W., Smith, L., Sego, D.C.The Diavik waste rock project: geochemical and microbiological characterization of low sulfide content large-scale waste rock test piles.Applied Geochemistry, Vol. 65, pp. 54-72.Canada, Northwest TerritoriesDeposit - Diavik

Abstract: Two experimental waste-rock piles (test piles), each 15 m in height × 60 m × 50 m, were constructed at the Diavik diamond mine in Northern Canada to study the behavior of low-sulfide content waste rock, with a similarly low acid-neutralization potential, in a continuous permafrost region. One test pile with an average of 0.035 wt.% S (<50 mm fraction; referred to as Type I) and a second test pile with an average of 0.053 wt.% S (<50 mm fraction; referred to as Type III) were constructed in 2006. The average carbon content in the <50 mm fraction of waste rock in the Type I test pile was 0.031 wt.% as C and in the Type III test pile was 0.030 wt.% as C. The NP:AP ratio, based on the arithmetic mean of particle-size weighted NP and AP values, for the Type I test pile was 12.2, suggesting this test pile was non-acid generating and for the Type III test pile was 2.2, suggesting an uncertain acid-generating potential. The Type I test pile maintained near-neutral pH for the 4-year duration of the study. Sulfate and dissolved metal concentrations were low, with the exception of Ni, Zn, Cd, and Co in the fourth year following construction. The pore water in the Type III test pile contained higher concentrations of SO42- and dissolved metals, with a decrease in pH to <4.7 and an annual depletion of alkalinity. Maximum concentrations of dissolved metals (20 mg L-1 Ni, 2.3 mg L-1 Cu, 3.7 mg L-1 Zn, 35 µg L-1 Cd, and 3.8 mg L-1 Co) corresponded to decreases in flow rate, which were observed at the end of each field season when the contribution of the total outflow from the central portion of the test pile was greatest. Bacteria were present each year in spite of annual freeze/thaw cycles. The microbial community within the Type I test pile included a population of neutrophilic S-oxidizing bacteria. Each year, changes in the water quality of the Type III test-pile effluent were accompanied by changes in the microbial populations. Populations of acidophilic S-oxidizing bacteria and Fe-oxidizing bacteria became more abundant as the pH decreased and internal test pile temperatures increased. Irrespective of the cold-climate conditions and low S content of the waste rock, the geochemical and microbiological results of this study are consistent with other acid mine drainage studies; indicating that a series of mineral dissolution-precipitation reactions controls pH and metal mobility, and transport is controlled by matrix-dominated flow and internal temperatures.
DS1601-0003
2015
Bain & CompanyThe global diamond report 2015. Covers recent developments, rough diamond production, cutting and polishing, retailing, industry challenges, supply -demand balance through 2030.Bain & Company, Dec. 9, 48p. PdfGlobalReport - industry

Abstract: Welcome to the fifth annual report on the global diamond industry prepared by the Antwerp World Diamond Centre (AWDC) and Bain & Company. In this year’s edition, we take a comprehensive look at the year’s major developments along the diamond value chain. We focus on the reasons for the recent drop in rough and polished prices against the background of continued but slowing growth in the macro economy. As in previous years, we start with key developments along the value chain and a review of recent economic fundamentals that are the long-term drivers of diamond jewelry demand and prices. We look at the long- and short-term factors influencing prices to better understand the recent declines in polished and rough-diamond prices and expectations for their recovery. We compare 2014 results with the results of previous years and review the market to date in 2015, which has been marked by demand uncertainty and price declines. We also provide an update on the long-term outlook for the diamond industry through 2030. The 2030 supply-demand outlook is based on long-term macro-fundamental factors and incorporates the effects of the recent decline in demand from China.
DS1602-0192
2015
Bancroft, A.M., Brunton, F.R., Kleffner, M.A.Silurian conodont biostratigraphy and carbon ( delta 13 C carb) isotope stratigraphy of the Victor mine ( V-03-270-AH) core in the Moose River Basin.Canadian Journal of Earth Sciences, Vol. 52, pp. 1169-1181.Canada, Ontario, AttawapiskatDeposit - Victor

Abstract: The Moose River Basin in Ontario, Canada, contains nearly 1 km of Silurian marine strata, and although it has been studied for more than a century, its precise correlation globally has not been constrained. Herein, a core from the Victor Mine in the Moose River Basin was examined for conodont biostratigraphy and carbonate carbon (13Ccarb) isotope chemostratigraphy to provide a detailed chronostratigraphic framework for the Silurian strata (Severn River, Ekwan River, and Attawapiskat formations) in the Moose River Basin. The recovery of Aspelundia expansa, Aspelundia fluegeli fluegeli, Distomodus staurognathoides, Ozarkodina polinclinata estonica, Pterospathodus eopennatus, and Aulacognathus bullatus, as well as the lower Aeronian, upper Aeronian, lower Telychian (Valgu), and ascending limb of the Sheinwoodian (Ireviken) positive carbonate carbon (13Ccarb) isotope excursions provide significantly improved chronostratigraphic correlation of Llandovery strata in the Moose River Basin.
DS1601-0004
2015
Bancroft, A.M., Brunton, F.R., Kleffner, M.A., Jin, J.Silurian condodont biostratigraphy and carbon isotope stratigraphy of the Victor mine core in the Moose River basin.Canadian Journal of Earth Sciences, Vol. 52, 12, pp. 1169-1181.Canada, Ontario, AttawapiskatDeposit - Victor

Abstract: The Moose River Basin in Ontario, Canada, contains nearly 1 km of Silurian marine strata, and although it has been studied for more than a century, its precise correlation globally has not been constrained. Herein, a core from the Victor Mine in the Moose River Basin was examined for conodont biostratigraphy and carbonate carbon (d13Ccarb) isotope chemostratigraphy to provide a detailed chronostratigraphic framework for the Silurian strata (Severn River, Ekwan River, and Attawapiskat formations) in the Moose River Basin. The recovery of Aspelundia expansa, Aspelundia fluegeli fluegeli, Distomodus staurognathoides, Ozarkodina polinclinata estonica, Pterospathodus eopennatus, and Aulacognathus bullatus, as well as the lower Aeronian, upper Aeronian, lower Telychian (Valgu), and ascending limb of the Sheinwoodian (Ireviken) positive carbonate carbon (d13Ccarb) isotope excursions provide significantly improved chronostratigraphic correlation of Llandovery strata in the Moose River Basin. Silurian Conodont Biostratigraphy and Carbon (d13Ccarb) Isotope Stratigraphy of the Victor Mine (V-03-270-AH) Core in the Moose River Basin.
DS1612-2279
2016
Bardukhinov, L.D., Spetsius, Z.V., Monkhorov, R.V.Coesite inclusions in diamonds of Yakutia. Doklady Earth Sciences, Vol. 470, 2, pp. 1042-1045.Russia, YakutiaDeposit - Zapolyarnaya, Maiskaya, Komsomolskaya-Magnitnaya

Abstract: The results of the study of diamonds with inclusions of high-pressure modification of SiO2 (coesite) by Raman spectroscopy are reported. It is established that the octahedral crystal from the Zapolyarnaya pipe is characterized by the highest residual pressure (2.7 ± 0.07 GPa). An intermediate value of this parameter (2.1 ± 0.07 GPa) was obtained for a crystal of transitional habit from the Maiskaya pipe. The minimal Raman shift was registered for coesite in diamond from the Komsomol’skaya-Magnitnaya pipe and provided a calculated residual pressure of 1.8 ± 0.03 GPa. The residual pressures for crystals from the placer deposits of the Kuoika and Bol’shaya Kuonamka rivers are 2.7 ± 0.07 and 3.1 ± 0.1 GPa, respectively. Octahedral crystals were formed in the mantle at a higher pressure than rhombododecahedral diamonds.
DS1612-2280
2016
Basson, I.J., Creus, P.K., Anthonissen, C.J., Stoch, B., Ekkerd, J.Structural analysis and implicit 3D modelling of high grade host rocks to the Venetia kimberlite diatremes, central zone, Limpopo belt, South Africa.Journal of Structural Geology, Vol. 86, pp. 47-61.Africa, South AfricaDeposit - Venetia

Abstract: The Beit Bridge Complex of the Central Zone (CZ) of the Limpopo Belt hosts the 519 ± 6 Ma Venetia kimberlite diatremes. Deformed shelf- or platform-type supracrustal sequences include the Mount Dowe, Malala Drift and Gumbu Groups, comprising quartzofeldspathic units, biotite-bearing gneiss, quartzite, metapelite, metacalcsilicate and ortho- and para-amphibolite. Previous studies define tectonometamorphic events at 3.3-3.1 Ga, 2.7-2.5 Ga and 2.04 Ga. Detailed structural mapping over 10 years highlights four deformation events at Venetia. Rules-based implicit 3D modelling in Leapfrog Geo provides an unprecedented insight into CZ ductile deformation and sheath folding. D1 juxtaposed gneisses against metasediments. D2 produced a pervasive axial planar foliation (S2) to isoclinal F2 folds. Sheared lithological contacts and S2 were refolded into regional, open, predominantly southward-verging, E-W trending F3 folds. Intrusion of a hornblendite protolith occurred at high angles to incipient S2. Constrictional-prolate D4 shows moderately NE-plunging azimuths defined by elongated hornblendite lenses, andalusite crystals in metapelite, crenulations in fuchsitic quartzite and sheath folding. D4 overlaps with a: 1) 2.03-2.01 Ga regional M3 metamorphic overprint; b) transpressional deformation at 2.2-1.9 Ga and c) 2.03 Ga transpressional, dextral shearing and thrusting around the CZ and d) formation of the Avoca, Bellavue and Baklykraal sheath folds and parallel lineations.
DS1610-1844
2016
Bataleva, Y.V., Palyanov, Y.N., Borzdov, Y.M., Kupriyanov, I.N., Sokol, A.G.Synthesis of diamonds with mineral, fluid and melt inclusions.Lithos, in press available 12p.TechnologyDiamond inclusions

Abstract: Experiments on the synthesis of inclusions-bearing diamond were performed in the SiO2-((Mg,Ca)CO3-(Fe,Ni)S system at 6.3 GPa and 1650-1750 °C, using a multi-anvil high pressure apparatus of the "split-sphere" type. Diamond synthesis was realized in the "sandwich-type" experiments, where the carbonate-oxide mixture acted as a source of both CO2-dominated fluid and carbonate-silicate melt, and Fe,Ni-sulfide played a role of reducing agent. As a result of redox reactions in the carbonate-oxide-sulfide system, diamond was formed in association with graphite and Mg,Fe-silicates, coexisting with CO2-rich fluid, carbonate-silicate and sulfide melts. The synthesized diamonds are predominantly colorless or light-yellow monocrystals with octahedral habit (20-200 µm), and polycrystalline aggregates (300-400 µm). Photoluminescence spectroscopy revealed defects related to nickel impurity (S3 optical centers), which are characteristic of many diamonds in nature. The density of diamond crystallization centers over the entire reaction volume was ~3 × 102-103 cm- 3. The overwhelming majority of diamonds synthesized were inclusions-bearing. According to Raman spectroscopy data, diamond trapped a wide variety of inclusions (both mono- and polyphase), including orthopyroxene, olivine, carbonate-silicate melt, sulfide melt, CO2-fluid, graphite, and diamond. The Raman spectral pattern of carbonate-silicate melt inclusions have bands characteristic of magnesite and orthopyroxene (± SiO2). The spectra of sulfide melt displayed marcasite and pyrrhotite peaks. We found that compositions of sulfide, silicate and carbonate phases are in good agreement not only with diamond crystallization media in experiments, but with data on natural diamond inclusions of peridotitic and eclogitic parageneses. The proposed methodological approach of diamond synthesis can be used for experimental simulation of the formation of several types of mineral, fluid and melt inclusions, observed in natural diamonds.
DS1601-0005
2015
Bataleva, Y.V., Palyanov, Y.N., Sokol, A.G., Borzdov, Y.M., Bayukov, O.A.Wustite stability in the presence of CO2 -fluid and a carbonate silicate melt: implications for the graphite/diamond formation and generation of Fe-rich mantle metasomatic agents.Lithos, in press available, 40p.MantleMelting
DS1602-0193
2016
Bataleva, Y.V., Palyanov, Y.N., Sokol, A.G., Borzdov, Y.M., Bayukov, O.A.Wustite stability in the presence of CO2 fluid and a carbonate silicate melt: implications for the graphite/diamond formation and generation of Fe rich mantle metasomatic agents.Lithos, Vol. 244, pp. 20-29.GlobalFerropericlase inclusions

Abstract: Experimental simulation of the interaction of wüstite with a CO2-rich fluid and a carbonate-silicate melt was performed using a multianvil high-pressure split-sphere apparatus in the FeO-MgO-CaO-SiO2-Al2O3-CO2 system at a pressure of 6.3 GPa and temperatures in the range of 1150 °C–1650 °C and with run time of 20 h. At relatively low temperatures, decarbonation reactions occur in the system to form iron-rich garnet (Alm75Prp17Grs8), magnesiowüstite (Mg# = 0.13), and CO2-rich fluid. Under these conditions, magnesiowüstite was found to be capable of partial reducing CO2 to C0 that leads to the formation of Fe3+-bearing magnesiowüstite, crystallization of magnetite and metastable graphite, and initial growth of diamond seeds. At T = 1450 °C, an iron-rich carbonate-silicate melt (FeO ~ 56 wt.%, SiO2 ~ 12 wt.%) forms in the system. Interaction between (Fe,Mg)O, SiO2, fluid and melt leads to oxidation of magnesiowüstite and crystallization of fayalite-magnetite spinel solid solution (1450 °C) as well as to complete dissolution of magnesiowüstite in the carbonate-silicate melt (1550 °C–1650 °C). In the presence of both carbonate-silicate melt and CO2-rich fluid, dissolution (oxidation) of diamond and metastable graphite was found to occur. The study results demonstrate that under pressures of the lithospheric mantle in the presence of a CO2-rich fluid, wüstite/magnesiowüstite is stable only at relatively low temperatures when it is in the absolute excess relative to CO2-rich fluid. In this case, the redox reactions, which produce metastable graphite and diamond with concomitant partial oxidation of wüstite to magnetite, occur. Wüstite is unstable under high concentrations of a CO2-rich fluid as well as in the presence of a carbonate-silicate melt: it is either completely oxidized or dissolves in the melt or fluid phase, leading to the formation of Fe2 +- and Fe3 +-enriched carbonate-silicate melts, which are potential metasomatic agents in the lithospheric mantle.
DS1607-1284
2016
Baudouin, C., Parat, F., Denis, C.M.M., Mangasini, F.Nephelinite lavas at early stage of rift inititian ( Hanang volcano) North Tanzanian Divergence.Contributions to Mineralogy and Petrology, Vol. 171, 7, 20p.Africa, TanzaniaTectonics

Abstract: North Tanzanian Divergence is the first stage of continental break-up of East African Rift (<6 Ma) and is one of the most concentrated areas of carbonatite magmatism on Earth, with singular Oldoinyo Lengai and Kerimasi volcanoes. Hanang volcano is the southernmost volcano in the North Tanzanian Divergence and the earliest stage of rift initiation. Hanang volcano erupted silica-undersaturated alkaline lavas with zoned clinopyroxene, nepheline, andradite-schorlomite, titanite, apatite, and pyrrhotite. Lavas are low MgO-nephelinite with low Mg# and high silica content (Mg# = 22.4–35.2, SiO2 = 44.2–46.7 wt%, respectively), high incompatible element concentrations (e.g. REE, Ba, Sr) and display Nb–Ta fractionation (Nb/Ta = 36–61). Major elements of whole rock are consistent with magmatic differentiation by fractional crystallization from a parental melt with melilititic composition. Although fractional crystallization occurred at 9–12 km and can be considered as an important process leading to nephelinite magma, the complex zonation of cpx (e.g. abrupt change of Mg#, Nb/Ta, and H2O) and trace element patterns of nephelinites recorded magmatic differentiation involving open system with carbonate–silicate immiscibility and primary melilititic melt replenishment. The low water content of clinopyroxene (3–25 ppm wt. H2O) indicates that at least 0.3 wt% H2O was present at depth during carbonate-rich nephelinite crystallization at 340–640 MPa and 1050–1100 °C. Mg-poor nephelinites from Hanang represent an early stage of the evolution path towards carbonatitic magmatism as observed in Oldoinyo Lengai. Paragenesis and geochemistry of Hanang nephelinites require the presence of CO2-rich melilititic liquid in the southern part of North Tanzanian Divergence and carbonate-rich melt percolations after deep partial melting of CO2-rich oxidized mantle source.
DS1605-0809
2016
Bekker, E.DMC basics - a hollistic view.Diamonds Still Sparkling SAIMM 2016 Conference, Mar. 14-17, pp. 275-286.Economics
DS1608-1390
2016
Bell, E.A., Boehnke, P., Harrison, T.M.Recovering the primary geochemistry of Jack Hills zircons through quantitative estimates of chemical alteration.Geochimica et Cosmochimica Acta, Vol. 191, pp. 187-202.AustraliaJack Hills REE

Abstract: Despite the robust nature of zircon in most crustal and surface environments, chemical alteration, especially associated with radiation damaged regions, can affect its geochemistry. This consideration is especially important when drawing inferences from the detrital record where the original rock context is missing. Typically, alteration is qualitatively diagnosed through inspection of zircon REE patterns and the style of zoning shown by cathodoluminescence imaging, since fluid-mediated alteration often causes a flat, high LREE pattern. Due to the much lower abundance of LREE in zircon relative both to other crustal materials and to the other REE, disturbance to the LREE pattern is the most likely first sign of disruption to zircon trace element contents. Using a database of 378 (148 new) trace element and 801 (201 new) oxygen isotope measurements on zircons from Jack Hills, Western Australia, we propose a quantitative framework for assessing chemical contamination and exchange with fluids in this population. The Light Rare Earth Element Index is scaled on the relative abundance of light to middle REE, or LREE-I = (Dy/Nd) + (Dy/Sm). LREE-I values vary systematically with other known contaminants (e.g., Fe, P) more faithfully than other suggested proxies for zircon alteration (Sm/La, various absolute concentrations of LREEs) and can be used to distinguish primary compositions when textural evidence for alteration is ambiguous. We find that zircon oxygen isotopes do not vary systematically with placement on or off cracks or with degree of LREE-related chemical alteration, suggesting an essentially primary signature. By omitting zircons affected by LREE-related alteration or contamination by mineral inclusions, we present the best estimate for the primary igneous geochemistry of the Jack Hills zircons. This approach increases the available dataset by allowing for discrimination of on-crack analyses (and analyses with ambiguous or no information on spot placement or zircon internal structures) that do not show evidence for chemical alteration. It distinguishes between altered and unaltered samples in ambiguous cases (e.g., relatively high Ti), identifying small groups with potentially differing provenance from the main Jack Hills population. Finally, filtering of the population using the LREE-I helps to more certainly define primary correlations among trace element variables, potentially relatable to magmatic compositional evolution.
DS1611-2099
2016
Bell, E.A., Boehnke, P., Harrison, T.M.Recovering the primary geochemistry of Jack Hills zircons through quantitative estimates of chemical alteration.Geochimica et Cosmochimica Acta, Vol. 191, pp. 187-202.AustraliaGeochemistry

Abstract: Despite the robust nature of zircon in most crustal and surface environments, chemical alteration, especially associated with radiation damaged regions, can affect its geochemistry. This consideration is especially important when drawing inferences from the detrital record where the original rock context is missing. Typically, alteration is qualitatively diagnosed through inspection of zircon REE patterns and the style of zoning shown by cathodoluminescence imaging, since fluid-mediated alteration often causes a flat, high LREE pattern. Due to the much lower abundance of LREE in zircon relative both to other crustal materials and to the other REE, disturbance to the LREE pattern is the most likely first sign of disruption to zircon trace element contents. Using a database of 378 (148 new) trace element and 801 (201 new) oxygen isotope measurements on zircons from Jack Hills, Western Australia, we propose a quantitative framework for assessing chemical contamination and exchange with fluids in this population. The Light Rare Earth Element Index is scaled on the relative abundance of light to middle REE, or LREE-I = (Dy/Nd) + (Dy/Sm). LREE-I values vary systematically with other known contaminants (e.g., Fe, P) more faithfully than other suggested proxies for zircon alteration (Sm/La, various absolute concentrations of LREEs) and can be used to distinguish primary compositions when textural evidence for alteration is ambiguous. We find that zircon oxygen isotopes do not vary systematically with placement on or off cracks or with degree of LREE-related chemical alteration, suggesting an essentially primary signature. By omitting zircons affected by LREE-related alteration or contamination by mineral inclusions, we present the best estimate for the primary igneous geochemistry of the Jack Hills zircons. This approach increases the available dataset by allowing for discrimination of on-crack analyses (and analyses with ambiguous or no information on spot placement or zircon internal structures) that do not show evidence for chemical alteration. It distinguishes between altered and unaltered samples in ambiguous cases (e.g., relatively high Ti), identifying small groups with potentially differing provenance from the main Jack Hills population. Finally, filtering of the population using the LREE-I helps to more certainly define primary correlations among trace element variables, potentially relatable to magmatic compositional evolution.
DS1607-1285
2009
Benittez, L.Provincias diamantiferas de Minas Gerais: uma proposta para a caracterizacao de popilacoes de diamantes tipicas como subsidio a certificacao Kimberley.Thesis,Universidade Federal de Minas Gerais Instituto de geosciencias, pdf availableSouth America, Brazil, Minas GeraisDiamond populations
DS1605-0810
2016
Bennett, M.The state of the industry - the view from the smaller end of town.SEG Newsletter, No. 105, Apr. pp. 25-26.TechnologyExploration
DS1603-0365
2016
Berger, J.Discovery of metamorphic microdiamonds from the parautochthonous units of the Variscan French Massif Central: comment.Gondwana Research, in press available 2p.EuropeMicrodiamonds

Abstract: The Variscan French Massif Central (FMC) is classically described as a stack of nappes with increasing metamorphism from the bottom (parautochthonous unit) to the top (lower and upper gneiss units). Ultra-high pressure (UHP) metamorphism was already recognized in the uppermost units, with notably coesite-bearing rocks. We report the first finding of metamorphic microdiamonds in the parautochthonous unit, revealing that the UHP event affected the whole stack of nappes and also that the pressures reached are above what was previously expected, since the presence of diamond, according to the peak temperature estimates for this unit, indicates pressures of ca. 3 GPa (i.e. 100 km depth). At the scale of the FMC, this finding adds complexity to the established models. On a broader scale, this adds evidence of similarity between this part of the belt and other UHP Variscan terranes such as the Erzgebirge and the Bohemian Massif.
DS1608-1391
2016
Bergstein, R.Brilliance and fire: a biography of diamonds.Harper Collins NY., ISBN 978- 0062323774 US $ 30.00Book

Abstract: From the author of Women from the Ankle Down comes a lively cultural biography of diamonds, which explores our society’s obsession with the world’s most brilliant gemstone and the real-world characters who make them shine. "A diamond is forever." Who among us doesn’t recognize this phrase and, with it, the fascination that these shiny gemstones hold in our collective imagination as symbols of royalty, stars, and eternal love? But who gave us this catchphrase? Where do these gemstones and their colorful legacies originate? How did they become our culture’s symbol of engagement and marriage? Why have they retained their coveted status throughout the centuries? Rachelle Bergstein’s cultural biography of the diamond illuminates the enticing, often surprising story of our society’s enduring obsession with the hardest gemstone—and the people who have worked tirelessly to ensure its continued allure. From the South African mines where most diamonds have been sourced since the late 1890s to the companies who have fought to monopolize them; from the stars who have dazzled in them to the people behind the scenes who have carefully crafted our understanding of their value—Brilliance and Fire offers a glittering history of the world’s most coveted gemstone and its greatest champions and most colorful enthusiasts.
DS1606-1078
2016
Betts, P.G., Armit, R.J., Stewart, J., Aitken, A.R.A., Aileres, L., Donchak, P., Hutton, L., Withnall, I., Giles, D.Australia and Nuna.Geological Society of London Special Publication Supercontinent Cycles through Earth History., Vol. 424, pp. 47-81.AustraliaSupercontinents

Abstract: The Australian continent records c. 1860-1800 Ma orogenesis associated with rapid accretion of several ribbon micro-continents along the southern and eastern margins of the proto-North Australian Craton during Nuna assembly. The boundaries of these accreted micro-continents are imaged in crustal-scale seismic reflection data, and regional gravity and aeromagnetic datasets. Continental growth (c. 1860-1850 Ma) along the southern margin of the proto-North Australian Craton is recorded by the accretion of a micro-continent that included the Aileron Terrane (northern Arunta Inlier) and the Gawler Craton. Eastward growth of the North Australian Craton occurred during the accretion of the Numil Terrane and the Abingdon Seismic Province, which forms part of a broader zone of collision between the northwestern margins of Laurentia and the proto-North Australian Craton. The Tickalara Arc initially accreted with the Kimberley Craton at c. 1850 Ma and together these collided with the proto-North Australian Craton at c. 1820 Ma. Collision between the West Australian Craton and the proto-North Australian Craton at c. 1790-1760 Ma terminated the rapid growth of the Australian continent.
DS1610-1845
2016
Beyer, C., Klemme, S., Grutzner, T., Ireland, T.R., Magee, C.W., Frost, D.J.Fluorine partitioning between eclogitic garnet, clinopyroxene, and melt at upper mantle conditions.Chemical Geology, Vol. 437, pp. 88-97.MantleLamproite

Abstract: In this experimental study we obtained new mineral/melt (DF = cmineral/cmelt) partitioning data for fluorine in a bimineralic hydrous eclogite under Earth's upper mantle conditions (4-6 GPa, 1460-1550 °C). Omphacitic clinopyroxene displays mineral/melt partition coefficients between DF = 0.056 ± 0.005 and DF = 0.074 ± 0.001. Garnet partition coefficients are consistently lower with an average partition coefficient of DF = 0.016 ± 0.003. We found that omphacitic clinopyroxene is the dominant nominally fluorine-free phase in subducted oceanic crust and hence omphacite is expected to be the major fluorine carrier during subduction of crust into the deeper mantle. Together with previously obtained partitioning data we propose that the oceanic crust can host more fluorine per mass unit than the underlying depleted oceanic mantle. If the majority of entrained fluorine is recycled into Earth's transition zone it is possible that the fluorine is either incorporated into high-pressure transition zone phases or released during high-pressure phase transformations and forming fluorine-rich small degree partial melts. Both scenarios are supported by elevated fluorine concentration in ocean island basalts, kimberlites, and lamproites. Combining the fluorine partitioning data with water partitioning data yields a plausible process to generate lamproitic magmas with a high F/H2O ratio. The enrichment of fluorine relative to H2O is triggered by multiple episodes of small degree melting that deplete the residual more in H2O than in fluorine, caused by the approximately three times smaller mineral-melt partition coefficients of H2O.
DS1607-1330
2016
Bhardwaj, D.M.Delineation of REE bearing carbonatite by geophysical techniques - a case study on Mandwara alkaline igneus complex, Rajasthan, India.IGC 35th., Session Mineral Exploration 1p. AbstractIndiaCarbonatite
DS1605-0811
2016
Biggs, J., Robertson, E., Cashman, K.The lateral extent of volcanic interactions during unrest and eruption. Nature Geoscience, Vol. 9, pp. 308-311.MantleMagmatism

Abstract: Volcanic eruptions often occur simultaneously1, 2, 3, 4 or tap multiple magma reservoirs5, 6. Such lateral interactions between magmatic systems are attributed to stress changes7, 8 or hydraulic connections4, 8, 9, 10 but the precise conditions under which coupled eruptions occur have yet to be quantified. Here we use interferometric synthetic aperture radar satellite data to analyse the surface deformation generated by volcanic unrest in the Kenyan Rift. We identify several magma sources located at depths of 2-5?km; importantly, sources that are spaced less than about 10?km apart interact, whereas those spaced more than about 25?km apart do not. However, volcanoes up to 25?km apart have interacted in the geologic past1, 11. Thus, volcanic coupling is not simply controlled by the distance between the magma reservoirs. We then consider different tectonic settings globally, including intraplate volcanoes such as Hawaii and Yellowstone, arc volcanism in Alaska and Chile, and other rift settings, such as New Zealand, Iceland and Afar. We find that the most closely spaced magmatic interactions are controlled by the extent of a shallow crystal mush layer, stress changes can couple large eruptions over distances of about 20-40?km, and only large dyke intrusions or subduction earthquakes could generate coupled eruptions over distances of about 50-100?km.
DS1603-0366
2016
Bindi, L., Tamarova, A., Bobrov, A.V., Sirotkina, E.A., Tschauner, O., Walter, M.J., Irifune, T.Incorporation of high amounts of Na in ringwoodite: possible implications for transport of alkali into lower mantle.American Mineralogist, Vol. 101, pp. 483-486.MantleRingwoodite
DS1607-1286
2016
Bird, M.I., Wynn, J.G., Saiz, G., Wurster, C.W., McBeath, A.The pyrogenic carbon cycle.Annual Review of Earth and Planetary Sciences, Vol. 43, pp. 273-298.MantleCarbon

Abstract: Pyrogenic carbon (PyC; includes soot, char, black carbon, and biochar) is produced by the incomplete combustion of organic matter accompanying biomass burning and fossil fuel consumption. PyC is pervasive in the environment, distributed throughout the atmosphere as well as soils, sediments, and water in both the marine and terrestrial environment. The physicochemical characteristics of PyC are complex and highly variable, dependent on the organic precursor and the conditions of formation. A component of PyC is highly recalcitrant and persists in the environment for millennia. However, it is now clear that a significant proportion of PyC undergoes transformation, translocation, and remineralization by a range of biotic and abiotic processes on comparatively short timescales. Here we synthesize current knowledge of the production, stocks, and fluxes of PyC as well as the physical and chemical processes through which it interacts as a dynamic component of the global carbon cycle.
DS1605-0812
2016
Blundy, J.D., Annen, C.J.Enigmatic relationship between silicic volcanic and plutonic rocks: crustal magmatic systems from the perspective of heat transfer.Elements, Vol. 12, pp. 115-120.TechnologyMagmatism
DS1605-0813
2016
Bomman, F., Malope, K.Investigation of the optimal vortex finder length in DMS cyclones.Diamonds Still Sparkling SAIMM 2016 Conference, Mar. 14-17, pp. 229-238.TechnologyDMS - applied
DS1601-0006
2015
Boneh, Y., Morales, L.F.G., Kaminiski, E., Skemer, P.Modeling olivine CPO evolution with complex deformation histories: implications for the interpretation of seismic anisotropy in the mantle.Geochemistry, Geophysics, Geosystems: G3, Vol. 16, 10, pp. 3436-3455.MantleGeophysics - seismics

Abstract: Relating seismic anisotropy to mantle flow requires detailed understanding of the development and evolution of olivine crystallographic preferred orientation (CPO). Recent experimental and field studies have shown that olivine CPO evolution depends strongly on the integrated deformation history, which may lead to differences in how the corresponding seismic anisotropy should be interpreted. In this study, two widely used numerical models for CPO evolution—D-Rex and VPSC—are evaluated to further examine the effect of deformation history on olivine texture and seismic anisotropy. Building on previous experimental work, models are initiated with several different CPOs to simulate unique deformation histories. Significantly, models initiated with a preexisting CPO evolve differently than the CPOs generated without preexisting texture. Moreover, the CPO in each model evolves differently as a function of strain. Numerical simulations are compared to laboratory experiments by Boneh and Skemer (2014). In general, the D-Rex and VPSC models are able to reproduce the experimentally observed CPOs, although the models significantly over-estimate the strength of the CPO and in some instances produce different CPO from what is observed experimentally. Based on comparison with experiments, recommended parameters for D-Rex are: M*?=?10, ?*?=?5, and ??=?0.3, and for VPSC: a?=?10-100. Numerical modeling confirms that CPO evolution in olivine is highly sensitive to the details of the initial CPO, even at strains greater than 2. These observations imply that there is a long transient interval of CPO realignment which must be considered carefully in the modeling or interpretation of seismic anisotropy in complex tectonic settings.
DS1605-0814
2016
Bookless, T.The selection of high-pressure grinding rolls for a diamond flow sheet.Diamonds Still Sparkling SAIMM 2016 Conference, Mar. 14-17, pp. 117-128.TechnologyMining - applied
DS1610-1846
2016
Borges, M.P.A.C., Moura, M.A., Lenharo, S.L.R., Smith, C.B., Araujo, D.P.Mineralogical characaterization of diamonds from Roosevelt Indigenous Reserve, Brazil, using non-destructive methods. Lithos, in press available 17p.South America, Brazil, RondoniaDeposit - Igarape Lajes Diggings

Abstract: In this study, 660 diamonds from Igarapé Lajes Diggings (Roosevelt and Aripuanã Park indigenous areas), in Amazonian craton, Rondônia State, Brazil, were investigated. Their morphological, optical and surface characteristics were described using optical and scanning electron microscopy (SEM), cathodoluminescence (CL) and infrared spectroscopy (FTIR). The results demonstrated a predominance of resorbed crystals with many surface corrosion features, generally colorless, and led to the identification of four distinct groups: G1, G2, G3 and G4. Group G1 presents features of secondary sources while G2 and G4 show only primary features, some of which are not described in literature. Group G3 is similar to the other groups, however, is composed of less resorbed specimens with primary octahedral morphology relatively well preserved, indicating shorter time of exposure to dissolution effects. Cathodoluminescence in G2 is attributed to features of plastic deformation and to low contents of nitrogen (< 100 ppm, Type II) and high aggregation (IaB). G4 shows homogeneous blue CL, high contents of nitrogen (700 to 1000 ppm) and intermediate aggregation (IaAB). G1 presents luminescence influenced by radiation effects and populations with N contents and aggregation in the same ranges of G2 and G4, suggesting that the primary sources of the three groups can be the same. The relationship of nitrogen content versus aggregation state indicates higher temperatures of formation for G2 and lower for G4. The obtained data suggests that diamonds of G2 originated in sublithospheric mantle as has also been reported in nearby deposits (Machado River and Juína). The employed techniques were also effective in distinguishing diamonds from Roosevelt Reserve and from other localities, indicating that they could be used for improvement of certification procedures of diamonds of unknown origin.
DS1609-1704
2010
Bornman, F.Letseng mine no. 2 plant project - a process engineering and design review.The 4th Colloquium on Diamonds - source to use held Gabarone March 1-3, 2010, 14p.Africa, LesothoDeposit - Letseng

Abstract: Bateman Engineering managed the establishment of a second diamond treatment plant at the Letseng Mine in the Mokhotlong District of northern Lesotho, about 100 km from the town of Buthe Buthe. Letseng Diamonds Proprietary Limited, is owned 70 % by Gem Diamonds and 30 % by the Government of the Kingdom of Lesotho. The second plant, which commenced construction in late 2006, doubled Letseng Mines' hard rock processing capacity from 2.6 million t/yr to 5.2 million t/yr, making it the worlds' seventh largest diamond mine by throughput. Bateman Engineering provided the engineering design, procurement and construction management of the new plant.
DS1604-0594
2016
Borst, A.M., Friis, H., Andersen, T., Nielsen, T.F.D., Waight, T.E., Smit, M.A.Zirconosilicates in the kakortokites of the Ilmmaussaq complex, South Greenland: implications for fluid evolution and high field strength and rare earth element mineralization in agpaitic systems.Mineralogical Magazine, Vol. 80, 1, pp. 5-30.Europe, GreenlandRare earths

Abstract: The layered agpaitic nepheline syenites (kakortokites) of the Ilímaussaq complex, South Greenland, host voluminous accumulations of eudialyte-group minerals (EGM). These complex Na-Ca-zirconosilicates contain economically attractive levels of Zr, Nb and rare-earth elements (REE), but have commonly undergone extensive autometasomatic/hydrothermal alteration to a variety of secondary mineral assemblages. Three EGM alteration assemblages are recognized, characterized by the secondary zirconosilicates catapleiite, zircon and gittinsite. Theoretical petrogenetic grid models are constructed to assess mineral stabilities in terms of component activities in the late-stage melts and fluids. Widespread alteration of EGM to catapleiite records an overall increase in water activity, and reflects interaction of EGM with late-magmatic Na-, Cl- and F-rich aqueous fluids at the final stages of kakortokite crystallization. Localized alteration of EGM and catapleiite to the rare Ca-Zr silicate gittinsite, previously unidentified at Ilímaussaq, requires an increase in CaO activity and suggests post-magmatic interaction with Ca-Sr bearing aqueous fluids. The pseudomorphic replacement of EGM in the kakortokites was not found to be associated with significant remobilization of the primary Zr, Nb and REE mineralization, regardless of the high concentrations of potential transporting ligands such as F and Cl. We infer that the immobile behaviour essentially reflects the neutral to basic character of the late-magmatic fluids, in which REE-F compounds are insoluble and remobilization of REE as Cl complexes is inhibited by precipitation of nacareniobsite-(Ce) and various Ca-REE silicates. A subsequent decrease in F- activity would furthermore restrict the mobility of Zr as hydroxyl-fluoride complexes, and promote precipitation of the secondary zirconosilicates within the confines of the replaced EGM domains.
DS1607-1331
2016
Bosch, P.The importance of Dwyka group glaciation with regards to alluvial diamond transportation, concentration and entrapment in South Africa.IGC 35th., Session Mineral Exploration 1p. AbstractAfrica, South AfricaAlluvials, diamonds
DS1610-1847
2014
Boshoff, E.T.Identifying critical parameters in the settling of African kimberlite slimes.Thesis, University of Pretoria, Ms Metallurgical Engineering 279p. PdfAfrica, Angola, South AfricaDeposit - AC 56-5-1, Venetia Red

Abstract: Kimberlite is the host rock from which diamonds are mined. The mineralogical features for kimberlites vary greatly with country, origin, depth and type of kimberlite. Kimberlites can contain various clay species with some kimberlites containing predominantly clay minerals. The presence of these clay minerals in the ore can cause difficulty in dewatering due to high flocculant demand, poor supernatant clarity and low settling rates. Identifying critical parameters that can predict the settling behaviour of African kimberlite slurries will assist the process engineer to predict the settling behaviour of different kimberlite slurries. Especially identifying the kimberlites that will most likely not settle with normal flocculant dosage rates is useful. From first principles the settling of a particle is described by Stoke’s law which incorporates the density of the particle and size of the particle as the inherent particle variables. In this case density is assumed constant and therefore the size of particles influence the settling rate of particles to a great extent. This study therefore investigated the influence of particle size on settling rate and whether the particle size distribution showed correlation with settling rate when regression modelling was fitted on the data. Other variables that were tested for correlation with settling were pH when the kimberlite is mixed in water as well as various mineralogical features of the ore. Fitting a simple model to any of these properties or combinations of these properties was attempted which would allow for prediction of settling behaviour. The mineralogical features were classified by evaluating the mineral composition, fractional elemental analysis, cation exchange capacity and the exchangeable sodium percentage of the different kimberlites. These variables were tested as well as their settling behaviour with 18 different African kimberlite samples. The settling rate and slurry bed compaction during natural settling as well coagulant and flocculant assisted settling were measured for the kimberlite slurries. The best performing coagulant and flocculant for each kimberlite were combined to evaluate potential improvements in the settling rates and slurry bed compaction compared to current settling practices that only utilise flocculant additions. Especially the use of coagulant for kimberlites that did not show settling with only flocculants was evaluated. For these 18 kimberlites only 2 kimberlites did not settle with the use of flocculants with settling rates varying between 10.7m/h and 25m/h. Both these kimberlites also did not settle with the combination of coagulant and flocculant, but could only settle with only coagulant additions at settling rates of 1.9 m/h and 2.2 m/h. Regression analysis fitted to the settling rate investigated the influence of particle size, pH and mineralogical features on settling. For representation of the particle size two data points from the Particle Size Distribution (PSD) was utilised which represented the fine material and the coarser material. These two data points were taken at percentage passing 7.5 µm and 75 µm. Regression data for kimberlite with flocculant additions showed that particle size and the pH of the slurry were identified as significant parameters in predicting settling. The regression data showed a R2 of 0.78 for the settling rate and an adjusted R2 of 0.79 for the slurry bed depth.
DS1609-1705
2010
Botha, J., Nichol, S., Swarts, B.Rapid underground development optimization at Cullinan diamond mine using computer simulation.The 4th Colloquium on Diamonds - source to use held Gabarone March 1-3, 2010, 14p.Africa, South AfricaDeposit - Cullinan

Abstract: There are many underground mining software tools available to plan and schedule the development of underground mines. A shortfall of these tools is the optimization of the underground equipment and strategy in order to maximize the development rate. This paper will illustrate how the SimMine® software was used to maximize underground development at Petra Diamonds' Cullinan Diamond Mine. It will also determine the effect of various development strategies and equipment capacities on the underground development rate and pinpoint potential bottlenecks in the mine development cycle. Full Article Download:
DS1605-0815
2016
Botswana Geological PortalPartnership of Botswana Geoscience Institute and Geosoft. Data includes airborne and ground geophysics, geochemistry.http://geoscienceportal.geosoft.com/ Botswana/search, Apr. 12, 1p.Africa, BotswanaDatabase

Abstract: Geosoft is pleased to announce the launch of the Botswana Geoscience Portal, a partnership initiative with the Botswana Geoscience Institute and industry sponsors. Developed and hosted by Geosoft, the portal provides free access to multi-disciplinary datasets from Ngamiland, a district in the country's northwest. It is available online at: http://geoscienceportal.geosoft.com/Botswana/search. The geoscience portal aims to help Botswana attract new investment in resource exploration, improve transparency and stimulate collaboration between government, industry and the public to advance understanding of the economic and social needs of the North-West district. Tiyapo Hudson Ngwisanyi, Chief Executive Officer of the Botswana Geoscience Institute said: “Making geoscientific data more accessible and transparent is critical to furthering understanding of the North-West district, and encouraging new investment in resource exploration within Africa. The portal is a welcome development that will assist us in promoting ongoing, productive collaboration between government and industry.” “Geosoft is excited to be part of an initiative that demonstrates how government and industry can work together to encourage mineral exploration investment and thus downstream economic growth in the country,” said Tim Dobush, Chief Executive Officer of Geosoft. “We are continually engaging with government organizations like the Botswana Geoscience Institute and industry leaders to innovate, and maximize the value of geoscience data for resource discovery and to meet the social/economic needs of the broader public sector.” Data available on the Botswana Geoscience Portal includes airborne geophysics, ground geophysics and geochemistry. Future updates will provide access to borehole data, remote sensing, seismic surveys and information products including interpretations and 3D models.- See more at: http://www.geosoft.com/news/botswana-geoscience-portal-goes-live#sthash.CZGrHC4h.dpuf
DS1609-1706
2016
Boyce, A., Bastow, I.D., Darbyshire, F.A., Ellwood, A.G., Gilligan, A., Levin, V., Menke, W.Subduction beneath Laurentia modifies the eastern North American cratonic edge: evidence from P wave and S wave tomography.Journal of Geophysical Research,, Vol. 121, 7, pp. 5013-5030.CanadaSubduction

Abstract: The cratonic cores of the continents are remarkably stable and long-lived features. Their ability to resist destructive tectonic processes is associated with their thick (~250 km), cold, chemically depleted, buoyant lithospheric keels that isolate the cratons from the convecting mantle. The formation mechanism and tectonic stability of cratonic keels remains under debate. To address this issue, we use P wave and S wave relative arrival-time tomography to constrain upper mantle structure beneath southeast Canada and the northeast USA, a region spanning three quarters of Earth's geological history. Our models show three distinct, broad zones: Seismic wave speeds increase systematically from the Phanerozoic coastal domains, through the Proterozoic Grenville Province, and to the Archean Superior craton in central Québec. We also recover the NW-SE trending track of the Great Meteor hot spot that crosscuts the major tectonic domains. The decrease in seismic wave speed from Archean to Proterozoic domains across the Grenville Front is consistent with predictions from models of two-stage keel formation, supporting the idea that keel growth may not have been restricted to Archean times. However, while crustal structure studies suggest that Archean Superior material underlies Grenvillian age rocks up to ~300 km SE of the Grenville Front, our tomographic models show a near-vertical boundary in mantle wave speed directly beneath the Grenville Front. We interpret this as evidence for subduction-driven metasomatic enrichment of the Laurentian cratonic margin, prior to keel stabilization. Variable chemical depletion levels across Archean-Proterozoic boundaries worldwide may thus be better explained by metasomatic enrichment than inherently less depleted Proterozoic composition at formation.
DS1608-1392
2016
Bradley, D.Improving rare earth extraction efficiency. Bastnasites ( structure and crystal properties)Journal of Physical Chemistry, 10.1002/ chemv.201600068TechnologyRare earths

Abstract: Scientists in the U.S. have provided a new understanding of the structure and crystal properties of the main mineral source of rare earth metals, bastnäsites. They are fluoro-carbonate minerals which contain ytterbium, lanthanum, and cerium, among other elements. The researchers used powder X-ray diffraction (XRD) and density functional theory (DFT) to reveal details of the minerals' structure and interfacial energy. The work could help in the design of new reagents for selective binding to mineral interfaces and could improve the recovery of rare metals by froth flotation, which is the major stage of ore beneficiation. Increasing flotation concentrate grades makes the subsequent leaching and rare earth separations more efficient and economic. Rare earth elements are increasingly important in modern technology - for electronics, catalysis, possible future quantum devices, and especially for clean energy applications like wind and solar energy, energy-efficient lighting, and electric vehicles. For example, neodymium and praseodymium are used in strong permanent magnets, lanthanum and cerium are used in batteries, metal alloys, petroleum refining, and catalysis, and ytterbium is a common material in phosphors for displays and in high-tech ceramics. These elements, which are defined as the fifteen lanthanides, as well as scandium and yttrium, are commonly found in the same ores. Despite what their name suggests, they are not actually rare, but they are difficult and costly to refine. As such, it is crucial that scientists and technologists optimize ore beneficiation to provide an enriched feedstock for the subsequent efficient extraction of these elements from the mined mineral ores in which they are found.
DS1607-1332
2016
Bradshaw, J.The history of the Gondwana continent and the chronology of break up.IGC 35th., Session A Dynamic Earth 1p. AbstractMantleGondwana
DS1607-1333
2016
Brandon, A.Mapping off-craton subcontinental mantle lithosphere growth and destruction in the southwest United States using Os isotopes.IGC 35th., Session A Dynamic Earth 1p. AbstractUnited StatesGeochronology
DS1610-1848
2016
Brandon, A.Tectonics: changing of the plates.Nature Geoscience, Vol. 9, pp. 731-732.MantleMelting

Abstract: The composition of Earth's crust depends on the style of plate tectonics and of the melting regimes in the mantle. Analyses of the oldest identified rocks suggest that these styles and the resulting crust have changed over Earth's history.
DS1601-0007
2015
Breeding, C.Diamond bearing eclogite xenoliths from the Ardo So Ver dykes. ( Kimberley area)Gems & Gemology News International, Vol. 51, 2, summer 2p.Africa, South AfricaDeposit - Ardo so Ver
DS1608-1393
2016
Breeding, C.M.The art and science of diamond fluorescence: what it tells us about the growth history of natural and synthetic gem diamonds.GSA Annual Meeting, Abstract, 1p.TechnologyFluorescence

Abstract: Gem diamonds are highly valued for their color, or the absence of it. However, the myriad of colors and patterns that are revealed when a diamond is exposed to ultraviolet light are often more impressive than the stones themselves. High energy (i.e., ultra-shortwave <230 nm) UV light from the DiamondView instrument excites fluorescence from natural and synthetic diamonds that not only provides a tremendous amount of information about defect incorporation during growth, but also stunningly artistic designs. Fluorescence patterns reveal details about the original morphology of a diamond even after all of the natural surfaces are removed. In addition, concentrations of luminescent centers along structurally controlled planes in a natural diamond lattice provide information about the original distribution of impurities and other defects and the thermal and deformational history of diamonds as they spend millions (or billions) of years in the Earth’s mantle and then are rapidly erupted in a kimberlite magma. Likewise, the distribution of nitrogen, boron, and nickel-related luminescence in synthetic diamonds give clues to the temperature, pressure, and catalytic conditions under which they were grown in a laboratory. Evaluation of the fluorescence patterns from diamonds helps the scientist better understand the incorporation and migration of atomic level defects in the diamond structure while allowing the artist to appreciate some of the most unusual and amazing patterns that nature produces.
DS1608-1394
2015
Brett, C.The scent of kimberlitic magmas.Geology Today, Vol. 31, 5, pp. 171-173.TechnologyKimberlite origin
DS1602-0194
2016
Bristow, J.Changes, consolidation and the future of the international diamond business.PDAC 2016, 1p. abstractGlobalDiamond market
DS1607-1334
2016
Bristow, J.The international diamond business: the role of southern African producers in change and consolidation.IGC 35th., Session Mineral Exploration 1p. AbstractAfrica, South AfricaDiamond markets
DS1609-1707
2016
Broom-Fendley, S., Heaton, T., Wall, F., Gunn, G.Tracing the fluid source of heavy REE mineralization in carbonatites using a novel method of oxygen isotope analysis in apatite: the example of Songwe Hill, Malawi.Chemical Geology, Vol. 440, pp. 275-287.Africa, MalawiCarbonatite

Abstract: Stable (C and O) isotope data from carbonates are one of the most important methods used to infer genetic processes in carbonatites. However despite their ubiquitous use in geological studies, it is suspected that carbonates are susceptible to dissolution-reprecipitation and isotopic resetting, especially in shallow intrusions, and may not be the best records of either igneous or hydrothermal processes. Apatite, however, should be much less susceptible to these resetting problems but has not been used for O isotope analysis. In this contribution, a novel bulk-carbonatite method for the analysis of O isotopes in the apatite PO4 site demonstrates a more robust record of stable isotope values. Analyses of apatite from five carbonatites with magmatic textures establishes a preliminary Primary Igneous Apatite (PIA) field of d18O = + 2.5 to + 6.0‰ (VSMOW), comparable to Primary Igneous Carbonatite (PIC) compositions from carbonates. Carbonate and apatite stable isotope data are compared in 10 carbonatite samples from Songwe Hill, Malawi. Apatite is heavy rare earth element (HREE) enriched at Songwe and, therefore, oxygen isotope analyses of this mineral are ideal for understanding HREE-related mineralisation in carbonatites. Carbonate C and O isotope ratios show a general trend, from early to late in the evolution, towards higher d18O values (+ 7.8 to + 26.7‰, VSMOW), with a slight increase in d13C (- 4.6 to - 0.1‰, VPDB). Oxygen isotope ratios from apatite show a contrary trend, decreasing from a PIA field towards more negative values (+ 2.5 to - 0.7‰, VSMOW). The contrasting results are interpreted as the product of the different minerals recording fluid interaction at different temperatures and compositions. Modelling indicates the possibility of both a CO2 rich fluid and mixing between meteoric and deuteric waters. A model is proposed where brecciation leads to depressurisation and rapid apatite precipitation. Subsequently, a convection cell develops from a carbonatite, interacting with surrounding meteoric water. REE are likely to be transported in this convection cell and precipitate owing to decreasing salinity and/or temperature.
DS1604-0595
2016
Broom-Fendley, S., Styles, M.T., Appleton, J.D., Gunn, G., Wall, F.Evidence for dissolution reprecipitation of apatite and preferential LREE mobility in carbonatite derived late stage hydrothermal processes.American Mineralogist, Vol. 101, pp. 596-611.Africa, MalawiCarbonatite

Abstract: The Tundulu and Kangankunde carbonatite complexes in the Chilwa Alkaline Province, Malawi, contain late-stage, apatite-rich lithologies termed quartz-apatite rocks. Apatite in these rocks can reach up to 90 modal% and displays a distinctive texture of turbid cores and euhedral rims. Previous studies of the paragenesis and rare earth element (REE) content of the apatite suggest that heavy REE (HREE)-enrichment occurred during the late-stages of crystallization. This is a highly unusual occurrence in intrusions that are otherwise light REE (LREE) enriched. In this contribution, the paragenesis and formation of the quartz-apatite rocks from each intrusion is investigated and re-evaluated, supported by new electron microprobe (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data to better understand the mechanism of HREE enrichment. In contrast to the previous work at Tundulu, we recognize three separate stages of apatite formation, comprising an “original” euhedral apatite, “turbid” apatite, and “overgrowths” of euhedral late apatite. The crystallization of synchysite-(Ce) is interpreted to have occurred subsequent to all phases of apatite crystallization. The REE concentrations and distributions in the different minerals vary, but generally higher REE contents are found in later-stage apatite generations. These generations are also more LREE-enriched, relative to apatite that formed earlier. A similar pattern of increasing LREE-enrichment and increased REE concentrations toward later stages of the paragenetic sequence is observed at Kangankunde, where two generations of apatite are observed, the second showing higher REE concentrations, and relatively higher LREE contents. The changing REE distribution in the apatite, from early to late in the paragenetic sequence, is interpreted to be caused by a combination of dissolution-reprecipitation of the original apatite and the preferential transport of the LREE complexes by F- and Cl-bearing hydrothermal fluids. Successive pulses of these fluids transport the LREE out of the original apatite, preferentially re-precipitating it on the rim. Some LREE remained in solution, precipitating later in the paragenetic sequence, as synchysite-(Ce). The presence of F is supported by the F content of the apatites, and presence of REE-fluorcarbonates. Cl is not detected in the apatite structure, but the role of Cl is suggested from comparison with apatite dissolution experiments, where CaCl2 or NaCl cause the reprecipitation of apatite without associated monazite. This study implies that, despite the typically LREE enriched nature of carbonatites, significant degrees of hydrothermal alteration can lead to certain phases becoming residually enriched in the HREE. Although at Tundulu the LREE-bearing products are re-precipitated relatively close to the REE source, it is possible that extensive hydrothermal activity in other carbonatite complexes could lead to significant, late-stage fractionation of the REE and the formation of HREE minerals.
DS1612-2281
2016
Brown, E.L., Lesher, C.E.REEBOX PRO: a forward model simulating melting of thermally and lithologically variable upwelling mantle.Geochemistry, Geophysics, Geosystems: G3, Vol. 17, 10, pp. 3929-3968.MantleMelting
DS1607-1335
2016
Brown, L.Imaging the crust and large N arrays.IGC 35th., Session The Deep Earth 1 p. abstractMantleGeophysics - seismics
DS1601-0008
2015
Browne, J.Seven elements that have changed the world. Carbon, silicon, titanium, iron, silver, gold, uraniumWeidenfeld & Nicholson London Book Publisher, Amazon.com approx. 12.00 paperbackTechnologyBook

Abstract: Humans have put the Earth’s resources to extraordinary use. Carbon provides us with heat, light and mobility at the flick of a switch. From silver came photography, the preservation of memories, and a task which for centuries was confined to painters, sketchers and our imaginations. Silver in turn was eventually replaced by silicon, an element which enables us to communicate and transmit information across the globe in an instant. But our use of the Earth’s resources is not always for the benefit of humankind. Our relationship with the elements is one of great ambivalence. Uranium produces both productive nuclear power and destructive atomic bombs; iron is the bloody weapon of war, but also the economic tool of peace; our desire for alluring gold is the foundation of global trade, but has also led to the death of millions. This book vividly describes how seven key elements have shaped the world around us - for good and for bad. Seven Elements takes you on an adventure of human passion, ingenuity and discovery. This journey is far from over: we continue to find surprising new uses for these seven elements. Discover how titanium pervades modern consumer society; how natural gas is transforming the global energy sector; and how an innovative new form of carbon could be starting a technological revolution. Seven Elements is a unique mix of science, history and politics, interwoven with the author’s extensive personal and professional experience.
DS1603-0367
2015
Bruffaerts, L.A diamantaire struggle: redefining conflict diamonds in the Kimberley Process.International Affairs, Vol. 91, 5, pp. 1085-1101.GlobalKP

Abstract: Diamonds are forever. But what of the definition of conflict diamonds used by the Kimberley Process (KP)? Despite the fact that civil society has raised attention to the cloudy issue of state-perpetrated diamond-related human rights abuses throughout the past decade, the continued longevity of the central definition around which the Kimberley Process revolves still appears to be a crystal-clear fact. As it turns out, calls to broaden the scope of the conflict diamond definition have not been successful because several discourse manipulations within the KP have had formative effects on other actors’ identities and interests. Discourse spacing-the strategic allocation of ‘appropriate’ spaces for certain discourses within a particular institutionalized setting-has been strategically employed in an attempt to place boundaries on the redefinition discourse. By claiming that addressing human rights abuses lies beyond the mandate of the KP, several KP participant states have sought to convince others that discussing redefinition has no place on the KP reform agenda. Discourse timing has also been key, where numerous African states’ perceptions of redefinition were influenced by accusations of neo-colonial intent on the part of western KP participant states that stemmed from a sanctions debate that was taking place parallel to the redefinition debate. The article finds that these two occurrences, alongside the KP’s consensus based decision-making structure and several KP participant states’ fears about setting a human rights precedent, have obstructed the road to the redefinition of conflict diamonds.
DS1608-1395
2016
Brune, S., Williams, S.E., Butterworth, N.P., Muller, R.D.Abrupt plate accelerations shape rifted continental margins.Nature Geoscience, July 18, online 16p.MantleRifting

Abstract: Rifted margins are formed by persistent stretching of continental lithosphere until breakup is achieved. It is well known that strain-rate-dependent processes control rift evolution1, 2, yet quantified extension histories of Earth’s major passive margins have become available only recently. Here we investigate rift kinematics globally by applying a new geotectonic analysis technique to revised global plate reconstructions. We find that rifted margins feature an initial, slow rift phase (less than ten millimetres per year, full rate) and that an abrupt increase of plate divergence introduces a fast rift phase. Plate acceleration takes place before continental rupture and considerable margin area is created during each phase. We reproduce the rapid transition from slow to fast extension using analytical and numerical modelling with constant force boundary conditions. The extension models suggest that the two-phase velocity behaviour is caused by a rift-intrinsic strength-velocity feedback, which can be robustly inferred for diverse lithosphere configurations and rheologies. Our results explain differences between proximal and distal margin areas3 and demonstrate that abrupt plate acceleration during continental rifting is controlled by the nonlinear decay of the resistive rift strength force. This mechanism provides an explanation for several previously unexplained rapid absolute plate motion changes, offering new insights into the balance of plate driving forces through time.
DS1602-0195
2016
Bruno, M., Rubbo, M., Aquilano, D., Massaro, F.R., Nestola, F.Diamond and olivine inclusions: a strange relation revealed by ab initio simulations.Earth and Planetary Science Letters, Vol. 435, 1, pp. 31-35.RussiaDeposit - Udachnaya

Abstract: The study of diamond and its solid inclusions is of paramount importance to acquire direct information on the deepest regions of the Earth. However, although diamond is one of the most studied materials in geology, the diamond-inclusion relationships are not yet understood: do they form simultaneously (syngenesis) or are inclusions pre-existing objects on which diamond nucleated (protogenesis)? Here we report, for the first time, adhesion energies between diamond (D) and forsterite (Fo) to provide a crucial contribution to the syngenesis/protogenesis debate. The following interfaces were investigated at quantum-mechanical level: (i) (001)D/(001)Fo, (ii) (001)D/(021)Fo, and (iii) (111)D/(001)Fo. Our data, along with the ones recently obtained on the (110)D/(101)Fo interface, revealed an unexpected thermodynamic behaviour, all interfaces showing almost equal and low adhesion energies: accordingly, diamond and olivine have an extremely low chemical affinity and cannot develop preferential orientations, even during an eventual epitaxial growth. Combining these results with those of our previous work concerning the morphology constraints of diamond on its inclusions, we can state that the two main arguments used so far in favour of diamond/inclusions syngenesis cannot be longer considered valid, at least for olivine.
DS1605-0816
2016
Buikin, A.I., Verchovsky, A.B., Kogarko, L.N., Grinenko, V.A., Kuznetsova, O.V.The fluid phase evolution during the formation of carbonatite of the Guli Massif: evidence from the isotope ( C, N, Ar) data.Doklady Earth Sciences, Vol. 466, 2, Feb. pp. 135-137.RussiaCarbonatite

Abstract: The first data on variations of the isotope composition and element ratios of carbon, nitrogen, and argon in carbonatites of different generations and ultrabasic rocks of the Guli massif obtained by the method of step crushing are reported. It is shown that early carbonatite differs significantly from the later ones by the concentration of highly volatile components, as well as by the isotope compositions of carbon (CO2), argon, and hydrogen (H2O). The data obtained allow us to conclude that the mantle component predominated in the fluid at the early stages of formation of rocks of the Guli massif, whereas the late stages of carbonatite formation were characterized by an additional fluid source, which introduced atmospheric argon, and most likely a high portion of carbon dioxide with isotopically heavy carbon.
DS1607-1287
2016
Bunin, I. Zh., Chanturia, V.A., Anashkina, N.E., Ryazantseva, M.V.Experimental validation of mechanism for pulsed energy effect on structure, chemical properties and microhardness of rock forming minerals of kimberlites.Journal of Mining Science, Vol. 51, 4, pp. 799-810.RussiaSpectroscopy

Abstract: Using the Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), microscopy and microhardness test methods, the change in the crystalline and chemical properties and in microhardness of rock-forming minerals of kimberlites as a result of exposure to high-power nanosecond electromagnetic pulses (HPEM) has been studied. From FTIR and XPS data the non-thermal effect of HPEM results in damage of surface microstructure of dielectric minerals due to formation of microcracks, surface breakdowns and other defects, which ensure effective weakening of rock-forming minerals and reduction in their microhardness by 40-66%.
DS1612-2282
2016
Bureau, H., Frost, D.J., Bolfan-Casanova, N., Leroy, C.Diamond growth in mantle fluids.Lithos, Vol. 265, pp. 4-15.MantleDiamond morphology

Abstract: In the upper mantle, diamonds can potentially grow from various forms of media (solid, gas, fluid) with a range of compositions (e.g. graphite, C-O-H fluids, silicate or carbonate melts). Inclusions trapped in diamonds are one of the few diagnostic tools that can constrain diamond growth conditions in the Earth's mantle. In this study, inclusion-bearing diamonds have been synthesized to understand the growth conditions of natural diamonds in the upper mantle. Diamonds containing syngenetic inclusions were synthesized in multi-anvil presses employing starting mixtures of carbonates, and silicate compositions in the presence of pure water and saline fluids (H2O-NaCl). Experiments were performed at conditions compatible with the Earth's geotherm (7 GPa, 1300-1400 °C). Results show that within the timescale of the experiments (6 to 30 h) diamond growth occurs if water and carbonates are present in the fluid phase. Water promotes faster diamond growth (up to 14 mm/year at 1400 °C, 7 GPa, 10 g/l NaCl), which is favorable to the inclusion trapping process. At 7 GPa, temperature and fluid composition are the main factors controlling diamond growth. In these experiments, diamonds grew in the presence of two fluids: an aqueous fluid and a hydrous silicate melt. The carbon source for diamond growth must be carbonate (CO32) dissolved in the melt or carbon dioxide species in the aqueous fluid (CO2aq). The presence of NaCl affects the growth kinetics but is not a prerequisite for inclusion-bearing diamond formation. The presence of small discrete or isolated volumes of water-rich fluids is necessary to grow inclusion-bearing peridotitic, eclogitic, fibrous, cloudy and coated diamonds, and may also be involved in the growth of ultradeep, ultrahigh-pressure metamorphic diamonds.
DS1607-1336
2016
Burness, S.The role of sulphur during partial melting of the eclogitic cratonic mantle.IGC 35th., Session A Dynamic Earth 1p. AbstractMantleEclogite
DS1608-1396
2016
Burnham, A.D., Bulanova, G.P., Smith, C.B., Whitehead, S.C., Kohn, S.C., Gobbo, L., Walter, M.J.Diamonds from the Machado River alluvial deposit, Rondona, Brazil, derived from both lithospheric and sublithospheric mantle.Lithos, in press available, 15p.South America, BrazilMorphology, textures, chemistry

Abstract: Diamonds from the Machado River alluvial deposit have been characterised on the basis of external morphology, internal textures, carbon isotopic composition, nitrogen concentration and aggregation state and mineral inclusion chemistry. Variations in morphology and features of abrasion suggest some diamonds have been derived directly from local kimberlites, whereas others have been through extensive sedimentary recycling. On the basis of mineral inclusion compositions, both lithospheric and sublithospheric diamonds are present at the deposit. The lithospheric diamonds have clear layer-by-layer octahedral and/or cuboid internal growth zonation, contain measurable nitrogen and indicate a heterogeneous lithospheric mantle beneath the region. The sublithospheric diamonds show a lack of regular sharp zonation, do not contain detectable nitrogen, are isotopically heavy (d13CPDB predominantly - 0.7 to - 5.5) and contain inclusions of ferropericlase, former bridgmanite, majoritic garnet and former CaSiO3-perovskite. This suggests source lithologies that are Mg- and Ca-rich, probably including carbonates and serpentinites, subducted to lower mantle depths. The studied suite of sublithospheric diamonds has many similarities to the alluvial diamonds from Kankan, Guinea, but has more extreme variations in mineral inclusion chemistry. Of all superdeep diamond suites yet discovered, Machado River represents an end-member in terms of either the compositional range of materials being subducted to Transition Zone and lower mantle or the process by which materials are transferred from the subducted slab to the diamond-forming region.
DS1609-1708
2010
Bush, D.An overview of the estimation of kimberlite diamond deposits.The 4th Colloquium on Diamonds - source to use held Gabarone March 1-3, 2010, 12p.Africa, South AfricaDeposit - Venetia

Abstract: The nature of diamond deposits are such that most mineral resource reporting codes contain a sub-section unique to diamond estimation and classification. These codes identify a number of criteria which define the uniqueness of diamond deposits, including, the low and variable grade of diamond deposits; the particulate nature of diamonds which affects both size and revenue of individual particles and finally the inherent difficulties and uncertainties in the estimation of diamond resources. These criteria are expanded on to provide an overview of the estimation of kimberlite diamond deposits. Placer deposits have been excluded as they constitute a particularly complex example of particulate distributions. Diamond grade, typically of the order of parts per million (ppm), is dependent on the number of stones per unit volume or mass as well as the diamond size distribution while diamond revenue is dependent on size, model, colour and quality. These parameters of a discrete particle result in a conmlOdily which requires some unique estimation and modelling methodologies. For most commodities "grade" is a measure of concentration and is directly proportional to value. [n the case of diamonds however the same stone grade (e.g. stones per 100 tonnes) may have significantly different carat grades and revenue, depending on the characteristics of the individual stones (size, model, colour and quality). The De _Beers Consolidated Mines Venetia Mine is used as an example of diamond eslimation as well as to highlighl some propriety grade eslimation techniques. The mine has been sampled for grade using a number of different sample supports, from 36" diameter reverse circulation drillholes to micro diamond core drilling. De Beers Group Services (Ply) Lld (DBGS) have developed a technique of mixed (or multiple) support kriging which allows for the combination of samples of different sizes (and therefore grade distributions) in the estimation process. In addition DBGS have researched techniques of both global and local grade estimation using micro diamonds. The estimation of kimberlite diamond deposits has a number of unique components resulting from the discrete nature of the diamond distribution. It is however equally fundamentally important to understand exactly what the sampling data represents; the constraints Wlder which the data were coUected (e.g. bottom cut ofJ) and the adjustments necessary to ensure parity Page 73 The Southern African Institute of Mining and Metallurgy Diamonds - Source to Use 2010 DBush between and within sampling programmes as well as the likely metallurgical process III a production environment.
DS1605-0817
2016
Busseweiler, Y.Al-in-olivine thermometry: experimental versus empirical calibration and analytical challenges.DCO Edmonton Diamond Workshop, June 8-10TechnologyGeothermometry
DS1604-0596
2016
Bussweiler, Y., Pearson, D.G., Luth, R.W., Kjarsgaard, B.A., Stachel, T.The evolution of calcite-bearing kimberlite by rock-melt reaction during ascent - evidence from polymineralic inclusions within Cr- diopside and Cr-pyrope megacrysts from Lac de Gras kimberlites, Northwest Territories, Canada.GAC MAC Meeting Special Session SS11: Cratons, kimberlites and diamonds., abstract 1/4p.Canada, Northwest TerritoriesDeposit - Lac de Gras
DS1607-1288
2016
Bussweiler, Y., Stone, R.S., Pearson, D.G., Luth, R.W., Stachel, T., Kjarsgaard, B.A., Menzies, A.The evolution of calcite bearing kimberlites by melt rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada.Contributions to Mineralogy and Petrology, Vol. 171, 7, 25p.Canada, Northwest TerritoriesDeposit - Lac de Gras arena

Abstract: Megacrystic (>1 cm) clinopyroxene (Cr-diopside) and garnet (Cr-pyrope) xenocrysts within kimberlites from Lac de Gras (Northwest Territories, Canada) contain fully crystallized melt inclusions. These ‘polymineralic inclusions’ have previously been interpreted to form by necking down of melts at mantle depths. We present a detailed petrographical and geochemical investigation of polymineralic inclusions and their host crystals to better understand how they form and what they reveal about the evolution of kimberlite melt. Genetically, the megacrysts are mantle xenocrysts with peridotitic chemical signatures indicating an origin within the lithospheric mantle (for the Cr-diopsides studied here ~4.6 GPa, 1015 °C). Textural evidence for disequilibrium between the host crystals and their polymineralic inclusions (spongy rims in Cr-diopside, kelyphite in Cr-pyrope) is consistent with measured Sr isotopic disequilibrium. The preservation of disequilibrium establishes a temporal link to kimberlite eruption. In Cr-diopsides, polymineralic inclusions contain phlogopite, olivine, chromite, serpentine, and calcite. Abundant fluid inclusion trails surround the inclusions. In Cr-pyropes, the inclusions additionally contain Al-spinel, clinopyroxene, and dolomite. The major and trace element compositions of the inclusion phases are generally consistent with the early stages of kimberlite differentiation trends. Extensive chemical exchange between the host phases and the inclusions is indicated by enrichment of the inclusions in major components of the host crystals, such as Cr2O3 and Al2O3. This chemical evidence, along with phase equilibria constraints, supports the proposal that the inclusions within Cr-diopside record the decarbonation reaction: dolomitic melt + diopside ? forsterite + calcite + CO2, yielding the observed inclusion mineralogy and producing associated (CO2-rich) fluid inclusions. Our study of polymineralic inclusions in megacrysts provides clear mineralogical and chemical evidence for an origin of kimberlite that involves the reaction of high-pressure dolomitic melt with diopside-bearing mantle assemblages producing a lower-pressure melt that crystallizes a calcite-dominated assemblage in the crust.
DS1608-1397
2016
Bussweiler, Y., Stone, R.S., Pearson, D.G., Luth, R.W., Stachel, T., Kjarsgaard, B.A., Menzies, A.The evolution of calcite bearing kimberlites by melt rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada.Contributions to Mineralogy and Petrology, in press available 25p.Canada, Northwest TerritoriesDeposit - Lac de Gras

Abstract: Megacrystic (>1 cm) clinopyroxene (Cr-diopside) and garnet (Cr-pyrope) xenocrysts within kimberlites from Lac de Gras (Northwest Territories, Canada) contain fully crystallized melt inclusions. These ‘polymineralic inclusions’ have previously been interpreted to form by necking down of melts at mantle depths. We present a detailed petrographical and geochemical investigation of polymineralic inclusions and their host crystals to better understand how they form and what they reveal about the evolution of kimberlite melt. Genetically, the megacrysts are mantle xenocrysts with peridotitic chemical signatures indicating an origin within the lithospheric mantle (for the Cr-diopsides studied here ~4.6 GPa, 1015 °C). Textural evidence for disequilibrium between the host crystals and their polymineralic inclusions (spongy rims in Cr-diopside, kelyphite in Cr-pyrope) is consistent with measured Sr isotopic disequilibrium. The preservation of disequilibrium establishes a temporal link to kimberlite eruption. In Cr-diopsides, polymineralic inclusions contain phlogopite, olivine, chromite, serpentine, and calcite. Abundant fluid inclusion trails surround the inclusions. In Cr-pyropes, the inclusions additionally contain Al-spinel, clinopyroxene, and dolomite. The major and trace element compositions of the inclusion phases are generally consistent with the early stages of kimberlite differentiation trends. Extensive chemical exchange between the host phases and the inclusions is indicated by enrichment of the inclusions in major components of the host crystals, such as Cr2O3 and Al2O3. This chemical evidence, along with phase equilibria constraints, supports the proposal that the inclusions within Cr-diopside record the decarbonation reaction: dolomitic melt + diopside ? forsterite + calcite + CO2, yielding the observed inclusion mineralogy and producing associated (CO2-rich) fluid inclusions. Our study of polymineralic inclusions in megacrysts provides clear mineralogical and chemical evidence for an origin of kimberlite that involves the reaction of high-pressure dolomitic melt with diopside-bearing mantle assemblages producing a lower-pressure melt that crystallizes a calcite-dominated assemblage in the crust.
DS1601-0009
2015
Cafferky, S., Schmandt, B.Teleseismic P wave spectra from USArray and implications for upper mantle attentuation and scattering.Geochemistry, Geophysics, Geosystems: G3, Vol. 16, 10, pp. 3343-3361.United StatesGeophysics - seismics

Abstract: Teleseismic P wave amplitude spectra from deep earthquakes recorded by USArray are inverted for maps of upper mantle ?t* for multiple frequency bands within 0.08-2 Hz. All frequency bands show high ?t* regions in the southwestern U.S., southern Rocky Mountains, and Appalachian margin. Low ?t* is more common across the cratonic interior. Inversions with narrower frequency bands yield similar patterns, but greater ?t* magnitudes. Even the two standard deviation ?t* magnitude for the widest band is ~2-7 times greater than predicted by global QS tomography or an anelastic olivine thermal model, suggesting that much of the ?t* signal is nonthermal in origin. Nonthermal contributions are further indicated by only a moderate correlation between ?t* and P travel times. Some geographic variations, such as high ?t* in parts of the cratonic interior with high mantle velocities and low heat flow, demonstrate that the influence of temperature is regionally overwhelmed. Transverse spectra are used to investigate the importance of scattering because they would receive no P energy in the absence of 3-D heterogeneity or anisotropy. Transverse to vertical (T/Z) spectral ratios for stations with high ?t* are higher and exhibit steeper increases with frequency compared to T/Z spectra for low ?t* stations. The large magnitude of ?t* estimates and the T/Z spectra are consistent with major contributions to ?t* from scattering. A weak positive correlation between intrinsic attenuation and apparent attenuation due to scattering may contribute to ?t* magnitude and the moderate correlation of ?t* with travel times.
DS1602-0196
2016
Cagney, N., Crameri, F., Newsome, W.H., Lithgow-Bertelloni, C., Cotel, A., Hart, S.R., Whitehead, J.A.Constraining the source of mantle plumes.Earth and Planetary Science Letters, Vol. 435, 1, pp. 55-63.MantlePlume

Abstract: In order to link the geochemical signature of hot spot basalts to Earth's deep interior, it is first necessary to understand how plumes sample different regions of the mantle. Here, we investigate the relative amounts of deep and shallow mantle material that are entrained by an ascending plume and constrain its source region. The plumes are generated in a viscous syrup using an isolated heater for a range of Rayleigh numbers. The velocity fields are measured using stereoscopic Particle-Image Velocimetry, and the concept of the ‘vortex ring bubble’ is used to provide an objective definition of the plume geometry. Using this plume geometry, the plume composition can be analysed in terms of the proportion of material that has been entrained from different depths. We show that the plume composition can be well described using a simple empirical relationship, which depends only on a single parameter, the sampling coefficient, scsc. High-scsc plumes are composed of material which originated from very deep in the fluid domain, while low-scsc plumes contain material entrained from a range of depths. The analysis is also used to show that the geometry of the plume can be described using a similarity solution, in agreement with previous studies. Finally, numerical simulations are used to vary both the Rayleigh number and viscosity contrast independently. The simulations allow us to predict the value of the sampling coefficient for mantle plumes; we find that as a plume reaches the lithosphere, 90% of its composition has been derived from the lowermost 260–750 km in the mantle, and negligible amounts are derived from the shallow half of the lower mantle. This result implies that isotope geochemistry cannot provide direct information about this unsampled region, and that the various known geochemical reservoirs must lie in the deepest few hundred kilometres of the mantle.
DS1605-0818
2016
Callan, N.J.Geological mapping in exploration: a view from the trenches.SEG Newsletter, No. 105, Apr. pp. 13-15.TechnologyExploration

Abstract: Kevin Heather’s (SEG 1998 F) presentation at the September 2015 Chile- Explore Congress, entitled “The Lost Art of Geological Mapping: Should We Care?,” regrettably came as no surprise to me, although I have to admit to being more than a little disappointed. Most senior explorationists, I suspect, would probably share these sentiments. Geological mapping is, after all, the very embodiment of all the basic field skills we learn as geologists, and the simple fact is that the alarm bells have been sounding loudly for some time now in our industry: basic field geological skills have been lost in the emerging generation of exploration geologists. As a geologist with some 30 years of experience in the exploration and mining industry, almost entirely in a fieldbased technical capacity, I have always maintained that careful geological mapping, based on sound observation, is one of the cornerstones of successful exploration. Indeed, given that our industry is founded on combinations of fortuitous geological phenomena in a complex framework, why would geological mapping and field geology not be positioned at the very forefront the discovery process? A large part of the debate as to the underlying causes for the general demise of geological field skills has focused on issues at the university level (e.g., fieldwork reduction due to funding cuts and increased liability, changes in undergraduate curricula to more closely reflect the broadening range of geological disciplines to serve wider needs of society, an emphasis on rapidly publishable experimental and modeling research at the expense of more costly field-based studies, etc.). The mining industry has responded by promoting its specific technical and skill set requirements at university level via collaborative research, student training initiatives, and funding programs. The focus of this Views contribution is to examine several internal industry issues which I believe have contributed to falling standards of geological fieldwork, and which have become apparent to me during extensive time spent in the field in a consulting capacity for numerous major, mid-tier, and junior companies.
DS1607-1289
2016
Calo, M., Bodin, T., Romanowicz, B.Layered structure in the upper mantle across North America from joint inversion of long and short period seismic data.Earth and Planetary Science Letters, Vol. 449, pp. 164-175.United States, CanadaGeophysics - seismics

Abstract: We estimate crustal and uppermost mantle shear velocity structure beneath 30 stations in North America by jointly inverting the high frequency scattered wavefield observed in the P wave coda, together with long period surface wave phase and group dispersion data. Several features distinguish our approach from previous such joint inversions. 1) We apply a cross-convolution method, rather than more standard deconvolution approaches used in receiver function studies, and consider both Love and Rayleigh wave dispersion, allowing us to infer profiles of radial anisotropy. 2) We generate probabilistic 1D radially anisotropic depth profiles across the whole uppermost mantle, down to ~350 km depth. 3) The inverse problem is cast in a trans-dimensional Bayesian formalism, where the number of isotropic and anisotropic layers is treated as unknown, allowing us to obtain models described with the least number of parameters. Results show that the tectonically active region west of the Rocky Mountain Front is marked by a Lithospheric Asthenosphere Boundary and a Lehmann Discontinuity occurring at relatively shallow depths (60-150 km and 100-200 km, respectively), whereas further east, in the stable craton, these discontinuities are deeper (170-200 km and 200-250 km, respectively). In addition, in the stable part of the continent, at least two Mid-Lithospheric Discontinuities are present at intermediate depths, suggesting the existence of strong lithospheric layering, and a mechanism for lithospheric thickening by underplating of additional layers as cratonic age increases. The Moho across the continent as well as mid-crustal discontinuities in the craton are also imaged, in agreement with independent studies.
DS1612-2283
2016
Cambeses, A., Garcia-Casco, A., Scarrow, J.H., Montero, P., Perez-Valera, L.A., Bea, F.Mineralogical evidence for lamproite magma mixing and storage at mantle depths: Socovos fault lamproites, SE Spain.Lithos, Vol. 266-267, pp. 182-201.Europe, SpainLamproite

Abstract: Detailed textural and mineral chemistry characterisation of lamproites from the Socovos fault zone, SE Spain Neogene Volcanic Province (NVP) combining X-ray element maps and LA-ICP-MS spot analyses has provided valuable information about mantle depth ultrapotassic magma mixing processes. Despite having similar whole-rock compositions, rocks emplaced in the Socovos fault are mineralogically varied: including type-A olivine-phlogopite lamproites; and type-B clinopyroxene-phlogopite lamproites. The Ol-lacking type-B predates Ol-bearing type-A by c. 2 million years. We propose that the mineralogical variations, which are representative of lamproites in the NVP as a whole, indicate mantle source heterogeneities. Major and trace element compositions of mineral phases suggest both metasomatised harzburgite and veined pyroxenite sources that were most likely closely spatially related. Thin section scale textural and compositional variations in mineral phases reveal heterogeneous mantle- and primitive magma-derived crystals. The variety of crystals points to interaction and mingling-mixing of ultrapotassic magma batches at mantle depths prior crustal emplacement. The mixing apparently occurred in a mantle melting zone with a channelised flow regime and localised magma chambers-reservoirs. Magma interaction was interrupted when the Socovos and other lithosphere-scale faults tore down to the mantle source region, triggering rapid ascent of the heterogeneous lamproite magma.
DS1609-1709
2010
Campbell, J.A.H., Lamb, W., Clarke, J., Petersen, K.The development of AK6.The 4th Colloquium on Diamonds - source to use held Gabarone March 1-3, 2010, 20p.Africa, BotswanaDeposit - AK6
DS1612-2284
2016
Cao, Y.H., Linnen, R.L., Good, D.J., Samson, I.M., Epstein, R.The application of portable XRF and benchtop SEM-EDS to Cu-Pd exploration in the Coldwell alkaline complex, Ontario, Canada.Geochemistry: Exploration, Environment, Analysis, Vol. 16, 3-4, pp. 193-212.Canada, OntarioAlkalic

Abstract: Mineral exploration is increasingly taking advantage of real time techniques that dramatically reduce the costs and time taken to obtain results compared to traditional analytical methods. Portable X-ray fluorescence (pXRF) is now a well-established technique that is used to acquire lithogeochemical data. To date, however, benchtop scanning electron microscopes, equipped with energy dispersive systems (bSEM-EDS) have received little attention as a possible mineral exploration tool. This study examines the utility of combining pXRF and bSEM-EDS to characterize the igneous stratigraphy and its relationship to Cu-Pd mineralization in a drill hole at the Four Dams occurrence, located within the Eastern Gabbro assemblage of the Coldwell Alkaline Complex, Canada. The first part of this study compares field portable and laboratory techniques. Seventy-two powdered samples analysed by pXRF are compared with traditional major elements analysed by inductively coupled atomic emission spectroscopy (ICP-AES) and trace elements by inductively coupled plasma spectrometry (ICP-MS), and the compositions of 128 olivine, clinopyroxene and plagioclase grains analysed by bSEM-EDS are compared with traditional electron microprobe data. Our results show that each portable technique yields results similar to their lab-based counterparts within the analytical capabilities and precisions of the respective instruments. The second part presents a case study for the application of pXRF and bSEM-EDS to resolve questions related to igneous stratigraphy as an aid to mineral exploration in a complicated geological setting. A major problem for Cu-Pd exploration in the Coldwell Complex of NW Ontario is that the oxide-rich units that host Cu-Pd mineralization in the Marathon Series are petrographically similar to the barren oxide-rich units in the Layered Series. However, the mineralized units are geochemically distinctive. Our results show that the mineralized Marathon Series can be distinguished from the barren Layered Series, including oxide-rich units of both, by combinations of P2O5, Ba, Zr and V/Ti values, determined by pXRF, combined with plagioclase, olivine or clinopyroxene compositions measured by bSEM-EDS. The combination of pXRF and bSEM-EDS thus shows considerable promise as an exploration technique.
DS1606-1079
2016
Caran, S.Mineralogy and petrology of leucite ankaratrites with affinities to kamafugites and carbonatites from the Kayikoy area, Isparta, SW Anatolia, Turkey: implications for the influences of carbonatite metasomatism into the parental mantle sources of silica-unLithos, Vol. 256-257, pp. 13-25.Europe, TurkeyCarbonatite

Abstract: In the Kayiköy area of Isparta-Gölcük district, Inner Isparta Angle, SW Anatolia, Turkey, a small volume of newly discovered K-rich mafic potassic magma was emplaced in the form of dome in the vicinity of graben structures under Pliocene (3.68 ± 0.5 Ma) extensional tectonics. Kayiköy leucite ankaratrites are made up of abundant diopside, barian phlogopite and leucite, and lesser olivine, that rarely contains Cr-spinel, nepheline and haüyne, with abundant magnetite. They have low SiO2 (44.00-46.04 wt.%) and Al2O3 (12.10-12.64 wt.%) with high K2O (4.00-4.42 wt.%), CaO (13.50-14.40 wt.%) and MgO (8.52-9.36 wt.%), with high Cr (397-547 ppm) and moderate Ni (57-74 ppm) contents. They represent the less evolved silica-undersaturated mafic potassic magmas within the Isparta-Gölcük volcanic province, and may be considered another parental source to the wide spectrum of the K-rich rocks. They are highly enriched in most of the incompatible elements (e.g., Ba, 2761 to > 10,000 ppm; Sr, 3700-4074 ppm; Th, 33.60-36.99 ppm; Zr, 274-321 ppm) with high LREEs, low HREEs and elevated LREEs/HREEs ratios [(La/Yb)N, 73-80] and are comparable with kamafugite and carbonatites. Trace element patterns have negative P, Ti and Nb-Ta anomalies in common with the Italian kamafugite province and lack of a Eu anomaly, in contrast to the negative Eu anomaly of the Italian province. Their Sr87/86-Nd143/144 (0.703877-0.512765) isotopic compositions, together with those of other potassic volcanics from the Inner Isparta Angle, coincide with the West Quinling (China) kamafugites with highly depleted mantle signatures, and young East African carbonatites. Olivine-Cr-spinel pairs, high Mg# (0.69-0.73) numbers and Cr values, and high incompatible and LREE contents in Kayiköy leucite ankaratritic magma are consistent with near-primary magmas equilibrated with enriched and heterogeneous (peridotitic/pyroxenitic) mantle sources. On the basis of (i) their geochemical signatures [low Ti/Eu, elevated CaO/Al2O3 and (La/Yb)N ratios], (ii) consistency of parental magma compositions with experimental melt compositions for carbonated peridotites, and (iii) geochemical and isotopic affinities to kamafugites and carbonatites, it is inferred that the carbonatitic melts infiltrated the mantle sources of Kayiköy leucite ankaratritic magma, and induced the depletion of its SiO2 contents. Carbonate-bearing phonolitic parental melts formed by mixing of both silicate and carbonate-asthenospheric melts from convecting mantle, react with wall-rock peridotite to form diopside + phlogopite + olivine + apatite metasomatic veins as wehrlitic metasomes. Partial melting of such newly generated wehrlitic metasomes in the subcontinental lithospheric mantle resulted in the parental melts of Kayiköy leucite ankaratrites. Results also imply that the nature and composition of asthenosphere-derived silicate melts (basanitic, phonolitic or tephriphonolitic in composition) and percentage of mixed carbonatitic melts lead to the formation of discrete mantle metasomes within the Inner Isparta Angle lithospheric mantle. These metasomes are conducive to the generation of coeval potassic magmas with contrasting geochemical signatures (e.g., lamproitic, lamprophyric, kamafugitic) in a single tectonic setting.
DS1606-1080
2016
Casey, K., Glennerster, R.Reconciliation in Sierra Leone. Conflicts, civil war.Science, Vol. 352, 6287, May 13, pp. 766-767.Africa, Sierra LeoneHistory

Abstract: Since the end of World War II, there have been 259 armed conflicts in 159 locations (1). Sierra Leone's civil war began 25 years ago, at a time when roughly 25% of all countries worldwide were experiencing civil war (2). How can individuals and groups recover from such violent conflicts? On page 787 of this issue, Cilliers et al. (3) provide rigorous evidence on the efficacy of one postwar reconciliation strategy that was implemented in 100 communities in Sierra Leone (4).
DS1605-0819
2016
Castillo-Oliver, M., Gali, S., Melgarejo, J.C., Griffin, W.L., Belousova, E., Pearson, N.J., Watangua, M., O'Reilly, S.Y.Trace element geochemistry and U-Pb dating of perovskite in kimberlites of the Lunda Norte province ( NE Angola): petrogenetic and tectonic implications.Chemical Geology, Vol. 426, pp. 118-134.Africa, AngolaDeposit - Alto Cuilo

Abstract: Perovskite (CaTiO3) has become a very usefulmineral for dating kimberlite eruptions, aswell as for constraining the compositional evolution of a kimberlitic magma and its source. Despite the undeniable potential of such an approach, no similar study had been done in Angola, the fourth largest diamond producer in Africa. Here we present the firstwork of in situ U-Pb geochronology and Sr-Ndisotope analyses of perovskite in six Angolan kimberlites, supported by a detailed petrographic and geochemical study of their perovskite populations. Four types of perovskitewere identified, differing in texture,major- and trace-element composition, zoning patterns, type of alteration and the presence or absence of inclusions. Primary groundmass perovskite is classified either as anhedral, Na-, Nb- and LREE-poor perovskite (Ia); or euhedral, strongly zoned, Na-, Nb- and LREE-rich perovskite (Ib). Secondary perovskite occurs as reaction rims on ilmenite (IIa) or as high Nb (up to 10.6 wt% Nb2O5) perovskite rims on primary perovskite (IIb). The occurrence of these four types within the Mulepe kimberlites is interpreted as an evidence of a complex, multi-stage process that involved mingling of compositionally different melts. U-Pb dating of these perovskites yielded Lower Cretaceous ages for four of the studied kimberlites: Mulepe 1 (116.2±6.5Ma),Mulepe 2 (123.0±3.6Ma), Calonda (119.5±4.3 Ma) and Cat115 (133±10Ma). Kimberlite magmatism occurred in NE Angola likely due to reactivation of deep-seated translithospheric faults (N300 km) during the break-up of Gondwana. Sr-Nd isotope analyses of four of these kimberlites indicate that they are Group I kimberlites, which is consistent with the petrological observations.
DS1604-0597
2016
Castilo-Oliver, M., Gali, S., Melgarejo, J.C., Griffin, W.L., Belousova, E., Pearson, N.J., Watangua, M., O'Reilly, S.Y.Trace element geochemistry and U-Pb dating of perovskite in kimberlites of the Lunda Norte province ( NE Angola): petrogenetic and tectonic implications.Chemical Geology, Vol. 426, pp. 118-134.Africa, AngolaGeochronology

Abstract: Perovskite (CaTiO3) has become a very useful mineral for dating kimberlite eruptions, as well as for constraining the compositional evolution of a kimberlitic magma and its source. Despite the undeniable potential of such an approach, no similar study had been done in Angola, the fourth largest diamond producer in Africa. Here we present the first work of in situ U-Pb geochronology and Sr-Nd isotope analyses of perovskite in six Angolan kimberlites, supported by a detailed petrographic and geochemical study of their perovskite populations. Four types of perovskite were identified, differing in texture, major- and trace-element composition, zoning patterns, type of alteration and the presence or absence of inclusions. Primary groundmass perovskite is classified either as anhedral, Na-, Nb- and LREE-poor perovskite (Ia); or euhedral, strongly zoned, Na-, Nb- and LREE-rich perovskite (Ib). Secondary perovskite occurs as reaction rims on ilmenite (IIa) or as high Nb (up to 10.6 wt% Nb2O5) perovskite rims on primary perovskite (IIb). The occurrence of these four types within the Mulepe kimberlites is interpreted as an evidence of a complex, multi-stage process that involved mingling of compositionally different melts. U-Pb dating of these perovskites yielded Lower Cretaceous ages for four of the studied kimberlites: Mulepe 1 (116.2 ± 6.5 Ma), Mulepe 2 (123.0 ± 3.6 Ma), Calonda (119.5 ± 4.3 Ma) and Cat115 (133 ± 10 Ma). Kimberlite magmatism occurred in NE Angola likely due to reactivation of deep-seated translithospheric faults (> 300 km) during the break-up of Gondwana. Sr-Nd isotope analyses of four of these kimberlites indicate that they are Group I kimberlites, which is consistent with the petrological observations.
DS1612-2285
2016
Cavalcante, G.C.C., Viegas, G., Archanjo, C.J.The influence of partial melting and melt migration on the rheology of the continental crust.Journal of Geodynamics, Vol. 101, pp. 186-199.MantleMelting

Abstract: The presence of melt during deformation produces a drastic change in the rheological behavior of the continental crust; rock strength is decreased even for melt fractions as low as ~7%. At pressure/temperature conditions typical of the middle to lower crust, melt-bearing systems may play a critical role in the process of strain localization and in the overall strength of the continental lithosphere. In this contribution we focus on the role and dynamics of melt flow in two different mid-crustal settings formed during the Brasiliano orogeny: (i) a large-scale anatectic layer in an orthogonal collision belt, represented by the Carlos Chagas anatexite in southeastern Brazil, and (ii) a strike-slip setting, in which the Espinho Branco anatexite in the Patos shear zone (northeast Brazil) serves as an analogue. Both settings, located in eastern Brazil, are part of the Neoproterozoic tectonics that resulted in widespread partial melting, shear zone development and the exhumation of middle to lower crustal layers. These layers consist of compositionally heterogeneous anatexites, with variable former melt fractions and leucosome structures. The leucosomes usually form thick interconnected networks of magma that reflect a high melt content (>30%) during deformation. From a comparison of previous work based on detailed petrostructural and AMS studies of the anatexites exposed in these areas, we discuss the rheological implications caused by the accumulation of a large volume of melt “trapped” in mid-crustal levels, and by the efficient melt extraction along steep shear zones. Our analyses suggest that rocks undergoing partial melting along shear settings exhibit layers with contrasting competence, implying successive periods of weakening and strengthening. In contrast, regions where a large amount of magma accumulates lack clear evidence of competence contrast between layers, indicating that they experienced only one major stage of dramatic strength drop. This comparative analysis also suggests that the middle part of both belts contained large volumes of migmatites, attesting that the orogenic root was partially molten and encompassed more than 30% of granitic melt at the time of deformation.
DS1607-1290
2016
Cawood, P.A., Strachan, R.A., Pisarevsky, S.A., Gladkochub, D.P., Murphy, J.B.Linking collisional and accretionary orogens during Rodinia assembly and breakup: implications for models of supercontinent cycles.Earth and Planetary Science Letters, Vol. 449, pp. 118-126.Gondwana, RodiniaSubduction

Abstract: Periodic assembly and dispersal of continental fragments has been a characteristic of the solid Earth for much of its history. Geodynamic drivers of this cyclic activity are inferred to be either top-down processes related to near surface lithospheric stresses at plate boundaries or bottom-up processes related to mantle convection and, in particular, mantle plumes, or some combination of the two. Analysis of the geological history of Rodinian crustal blocks suggests that internal rifting and breakup of the supercontinent were linked to the initiation of subduction and development of accretionary orogens around its periphery. Thus, breakup was a top-down instigated process. The locus of convergence was initially around north-eastern and northern Laurentia in the early Neoproterozoic before extending to outboard of Amazonia and Africa, including Avalonia-Cadomia, and arcs outboard of Siberia and eastern to northern Baltica in the mid-Neoproterozoic (~760 Ma). The duration of subduction around the periphery of Rodinia coincides with the interval of lithospheric extension within the supercontinent, including the opening of the proto-Pacific at ca. 760 Ma and the commencement of rifting in east Laurentia. Final development of passive margin successions around Laurentia, Baltica and Siberia was not completed until the late Neoproterozoic to early Paleozoic (ca. 570-530 Ma), which corresponds with the termination of convergent plate interactions that gave rise to Gondwana and the consequent relocation of subduction zones to the periphery of this supercontinent. The temporal link between external subduction and internal extension suggests that breakup was initiated by a top-down process driven by accretionary tectonics along the periphery of the supercontinent. Plume-related magmatism may be present at specific times and in specific places during breakup but is not the prime driving force. Comparison of the Rodinia record of continental assembly and dispersal with that for Nuna, Gondwana and Pangea suggests grouping into two supercycles in which Nuna and Gondwana underwent only partial or no break-up phase prior to their incorporation into Rodinia and Pangea respectively. It was only after this final phase of assembly that the supercontinents then underwent full dispersal.
DS1601-0010
2015
Chalapathai Rao, N.V., Atiullah, Burgess, A.R.,Nanda, P., Choudhary, A.K., Sahoo, S., Lehman, B., Chahong, N.Petrology, 40Ar/39Ar, Sr-Nd isotope systematics, and geodynamic significance of an ultrapotassic ( lamproitic) dyke with affinities to kamafugite from the easternmost margin of the Bastar Craton, India.Mineralogy and Petrology, in press available, 25p.IndiaLamproites - Nuapada field

Abstract: We report the mineralogy, bulk-rock geochemistry, 40Ar/39Ar (whole-rock) age and radiogenic (Sr and Nd) isotope composition of an ultrapotassic dyke from Sakri (Nuapada lamproite field) located at the tectonic contact between the easternmost margin of the Bastar craton and Eastern Ghats Mobile Belt, India. The Sakri dyke has a mineralogy which strongly resembles a lamproite sensu stricto (viz.,Ti-rich phlogopite, Na-poor diopside, Fe-rich sanidine, ulvospinel trend and Sr-rich apatite). However, its bulk-rock major element geochemical characteristics (viz., extreme silica-undersaturated nature) resemble sensu lato kamafugite from Toro Ankole, Uganda, East African Rift, and Alto Paranaiba Province, Brazil. The Sakri dyke also displays certain compositional peculiarities (viz., high degree of evolution of mica composition from phlogopite to biotite, elevated titanium and aluminum in clinopyroxene and significantly lower bulk Mg#) when compared to the ultrapotassic rocks from various Indian cratons. 40Ar/39Ar dating gave a plateau age of 1045?±?9 Ma which is broadly similar to that of other Mesoproterozoic (i) lamproites from the Bastar and Bundelkhand cratons, and (ii) kimberlites from the Eastern Dharwar craton. Initial bulk-rock Sr (0.705865-0.709024) and Nd (0.511063-0.511154) isotopic ratios reveal involvement of an ‘enriched’ source region with long-term incompatible element enrichment and a depleted mantle (TDM) Nd model age of 2.56 Ga straddling the Archaean-Proterozoic chronostratigraphic boundary. The bulk-rock incompatible trace element ratios (Ta/Yb, Th/Yb, Rb/Ba and Ce/Y) of the Sakri ultrapotassic dyke negate any significant influence of crustal contamination. Small-degree melting (1 to 1.5 %) of a mixed garnet-facies and spinel-facies phlogopite lherzolite can account for its observed REE concentrations. Whereas the emplacement of the Sakri ultrapotassic dyke is related to the amalgamation of the supercontinent of Rodinia, its overlapping geochemical characteristics of lamproite and kamafugite (also displayed by two other lamproites of the Nuapada field at Amlidadar and Parkom) are linked to the emplacement in a unique geological setting at the craton-mobile belt contact and hence of geodynamic significance.
DS1604-0598
2016
Chalapathi Rao, N.V., Atiullah, Burgess, R., Nanda, P., Choudhary, A.K., Sahoo, S., Lehmann, B., Chahong, N.Petrology, 40Ar/39Ar age, Sr-Nd isotope systematics, and geodynamic significance of an ultrapotassic ( lamproitic) dyke with affinities to kamafugite from the easternmost margin of the Bastar Craton, India.Mineralogy and Petrology, in press available, 25p.IndiaDeposit - Sakri Nuapada

Abstract: We report the mineralogy, bulk-rock geochemistry, 40Ar/39Ar (whole-rock) age and radiogenic (Sr and Nd) isotope composition of an ultrapotassic dyke from Sakri (Nuapada lamproite field) located at the tectonic contact between the easternmost margin of the Bastar craton and Eastern Ghats Mobile Belt, India. The Sakri dyke has a mineralogy which strongly resembles a lamproite sensu stricto (viz.,Ti-rich phlogopite, Na-poor diopside, Fe-rich sanidine, ulvospinel trend and Sr-rich apatite). However, its bulk-rock major element geochemical characteristics (viz., extreme silica-undersaturated nature) resemble sensu lato kamafugite from Toro Ankole, Uganda, East African Rift, and Alto Paranaiba Province, Brazil. The Sakri dyke also displays certain compositional peculiarities (viz., high degree of evolution of mica composition from phlogopite to biotite, elevated titanium and aluminum in clinopyroxene and significantly lower bulk Mg#) when compared to the ultrapotassic rocks from various Indian cratons. 40Ar/39Ar dating gave a plateau age of 1045?±?9 Ma which is broadly similar to that of other Mesoproterozoic (i) lamproites from the Bastar and Bundelkhand cratons, and (ii) kimberlites from the Eastern Dharwar craton. Initial bulk-rock Sr (0.705865-0.709024) and Nd (0.511063-0.511154) isotopic ratios reveal involvement of an ‘enriched’ source region with long-term incompatible element enrichment and a depleted mantle (TDM) Nd model age of 2.56 Ga straddling the Archaean-Proterozoic chronostratigraphic boundary. The bulk-rock incompatible trace element ratios (Ta/Yb, Th/Yb, Rb/Ba and Ce/Y) of the Sakri ultrapotassic dyke negate any significant influence of crustal contamination. Small-degree melting (1 to 1.5 %) of a mixed garnet-facies and spinel-facies phlogopite lherzolite can account for its observed REE concentrations. Whereas the emplacement of the Sakri ultrapotassic dyke is related to the amalgamation of the supercontinent of Rodinia, its overlapping geochemical characteristics of lamproite and kamafugite (also displayed by two other lamproites of the Nuapada field at Amlidadar and Parkom) are linked to the emplacement in a unique geological setting at the craton-mobile belt contact and hence of geodynamic significance.
DS1609-1710
2016
Chalapathi Rao, N.V., Dongre, A., Wu, F-Y., Lehmann, B.A Late Cretaceous ( ca.90Ma) kimberlite event in southern India: implication for sub-continental lithospheric mantle evolution and diamond exploration.Gondwana Research, Vol. 35, pp. 378-389.India, MadagascarDeposit - Wajrakarur

Abstract: We report groundmass perovskite U -Pb (SIMS) ages, perovskite Nd isotopic (LA-ICPMS) composition and bulk-rock geochemical data of the Timmasamudram diamondiferous kimberlite cluster, Wajrakarur kimberlite field, in the Eastern Dharwar craton of southern India. The kimberlite pipes gave similar Mesoproterozoic ages of 1086 ± 19 Ma (TK-1, microcrystic variant) and 1119 ± 12 Ma (TK-3). However, a perovskite population sampled from the macrocrystic variant of TK-1 gave a much younger Late Cretaceous age of ca. 90 Ma. This macrocrystic kimberlite phase intrudes the Mesoproterozoic microcrystic phase and has a distinct bulk-rock geochemistry. The Nd-isotope composition of the ~ 1100 Ma perovskites in the cluster show depleted eNd(T) values of 2.1 ± 0.6 to 6.7 ± 0.3 whereas the ~ 90 Ma perovskites have enriched eNd(T) values of - 6.3 ± 1.3. The depleted-mantle (DM) model age of the Cretaceous perovskites is 1.2 Ga, whereas the DM model age of the Proterozoic perovskites is 1.2 to 1.5 Ga. Bulk-rock incompatible trace element ratios (La/Sm, Gd/Lu, La/Nb and Th/Nb) of all Timmasamudram kimberlites show strong affinity with those from the Cretaceous Group II kimberlites from the Bastar craton (India) and Kaapvaal craton (southern Africa). As the Late Cretaceous age of the younger perovskites from the TK-1 kimberlite is indistinguishable from that of the Marion hotspot-linked extrusive and intrusive igneous rocks from Madagascar and India, we infer that all may be part of a single Madagascar Large Igneous Province. Our finding constitutes the first report of Cretaceous kimberlite activity from southern India and has significant implications for its sub-continental lithospheric mantle evolution and diamond exploration programs.
DS1608-1398
2016
Chalapathi Rao, N.V., Srivastava, R.K.Kimberlites, lamproites, lamprophyres, varbonatites, other alkaline rocks and mafic dykes from the Indian shield: glimpses of research ( 2012-2016).Proceedings National Academy of Sciences India , Vol. 82, 3, July special issue pp. 515-536.IndiaKimberlites, lamproites

Abstract: Major highlights of researches carried out on kimberlites, lamproites, lamprophyres, carbonatites, other alkaline rocks and mafic dykes from the Indian shield during 2012-2016 are presented. New findings involving field mapping, petrology, geochemistry (including high quality mineral based in situ isotopic studies) and geophysics have provided remarkable insights on the mode of their occurrence, timing of emplacement, mineralogy and bulk-rock composition, redox conditions, relative contribution of the lithosphere and asthenosphere, as well as their economic potential. Several large-scale geodynamic aspects such as plume-lithosphere interactions, ancient subduction events, layered structure of the sub-continental lithospheric mantle, spatial extent of the Precambrian large igneous provinces and supercontinent configurations could be unraveled from these studies on deep-mantle derived small-volume magmatic rocks.
DS1612-2286
2016
Chandra Phani, P.R., Srinivas, M.Regolith geochemical studies in kimberlitic terrain: a case study from Lattavaram kimberlite cluster, eastern Dharwar Craton, southern India.Acta Geologica Sinica, Vol. 90, July abstract p. 191.IndiaDeposit - Lattavaram

Abstract: Utility of geochemistry in mineral exploration is known since more than half-a-century. In reconnaissance diamond exploration, regolith geochemistry is a well known tool worldwide and helps in distinguishing bedrock geology in hard rock terrains. More than 100 kimberlite pipes were discovered so far in the Eastern Dharwar Craton (EDC) of South India by various public and private organizations. Within the EDC, majority of diamondiferous pipe clusters occur in Anantapur District of Andhra Pradesh state in India. Lattavaram kimberlite cluster (LKC) is one among them in this district and four pipes in this cluster are reported to be diamondiferous along with two kimberlite bodies at Muligiripalli. The kimberlite pipes at Lattavaram occur in semi-circular shape whereas a kimberlite body exposed at Muligiripalli village occurs as a dyke within the granitoid country. The pipe 4 at Lattavaram exhibits conspicuous difference in the soil color and texture i.e., greenish color and mottled texture when compared with the reddish brown compact residual soils of granitic country rock. In the Indian context, soil regolith geochemistry is not a popular subject in search of kimberlites. It is observed that little or no literature is available on the utility of regolith geochemistry applied to kimberlite or diamond exploration in India. An attempt is made in this study, to demonstrate and understand the spatial surface geochemical signatures using residual soil geochemistry on known kimberlite pipes viz., 3 and 4 of LKC. Spatial and statistical analysis of trace and rare earth elements revealed that certain elements show predominance in the vicinity of the kimberlite pipes which can act as an exploration guide in distinguishing kimberlitic rocks within a granitoid country. These elements show distinct variation in their dispersion in the soil which can be attributed to basement lithology. It is observed that elements like Cr, Ni, Co, Cu, Nb, Zr, Ti, Ba and rare earth elements (REE) are significantly enriched in the mottled zone and calcretized duricrust relative to the country rock granitoids. A suite of trace elements comprising those associated with ultramafic rocks (Cr, Co & Ni) and felsic rocks (Nb, La, Sm and P) can readily distinguish the ultramafic/kimberlitic regolith from that derived from granitoid or felsic rocks which can be used as an exploration path finder.
DS1603-0368
2015
Chang, Y-Y., Jacobsen, S.D., Bina, C.R., Thomas, S-M., Smyth, J.R., Frost, D.J., Boffa Ballaran, T., McCammon, C.A., Hauri, E.H., Inoue, T., Yurimoto, H., Meng, Y., Dera, P.Comparative compressibility of hydrous wadsleyite and ringwoodite: effect of H2O and implications for detecting water in the transition zone.Journal of Geophysical Research,, Vol. 120, 12, pp. 8259-8280.MantleRingwoodite

Abstract: Review of recent mineral physics literature shows consistent trends for the influence of Fe and H2O on the bulk modulus (K0) of wadsleyite and ringwoodite, the major phases of Earth's mantle transition zone (410-660?km). However, there is little consensus on the first pressure derivative, K0'?=?(dK/dP)P=0, which ranges from about 4 to >5 across experimental studies and compositions. Here we demonstrate the importance of K0' in evaluating the bulk sound velocity of the transition zone in terms of water content and provide new constraints on the effect of H2O on K0' for wadsleyite and ringwoodite by conducting a comparative compressibility study. In the experiment, multiple crystals of hydrous Fo90 wadsleyite containing 2.0 and 0.25?wt?% H2O were loaded into the same diamond anvil cell, along with hydrous ringwoodite containing 1.4?wt?% H2O. By measuring their pressure-volume evolution simultaneously up to 32?GPa, we constrain the difference in K0' independent of the pressure scale, finding that H2O has no effect on K0', whereas the effect of H2O on K0 is significant. The fitted K0' values of hydrous wadsleyite (0.25 and 2.0?wt?% H2O) and hydrous ringwoodite (1.4?wt?% H2O) examined in this study were found to be identical within uncertainty, with K0' ~3.7(2). New secondary-ion mass spectrometry measurements of the H2O content of these and previously investigated wadsleyite samples shows the bulk modulus of wadsleyite is reduced by 7.0(5)?GPa/wt?% H2O, independent of Fe content for upper mantle compositions. Because K0' is unaffected by H2O, the reduction of bulk sound velocity in very hydrous regions of transition zone is expected to be on the order of 1.6%, which is potentially detectible in high-resolution, regional seismology studies.
DS1611-2100
2015
Chanturia, V.A., Dvoichenkova, G.P., Kovalchuk, O.E., Timofeev, A.S.Surface composition and role of hydrophilic diamonds in foam separation.Journal of Mining Science , Vol. 51, 5, pp. 1235-1241.RussiaMineral processing ** in Russian

Abstract: The article presents new test results on structural and chemical properties of mineral formations on the surface of natural hydrophilic diamonds using Raman, X-ray phase and Auger spectroscopy methods. Analysis of morphological features of nano formations involved scanning electron microscope Jeol-5610 and analyzer INCA. Based on the studies into phase composition of diamonds non-recovered in the circuit of kimberlite ore processing, two types of mineral formations are discovered on their surface: microformations as silicate nature globules less than 1 µm in size and silicate nano films more than 5 nm thick. The tests detect also presence of layered talc silicates that make diamond surface hydrophilic.
DS1610-1849
2016
Chatterjee, R., Lassiter, J.C.186Os/188Os variations in upper mantle peridotites: constraints on the Pt/Os ratio of primitive upper mantle, implications for late veneer accretion and mantle mixing timescales.Chemical Geology, Vol. 442, pp. 11-22.United States, Colorado PlateauPeridotite

Abstract: 186Os/188Os variations in mantle peridotites provide constraints on the long-term Pt/Os evolution of the depleted mantle and the Pt/Os ratio of the primitive upper mantle (PUM). We report new 186Os/188Os data for mantle peridotites from continental (Rio Grande Rift and Colorado Plateau) and oceanic (Lena Trough and Hawaiian Islands) settings that span a wide range in fertility (Al2O3 ˜ 0.67-4.42 wt.%) and 187Os/188Os ratios (0.1138-0.1305). Although peridotite 186Os/188Os values span only a narrow range (from 0.1198345 to 0.1198384), 186Os/188Os broadly correlates with indices of melt depletion including bulk rock Al2O3, spinel Cr#, and clinopyroxene Cr#, consistent with Pt depletion in residual peridotites. PUM 186Os/188Os is estimated to be 0.1198378 ± 23 (2 SD) based on extrapolation of 186Os/188Os-fertility trends, which is very slightly lower than H-chondrites [˜ 0.1198398 ± 16 (2 SD); Brandon et al., 2006]. This value is consistent with a PUM Pt/Os of 1.7 ± 0.2, similar to average Pt/Os ratios of fertile continental peridotites. The inferred PUM Pt/Os is slightly lower than but within error of Pt/Os values measured in several classes of chondrites [Carbonaceous ˜ 1.8 ± 0.2, Ordinary ˜ 1.9 ± 0.1, and Enstatite ˜ 1.9 ± 0.1 (Brandon et al., 2006)] indicating that PUM Pt/Os is broadly chondritic. In contrast, estimates for PUM Ru/Ir and Pd/Ir (cf. Becker et al., 2006) are suprachondritic. The addition of a chondritic late veneer alone cannot create a combination of chondritic and suprachondritic HSE ratios for the PUM. Instead, minor core segregation occurring concurrently with the addition of a late veneer may explain the observed mantle HSE abundances and ratios. Combined 186Os/188Os-187Os/188Os isotopic and Pt/Os and Re/Os variability in peridotites suggest an average mantle homogenization timescale of ~ 1.2 Ga. In contrast, combined Hf-Nd isotopic and Lu/Hf and Sm/Nd variability in peridotites indicate much shorter homogenization timescales (< 0.4 Ga), potentially reflecting enhanced homogenization by melt-rock interaction to which the Pt-Os and Re-Os systems are relatively immune. The mechanical mixing timescale inferred from Os isotopes is consistent with timescales predicted for whole mantle convection.
DS1612-2287
2016
Chaves, C., Ussami, N., Ritsema, J.Density and P-wave velocity structure beneath the Parana magmatic province: refertilization of an ancient lithospheric mantle.Geochemistry, Geophysics, Geosystems: G3, Vol. 17, 10, 1002/ 2016GC006369.South AmericaMagmatism

Abstract: We estimate density and P-wave velocity perturbations in the mantle beneath the southeastern South America plate from geoid anomalies and P-wave traveltime residuals to constrain the structure of the lithosphere underneath the Paraná Magmatic Province (PMP) and conterminous geological provinces. Our analysis shows a consistent correlation between density and velocity anomalies. The P-wave speed and density are 1% and 15 kg/m3 lower, respectively, in the upper mantle under the Late Cretaceous to Cenozoic alkaline provinces, except beneath the Goiás Alkaline Province (GAP), where density (+20 kg/m3) and velocity (+0.5%) are relatively high. Underneath the PMP, the density is higher by about 50 kg/m3 in the north and 25 kg/m3 in the south, to a depth of 250?-?300 km. These values correlate with high-velocity perturbations of +0.5% and +0.3%, respectively. Profiles of density perturbation versus depth in the upper mantle are different for the PMP and the adjacent Archean São Francisco (SFC) and Amazonian (AC) cratons. The Paleoproterozoic PMP basement has a high-density root. The density is relatively low in the SFC and AC lithospheres. A reduction of density is a typical characteristic of chemically depleted Archean cratons. A more fertile Proterozoic and Phanerozoic subcontinental lithospheric mantle has a higher density, as deduced from density estimates of mantle xenoliths of different ages and composition. In conjunction with Re-Os isotopic studies of the PMP basalts, chemical and isotopic analyses of peridodite xenoliths from the GAP in the northern PMP, and electromagnetic induction experiments of the PMP lithosphere, our density and P-wave speed models suggest that the densification of the PMP lithosphere and flood basalt generation are related to mantle refertilization. Metasomatic refertilization resulted from the introduction of asthenospheric components from the mantle wedge above Proterozoic subduction zones, which surrounded the Paraná lithosphere. The high-density PMP lithosphere is presently gravitationally unstable and prone to delamination.
DS1602-0197
2016
Chen, J.Lower mantle materials under pressure.Science, Vol. 351, 6269, pp. 122-123.MantleDynamics

Abstract: Modern high-pressure experimental techniques have enabled us to achieve the pressure and temperature at the center of Earth (about 360 GPa and 6000 K) in laboratories. However, studies of rheological properties of minerals under controlled strain rate (creep experiments) have been limited to the pressure equivalent to that in Earth's transition zone, a depth only about one-tenth of Earth's radius. Determinations of rheological laws that govern the flows and viscosities of minerals in Earth's deep mantle have been far beyond our reach. In the absence of such critical data, the nature of mantle dynamics-such as whether the convection involves the entire lower mantle, yielding a chemically homogeneous deep mantle-remains controversial. Discovery of the breakdown of ringwoodite into the denser bridgmanite and magnesiowüstite phases at 24 GPa (1) removed the need for a major chemical discontinuity in Earth inferred from observations of a strong seismic reflector at 660 km depth. On page 144 of this issue, Girard et al. (2) report on the detailed rheological nature of this bridgmanite plus magnesiowüstite mineral aggregate, shedding more light on the mantle convection. The integration of brilliant synchrotron radiations and rotating apposed anvils enables creep experiments for large strain at pressures equivalent to that in Earth's lower mantle.
DS1602-0198
2015
Chen, Y., Gu, Y.J., Dokht, R.M.H., Sacchi, M.D.Crustal imprints of Precambrian orogenesis in western Laurentia.Journal of Geophysical Research, Vol. 120, 10, pp. 6993-7012.Canada, AlbertaGeophysics - seismics LVZs

Abstract: Crustal low-velocity zones (LVZs) have been reported in active orogens such as the Himalayas and the Andes but rarely in stable cratonic regions. In this study, we provide compelling evidence for a significant midcrustal LVZ beneath eastern-central Alberta, an integral part of the Precambrian Canadian Shield covered by thick Phanerozoic sedimentary deposits. This 200?km wide, over 10?km thick midcrustal LVZ is well resolved by shear velocity inversions using P-to-S receiver functions from more than 4600 earthquakes. It is generally overlain by a high-velocity upper crust in the depth range of 8-15?km, especially in western-central Alberta, which coincides with the previously documented Winagami reflection sequence. We interpret the LVZ to be of granitic composition, potentially in connection with the crystallization of partially molten crust during the Paleoproterozoic eon. In addition to the Precambrian tectonic history of western Laurentia, which featured plate convergence conducive to crustal melting, our crustal model is further supported by (1) a moderate spatial correlation between the LVZ and heat flow, and (2) shear velocities consistent with that of granite. The well preserved Winagami reflection sequence and the LVZ are potential evidence of distinct episodes of magmatism and crust modification in the Precambrian basement of the Western Canada Sedimentary Basin. The existence of a broad crustal LVZ suggests extensive subduction, orogenesis, and crustal melting during the Precambrian assembly of the North American craton.
DS1611-2101
2016
Chen, Z., Schellart, W.P., Strak, V., Duarte, J.C.Does subduction induced mantle flow drive backarc extension?Earth and Planetary Science Letters, Vol. 441, pp. 200-210.MantleSubduction

Abstract: Subduction zones are one of the most striking feature on Earth. They represent one of the two types of convergent plate boundaries, in which one tectonic plates sinks underneath another into the Earth’s mantle. Soon after the advent of the theory of plate tectonics scientists recognized that subduction zones are one of the main drivers of plate motion and mantle convection [Elsasser, 1971]. With trench motion during progressive subduction, overriding plates incorporated in subduction zones may follow the trench and/or deform internally. Such deformation is often characterized by backarc extension, which leads to opening of backarc basins, such as the Tyrrhenian Sea, the Scotia Sea, the Aegean Sea, the North Fiji Basin, and the Lau Basin.
DS1607-1291
2016
Chepurov, A., Turkin A., Dereppe, J-M. .Interaction of serpentine and chromite as a possible formation mechanism of subcalcic chromium garnet in the upper mantle: an experimental study.European Journal of Mineralogy, Vol. 28, pp. 329-336.RussiaDeposit - Udachnaya

Abstract: An experimental simulation of serpentine and chromite interaction was conducted at the pressure (P) and temperature (T) conditions of garnet-peridotite stability in order to clarify the potential role of serpentinite as a source for the crystallization of subcalcic garnet in the depleted subcratonic mantle. The experiments were performed at 4 GPa and 1100 C and 5.5 GPa and 1200 C using the high-pressure apparatus BARS. Natural antigorite from ophiolites of the Eastern Sayan (Russia) was used as a starting material. Two groups of chromite grains with different Cr# ¼ 100Cr/(Cr þ Al) ratios (from spinel peridotite xenoliths from the Udachnaya kimberlite pipe, Yakutia) were added to the antigorite. Newly formed garnet, spinel, olivine and orthopyroxene were observed as the products in the experiments. Garnet formed only around chromite grains with the lower Cr# value (46.4). Garnet has low CaO contents (,0.05 -1.10 wt.%) with chromium contents showing wide intra- and inter-grain variations (Cr# ¼ 0.7 -33.5). The Cr content increases from core to rim with the outer zones corresponding most closely to the equilibrium composition of the relevant bulk composition. The garnet total FeO content is in the range 3.4 -5.8 wt.%. The experiments demonstrate that serpentinite decomposed at a temperature of 700 C to olivine þ orthopyroxene þ water. If mingled mechanically with spinel-bearing mantlewedge peridotite upon subduction, it could react to form the range of subcalcic garnet compositions found as inclusions in diamonds.
DS1603-0369
2015
Cherepanova, Y., Artemieva, I.M.Density heterogeneity of the cratonic lithosphere: a case study of the Siberian craton.Gondwana Research, Vol. 28, 4, pp. 1344-1360.RussiaGeophysics - seismics

Abstract: Using free-board modeling, we examine a vertically-averaged mantle density beneath the Archean-Proterozoic Siberian Craton in the layer from the Moho down to base of the chemical boundary layer (CBL). Two models are tested: in Model 1 the base of the CBL coincides with the LAB, whereas in Model 2 the base of the CBL is at a 180 km depth. The uncertainty of density model is < 0.02 t/m3 or < 0.6% with respect to primitive mantle. The results, calculated at in situ and at room temperature (SPT) conditions, indicate a heterogeneous density structure of the Siberian lithospheric mantle with a strong correlation between mantle density variations and the tectonic setting. Three types of cratonic mantle are recognized from mantle density anomalies. ‘Pristine’ cratonic regions not sampled by kimberlites have the strongest depletion with density deficit of 1.8-3.0% (and SPT density of 3.29-3.33 t/m3 as compared to 3.39 t/m3 of primitive mantle). Cratonic mantle affected by magmatism (including the kimberlite provinces) has a typical density deficit of 1.0-1.5%, indicative of a metasomatic melt-enrichment. Intracratonic sedimentary basins have a high density mantle (3.38-3.40 t/m3 at SPT) which suggests, at least partial, eclogitization. Moderate density anomalies beneath the Tunguska Basin imply that the source of the Siberian LIP lies outside of the Craton. In situ mantle density is used to test the isopycnic condition of the Siberian Craton. Both CBL thickness models indicate significant lateral variations in the isopycnic state, correlated with mantle depletion and best achieved for the Anabar Shield region and other intracratonic domains with a strongly depleted mantle. A comparison of synthetic Mg# for the bulk lithospheric mantle calculated from density with Mg# from petrological studies of peridotite xenoliths from the Siberian kimberlites suggests that melt migration may produce local patches of metasomatic material in the overall depleted mantle.
DS1610-1850
2016
Chetoumani, K., Bondinier, J-L., Garrido, C.J., Marchesi, C., Amri, I., Targusiti, K.Spatial variability of pyroxenite layers in the Beni Bousera orogenic peridotite ( Morocco) and implications for their origin.Comptes Rendus Geoscience, in press available 11p.Africa, MoroccoPeridotite

Abstract: The Beni Bousera peridotite contains a diversity of pyroxenite layers. Several studies have postulated that at least some of them represent elongated strips of oceanic lithosphere recycled in the convective mantle. Some pyroxenites were, however, ascribed to igneous crystal segregation or melt-rock reactions. To further constrain the origin of these rocks, we collected 171 samples throughout the massif and examined their variability in relation with the tectono-metamorphic domains. A major finding is that all facies showing clear evidence for a crustal origin are concentrated in a narrow corridor of mylonitized peridotites, along the contact with granulitic country rocks. These peculiar facies were most likely incorporated at the mantle-crust boundary during the orogenic events that culminated in the peridotite exhumation. The other pyroxenites derive from a distinct protolith that was ubiquitous in the massif before its exhumation. They were deeply modified by partial melting and melt-rock reactions associated with lithospheric thinning.
DS1609-1711
2010
Chinn, I.L., Krug, M.A., Minnie, W.P., Rikhotso, C.T.Decoding the diamonds from the AK6 kimberlite.The 4th Colloquium on Diamonds - source to use held Gabarone March 1-3, 2010, 8p.Africa, BotswanaDeposit - AK6

Abstract: The AK6 kimberlite is situated 25 km south of the Debswana Orapa Mine in Botswana and was discovered by De Beers geologists in 1969 during the follow-up of geophysical targets in the Orapa area. The kimberlite was not extensively pursued at the time as the initial bulk sampling indicated it to be of limited size and low grade, factors largely contributed to by the basalt breccia capping. Completion of high resolution integrated geophysical techniques and drill bulk sampling to depth recovered 97 tons of kimberlite during 2003 and 2004, which led to the increased size and grade estimates. Bulk sampling by Large Diameter Drilling (LDD, 23 inch diameter) commenced in 2005; 13 holes were drilled to a cumulative depth of 3,699 m and 689 carats of diamonds were recovered. In July 2006 the De Beers Mineral Resource Classification Committee classified these Phase I LOO results at a High Inferred level with an average grade of 24 carats per hundred tonnes (cpht) at a bottom cut-off of +1 mm, and a modeled average diamond value of 150 dollars per carat. A second phase of LDO drilling was initiated in 2006, and bulk sampling by trenching commenced in 2007 in order to deliver a resource estimate at indicated level. An Indicated Resource of 11.1 million carats at an average grade of 22 cpht was declared for the deposit mining lease application lodged in 2007.
DS1610-1851
2010
Chirico, P.G., Barthelemy, F., Kone, F.Alluvial diamond resource potential and production capacity assessment of Mali.U.S. Geological Survey, Report 2010-5044, 23p.Africa, MaliAlluvials, resources

Abstract: South Africa, and attended by representatives of the diamond industry and leaders of African governments to develop a certification process intended to assure that rough, exported diamonds were free of conflictual concerns. This meeting was supported later in 2000 by the United Nations in a resolution adopted by the General Assembly. By 2002, the Kimberley Process Certification Scheme (KPCS) was ratified and signed by diamond-producing and diamond-importing countries. Over 70 countries were included as members of the KPCS at the end of 2007. To prevent trade in "conflict diamonds" while protecting legitimate trade, the KPCS requires that each country set up an internal system of controls to prevent conflict diamonds from entering any imported or exported shipments of rough diamonds. Every diamond or diamond shipment must be accompanied by a Kimberley Process (KP) certificate and be contained in tamper-proof packaging. The objective of this study was (1) to assess the naturally occurring endowment of diamonds in Mali (potential resources) based on geological evidence, previous studies, and recent field data and (2) to assess the diamond-production capacity and measure the intensity of mining activity. Several possible methods can be used to estimate the potential diamond resource. However, because there is generally a lack of sufficient and consistent data recording all diamond mining in Mali and because time to conduct fieldwork and accessibility to the diamond mining areas are limited, four different methodologies were used: the cylindrical calculation of the primary kimberlitic deposits, the surface area methodology, the volume and grade approach, and the content per kilometer approach. Approximately 700,000 carats are estimated to be in the alluvial deposits of the Kenieba region, with 540,000 carats calculated to lie within the concentration grade deposits. Additionally, 580,000 carats are estimated to have been released from the primary kimberlites in the region. Therefore, the total estimated diamond resources in the Kenieba region are thought to be nearly 1,300,000 carats. The Bougouni zones are estimated to have 1,000,000 carats with more than half, 630,000 carats, contained in concentrated deposits. When combined, the Kenieba and Bougouni regions of Mali are estimated to be host to 2,300,000 carats of diamonds.
DS1610-1852
2010
Chirico, P.G., Malpeti, K.C., Anum, S., Phillips, E.C.Alluvial diamond resource potential and production capacity assessment of Ghana.U.S. Geological Survey, Report 2010-5045, 25p.Africa, GhanaAlluvials, resources

Abstract: In May of 2000, a meeting was convened in Kimberley, South Africa, and attended by representatives of the diamond industry and leaders of African governments to develop a certification process intended to assure that rough, exported diamonds were free of conflictual concerns. This meeting was supported later in 2000 by the United Nations in a resolution adopted by the General Assembly. By 2002, the Kimberley Process Certification Scheme (KPCS) was ratified and signed by both diamond-producing and diamond-importing countries. Over 70 countries were included as members at the end of 2007. To prevent trade in "conflict" diamonds while protecting legitimate trade, the KPCS requires that each country set up an internal system of controls to prevent conflict diamonds from entering any imported or exported shipments of rough diamonds. Every diamond or diamond shipment must be accompanied by a Kimberley Process (KP) certificate and be contained in tamper-proof packaging. The objective of this study was to assess the alluvial diamond resource endowment and current production capacity of the alluvial diamond-mining sector in Ghana. A modified volume and grade methodology was used to estimate the remaining diamond reserves within the Birim and Bonsa diamond fields. The production capacity of the sector was estimated using a formulaic expression of the number of workers reported in the sector, their productivity, and the average grade of deposits mined. This study estimates that there are approximately 91,600,000 carats of alluvial diamonds remaining in both the Birim and Bonsa diamond fields: 89,000,000 carats in the Birim and 2,600,000 carats in the Bonsa. Production capacity is calculated to be 765,000 carats per year, based on the formula used and available data on the number of workers and worker productivity. Annual production is highly dependent on the international diamond market and prices, the numbers of seasonal workers actively mining in the sector, and environmental conditions, which influence seasonal farming.
DS1610-1853
2014
Chirico, P.G., Malpeti, K.C., Van Bockstael, M., Mamandou, D., Cisse, K., Diallo, T.A., Sano, M.Alluvial diamond resource potential and production capacity assessment of Guinea.U.S. Geological Survey, Report 2012-5256, 49p.Africa, GuineaAlluvials, resources

Abstract: In May of 2000, a meeting was convened in Kimberley, South Africa, by representatives of the diamond industry and leaders of African governments to develop a certification process intended to assure that export shipments of rough diamonds were free of conflict concerns. Outcomes of the meeting were formally supported later in December of 2000 by the United Nations in a resolution adopted by the General Assembly. By 2002, the Kimberley Process Certification Scheme (KPCS) was ratified and signed by diamond-producing and diamond-importing countries. The goal of this study was to estimate the alluvial diamond resource endowment and the current production capacity of the alluvial diamond mining sector of Guinea. A modified volume and grade methodology was used to estimate the remaining diamond reserves within Guinea’s diamondiferous regions, while the diamond-production capacity of these zones was estimated by inputting the number of artisanal miners, the number of days artisans work per year, and the average grade of the deposits into a formulaic expression. Guinea’s resource potential was estimated to be approximately 40 million carats, while the production capacity was estimated to lie within a range of 480,000 to 720,000 carats per year. While preliminary results have been produced by integrating historical documents, five fieldwork campaigns, and remote sensing and GIS analysis, significant data gaps remain. The artisanal mining sector is dynamic and is affected by a variety of internal and external factors. Estimates of the number of artisans and deposit variables, such as grade, vary from site to site and from zone to zone. This report has been developed on the basis of the most detailed information available at this time. However, continued fieldwork and evaluation of artisanally mined deposits would increase the accuracy of the results.
DS1607-1337
2016
Chisenga, C., Kamanga, T.F.Integrating magnetic and gravity for mapping the Earth structure using color scheme: a case study of Botswana.IGC 35th., Session The Deep Earth 1 p. abstractAfrica, BotswanaGeophysics
DS1605-0820
2016
Chitate, W.Step change in blasting methodology to achieve plant requirements, the concept of mine to mill operationalized.Diamonds Still Sparkling SAIMM 2016 Conference, Mar. 14-17, pp. 37-46.TechnologyMining - applied
DS1612-2288
2016
Chuvashova, I., Rasskazov, S., Yasnygina, T.Mid-Miocene thermal impact on the lithosphere by sub-lithospheric convective mantle material: transition from high- to moderate MG magmatism beneath Vitim Plateau, Siberia.Geoscience Frontiers, in press availableRussia, SiberiaConvection

Abstract: High-Mg lavas are characteristic of the mid-Miocene volcanism in Inner Asia. In the Vitim Plateau, small volume high-Mg volcanics erupted at 16-14 Ma, and were followed with voluminous moderate-Mg lavas at 14-13 Ma. In the former unit, we have recorded a sequence of (1) initial basaltic melts, contaminated by crustal material, (2) uncontaminated high-Mg basanites and basalts of transitional (K-Na-K) compositions, and (3) picrobasalts and basalts of K series; in the latter unit a sequence of (1) initial basalts and basaltic andesites of transitional (Na-K-Na) compositions and (2) basalts and trachybasalts of K-Na series. From pressure estimation, we infer that the high-Mg melts were derived from the sub-lithospheric mantle as deep as 150 km, unlike the moderate-Mg melts that were produced at the shallow mantle. The 14-13 Ma rock sequence shows that initial melts equilibrated in a garnet-free mantle source with subsequently reduced degree of melting garnet-bearing material. No melting of relatively depleted lithospheric material, evidenced by mantle xenoliths, was involved in melting, however. We suggest that the studied transition from high- to moderate-Mg magmatism was due to the mid-Miocene thermal impact on the lithosphere by hot sub-lithospheric mantle material from the Transbaikalian low-velocity (melting) domain that had a potential temperature as high as 1510 °?. This thermal impact triggered rifting in the lithosphere of the Baikal Rift Zone.
DS1605-0821
2016
Coleman, D.S., Mills, R.D., Zimmerer, M.J.Enigmatic relationship between silicic volcanic and plutonic rocks: the pace of plutonism.Elements, Vol. 12, pp. 97-102.TechnologyMagmatism
DS1609-1712
2016
Comin-Chiaramonti, P., Renzulli, A., Ridolfi, F., Enrich, G.E.R., Gomes, C.B., De Min, A., Azzone, R.G., Ruberti, E.Late stage magmatic to deuteric metasomatic accessory minerals from the Cerro Boggiani agpaitic complex ( Alto Paraguay alkaline province.Journal of South American Earth Sciences, Vol. 71, pp. 248-261.South America, ParaguayCarbonatite

Abstract: This work describes rare accessory minerals in volcanic and subvolcanic silica-undersaturated peralkaline and agpaitic rocks from the Permo-Triassic Cerro Boggiani complex (Eastern Paraguay) in the Alto Paraguay Alkaline Province. These accessory phases consist of various minerals including Th-U oxides/silicates, Nb-oxide, REE-Sr-Ba bearing carbonates-fluorcarbonates-phosphates-silicates and Zr-Na rich silicates. They form a late-stage magmatic to deuteric/metasomatic assemblage in agpaitic nepheline syenites and phonolite dykes/lava flows made of sodalite, analcime, albite, fluorite, calcite, ilmenite-pyrophanite, titanite and zircon. It is inferred that carbonatitic fluids rich in F, Na and REE percolated into the subvolcanic system and metasomatically interacted with the Cerro Boggiani peralkaline and agpaitic silicate melts at the thermal boundary layers of the magma chamber, during and shortly after their late-stage magmatic crystallization and hydrothermal deuteric alteration.
DS1612-2289
2016
Condamine, P., Medard, E., Devidal, J-L.Experimental melting of phlogopite-peridotite in the garnet stability field.Contributions to Mineralogy and Petrology, Vol. 171, pp. 95-121.TechnologyMelting - peridotite

Abstract: Melting experiments have been performed at 3 GPa, between 1150 and 1450 °C, on a phlogopite-peridotite source in the garnet stability field. We succeeded to extract and determine the melt compositions of both phlogopite-bearing lherzolite and harzburgite from low to high degrees of melting (? = 0.008-0.256). Accounting for the presence of small amounts of F in the mantle, we determined that phlogopite coexists with melt >150 °C above the solidus position (1150-1200 °C). Fluorine content of phlogopite continuously increases during partial melting from 0.2 to 0.9 wt% between 1000 and 1150 °C and 0.5 to 0.6 wt% between 1150 and 1300 °C at 1 and 3 GPa, respectively. The phlogopite continuous breakdown in the lherzolite follows the reaction: 0.59 phlogopite + 0.52 clinopyroxene + 0.18 garnet = 0.06 olivine + 0.23 orthopyroxene + 1.00 melt. In the phlogopite-harzburgite, the reaction is: 0.93 phlogopite + 0.46 garnet = 0.25 olivine + 0.14 orthopyroxene + 1.00 melt. Melts from phlogopite-peridotite sources at 3 GPa are silica-undersaturated and are foiditic to trachybasaltic in composition from very low (0.8 wt%) to high (25.6 wt%) degrees of melting. As observed at 1 GPa, the potassium content of primary mantle melts is buffered by the presence of phlogopite, but the buffering values are higher, from 6.0 to 8.0 wt% depending on the source fertility. We finally show that phlogopite garnet-peridotite melts are very close to the composition of the most primitive post-collisional lavas described worldwide.
DS1609-1713
2016
Cook, C.R.Diamonds are Forever? Press coverage of African conflicts and the Westphalian filter of resource wars.Journal of African Media Studies, Vol. 8, 2, pp. 109-126.AfricaHistory

Abstract: This paper argues that the western press often ignores the private sphere of economics in reporting conflict in the developing world. This matters when it comes to resource wars and conflict over natural resources. To explore this concept further I examine American and British press coverage of conflict diamonds in the Angola, Congo and Sierra Leone wars in the pages of four newspapers of record. Overall while conflict diamonds were present in the reporting the press ignored the full extent of private companies and capital in the financing and trading of conflict diamonds. The most common word used was government.
DS1612-2290
2016
Cook, T.A significantly hotter mantle beneath Iceland.EOS Transaction of AGU, online Nov. 18, 1p.Europe, IcelandMantle

Abstract: Variations in the temperature of the mantle drive its convective circulation, a process that links the deep mantle with the atmosphere and oceans through volcanic and tectonic activity. Because of this connection, effective models of Earth’s evolution must incorporate the planet’s thermal history, for which a crucial constraint is the mantle’s current temperature. Researchers look at chemistry of Iceland’s newly erupted lava to analyze the temperature of the mantle below. A false-color backscatter electron image of an olivine crystal from Borgarhraun, a lava field in northern Iceland. The crystal contains a spinel inclusion, set in a fine-grained crystalline groundmass. The chemistry of these crystals records the temperatures at which they crystallized. The image is approximately 1.5 millimeters wide. Credit: S. Matthews. Because the mantle’s temperature cannot be measured directly, scientists have devised a number of creative methods to derive this information, but these have produced widely varying results. Now Matthews et al. offer new constraints on this parameter beneath Iceland, one of the few places on Earth where a divergent plate boundary is subaerially exposed because of an anomalously large amount of melting occurring beneath the island. Using a recently developed mineral thermometry technique, the researchers found that lava flows from four different eruptions along Iceland’s Northern Volcanic Zone crystallized at substantially higher temperatures (maximum 1399°C) than average mid-ocean ridge samples that have experienced little melting (maximum 1270°C). Next, the team developed a thermal model of mantle melting and used it, along with other observations such as the local thickness of the crust, to quantify the uncertainties in deriving mantle temperatures from their data. Researchers look at chemistry of Iceland’s newly erupted lava to analyze the temperature of the mantle below. An analysis of fresh lavas from Iceland indicates the mantle below the island is much hotter than beneath other locations on divergent plate boundaries. Credit: Terri Cook and Lon Abbott. Their results indicate that the mantle below Iceland is at least 140°C hotter than that beneath average mid-ocean ridges. This outcome should shed light on the factors that control the extent of melting beneath Iceland, including the ongoing debate about whether the voluminous melting is due to a deep mantle plume and, if so, whether changes in its magma production reflect variations in the plume’s temperature.
DS1612-2291
2016
Cook, Y.A., Sanislav, I.V., Hammerli, J., Blenkinsop, T.G., Dirks, P.H.G.M.A primitive mantle source for the Neoarchean mafic rocks from the Tanzania Craton.Geoscience Frontiers, Vol. 7, pp. 911-926.Africa, TanzaniaMantle

Abstract: Mafic rocks comprising tholeiitic pillow basalt, dolerite and minor gabbro form the basal stratigraphic unit in the ca. 2.8 to 2.6 Ga Geita Greenstone Belt situated in the NW Tanzania Craton. They outcrop mainly along the southern margin of the belt, and are at least 50 million years older than the supracrustal assemblages against which they have been juxtaposed. Geochemical analyses indicate that parts of the assemblage approach high Mg-tholeiite (more than 8 wt.% MgO). This suite of samples has a restricted compositional range suggesting derivation from a chemically homogenous reservoir. Trace element modeling suggests that the mafic rocks were derived by partial melting within the spinel peridotite field from a source rock with a primitive mantle composition. That is, trace elements maintain primitive mantle ratios (Zr/Hf = 32-35, Ti/Zr = 107-147), producing flat REE and HFSE profiles [(La/Yb)pm = 0.9-1.3], with abundances of 3-10 times primitive mantle and with minor negative anomalies of Nb [(Nb/La)pm = 0.6-0.8] and Th [(Th/La)pm = 0.6-0.9]. Initial isotope compositions (?Nd) range from 1.6 to 2.9 at 2.8 Ga and plot below the depleted mantle line suggesting derivation from a more enriched source compared to present day MORB mantle. The trace element composition and Nd isotopic ratios are similar to the mafic rocks outcropping ~50 km south. The mafic rocks outcropping in the Geita area were erupted through oceanic crust over a short time period, between ~2830 and ~2820 Ma; are compositionally homogenous, contain little to no associated terrigenous sediments, and their trace element composition and short emplacement time resemble oceanic plateau basalts. They have been interpreted to be derived from a plume head with a primitive mantle composition.
DS1601-0011
2015
Cordier, C., Sauzeat, L., Arndt, N.T., Boullier, A-M., Batanova, V., Barou, F.Metasomatism of the lithospheric mantle immediately precedes kimberlite eruption: new evidence from olivine composition and mircostructures.Journal of Petrology, Vol. 56, 9, pp. 1775-1796.Europe, GreenlandDeposit - Kangamiut field

Abstract: Most kimberlites contain abundant dunitic nodules. These are centimetre-sized, rounded and multi-grained assemblages of xenocrystic olivine with a wide range of compositions (Fo83 to Fo94). The absence of orthopyroxene and other mantle minerals and the range of olivine compositions have been attributed to reaction between mantle peridotite and (proto)kimberlitic fluid or melt, but the timing of the reaction is a subject of debate. In a kimberlite from the Kangamiut region of Greenland, nodule cores are surrounded by fine-grained outer margins with near-constant Fo contents (~Fo88) but highly variable minor element contents (e.g. 500-2500 ppm Ni). These margins crystallized from the kimberlite melt and we show that their compositions can be explained by crystallization of olivine alone, if a high partition coefficient for Ni between melt and olivine (DNi > 20) is assumed. Orthopyroxene assimilation is not required, removing the constraint that its dissolution occurred during ascent of the kimberlite magma. Within some nodules, in addition to the usual core-to-margin gradients, we observe asymmetric compositional changes (variable Fo but near-constant minor element contents) across mobile grain boundaries. These changes document fluid percolation at the grain scale that occurred during dynamic recrystallization in the deforming lithospheric mantle. We note that chemical gradients associated with mobile grain boundaries are observed in olivines that cover the entire compositional range of the nodules, and propose that fluid-assisted dynamic recrystallization took place in dunite that was already compositionally heterogeneous. Reaction between peridotite and protokimberlitic melt or fluid and dissolution of orthopyroxene thus occurred within the lithospheric mantle, immediately (a few days) prior to the ascent of the kimberlite melt and the entrainment of the dunite nodules. We propose that the grain boundary zones probably mimic, at a fine scale, the fluid-peridotite interaction that caused, at a larger scale, orthopyroxene dissolution and formation of compositionally diverse olivine in kimberlites.
DS1610-1854
2016
Crameri, F., Tackley, P.J.Subduction initiation from a stagnant lid and global overturn: new insights from numerical models with a free surface.Progress in Earth and Planetary Science, Open accessMantleConvection, geodynamics

Abstract: Subduction initiation is a key in understanding the dynamic evolution of the Earth and its fundamental difference to all other rocky planetary bodies in our solar system. Despite recent progress, the question about how a stiff, mostly stagnant planetary lid can break and become part in the global overturn of the mantle is still unresolved. Many mechanisms, externally or internally driven, are proposed in previous studies. Here, we present the results on subduction initiation obtained by dynamically self-consistent, time-dependent numerical modelling of mantle convection. We show that the stress distribution and resulting deformation of the lithosphere are strongly controlled by the top boundary formulation: A free surface enables surface topography and plate bending, increases gravitational sliding of the plates and leads to more realistic, lithosphere-scale shear zones. As a consequence, subduction initiation induced by regional mantle flow is demonstrably favoured by a free surface compared to the commonly applied, vertically fixed (i.e. free-slip) surface. In addition, we present global, three-dimensional mantle convection experiments that employ basal heating that leads to narrow mantle plumes. Narrow mantle plumes impinging on the base of the plate cause locally weak plate segments and a large topography at the lithosphere-asthenosphere boundary. Both are shown to be key to induce subduction initiation. Finally, our model self-consistently reproduces an episodic lid with a fast global overturn due to the hotter mantle developed below a former stagnant lid. We conclude that once in a stagnant-lid mode, a planet (like Venus) might preferentially evolve by temporally discrete, global overturn events rather than by a continuous recycling of lid and that this is something worth testing more rigorously in future studies.
DS1611-2102
2016
Currie, C.A., van Wijk, J.How craton margins are preserved: insights from geodynamic models.Journal of Geodynamics, Vol. 100, pp. 144-158.MantleConvection

Abstract: Lateral variations in lithosphere thickness are observed in many continental regions, especially at the boundary between the ancient cratonic core and the adjacent more juvenile lithosphere. In some places, such as the North America craton margin in western Canada and the Sorgenfrei-Tornquist Zone in northern Europe, the transition in lithosphere thickness has a steep gradient (>45°) and it appears to be a long-lived feature (at least 50 Ma). We use thermal-mechanical numerical models to address the dynamics of lithospheric thickness changes on timescales of 100 Ma. Models start with the juxtaposition of 60 km thick lithosphere ("mobile belt") and 160 km thick lithosphere ("craton"). In the reference model, all mantle materials have a damp olivine rheology and a density comparable to primitive mantle. With this configuration, edge-driven mantle convection occurs at the craton boundary, resulting in a lateral smoothing of the thickness transition. The density and rheology of the craton mantle lithosphere are then varied to approximate changes in composition and water content. For all densities, a steep transition is maintained only if the craton strength is 5-50 times stronger than the reference damp olivine. If dry olivine is an upper limit on strength, only cratonic mantle with moderate compositional buoyancy (20-40 kg/m3 less dense than primitive mantle) remains stable. At higher densities, the thick lithosphere is eroded through downwellings, and the craton margin migrates inboard. Conversely, a compositionally buoyant craton destabilises through lateral spreading below the mobile belt.
DS1605-0822
2016
Currie, C.A., vanWijk, J.How craton margins are preserved: insights into geodynamic models.Journal of Geodynamics, in press available 48p.CanadaNorth American craton
DS1605-0823
2016
Czas, J.Diamond formation and evolution beneath the Sask craton, Canada.DCO Edmonton Diamond Workshop, June 8-10Canada, SaskatchewanDiamond genesis
DS1604-0599
2016
Czas, J., Stachel, T., Morton, R.Diamond genesis and evolution of the FALC area of Saskatchewan Craton.GAC MAC Meeting Special Session SS11: Cratons, kimberlites and diamonds., abstract 1/4p.Canada, SaskatchewanFort a la Corne area
DS1606-1081
2016
Dahl, T.W.Identifiying remnants of early Earth.Science, Vol. 352, 6287, May 13, pp. 768-769.MantleDynamics - convection

Abstract: The chemical composition of Earth's mantle can tell us how our planet formed and how subsequent mantle dynamics have since homogenized the mantle through convective processes. Most terrestrial rocks have a similar tungsten (W) isotope composition (1), but some rocks that have been dated at 2.8 Ga (billion years old) (2), 3.8 Ga (3), and 3.96 Ga (4) have elevated 182W/184W ratios. This is reported as µ182W, in parts per million (ppm) deviation from the bulk silicate Earth. Until now, the outliers have included only these ancient rock samples with a small µ182W excess (=15 ppm) that can be attributed to the final ~0.5% of Earth's mass that accreted late in its accretion history. On page 809 of this issue, Rizo et al. (5) report W isotope data from young mantle-derived rocks with µ182W excesses of 10 to 48 ppm. This result is spectacular because the range of µ182W values in mantle-derived rocks is larger than can be accommodated by late accretion; the implication is that remnants of Earth's earliest mantle have been preserved over the entirety of Earth's history.
DS1610-1855
2016
Dalaison, M., Davies, R.Lithospheric thinning by mantle plumes.ASEG-PESA-AIG 2016 25th Geophysical Conference, Abstract 4p.MantleHotspots

Abstract: Thermo-mechanical thinning of the lithosphere by mantle plumes is essential for intra-plate volcanism, the initiation of rifting, the evolution of Earth’s lower continental crust and the genesis of metals, diamonds and hydrocarbons. To develop a new understanding of how a mantle plume thins the overlying lithosphere beneath moving plates, we use 2-D and 3-D numerical models based on a finite-element discretization on anisotropic adaptive meshes. Our models include Earth-like material properties for the upper mantle (e.g. temperature and viscosity contrasts, non-Newtonian rheology) discretised at a local mesh resolution that has previously been considered intractable. In our simulations, a plume is injected at the base of the model (670 km depth) with a prescribed mass flux that is consistent with surface observations of topographic swells: from 0.5 (e.g. Louisville, Bermuda, Darfur) to 7 Mg/s (Hawaii). We undertake a systematic numerical study, across a wide parameter space, to investigate the effect of plume buoyancy flux, plate velocity, rheology law and Rayleigh number on processes leading to a reduction of the depth of the Lithosphere Asthenosphere boundary (LAB), such as small-scale convection (SSC) (‘dripping’), or delamination of the lower lithosphere.
DS1607-1338
2016
Daly, M., Hawkesworth, C.Tectonic influences on the development of the continental crust.IGC 35th., Session A Dynamic Earth 1 p. abstractMantleTectonics
DS1602-0199
2016
D'Angelo, L.The art of governing contingency: rethinking the colonial history of diamond mining in Sierra Leone.Historical Research, Vol. 89, 243, pp. 136-157.Africa, Sierra LeoneHistory

Abstract: This article briefly outlines the history of the colonial diamond industry of Sierra Leone from 1930 to 1961, highlighting its contingent aspects and the bonds guiding the decisions and actions taken by local social actors in different contexts and at different times. By drawing on colonial documents and memoirs of colonial officers, it shows how the colonial government of Sierra Leone and the mining company that exercised a monopoly on diamond extraction collaborated on the establishment of a series of legislative and disciplinary devices that encompassed forms of biopolitical expertise.
DS1603-0370
2016
D'Angelo, L.The art of governing contingency: rethinking the colonial history of diamond mining in Sierra Leone.Historical Research, Vol. 89, no 243, pp. 136-157.Africa, Sierra LeoneHistory

Abstract: This article briefly outlines the history of the colonial diamond industry of Sierra Leone from 1930 to 1961, highlighting its contingent aspects and the bonds guiding the decisions and actions taken by local social actors in different contexts and at different times. By drawing on colonial documents and memoirs of colonial officers, it shows how the colonial government of Sierra Leone and the mining company that exercised a monopoly on diamond extraction collaborated on the establishment of a series of legislative and disciplinary devices that encompassed forms of biopolitical expertise.
DS1605-0824
2016
Daniel, M.J., Bellingan, P., Rauscher, M.The modelling of scrubbers and AG mills in the diamond industry and when to use them.Diamonds Still Sparkling SAIMM 2016 Conference, Mar. 14-17, pp. 167-186.TechnologyMining - applied
DS1609-1714
2010
Daniel, M.J., Morley, C.Can diamonds go all the way with HPGRs? High pressure grinding rolls.The 4th Colloquium on Diamonds - source to use held Gabarone March 1-3, 2010, 14p.TechnologyCrushing

Abstract: The diamond industry is no newcomer to High Pressure Grinding Rolls (HPGR) as it has used the technology for more than 20 years, predominantly in secondary crushing and recrushing roles. In fact it could be argued that the diamond industry has led the way for the wider minerals industry to consider its application. In existing conventional secondary cone crushing applications, large valuable diamonds are "won" through meticulously managing the recovery process within defined particle size ranges. COllventional crushers operate with relatively large closed side sehings, hut have the potential to damage diamonds by making direct contact with the sides of the crusher. Cone crushers also result in steep product size distributions that run a high risk of losing many of the smaller, un-liberated but more abundant diamonds from the rock. This current comminution paradigm of particle size reduction management results in recrushing processing applications or plants where HPGRs are often used. HPGRs operate under the seemingly odd condition where the gap between the rolls is largely a function of the roll diameter irrespective of the feed size. This otTern an opportun'ity for the diamond industry to consider using multiple HPGRs or units with high circulating loads to effectively generate a product with a very high proportion of fine material that can be rejected ahead of the beneficiation step. This in effect results in a new paradigm, a single comminution step, where all diamonds of all sizes are liberated and preserved. The circuit product size distribution will consist mainly of barren kimberlitic fines along with some grits, pebbJes, indicator minerals, as well as the prized lUldamaged diamonds. The HPGR product stream needs to be scrubbed, slurried and screened at t mm resulting in a greatly reduced volume of -diamond-rich particles that progress to the dense medium concentration and/or direct x-ray separation steps_ In this application, the HPGR is viewed "outside the box", but within the context of diamond winning processes. Examples of how "HPGR can go all the way" are presented in the paper. Page
DS1605-0825
2016
Danoczi, J., Creighton, S.Microdiamond analysis - a method for estimating the size frequency distribution of the macrodiamonds.Diamonds Still Sparkling SAIMM 2016 Conference, Mar. 14-17, pp. 287-300.TechnologyMicrodiamonds
DS1612-2292
2016
Dave, R., Li, A.Destruction of the Wyoming craton: seismic evidence and geodynamic processes.Geology, Vol. 44, 11, pp. 883-886.United States, Wyoming, Colorado PlateauWyoming craton - kimberlites

Abstract: Cratons are old and strong continental cores where the lithosphere is thick and remains largely undeformed for 2-3 b.y. Unlike typical cratons, the Wyoming craton underwent pervasive deformation ca. 80-55 Ma during the Laramide orogeny in the west-central United States, and has been subsequently encroached upon by the Yellowstone hotspot since 2.0 Ma. However, the mechanism for the deformation and the craton-hotspot interaction are not well understood. We present here a three-dimensional shear wave velocity model beneath the Wyoming craton constrained from Rayleigh wave data, which reveal new details about the cratonic lithosphere. The average lithosphere thickness beneath the craton is ~150 km, significantly thinner than a normal cratonic root (>200 km). Continuous low velocities are observed beneath the Yellowstone hotspot and the Cheyenne belt. A low-velocity column is also present in the central-eastern craton at depths of 115-250 km. These low velocities can be explained by hot temperature and partial melting, implying mantle upwelling. A high-velocity anomaly with a dripping shape in central Wyoming extends to 200-250 km depth, indicating mantle downwelling and lithosphere erosion. Our model provides the first seismic evidence for complex small-scale mantle convection beneath the Wyoming craton. The convection probably developed during the subduction of the Farallon plate and has been reinforced by the Yellowstone hotspot. We propose that the combination of flat-slab subduction, small-scale convection, and hotspot activity can lead to massive destruction of a cratonic lithosphere.
DS1602-0200
2016
Davidson, J.Petra Diamonds: a leading independent diamond producer.PDAC 2016, 1p. AbstractAfrica, South AfricaDeposit - mines
DS1607-1339
2016
Davies, A.Seismic velocity model of the Great Bear Fault Zone, NWT Canada.IGC 35th., Session A Dynamic Earth 1p. AbstractCanada, Northwest TerritoriesGeophysics - seismics
DS1607-1340
2016
Davies, R.Cluster analysis of chromites, Lena West diamond region, NWT Canada.IGC 35th., Session Mineral Exploration 1p. AbstractCanada, Northwest TerritoriesChromite
DS1607-1341
2016
Davies, R.Do mantle plumes preserve the heterogeneous structure of their deep mantle source?IGC 35th., Session The Deep Earth 1 p. abstractMantlePlume, hot spots
DS1607-1342
2016
De Meillon, L.The Orange and Riet River alluvial diamond deposits in the vicinity of Douglas, Northern Cape Province: geology, evaluation, and exploitation of unique South African large diamond producing deposits.IGC 35th., Session Mineral Exploration 1p. AbstractAfrica, South AfricaAlluvials, diamonds
DS1604-0600
2016
De Vries, J., Nimmo, F., Melosh, H., Jacobson, S., Morbidelli, A., Rubie, D.Impact induced melting during accretion of the Earth.Progress in Earth and Planetary Science, Vol. 3, 7p.MantleMelting

Abstract: Because of the high energies involved, giant impacts that occur during planetary accretion cause large degrees of melting. The depth of melting in the target body after each collision determines the pressure and temperature conditions of metal-silicate equilibration and thus geochemical fractionation that results from core-mantle differentiation. The accretional collisions involved in forming the terrestrial planets of the inner Solar System have been calculated by previous studies using N-body accretion simulations. Here we use the output from such simulations to determine the volumes of melt produced and thus the pressure and temperature conditions of metal-silicate equilibration, after each impact, as Earth-like planets accrete. For these calculations a parameterised melting model is used that takes impact velocity, impact angle and the respective masses of the impacting bodies into account. The evolution of metal-silicate equilibration pressures (as defined by evolving magma ocean depths) during Earth’s accretion depends strongly on the lifetime of impact-generated magma oceans compared to the time interval between large impacts. In addition, such results depend on starting parameters in the N-body simulations, such as the number and initial mass of embryos. Thus, there is the potential for combining the results, such as those presented here, with multistage core formation models to better constrain the accretional history of the Earth.
DS1601-0012
2016
De Wit, M.Southern Africa diamond producing projects - a summary.PDAC, 1p. AbstractAfrica, southern AfricaHistory- overview
DS1607-1343
2016
De Wit, M.Dwyka age diamondiferous eskers in the Lichtenburg/Ventersdorp diamond fields, North West Province, South AfricaIGC 35th., Session A Dynamic Earth 1p. AbstractAfrica, South AfricaAlluvials, diamonds
DS1609-1715
2010
De Wit, M.Identification of global diamond metallogenic clusters to assist exploration.The 4th Colloquium on Diamonds - source to use held Gabarone March 1-3, 2010, 24p.GlobalDatabase, ages

Abstract: Of the approximately 6,500 kimberlites known to date, less than 3% are diamondiferous and less than half of those are economically viable. Admittedly, this is a global figure and varies from area to area much depending on geological, logistical, and political circumstances. The number of diarnond~bearing kimberlites is an important geobarometer, and an age-frequency profile has been compiled in order to identify diamond metallogenic epochs and provinces. Four primary diamond clusters have been recognised: Siberia (332-370Ma), Kaapvaal South(114-144Ma), Kaapvaal Southwest(84-95Ma), and Slave (52-55Ma). In addition, three secondary clusters are the Kaapvaal Central (S06-S38Ma), the Man Craton (139-lS3Ma) and the Kasai Craton (120- 130Ma). The Kaapvaal is the only area where kimberlites with diamonds were discovered between 1870 and 1925, except for the Prairie Creek discovery in North America in 1906 and Colossus in Zimbabwe in 1907. Between 1906 and 1940 no major diamondiferous kimbcrlites were discovered, but many of Africa's alluvial deposits were found and exploited in that period. Advances in scientific prospecting in the 1940's rapidly accelerated the discovery rate that peaked in the 1990's; 39 diamondiferous occurrences were found in the 1980's, of which 8 became mines and 5 are in feasibility, and nearly 450ha of kimberlite was added to the global resource base. Despite the accelerated exploration expenditure, the last decade (e.g. 2000-2009) has been the leanest since the 1940's. The most important reason for this decline in exploration success is that any undiscovered deposits are largely buried by younger cover. Understanding complex and geophysical noisy basement geology, as well as decomposition of path-finder minerals are major challenges to further exploration success. Major investments in basic geological expertise and field research will have to be made in order to secure future diamond resources. Integrated geophysical studies, geochemistry diamond forensics, and improved imaging of Earth's upper mantle are perhaps foremost in this requirement, but the costs of these activities are such that government support will be required if countries are to sustain their diamond mining industry.
DS1609-1716
2016
De Wit, M., Bhebhe, Z., Davidson, J., Haggerty, S.E., Hundt, P., Jacob, J., Lynn, M., Marshall, T.R., Skinner, C., Smithson, K., Stiefenhofer, J., Robert, M., Revitt, A., Spaggiari, R., Ward, J.Overview of diamonds resources in Africa.Episodes, Vol. 9, 2, pp. 198-238.AfricaDiamond resources - overview

Abstract: From the discovery of diamonds in South Africa in 1866 until the end of 2013, Africa is estimated to have produced almost 3.2 Bct out of a total global production of 5.03 Bct, or 63.6% of all diamonds that have ever been mined. In 2013 African countries ranked 2nd (Botswana), 3rd (DRC), 6th (Zimbabwe), 7th (Angola), 8th (South Africa), and 9th (Namibia), in terms of carat production and 1st (Botswana), 4th (Namibia), 5th (Angola), 6th (South Africa), 7th (Zimbabwe), and 9th (DRC), in terms of value of the diamonds produced. In 2013 Africa produced 70.6 Mct out of a global total of 130.5 Mct or 54.1%, which was valued at US$ 8.7 billion representing 61.5% of the global value of US$ 14.1 billion.
DS1607-1292
2016
De Wit, M.C.J.Dwyka-age diamondiferous eskers in the Lichtenburg/Ventersdorp diamond fields, North West Province, South Africa.IGC 35th., 1p. AbstractAfrica, South AfricaDeposit - Lichtenburg Ventersdorp
DS1610-1856
2016
De Wit, M.C.J., Dorkin, G., Morris, D.The alluvial diamonds deposits … of the north west province and the Lower Val-Middle Orange Basin.IGC 35th., Field Trip Guide pre-6 Aug. 22-27, 45p. PdfAfrica, South AfricaGuidebook - alluvials
DS1604-0601
2016
De Wit, M.J., Furnes, H.3.5 Ga hydrothermal fields and diamictites in the Barberton greenstone belt - Paleoarchean crust in cold environments.Science Advance AEON and Earth Stewardship Science Research Institute, Nelson Mandela Metropolitan Univerisity, 13p.TechnologyGlacial remnants, exosphere, silica pipes

Abstract: Estimates of ocean temperatures on Earth 3.5 billion years ago (Ga) range between 26° and 85°C. We present new data from 3.47- to 3.43-Ga volcanic rocks and cherts in South Africa suggesting that these temperatures reflect mixing of hot hydrothermal fluids with cold marine and terrestrial waters. We describe fossil hydrothermal pipes that formed at ~200°C on the sea floor >2 km below sea level. This ocean floor was uplifted tectonically to sea level where a subaerial hydrothermal system was active at 30° to 270°C. We also describe shallow-water glacial diamictites and diagenetic sulfate mineral growth in abyssal muds. These new observations reveal that both hydrothermal systems operated in relatively cold environments and that Earth’s surface temperatures in the early Archean were similar to those in more recent times.
DS1601-0013
2015
Decree, S., Boulvais, P., Tack, L., Andre, L., Baele, J-M.Fluorapatite in carbonatite related phosphate deposits: the case for the Matongo carbonatite ( Burundi).Mineralogy and Petrology, in press available, 17p.Africa, BurundiCarbonatite

Abstract: The Matongo carbonatite intrusive body in the Neoproterozoic Upper Ruvubu alkaline plutonic complex (URAPC) in Burundi is overlain by an economic phosphate ore deposit that is present as breccia lenses. The ore exhibits evidence of supergene enrichment but also preserves textures related to the concentration of fluorapatite in the carbonatitic system. Magmatic fluorapatite is abundant in the ore and commonly occurs as millimeter-sized aggregates. It is enriched in light rare earth elements (LREE), which is especially apparent in the final generation of magmatic fluorapatite (up to 1.32 wt% LREE2O3). After an episode of metasomatism (fenitization), which led to the formation of K-feldspar and albite, the fluorapatite-rich rocks were partly brecciated. Oxygen and carbon isotope compositions obtained on the calcite forming the breccia matrix (d18O?=?22.1?‰ and d13C?=?-1.5?‰) are consistent with the involvement of a fluid resulting from the mixing of magmatic-derived fluids with a metamorphic fluid originating from the country rocks. In a subsequent postmagmatic event, the carbonates hosting fluorapatite were dissolved, leading to intense brecciation of the fluorapatite-rich rocks. Secondary carbonate-fluorapatite (less enriched in LREE with 0.07-0.24 wt% LREE2O3 but locally associated with monazite) and coeval siderite constitute the matrix of these breccias. Siderite has d18O values between 25.4 and 27.7?‰ and very low d13C values (from -12.4 to -9.2?‰), which are consistent with the contribution of organic-derived low d13C carbon from groundwater. These signatures emphasize supergene alteration. Finally, the remaining voids were filled with a LREE-poor fibrous fluorapatite (0.01 wt% LREE2O3), forming hardened phosphorite, still under supergene conditions. Pyrochlore and vanadiferous magnetite are other minerals accumulated in the eluvial horizons. As a consequence of the supergene processes and fluorapatite accumulation, the phosphate ore, which contains 0.72 to 38.01 wt% P2O5, is also enriched in LREE (LaN/YbN from 47.1 to 83.5; SREE between 165 and 5486 ppm), Nb (up to 656 ppm), and V (up to 1232 ppm). In the case of phosphate exploitation at Matongo, REE could prove to have a subeconomic potential to be exploited as by-products of phosphates.
DS1603-0371
2016
Delcamp, A., Delvaux, D., Kwelwa, S., Macheyeki, A., Kervyn, M.Sector collapse events at volcanoes in the North Tanzanian divergence zone and their implications for regional tectonics. ( Oldoinyo Lengai)Geological Society of America Bulletin, Vol. 128, 1/2, pp. 169-186.Africa, TanzaniaLineaments

Abstract: The North Tanzanian divergence zone along the East African Rift is characterized by active faults and several large volcanoes such as Meru, Ol Doinyo Lengai, and Kilimanjaro. Based on systematic morphostructural analysis of the Shuttle Radar Topographic Mission digital elevation model and targeted field work, 14 debris avalanche deposits were identified and characterized, some of them being - to our knowledge - previously unknown. Our field survey around Mount Meru allowed previous "lahar" deposits to be reinterpreted as debris avalanche deposits and three major collapse events to be distinguished, with the two older ones being associated with eruptions. We used topographic lineaments and faults across the North Tanzanian divergence zone to derive the main tectonic trends and their spatial variations and highlight their control on volcano collapse orientation. Based on previous analogue models, the tectonic regime is inferred from the orientation of the collapse scars and/or debris avalanche deposits. We infer two types of regime: extensional and transtensional/strike-slip. The strike-slip regime dominates along the rift escarpment, but an extensional regime is inferred to have operated for the recent sector collapses. The proposed interpretation of sector collapse scars and debris avalanche deposits therefore provides constraints on the tectonic regime in the region. It is possible that, in some cases, movement on regional faults triggered sector collapse.
DS1612-2293
2016
Demonterova, E.I., Ivanov, A.V., Savelyeva, V.B.Mafic, ultramafic and carbonatitic dykes in the southern Siberian Craton with age of ca 1 Ga: remnants of a new large igneous province?Acta Geologica Sinica, Vol. 90, July abstract p. 9.Russia, SiberiaCarbonatite
DS1601-0014
2015
Demouchy, S., Bolfan-Casanova, N.Distribution and transport of hydrogen in the lithospheric mantle: a review.Lithos, in press available 80p.MantleHydrogen

Abstract: Distribution and transport of hydrogen in the lithospheric mantle: a review.
DS1610-1857
2016
Dentith, M.Geophysical responses from mineral system components in the deep crust and upper mantle. Linear featuresASEG-PESA-AIG 2016 25th Geophysical Conference, Abstract 3p.GlobalGeophysics

Abstract: The concept of a mineral deposit forming via a mineral system that operates across areas of perhaps 1000s of squares kilometres and to mantle depths has important implications for greenfields mineral exploration. Geographically widespread datasets and deep penetrating geophysical methods are required to map key mineral system elements such as fluid/metal source zones and migration paths. Developed primarily for academic studies of the deep crust, there are several established geophysical techniques that can potentially be used to identify elements of mineral systems in the deep crust and upper mantle. Although the seismic reflection method produces the highest quality images, it is prohibitively expensive and the recommended approach is a combination of MT surveys and receiver function recordings with CCP stacking. Mineral system elements that can be detected in this fashion include major structures and geological boundaries which are potential controls on fluid flow and also areas of crust and mantle that have been altered by one or both of fluid creation and migration.
DS1603-0372
2014
Deus Borges, L.A., de Sa Carneiro Chaves, M.L., Karfunkel, J.Diamonds from Borrachudo River, Sao Francisco basin ( Tiros, MG): morphologic and dissolution aspects.REM: Revista Escola de Minas, Vol. 67, 2, pp. 159-165. *** in PortugueseSouth America, BrazilAlluvials, diamonds

Abstract: A representative set of diamonds from the Borrachudo River (114 stones) was described for the first time as to their physical characteristics, among them weight, morphology, dissolution figures, and abrasion. Most samples are low in weight (~51% less than 0.30 ct) and only ~3.5% are above 3.0 ct. However, considering the total weight, ~47% of it is concentrated in the range above 3 ct. On the other hand, there even occur diamonds with dozen of carats. The most common crystallographic forms are originated from the octahedral form by dissolution, although irregular shapes like chips and flats also occur. The diamonds show differences in form compared to their weight ranges; those up to 0.30 ct have various shapes; in the range of 0.31 to 1 ct the most common are octahedral forms and their descendants; and in stones larger than 1 ct chips and flats predominate. The general habitus of the crystals, identified by their final tetrahexahedroid shapes, chips and flats, corroborated by the dissolution figures, indicate that the diamond were submitted to strong dissolution in a magmatic environment. Residual hillocks and holes represent the final stage of dissolution. The study indicates that the abrasion by the fluvial transport was not expressive enough to cause mechanical wear, thus ca. 97% shows no sign of wear. This fact suggests a proximal source for most of these diamonds.
DS1611-2103
2014
Devriese, S.G.R., Corcoran, N., Cowan, D., Davis, K., Bild-Enkin, D., Fournier, D., Heagy, L., Kang, S., Marchant, D., McMillan, M.S., Mitchell, M., Rosenkjar, G., Yang, D., Oldenburg, D.W.Magnetic inversion of three airborne data sets over the Tli Kwi Cho kimberlite complex.SEG Annual Meeting Denver, pp. 1790-1794. pdfCanada, Northwest TerritoriesDeposit - Tli Kwi Cho

Abstract: The magnetic and electromagnetic responses from airborne systems at Tli Kwi Cho, a kimberlite complex in the Northwest Territories, Canada, have received considerable attention over the last two decades but a complete understanding of the causative physical properties is not yet at hand. Our analysis is distributed among three papers. In the first, we find a 3D magnetic susceptibility model for the area; in the second, we find a 3D conductivity model; and in the third paper, we find a 3D chargeability model. Our goal is to explain all the geophysical results within a geologic framework. In this first paper, we invert three independent airborne magnetic data sets flown over the Tli Kwi Cho kimberlite complex located in the Lac de Gras kimberlite field in Northwest Territories, Canada. The complex consists of two kimberlites known as DO-27 and DO- 18. An initial airborne DIGHEM survey was flown in 1992 and AeroTEM and VTEM data subsequently acquired in 2003 and 2004, respectively. In this paper, we invert each magnetic data set in three dimensions. Both kimberlites are recovered in each model, with DO-27 as a more susceptible body than DO-18. Our goal is to simultaneously invert the three data sets to generate a single susceptibility model for Tli Kwi Cho. This project is part of a larger, on-going investigation by UBC-GIF on inverting magnetic, electromagnetic, and induced polarization data from the Tli Kwi Cho area.
DS1611-2104
2016
Devriese, S.G.R., Davis, K., Oldenburg, D.W.Inversion of airborne geophysics over the Tli Kwi Cho kimberlite complex, Part I: potential fields.Tli Kwi Cho Workshop UBC, Sept. 8, 49p. Contact sdevriese@eos.ubc.caCanada, Northwest TerritoriesDeposit - Tli Kwi Cho
DS1605-0826
2016
D'Haenens-Johansson, U.Identification of treated synthetic diamonds.DCO Edmonton Diamond Workshop, June 8-10TechnologySynthetics
DS1605-0827
2016
Di Genova, D., Cimarelli, C., Hess, K-U., Dingwell, D.B.An advanced rotational rheometer system for extremely fluid liquids up to 1273 K and applications to alkali carbonate melts.American Mineralogist, Vol. 101, pp. 953-959.MantleCarbonatite

Abstract: A high-temperature rheometer equipped with a graphite furnace, characterized by an air-bearing-supported synchronous motor, has been enhanced by a custom-made Pt-Au concentric cylinder assembly. With this adaptation, viscosity measurements of highly fluid melts can be achieved at high temperatures, up to 1273 K. Due to the air-bearing-supported motor, this apparatus can perform measurements of extremely low torque ranging between 0.01 µNm and 230 mNm (resolution of 0.1 nNm), extending the typical range of viscosity measurements accessible in the present configuration to 10-3.5-103.5 Pa•s and shear rates up to 102 of s-1. We calibrated the system with distilled water, silicone oils, and the DGG-1 standard glass. We further present new data for the viscosity of Na2CO3, K2CO3, and Li2CO3 liquids. Finally, a comparison between our results and literature data is provided, to illustrate the effect of chemical composition and oxygen fugacity on the viscosity of alkali carbonate melts, which serve as analogs for both carbonatitic melts and molten carbonates of industrial relevance. This study substantially improves the database of alkali carbonate melts and dramatically increases the accuracy with respect to previous measurement attempts. The very low viscosity range data and their temperature dependence also helps to constrain very well the activation energy of these highly fluid systems and confirms the estimate of a universal pre-exponential factor for non-Arrhenian viscosity-temperature relationships.
DS1610-1858
2016
Di Massa, D., Kaminski, V., Viezzoli, A.Airborne IP: Drybones kimberlite VTEM data Cole-Cole inversion.ASEG-PESA-AIG 2016 25th Geophysical Conference, Abstract 4p.Canada, Northwest TerritoriesDeposit - Drybones

Abstract: A VTEM survey was flown over the Drybones kimberlite in 2005, followed by a ZTEM survey in 2009. These data sets were inverted on multiple previous occasions using various 1D, 2D, 3D and plate modelling algorithms. VTEM data showed AIP effects, manifested as negative voltages and otherwise skewed transients. This created artefacts in conventional inversions of VTEM data, which showed some inconsistencies with ZTEM inversions, as well as with the known geology. In 2015 the VTEM data were transferred to Aarhus Geophysics, reprocessed and reinverted using the modified "AarhusINV" code with Cole-Cole modelling. The results are presented in current abstract, they appear to be more interpretable and provide better data fit, than previous inversion attempts.
DS1602-0201
2016
Di Pierro, S., Gnos, E.Ca-Al-silicate inclusions in natural moissanite ( SiC).American Mineralogist, Vol. 101, pp. 71-81.Europe, TurkeyMoissanite

Abstract: Hundred-micrometer-sized calcium-aluminum-silicates (CAS) inclusions occur in moissanite-4H, moissanite-15R, and moissanite-6H from Turkey. These inclusions commonly consist of tabular exsolution lamellae of two different minerals. By combined electron microprobe and Raman spectroscopy analysis, at least eight different, essentially Mg- and Fe-free Ca-Al-silicate or Al-silicate phases have been discerned. The most common phase is dmisteinbergite, a hexagonal modification of CaAl2Si2O8, occurring in association with lamellae of Cax(Al,Si)1-xO3 or Ca1-x(Al,Si)2+xO5 compositions. All three phases contain significant amounts of BaO (up to 2 mol% of celsiane component in dmisteinbergite), SrO, SO3, and light rare earth elements (LREE). In particular, Ca1-x(Al,Si)2+xO5 contains up to 2.1 wt% of LREE, 3.9 wt% of F, and significant traces of Cl, while it is also associated to osbornite (TiN). Pure ghelenite, Ca2Al2SiO7, and three additional compositions, namely CaAl4-xSixO7, Ca1-x(Al,Si)3+xO6, and Ca3-x(Al,Si)6+xO14 have been found, either occurring as single grains or forming exsolution lamellae. They also contain significant amounts of BaO, SrO, SO3, and LREE. One last intriguing phase is composed in average of 65.9 wt% SiO2, 17.4% Al2O3, 3.0% alkalis, 6.0% BaO, 2.0% CaO+MgO, 0.9% ZrO2, and up to 0.5% LREE. Dmisteinbergite and ghelenite show Raman peaks in very good agreement with literature data, Cax(Al,Si)1-xO3 shows main Raman modes at 416 and 1009 cm-1, Ca1-x(Al,Si)3+xO6 at 531 and 1579 cm-1 while Ca3-x(Al,Si)6+xO14 has a strong peak at 553 cm-1. CaAl4-xSixO7 shows a weak Raman pattern, while Ca1-x(Al,Si)2+xO5 has no detectable Raman modes. Since the association moissanite-CAS is thermodynamically not stable at ambient pressure and moissanite crystals hosting the CAS phases have d13C values typical of deep-mantle origin, we interpret the CAS inclusions as partially retrogressed HP minerals. Striking analogies exist between observed CAS compositions and experimentally obtained HP-HT mineralogy. For instance, Cax(Al,Si)1-xO3 contains up to 25 mol% of Al2O3, which is considered as the upper limit of alumina solubility in Ca-perovskite. The study confirms that CAS phases are an important mantle depository for large ion lithophile elements (LILE) and LREE.
DS1608-1399
2016
Dirlam, D.Dona Dirlam receives WJA special services award for excellence. Founder and director of the GIA Richard T. Liddicott Gemological Library and Information Center.Idex Online, July 28, 1/2p.United States, CaliforniaAward
DS1602-0202
2015
Dobretsov, N.L.Periodicity and driving forces of volcanism.Russian Geology and Geophysics, Vol. 56, pp. 1663-1670.Global, JapanMantle plume

Abstract: The volume and style of volcanism change periodically, with cycles of three main scales, which have different causes and effects. Short cycles of volcanic activity last from tens to thousands of years and are associated with periodic accumulation of magma in shallow chambers and its subsequent eruptions. The eruptions either have internal causes or are triggered externally by variations in solar activity, tidal friction, and Earth’s rotation speed. Medium-scale cycles, hundreds of thousands to millions of years long, are due to changes in spreading and subduction rates. Long cycles (30–120 Ma) are related to ascent of mantle plumes, which take away material and heat from the core-mantle boundary and change the convection rate. These appear to be the major controls of the average periodicity. Acceleration of asthenospheric convection caused by periodic plume activity pulses can change spreading rates and, correspondingly, the relative positions of moving plates. The medium-scale periodicity of volcanism is illustrated by the examples of Kamchatka and Japan, where the intensity of subduction magmatism changes periodically in response to the opening of back-arc basins (Shikoku, Sea of Japan, and South Kurile basin).
DS1612-2294
2016
Dokukina, K.A., Mints, M.V., Konilov, A.N.Mesoarchean Gridino mafic dykes swarm of the Belomorian eclogite province of the Fennoscandian shield ( Russia). Acta Geologica Sinica, Vol. 90, July abstract p. 8.Russia, Kola PeninsulaDykes
DS1607-1293
2016
Domeier, M., Doubrovine, P.V., Torsvik, T.H., Spakman, W., Bull, A.L.Global correlation of mantle structure and past subduction.Geophysical Research Letters, Vol. 43, 10, pp. 4945-4953.MantleSubduction

Abstract: Advances in global seismic tomography have increasingly motivated identification of subducted lithosphere in Earth’s deep mantle, creating novel opportunities to link plate tectonics and mantle evolution. Chief among those is the quest for a robust subduction reference frame, wherein the mantle assemblage of subducted lithosphere is used to reconstruct past surface tectonics in an absolute framework anchored in the deep Earth. However, the associations heretofore drawn between lower mantle structure and past subduction have been qualitative and conflicting, so the very assumption of a correlation has yet to be quantitatively corroborated. Here we show that a significant, time-depth progressive correlation can be drawn between reconstructed subduction zones of the last 130 Myr and positive S wave velocity anomalies at 600 -2300 km depth, but that further correlation between greater times and depths is not presently demonstrable. This correlation suggests that lower mantle slab sinking rates average between 1.1 and 1.9 cmyr 1.
DS1607-1344
2016
Dongre, A.Classificication of diamond source rocks in the Wajrakarur kimberlite field of southern India: a mineral genetic approach.IGC 35th., Session A Dynamic Earth 1p. AbstractIndiaDeposit - Wajrakur
DS1612-2295
2016
Dongre, A., Chalapathi Rao, N.V., Viljoen, K.S., Lehmann, B.Petrology, genesis and geodynamic implication of the Mesoproterozoic- Late Cretaceous Timmasamudram kimberlite cluster, Wajrakarur field, eastern Dharwar craton, southern India.Geoscience Frontiers, in press availableIndiaDeposit - Timmasamudram

Abstract: New mineralogical and bulk-rock geochemical data for the recently recognised Mesoproterozoic (ca. 1100 Ma) and late Cretaceous (ca. 90 Ma) kimberlites in the Timmasamudram cluster (TKC) of the Wajrakarur kimberlite field (WKF), Eastern Dharwar Craton, southern India, are presented. On the basis of groundmass mineral chemistry (phlogopite, spinel, perovskite and clinopyroxene), bulk-rock chemistry (SiO2, K2O, low TiO2, Ba/Nb and La/Sm), and perovskite Nd isotopic compositions, the TK-1 (macrocrystic variety) and TK-4 (microcrystic variety) kimberlites in this cluster are here classified as orangeites (i.e. Group II kimberlites), with geochemical characteristics that are very similar to orangeites previously described from the Bastar Craton in central India, as well as the Kaapvaal Craton in South Africa. The remaining kimberlites (e.g., TK-2, TK-3 and the TK-1 microcrystic variant), are more similar to other 1100 Ma, Group I-type kimberlites of the Eastern Dharwar Craton, as well as the typical Group I kimberlites of the Kaapvaal Craton. Through the application of geochemical modelling, based on published carbonated peridotite/melt trace element partition coefficients, we show that the generation of the TKC kimberlites and the orangeites results from low degrees of partial melting of a metasomatised, carbonated peridotite.
DS1605-0828
2016
Dongre, A.N., Viljoen, K.S., Chalapathi Rao, N.V.Origins of Ti-rich garnets in the groundmass of Wajrakarur field kimberlites, southern India: insights from EPMA and Raman spectroscopy.Mineralogy and Petrology, Vol. 110, 2, pp. 295-307.IndiaDeposit - Wajrakarur

Abstract: Although Ti-rich garnets are commonly encountered in the groundmass of many alkaline igneous rocks, they are comparatively rare in kimberlites. Here we report on the occurrence of Ti-rich garnets in the groundmass of the P-15 and KL-3 kimberlites from the diamondiferous Wajrakarur field in the Eastern Dharwar craton of southern India. These garnets contain considerable Ti (11.7-23.9 wt.% TiO2), Ca (31.3-35.8 wt.% CaO), Fe (6.8-15.5 wt.% FeOT) and Cr (0.04-9.7 wt.% Cr2O3), but have low Al (0.2-5.7 wt.% Al2O3). In the case of the P-15 kimberlite they display a range in compositions from andradite to schorlomite, with a low proportion of grossular (andradite(17.7-49.9)schorlomite(34.6-49.5)-grossular(3.7-22.8)-pyrope(1.9-10.4)). A few grains also contain significant chromium and represent a solid solution between schorlomite and uvarovite. The Ti-rich garnets in the KL-3 kimberlite, in contrast, are mostly schorlomitic (54.9-90.9 mol %) in composition. The Ti-rich garnets in the groundmass of these two kimberlites are intimately associated with chromian spinels, perhaps suggesting that the garnet formed through the replacement of spinel. From the textural evidence, it appears unlikely that the garnets could have originated through secondary alteration, but rather seem to have formed through a process in which early magmatic spinels have reacted with late circulating, residual fluids in the final stages of crystallization of the kimberlite magma. Raman spectroscopy provides evidence for low crystallinity in the spinels which is likely to be a result of their partial transformation into andradite during their reaction with a late-stage magmatic (kimberlitic) fluid. The close chemical association of these Ti-rich garnets in TiO2-FeO-CaO space with those reported from ultramafic lamprophyres (UML) is also consistent with results predicted by experimental studies, and possibly implies a genetic link between kimberlite and UML magmas. The occurrence of Ti-rich garnets of similar composition in the Swartruggens orangeite on the Kaapvaal craton in South Africa, as well as in other kimberlites with an orangeitic affinity (e.g. the P-15 kimberlite on the Eastern Dharwar craton in southern India), is inferred to be a reflection of the high Ca- and high Ti-, and the low Al-nature, of the parent magma (i.e. Group II kimberlites).
DS1603-0373
2016
Dongre, A.N., Viljoen, K.S., Chalapathi Rao, N.V., Gucsik, A.Origin of Ti rich garnets in the groundmass of Wajrakarur field kimberlites, southern India: insights from EPMA and Raman spectroscopy.Mineralogy and Petrology, in press available, 13p.IndiaDeposit - Wajrakur

Abstract: Although Ti-rich garnets are commonly encountered in the groundmass of many alkaline igneous rocks, they are comparatively rare in kimberlites. Here we report on the occurrence of Ti-rich garnets in the groundmass of the P-15 and KL-3 kimberlites from the diamondiferous Wajrakarur field in the Eastern Dharwar craton of southern India. These garnets contain considerable Ti (11.7-23.9 wt.% TiO2), Ca (31.3-35.8 wt.% CaO), Fe (6.8-15.5 wt.% FeOT) and Cr (0.04-9.7 wt.% Cr2O3), but have low Al (0.2-5.7 wt.% Al2O3). In the case of the P-15 kimberlite they display a range in compositions from andradite to schorlomite, with a low proportion of grossular (andradite(17.7-49.9)schorlomite(34.6-49.5)-grossular(3.7-22.8)-pyrope(1.9-10.4)). A few grains also contain significant chromium and represent a solid solution between schorlomite and uvarovite. The Ti-rich garnets in the KL-3 kimberlite, in contrast, are mostly schorlomitic (54.9-90.9 mol %) in composition. The Ti-rich garnets in the groundmass of these two kimberlites are intimately associated with chromian spinels, perhaps suggesting that the garnet formed through the replacement of spinel. From the textural evidence, it appears unlikely that the garnets could have originated through secondary alteration, but rather seem to have formed through a process in which early magmatic spinels have reacted with late circulating, residual fluids in the final stages of crystallization of the kimberlite magma. Raman spectroscopy provides evidence for low crystallinity in the spinels which is likely to be a result of their partial transformation into andradite during their reaction with a late-stage magmatic (kimberlitic) fluid. The close chemical association of these Ti-rich garnets in TiO2-FeO-CaO space with those reported from ultramafic lamprophyres (UML) is also consistent with results predicted by experimental studies, and possibly implies a genetic link between kimberlite and UML magmas. The occurrence of Ti-rich garnets of similar composition in the Swartruggens orangeite on the Kaapvaal craton in South Africa, as well as in other kimberlites with an orangeitic affinity (e.g. the P-15 kimberlite on the Eastern Dharwar craton in southern India), is inferred to be a reflection of the high Ca- and high Ti-, and the low Al-nature, of the parent magma (i.e. Group II kimberlites).
DS1605-0829
2016
Dostal, J.Rare metal deposits associated with alkaline/peralkaline igneous rocks.SEG Reviews in Economic Geology, editors Verplanck, P.L., Hitzman, M.W., No. 18, pp. 33-54.Canada, Northwest Territories, Ontario, Europe, Greenland, Russia, Sweden, Africa, South AfricaThor, Nechalacho, Ilmmassaq, Loverzero, Kipawa, Noira Karr, Planesberg
DS1610-1859
2016
Doucet, L.S., Mattielli, N., Ionov, D.A., Debouage, W., Golovin A.V.Zn isotopic heterogeneity in the mantle: a melting control?Earth and Planetary Science Letters, Vol. 451, pp. 232-240.MantlePeridotite

Abstract: We present new Zn elemental and isotope data on seventeen fertile and refractory mantle peridotite xenoliths. Eleven fertile peridotites are garnet and spinel lherzolites from Vitim and Tariat (Siberia and Mongolia) and represent some of the most pristine fertile peridotites available. Six refractory peridotites are spinel harzburgites from the Udachnaya kimberlite (Siberian craton) that are nearly pristine residues of high-degree polybaric melting at high pressure (7-4 GPa). Geochemical data suggest that Zn isotopic compositions in the peridotites have not been affected by post-melting processes such as metasomatism, contamination by the host-magmas or alteration. The fertile peridotites have uniform Zn concentrations (59±2 ppm59±2 ppm) and Zn isotopic compositions with d66Zn (relative to JMC-Lyon-03-0749l)?=?+0.30?±?0.03‰ consistent with the Bulk Silicate Earth estimates of d66Zn?=?+0.28?±?0.05‰ (Chen et al., 2013). The refractory peridotites have Zn concentrations ranging from 30 to 48 ppm and d66Zn from +0.10±0.01‰+0.10±0.01‰ to +0.18±0.01‰+0.18±0.01‰ with an average of +0.14±0.03‰+0.14±0.03‰. Our data suggest that the lithospheric mantle has a heterogeneous Zn isotopic composition. Modeling of Zn isotope partitioning during partial melting of fertile mantle suggests that high degrees of melt extraction (>30%) may significantly fractionate Zn isotopes (up to 0.16‰) and that during mantle melting, Zn concentrations and isotopic compositions are mainly controlled by the stability of clinopyroxene and garnet within the melting residue. Because the stability of clinopyroxene and garnet is mainly pressure dependent we suggest that both the depth and the degrees of melt extraction may control Zn isotope fractionation during mantle melting.
DS1602-0203
2016
Downes, P.J., Dunkley, D.J., Fletcher, I.R., McNaughton, N.J., Rasmusson, B., Jaques, A.L., Verall, M., Sweetapple, M.T.Zirconolite, zircon and monazite-(Ce) U-Th-Pb age constraints on the emplacement, deformation and alteration history of the Cummins Range carbonatite complex, Halls Creek orogen, Kimberley region, Western Australia.Mineralogy and Petrology, In press available, 24p.AustraliaCarbonatite

Abstract: In situ SHRIMP U-Pb dating of zirconolite in clinopyroxenite from the Cummins Range Carbonatite Complex, situated in the southern Halls Creek Orogen, Kimberley region, Western Australia, has provided a reliable 207Pb/206Pb age of emplacement of 1009 ± 16 Ma. Variably metamict and recrystallised zircons from co-magmatic carbonatites, including a megacryst ~1.5 cm long, gave a range of ages from ~1043-998 Ma, reflecting partial isotopic resetting during post-emplacement deformation and alteration. Monazite-(Ce) in a strongly foliated dolomite carbonatite produced U-Th-Pb dates ranging from ~900-590 Ma. Although the monazite-(Ce) data cannot give any definitive ages, they clearly reflect a long history of hydrothermal alteration/recrystallisation, over at least 300 million years. This is consistent with the apparent resetting of the Rb-Sr and K-Ar isotopic systems by a post-emplacement thermal event at ~900 Ma during the intracratonic Yampi Orogeny. The emplacement of the Cummins Range Carbonatite Complex probably resulted from the reactivation of a deep crustal structure within the Halls Creek Orogen during the amalgamation of Proterozoic Australia with Rodinia over the period ~1000-950 Ma. This may have allowed an alkaline carbonated silicate magma that was parental to the Cummins Range carbonatites, and generated by redox and/or decompression partial melting of the asthenospheric mantle, to ascend from the base of the continental lithosphere along the lithospheric discontinuity constituted by the southern edge of the Halls Creek Orogen. There is no evidence of a link between the emplacement of the Cummins Range Carbonatite Complex and mafic large igneous province magmatism indicative of mantle plume activity. Rather, patterns of Proterozoic alkaline magmatism in the Kimberley Craton may have been controlled by changing plate motions during the Nuna-Rodinia supercontinent cycles (~1200-800 Ma).
DS1605-0830
2016
Doyle, B.Testing the economic viability of a diamondiferous kimberlite.Vancouver Kimberlite Cluster, May 5, 1p. AbstractTechnologyMicrodiamonds, sampling
DS1608-1400
2016
Driscoll, P.What did Earth's ancient magnetic field look like?Geophysical Research Letters , June 30, 4p.MantleGeophysics - magnetics

Abstract: New work from Carnegie’s Peter Driscoll suggests Earth’s ancient magnetic field was significantly different than the present day field, originating from several poles rather than the familiar two. It is published in Geophysical Research Letters. Earth generates a strong magnetic field extending from the core out into space that shields the atmosphere and deflects harmful high-energy particles from the Sun and the cosmos. Without it, our planet would be bombarded by cosmic radiation, and life on Earth’s surface might not exist. The motion of liquid iron in Earth’s outer core drives a phenomenon called the geodynamo, which creates Earth’s magnetic field. This motion is driven by the loss of heat from the core and the solidification of the inner core. But the planet’s inner core was not always solid. What effect did the initial solidification of the inner core have on the magnetic field? Figuring out when it happened and how the field responded has created a particularly vexing and elusive problem for those trying to understand our planet’s geologic evolution, a problem that Driscoll set out to resolve. Here’s the issue: Scientists are able to reconstruct the planet’s magnetic record through analysis of ancient rocks that still bear a signature of the magnetic polarity of the era in which they were formed. This record suggests that the field has been active and dipolar—having two poles—through much of our planet’s history. The geological record also doesn’t show much evidence for major changes in the intensity of the ancient magnetic field over the past 4 billion years. A critical exception is in the Neoproterozoic Era, 0.5 to 1 billion years ago, where gaps in the intensity record and anomalous directions exist. Could this exception be explained by a major event like the solidification of the planet’s inner core? In order to address this question, Driscoll modeled the planet’s thermal history going back 4.5 billion years. His models indicate that the inner core should have begun to solidify around 650 million years ago. Using further 3-D dynamo simulations, which model the generation of magnetic field by turbulent fluid motions, Driscoll looked more carefully at the expected changes in the magnetic field over this period. “What I found was a surprising amount of variability,” Driscoll said. “These new models do not support the assumption of a stable dipole field at all times, contrary to what we’d previously believed.” His results showed that around 1 billion years ago, Earth could have transitioned from a modern-looking field, having a “strong” magnetic field with two opposite poles in the north and south of the planet, to having a “weak” magnetic field that fluctuated wildly in terms of intensity and direction and originated from several poles. Then, shortly after the predicted timing of the core solidification event, Driscoll’s dynamo simulations predict that Earth’s magnetic field transitioned back to a “strong,” two-pole one. “These findings could offer an explanation for the bizarre fluctuations in magnetic field direction seen in the geologic record around 600 to 700 million years ago,” Driscoll added. “And there are widespread implications for such dramatic field changes.” Overall, the findings have major implications for Earth’s thermal and magnetic history, particularly when it comes to how magnetic measurements are used to reconstruct continental motions and ancient climates. Driscoll’s modeling and simulations will have to be compared with future data gleaned from high quality magnetized rocks to assess the viability of the new hypothesis.
DS1605-0831
2016
Du Toit, D., Meno, T., Telema, E., Boshoff, P., Hodder, A.Survey systems adopted to improve safety and efficiency at Finsch diamond mine.Diamonds Still Sparkling SAIMM 2016 Conference, Mar. 14-17, pp. 187-196.Africa, South AfricaDeposit - Finsch
DS1607-1294
2016
Ducea, M.N., Saleeby, J.B., Bergantz, G.The architecture, chemistry and evolution of continental magmatic arcs.Annual Review of Earth and Planetary Sciences, Vol. 43, pp. 299-331.MantleMagmatism

Abstract: Continental magmatic arcs form above subduction zones where the upper plate is continental lithosphere and/or accreted transitional lithosphere. The best-studied examples are found along the western margin of the Americas. They are Earth's largest sites of intermediate magmatism. They are long lived (tens to hundreds of millions of years) and spatially complex; their location migrates laterally due to a host of tectonic causes. Episodes of crustal and lithospheric thickening alternating with periods of root foundering produce cyclic vertical changes in arcs. The average plutonic and volcanic rocks in these arcs straddle the compositional boundary between an andesite and a dacite, very similar to that of continental crust; about half of that comes from newly added mafic material from the mantle. Arc products of the upper crust differentiated from deep crustal (>40 km) residual materials, which are unstable in the lithosphere. Continental arcs evolve into stable continental masses over time; trace elemental budgets, however, present challenges to the concept that Phanerozoic arcs are the main factories of continental crust.
DS1605-0832
2016
Dumanska-Slowik, M.Evolution of mariupolite ( nepheline syenite) in the alkaline Oktiabrski Massif ( Ukraine) as the host of potential Nb-Zr-REE mineralization.Ore Geology Reviews, Vol. 78, pp. 1-13.Europe, UkraineMetasomatism

Abstract: Mariupolite, aegirine-albite nepheline syenite, outcropping only in the Oktiabrski massif in south-eastern Ukraine, is a potential resource of Nb, Zr and REE for future exploration and development. Some types of this rock can be also used in ceramics, glass and building industry and jewellery. Mariupolite is composed of (1) magmatic and (2) subsolidus and hydrothermal components. The magmatic assemblage includes zircon, aegirine, nepheline, albite, K-feldspar, pyrochlore, fluorapatite, fluorbritholite-(Ce) and magnetite. Alkaline-carbonate-chloride-rich fluids exsolved very early in the history of the rock, in a late stage of, or directly after, its consolidation, induced intensive high-temperature alteration of the primary mariupolite components resulted in formation of cancrinite, calcite, fluorite, REE-bearing minerals such as monazite, parasite-(Ce), bastnäsite-(Ce), as well as sodalite, natrolite and hematite. The genesis of this peculiar mineralization seems to be associated with multistage magmatic and tectonic activity of the Ukrainian Shield and fluids mediated metasomatic processes.
DS1601-0015
2015
Eakin, C.M., Long, M.D., Scire, A., Beck, S.L., Wagner, L.S., Zandt, G., Tavera, H.Internal deformation of the subducted Nazca slab inferred from seismic anisotropy. ..new study suggests that the Earth's rigid tectonic plates stay strong when they slide under another plate, known as subduction, may not be universal.Nature Geoscience, 10.1038/ngeo2592MantleSubduction
DS1608-1401
2016
Eaton-Magana, S., Ardon, T.Temperature effects on luminescence centers in natural type.Diamond and Related Materials, Vol. 69, pp. 86-95India, Africa, South AfricaType IIb diamonds

Abstract: Blue diamonds are among the rarest and most valuable of naturally occurring gemstones. In this study, 12 rough naturally-sourced type IIb diamonds were subjected to HPHT annealing, three different irradiation energies, and then all were stepwise annealed from 200 °C to 1100 °C and the optical defects were documented by changes in phosphorescence and photoluminescence spectroscopy. Several optical features that are removed from natural type IIb diamonds by HPHT processing, such as 3H, 648.2 nm peak, 776.4 nm peak, and 660 nm band (red) phosphorescence, can be reintroduced into these diamonds with subsequent electron irradiation and annealing at low-to-moderate temperatures. The thermal stability of these centers along with their spatial distribution provided additional insights into their configuration and distinguished them from nitrogen-bearing diamonds.
DS1606-1082
2016
Eaton-Magana, S., Breeding, C.M.An introduction to photoluminescence spectroscopy for diamond and its application in gemology.Gems & Gemology, Vol. 52, 1, pp. 2-17.TechnologyIdentification of treated and synthetic diamonds.

Abstract: Photoluminescence (PL) spectroscopy is frequently mentioned in the gemological literature, but its relevance to the wider trade audience is rarely discussed. Due to the possibility of an undisclosed treatment or a synthetic origin, all type II diamonds (both colorless and fancy-color) and colorless type IaB diamonds submitted to gemological laboratories should ideally be tested using PL spectroscopy. Although the proportion of samples that require this testing is small, the failure to properly identify treated and synthetic diamonds could destabilize the diamond industry. This article seeks to clarify the underlying physics and methodology of this important tool for gemologists.
DS1612-2296
2016
Eaton-Magana, S., Shigley, J.E.Observations on CVD-grown synthetic diamonds: a review.Gems & Gemology, Vol. 52, 3, pp. 222-245.TechnologySynthetics

Abstract: This article presents statistical data and distinctive features from several hundred faceted CVD-grown synthetic diamonds examined by GIA researchers from 2003 through June 2016. This study, the first comprehensive summary published on such a large number of gem-quality CVD synthetics, describes the reliable means of identifying them, with a focus on material currently marketed for jewelry use. Most CVD synthetic diamonds analyzed by GIA have been in the near-colorless or pink color ranges, with clarity grades comparable to those of their natural counterparts. Faceted CVD samples are generally 2 ct or less, though the sizes are increasing. They can be identified by their distinctive fluorescence pattern using the DiamondView imaging instrument, and by the detection of the silicon-vacancy defect using photoluminescence (PL) spectroscopy. Some visual gemological characteristics provide indicators, but not definitive proof, of CVD origin.
DS1603-0374
2016
Eaton-Magana, S.C., Moe, K.S.Temperature effects on radiation stains in natural diamonds.Diamond and Related Materials, in press available 29p.TechnologyGreen diamonds

Abstract: The green coloration of natural diamonds typically results from exposure to natural irradiation. This creates the GR1 optical center and in many diamonds, surficial damage, principally due to alpha radiation, which helps verify natural origin. In this study, 13 naturally irradiated diamonds with pronounced radiation stains were stepwise annealed from 200 °C to 1400 °C and the changes in color and defects were documented by photomicrography and spectroscopy. Additionally 3 diamonds were subjected to isothermal annealing at 550 °C. The radiation stains correlated with radiation-damage Raman peaks — a broad and shifted diamond Raman peak and radiation-related peaks at 1500 and 1640 cm- 1. The color transitioned from green to brown after heating to 550-600 °C and the stains were essentially decolorized at 1400 °C. Confocal Raman depth profiling showed that the depth penetration of the radiation stain was about 10-15 µm into the diamond and this depth profile was distinctly different from depth profiles of ion-irradiation stains generated in a laboratory.
DS1612-2297
2016
Egorova, E.O., Afanasev, V.P., Pokhilenko, N.P.Middle Paleozoic kimberlite magmatism in the northeastern Siberia.Doklady Earth Sciences, Vol. 470, 2, pp. 1023-1026.Russia, SiberiaDeposit - Billyakh River placers

Abstract: The mineral chemistry and crystal morphology of kimberlite pyropes from the Billyakh River placer in the northeastern Siberian craton are characterised in terms of the placer history. The pyropes bear signatures of chemical weathering (dissolution), presumably in a Middle Paleozoic laterite profile, and therefore were originally hosted by Middle Paleozoic kimberlites. The broad occurrence of placer pyropes with lateritic dissolution signatures points to the presence of Middle Paleozoic diamond-bearing kimberlites in the study area.
DS1605-0833
2016
Elliott. B.Slave province surficial materials and permafrost study.DCO Edmonton Diamond Workshop, June 8-10Canada, Northwest TerritoriesGeomorphology

Abstract: The Slave Province is a geological formation that lies between Great Slave Lake and Coronation Gulf. The area contains some of the oldest known igneous and metamorphic rocks on Earth, and has a long history of mining. This project examines the surface sediment deposited during a number of past glaciations, as well as permafrost. Minerals of economic interest are found within the surface sediment and can be used to locate economic mineral deposits in the underlying bedrock. This project will improve our understanding of glacial sediments, stimulate exploration of diamond and metals in the Slave Province, and will determine permafrost conditions to inform future infrastructure development.
DS1607-1345
2016
Emry, E.Lithospheric and sub-lithospheric upper mantle structure of Africa from full wave long-period ambient noise tomography.IGC 35th., Session A Dynamic Earth 1p. AbstractAfricaGeophysics
DS1612-2298
2016
Ernst, R.E., Buchan, K.L., Botsyun, S.Map of mafic dyke swarms and related units of Russia and adjacent regions.Acta Geologica Sinica, Vol. 90, July abstract p. 22-23.Russia, SiberiaDykes
DS1607-1295
2016
Ernst, R.E., Hamilton, M.A., Soderlund, U., Hanes, J.A., Gladkochub, D.P., Okrugin, A.V., Kolotilina, T., Mekhonoshin, A.S., Bleeker, W., LeCheminant, A.N., Buchan, K.L., Chamberlain, K.R., Didenko, A.N.Long lived connection between southern Siberia and northern Laurentia in the Proterozoic.Nature Geoscience, Vol. 9, 6, pp. 464-469.Canada, RussiaProterozoic

Abstract: Precambrian supercontinents Nuna-Columbia (1.7 to 1.3 billion years ago) and Rodinia (1.1 to 0.7 billion years ago) have been proposed. However, the arrangements of crustal blocks within these supercontinents are poorly known. Huge, dominantly basaltic magmatic outpourings and intrusions, covering up to millions of square kilometres, termed Large Igneous Provinces, typically accompany (super) continent breakup, or attempted breakup and offer an important tool for reconstructing supercontinents. Here we focus on the Large Igneous Province record for Siberia and Laurentia, whose relative position in Nuna-Columbia and Rodinia reconstructions is highly controversial. We present precise geochronology—nine U -Pb and six Ar -Ar ages—on dolerite dykes and sills, along with existing dates from the literature, that constrain the timing of emplacement of Large Igneous Province magmatism in southern Siberia and northern Laurentia between 1,900 and 720 million years ago. We identify four robust age matches between the continents 1,870, 1,750, 1,350 and 720 million years ago, as well as several additional approximate age correlations that indicate southern Siberia and northern Laurentia were probably near neighbours for this 1.2-billion-year interval. Our reconstructions provide a framework for evaluating the shared geological, tectonic and metallogenic histories of these continental blocks.
DS1606-1083
2016
Evans, D.A.D., Li, Z.X., Murphy, J.B.Four dimensional context of Earth's supercontinents.Geological Society of London Special Publication Supercontinent Cycles through Earth History., Vol. 424, pp. 1-14.MantleSupercontinents

Abstract: The supercontinent-cycle hypothesis attributes planetary-scale episodic tectonic events to an intrinsic self-organizing mode of mantle convection, governed by the buoyancy of continental lithosphere that resists subduction during closure of old ocean basins, and consequent reorganization of mantle convection cells leading to opening of new ocean basins. Characteristic timescales of the cycle are typically 500-700 myr. Proposed spatial patterns of cyclicity range from hemispheric (introversion) to antipodal (extroversion), to precisely between those end-members (orthoversion). Advances in our understanding can arise from theoretical or numerical modelling, primary data acquisition relevant to continental reconstructions, and spatiotemporal correlations between plate kinematics, geodynamic events and palaeoenvironmental history. The palaeogeographic record of supercontinental tectonics on Earth is still under development. The contributions in this special publication provide snap-shots in time of these investigations and indicate that Earth's palaeogeographic record incorporates elements of all three endmember spatial patterns.
DS1606-1084
2016
Evans, D.A.D., Trindade, R.I.F., Catelani, E.L., D'Agrella-Filho, Heaman, L.M., Oliveira, E.P., Soderlund, U., Ernst, R.E., Smirnovm A.V., Salminen, J.M.Return to Rodinia? Moderate to high paleolatitude of the Sao Francisco/Congo craton at 920 Ma.Geological Society of London Special Publication Supercontinent Cycles through Earth History., Vol. 424, pp. 167-190.South America, BrazilSupercontinents

Abstract: Moderate to high palaeolatitudes recorded in mafic dykes, exposed along the coast of Bahia, Brazil, are partly responsible for some interpretations that the São Francisco/Congo craton was separate from the low-latitude Rodinia supercontinent at about 1050 Ma. We report new palaeomagnetic data that replicate the previous results. However, we obtain substantially younger U-Pb baddeleyite ages from five dykes previously thought to be 1.02- 1.01 Ga according to the 40 Ar/ 39 Ar method. Specifically, the so-called 'A-normal' remanence direction from Salva-dor is dated at 924.2 + 3.8 Ma, within error of the age for the 'C' remanence direction at 921.5 + 4.3 Ma. An 'A-normal' dyke at Ilhéus is dated at 926.1 + 4.6 Ma, and two 'A-normal' dykes at Olivença have indistinguishable ages with best estimate of emplacement at 918.2 + 6.7 Ma. We attribute the palaeomagnetic variance of the 'A-normal' and 'C' directions to lack of averaging of geomagnetic palaeosecular variation in some regions. Our results render previous 40 Ar/ 39 Ar ages from the dykes suspect, leaving late Mesoproterozoic palaeolatitudes of the São Francisco/Congo craton unconstrained. The combined 'A-normal' palaeomagnetic pole from coastal Bahia places the São Francisco/Congo craton in moderate to high palaeolatitudes at c. 920 Ma, allowing various possible positions of that block within Rodinia. Despite more than two decades of intense global research, the configuration of Neoproterozoic supercontinent Rodinia remains enigmatic. Following the first global synthesis by Hoffman (1991), most models include a central location for Laurentia, flanked by 'East' Gondwana-Land cra-tons along its proto-Cordilleran margin and 'West'
DS1602-0204
2016
Even-Zohar, C.The diamond industry in a perfect storm: profitability, demand, transparency & synthetics.PDAC 2016, 1p. AbstractGlobalMarkets, prices
DS1605-0834
2016
Even-Zohar, C.2015: producers lost leverage over clients - forever. Currency and price volatility destabilizing value chain.Diamond Intelligence Briefs, Vol. 32. no. 872, Mar. 3, pdfGlobalPipeline
DS1606-1085
2016
Even-Zohar, C.Swarovski joins the man-made diamond market. Launches its exclusive DIAMA brand.Diamond Intelligence Briefing, Vol. 32, 875, May 11, 8p.GlobalSwarovski - DIAMA
DS1608-1402
2016
Even-Zohar, C.The economic costs of the KP on government and industry stakeholders: an overview.israelidiamond.co, July 27, 5p. PrecisGlobalKimberley Process
DS1603-0375
2015
Falls, S.Clarity, cut and culture: the many meanings of diamonds. University Press, 224p. $ 22.00 paperback bookTechnologyHistory

Abstract: Images of diamonds appear everywhere in American culture. And everyone who has a diamond has a story to tell about it. Our stories about diamonds not only reveal what we do with these tiny stones, but also suggest how we create value, meaning, and identity through our interactions with material culture in general. Things become meaningful through our interactions with them, but how do people go about making meaning? What can we learn from an ethnography about the production of identity, creation of kinship, and use of diamonds in understanding selves and social relationships? By what means do people positioned within a globalized political-economy and a compelling universe of advertising interact locally with these tiny polished rocks? This book draws on 12 months of fieldwork with diamond consumers in New York City as well as an analysis of the iconic De Beers campaign that promised romance, status, and glamour to anyone who bought a diamond to show that this thematic pool is just one resource among many that diamond owners draw upon to engage with their own stones. The volume highlights the important roles that memory, context, and circumstance also play in shaping how people interpret and then use objects in making personal worlds. It shows that besides operating as subjects in an ad-burdened universe, consumers are highly creative, idiosyncratic, and theatrical agents.
DS1612-2299
2016
Fantsuzova, V.I., Danilov, K.B.The structure of the Lomonsov volcanic pipe in the Arkangelsk diamond province from anomalies of the microseismic field.Journal of Volcanology and Seismology, Vol. 10, 5, pp. 339-346.Russia, Kola Peninsula, ArchangelDeposit- Lomonsov

Abstract: This paper presents results from a study of the Lomonosov volcanic pipe as derived from anomalies of the microseismic field. Microseismic sounding revealed that this volcanic pipe is a cone-shaped body with a small gradient of microseismic intensity motion (2 to 5 dB). Discontinuities generally show greater contrasts compared with the variations of microseismic motion in the pipe body. Comparison of the results of this microseismic sounding with other geological and geophysical data showed that the intensities of the micro-seismic field along lines that traversed the pipe reflect realistic structures of a kimberlite pipe and the host rocks. The method of microseismic sounding was used to reconstruct the deeper structure of the volcanic pipe and the host rocks down to depths greater than 2 km. We estimated the velocity contrast and the errors involved in the identification of vertical boundaries of the pipe. The volcanic pipe has a shape that is consistent with a nearly vertical source situated at a depth of a few hundred meters. This is hypothesized to be a typical occurrence for other diamond-bearing pipes as well.
DS1611-2105
2016
Fedorova, N.M., Bzhenov, M.L., Meert, J.G., Kuznetsov, N.B.Edicaran-Cambrian paleogeography of Baltica: a paleomagnetic view from a diamond pit on the White Sea east coast.Lithosphere, Vol. 8, 5, pp. 564-573.Russia, Baltic ShieldPaleogeography

Abstract: The controversial late Ediacaran to Cambrian paleogeography is largely due to the paucity and low reliability of available paleomagnetic poles. Baltica is a prime example of these issues. Previously published paleomagnetic results from a thick clastic sedimentary pile in the White Sea region (northern Russia) provided valuable Ediacaran paleontological and paleomagnetic data. Until recently, Cambrian-age rocks in northern Russia were known mostly from boreholes or a few small outcrops. A recent mining operation in the Winter Coast region exposed >60 m of red sandstone and siltstone of the Cambrian Brusov Formation from the walls of a diamond pit. Paleomagnetic data from these rocks yield two major components. (1) A single-polarity A component is isolated in ~90% of samples between 200 and 650 °C. The corresponding pole (Pole Latitutde, Plat = 20°S; Pole Longitude, Plong = 227°E, a95 = 7°) agrees with the Early Ordovician reference pole for Baltica. (2) A dual-polarity B component is identified in ~33% of samples, mostly via remagnetization circles, isolated from samples above 650 °C. The corresponding pole (Plat = 12°S; Plong = 108°E, a95 = 5°) is close to other late Ediacaran data but far from all younger reference poles for Baltica. We argue for a primary magnetization for the B component and the secondary origin of the other Cambrian poles from Baltica. This in turn requires a major reshuffling of all continents and blocks around the North Atlantic. The early stages of Eurasia amalgamation and models for the evolution of the Central Asian Orogenic Belt require revision.
DS1604-0602
2016
Fedortchouk, Y., Zhang, Z., Chinn, I.Diamond resorption features as a new method for examining conditions of kimberlite emplacement.GAC MAC Meeting Special Session SS11: Cratons, kimberlites and diamonds., Keynote abstractTechnologyEmplacement

Abstract: The study develops a new approach utilizing parameters of trigonal etch pits on diamond crystals to infer the conditions of diamond residence in kimberlite magma. Diamond crystals from dissolution experiments conducted at 1 GPa and 1150-1350 °C in the presence of H2O-rich or CO2-rich fluid were studied with atomic force microscopy (AFM). The AFM data of resorbed diamond surfaces show that much deeper surface relief was produced in CO2 fluid. It also clearly distinguishes the profiles of the trigonal etch pits forming regular flat-bottomed trigons in H2O fluid, and round- or pointed-bottomed trigons in CO2 fluid. The relationship between the diameter and the depth of the trigonal pits is found to be another important indicator of the fluid composition. Dissolution in H2O fluid develops trigons with constant diameter and variable depth where the diameter increases with temperature. Trigons developed in CO2 fluid have a large range of diameters showing a strong positive correlation with the depth. The developed criteria applied to the natural diamond crystals from three Ekati Mine kimberlites indicate significant variation in CO2-H2O ratio and temperature of their magmatic fluid. This conclusion based on diamond resorption agrees with the mineralogy of microphenocrysts and groundmass of the studied kimberlites offering new method to study crystallization conditions of kimberlite magma.
DS1606-1086
2016
Feng, D., Maram, P.S., Mielewczyk-Gryn, A., Navotsky, A.Thermochemistry of rare earth perovskites Na3xRE.067-xTiO3 ( Re=La, Ce)American Mineralogist, Vol. 101, 5, pp. 1125-1128.TechnologyPerovskite
DS1604-0603
2013
Ferreira, J.Sampling and estimation of diamond content in kimberlite based on microdiamonds. IN ENGLISHEcole Nationale Superieure des Mines de Paris, 207p. PdfGlobalMicrodiamonds

Abstract: This research deals with diamond content estimation in kimberlite based on information obtained from microdiamond sampling. In spite of the abundance of diamonds smaller than 0.5mm square mesh the conventional approach of estimating diamond content is based on information derived from stones in the +0.5mm size fraction. While large samples are required to ensure recovery of sufficient numbers of diamonds for evaluation the largest number is therefore discarded as treatment tailings. As far back as the 1960’s this inspired the approach to lower the bottom screen aperture in order to recover microdiamonds, and was accompanied by the introduction of recovery methodology based on acid dissolution. As a consequence the required sample size is smaller, bringing along many practical advantages. The research deals with estimation of the weight of diamonds (diamond content) in kimberlite, based on information obtained from microdiamond sampling to a bottom screen diameter as low as 0.075 mm square mesh (~0.0000018 carats). Determination of the diamond size distribution has always been a challenge when estimating deposit diamond content. The method proposed in the research is based on the assumption of lognormality, which is in line with experience at all primary deposits. Over the years special techniques of estimating deposit diamond content have been developed and in this research have ‘matured’ into a proper sampling and estimation approach, taking cognizance of the fact that sampling is partially ‘flawed’ due to inevitable losses of diamonds during sample treatment. Some smaller diamonds are lost when they pass through the bottom cut-off screen used during diamond recovery, when according to their weight they should actually be recovered. Other losses of small diamonds occur when they remain locked in host rock particles and are discarded along with non-diamond bearing material. Modelling of diamond content is performed by means of an iterative process of simulating diamonds as distributed in their in situ state, followed by emulating recovery effects to reproduce a representative sample.
DS1603-0376
2016
Ferrero, S., Ziemann, M.A., Angel, R.J., Obrien, P.J., Wunder, B.Kumdykolite, kokchetavite, and cristobalite crystallized in nanogranites from felsic granulites, Orlica-Snieznik Dome, ( Bohemian Massif): not an evidence for ultrahigh-pressure conditions.Contributions to Mineralogy and Petrology, Vol. 171, pp. 1-12.EuropeBohemian

Abstract: A unique assemblage including kumdykolite and kokchetavite, polymorphs of albite and K-feldspar, respectively, together with cristobalite, micas, and calcite has been identified in high-pressure granulites of the Orlica-Snieznik dome (Bohemian Massif) as the product of partial melt crystallization in preserved nanogranites. Previous reports of both kumdykolite and kokchetavite in natural rocks are mainly from samples that passed through the diamond stability field. However, because the maximum pressure recorded in these host rocks is <3 GPa, our observations indicate that high pressure is not required for the formation of kumdykolite and kokchetavite, and their presence is not therefore an indicator of ultrahigh-pressure conditions. Detailed microstructural and microchemical investigation of these inclusions indicates that such phases should instead be regarded as (1) a direct mineralogical criteria to identify former melt inclusions with preserved original compositions, including H2O and CO2 contents and (2) indicators of rapid cooling of the host rocks. Thus, the present study provides novel criteria for the interpretation of melt inclusions in natural rocks and allows a more rigorous characterization of partial melts during deep subduction to mantle depth as well as their behavior on exhumation.
DS1601-0016
2015
Fiege, A., Cichy, S.B.Experimental constraints on bubble formation and growth during magma ascent: a review.American Mineralogist, Vol. 100, pp. 2426-2442.MantleMagmatism

Abstract: The number of studies investigating the vesiculation of natural samples and their implications to volcanic degassing and eruption mechanisms has been growing rapidly within the last decades. To interpret the natural rock textures, the geoscience community has produced a range of experimental and theoretical data sets on bubble nucleation, growth, and coalescence in magmatic systems. A robust experimental database is required to calibrate (theoretical and empirical) modeling approaches, which allow the calculation of magma ascent rates from volcanic ejecta mainly by the determination of the bubble number density (BND). Although, the available data set is still limited, it already shows that variations in melt (and volatile/fluid) composition can have a significant effect. In this manuscript we (re-)evaluate the existing experimental data set, while focusing mainly on the review and discussion of continuous decompression experiments. One aim of this review article is to encourage scientists to fill the gaps in the existing experimental data sets and help to acknowledge, use, and further develop the most promising experimental techniques. Therefore, we highlight different methods and discuss their advantages and possible limitations. We also discuss possible ways of how to better account for the influence of melt composition in models, which link BND to decompression rate.
DS1605-0835
2016
Fischer, R., Gerya, T.Early Earth plume-lid tectonics: a high resolution 3D numerical modellling approach.Journal of Geodynamics, in press available 17p.MantleSubduction

Abstract: Geological-geochemical evidence point towards higher mantle potential temperature and a different type of tectonics (global plume-lid tectonics) in the early Earth (>3.2 Ga) compared to the present day (global plate tectonics). In order to investigate tectono-magmatic processes associated with plume-lid tectonics and crustal growth under hotter mantle temperature conditions, we conduct a series of 3D high-resolution magmatic-thermomechanical models with the finite-difference code I3ELVIS. No external plate tectonic forces are applied to isolate 3D effects of various plume-lithosphere and crust-mantle interactions. Results of the numerical experiments show two distinct phases in coupled crust-mantle evolution: (1) a longer (80-100 Myr) and relatively quiet ‘growth phase’ which is marked by growth of crust and lithosphere, followed by (2) a short (~20 Myr) and catastrophic ‘removal phase’, where unstable parts of the crust and mantle lithosphere are removed by eclogitic dripping and later delamination. This modelling suggests that the early Earth plume-lid tectonic regime followed a pattern of episodic growth and removal also called episodic overturn with a periodicity of ~100 Myr.
DS1609-1717
2016
Fischer, R., Gerya, T.Regimes of subduction and lithospheric dynamics in the Precambrian: 3D thermomechanical modelling.Gondwana Research, Vol. 37, pp. 53-70.MantlePlate Tectonics

Abstract: Comparing the early Earth to the present day, geological-geochemical evidence points towards higher mantle potential temperature and a different type of tectonics. In order to investigate possible changes in Precambrian tectonic styles, we conduct 3D high-resolution petrological-thermomechanical numerical modelling experiments for oceanic plate subduction under an active continental margin at a wide range of mantle potential temperature TP (? TP = 0 - 250 K, compared to present day conditions). At present day mantle temperatures (? TP = 0 K), results of numerical experiments correspond to modern-style subduction, whereas at higher temperature conditions important systematic changes in the styles of both lithospheric deformation and mantle convection occur. For ? TP = 50 - 100 K a regime of dripping subduction emerges which is still very similar to present day subduction but is characterised by frequent dripping from the slab tip and a loss of coherence of the slab, which suggests a close relationship between dripping subduction and episodic subduction. At further increasing ? TP = 150 - 200 K dripping subduction is observed together with unstable dripping lithosphere, which corresponds to a transitional regime. For ? TP = 250 K, presumably equivalent to early Archean, the dominating tectonic style is characterised by small-scale mantle convection, unstable dripping lithosphere, thick basaltic crust and small plates. Even though the initial setup is still defined by present day subduction, this final regime shows many characteristics of plume-lid tectonics. Transition between the two end-members, plume-lid tectonics and plate tectonics, happens gradually and at intermediate temperatures elements of both tectonic regimes are present. We conclude, therefore, that most likely no abrupt geodynamic regime transition point can be specified in the Earth's history and its global geodynamic regime gradually evolved over time from plume-lid tectonics into modern style plate tectonics.
DS1610-1860
2016
Forster, M.W., Prelevic, D., Schmuck, H.R., Jacob, D.E.Melting and dynamic metasomatism of mixed harzburgite + glimmerite mantle source: implications for the genesis of orogenic potassic magmas.Chemical Geology, in press available 10p.MantleUltrapotassic magmas

Abstract: Tectonically young, orogenic settings are commonly the sites of post-collisional silica-rich ultrapotassic magmas with extreme K2O-contents of up to 9 wt% and K2O/Na2O > 2. Many experimental studies investigating the generation of these melts have concentrated on melting of homogenous phlogopite bearing peridotites, whereas geochemical signatures indicate the involvement of at least two types of source rocks: ultra-depleted and K and trace elements-enriched ones. We report the results of melting experiments at 1-2 GPa of mixed glimmerite and harzburgite, in which these rock types make up two halves each capsule. Melting begins in the glimmerite, and its metasomatic effects on the harzburgite are apparent at 1100 °C even before melt pools are visible. The first melts are Na-rich, seen in zoning of olivines and as growth of clinopyroxene in the harzburgite, but change at higher degrees of melting to produce a typical lamproite-like melt with K2O > 10 wt%. A major advantage of this study is the preservation of distinct melts in different parts of the capsule, which reflect a process of dynamic metasomatism: within the harzburgite matrix, the infiltrating melt derived from melting of the glimmerite changes consistently with the distance of travel through the harzburgite, enabling quantification of the metasomatic effects as an increase in SiO2 and K2O. This results principally from assimilation of orthopyroxene, which increases the Ol/Opx ratio of the residual harzburgite. The effects of quench olivine growth are recognizable and can be quantified due to a step-change in composition at the glimmerite/harzburgite border: the large total surface area of olivine and small melt fraction mean that the amount of quench olivine is high within the harzburgite, but negligible in the almost completely molten glimmerite. Melts of the glimmerite contain up to 8-10 wt% K2O and 53 wt% SiO2, which increase to 55-56 wt% after interaction with the harzburgite. Mediterranean lamproites resemble melts of glimmerite, whereas melts that have interacted with harzburgite are more similar to less potassic, but more SiO2-rich shoshonites of the Mediterranean region.
DS1609-1718
2016
Foster, R.Mineral deposits of Africa: a compilation ( 1907-2016) 300 papers sourced from Economic Geology, SP, Monographs, Newsletter.Society of Economic Geologists, Disc Compilation, Vol. 12, Member price $ 68. USAfricaCompilation of deposits ( not specific to diamonds)
DS1605-0836
2016
Fouchee, A., Stabbert, W.Technological advances of Longi-Multotec high intensity rare earth magnetic seperators improving DMS media circuits.Diamonds Still Sparkling SAIMM 2016 Conference, Mar. 14-17, pp. 153-158.TechnologyDMS - applied
DS1604-0604
2016
Foulger, G.R.Fundamentals of the plates vs plume plates.Japan Geoscience Union Meeting, 1p. AbstractMantleDebate - magmatism
DS1611-2106
2016
Fournier, D., Heagy, L.Where are the diamonds? - using Earth's potentialsSimPEG Team, 1p. Poster pdfTechnologyGeophysics - Magnetics, gravity
DS1611-2107
2014
Fournier, D., Heagy, L., Corcoran, N., Cowan, D., Devriese, S.G.R., Bild-Enkin, D., Davis, K., Marchant, M., McMillan, M.S., Mitchell, M., Rosenkjar, G., Yang, D., Oldenburg, D.W.Multi-EM systems inversion - towards a common conductivity model for Tli Kwi Cho complex.SEG Annual Meeting Denver, pp. 1795-1799. pdfCanada, Northwest TerritoriesDeposit - Tli Kwi Cho

Abstract: The magnetic and electromagnetic responses from airborne systems at Tli Kwi Cho, a kimberlite complex in the Northwest Territories, Canada, have received considerable attention over the last two decades but a complete understanding of the causative physical properties is not yet at hand. Our analysis is distributed among three posters. In the first we find a 3D magnetic susceptibility model for the area; in the second we find a 3D conductivity model; and in the third we find a 3D chargeability model that can explain the negative transient responses measured over the kimberlite pipes. In this second paper we focus upon the task of finding a conductivity model that is compatible with three airborne data sets flown between 1992 and 2004: one frequency-domain data set (DIGHEM) and two time-domain systems (AeroTEM and VTEM). The goal is to obtain a 3D model from which geologic questions can be answered, but even more importantly, to provide a background conductivity needed to complete the 3D IP inversion of airborne EM data. We begin by modifying our pre-existing 1D frequency and time domain inversion codes to produce models that have more lateral continuity. The results are useful in their own right but we have also found that 1D analysis is often very effective in bringing to light erroneous data, assisting in estimating noise floors, and providing some starting information for developing a background model for the 3D EM inversion. Here we show some results from our Laterally Constrained Inversion (LCI) framework. The recovered conductivity models seem to agree on the general location of the kimberlite pipes but disagree on the geometry and conductivity values at depth. The complete 3D inversions in time and frequency, needed to resolved these issues, are currently in progress.
DS1611-2108
2016
Fournier, D., Kang, S., McMillan, M.S., Oldenburg, D.W.Inversion of airborne geophysics over the Tli Kwi Cho kimberlite complex, Part II: electromagnetics.Tli Kwi Cho Workshop UBC, Sept. 8, 43p. Contact sdevriese @eos.ubc.caCanada, Northwest TerritoriesDeposit - Tli Kwi Cho
DS1610-1861
2016
Freeman, Z.W., Hames, W., Bridges, D.L.The Devonian Avon alkaline province, Missouri: characterization of subcontinental mantle source and evolution from olivine phenocrysts.GSA Annual Meeting, 1/2p. abstractUnited States, MissouriAlnoite, melilitite

Abstract: We present new data on the crystallization age of, and composition of olivine phenocrysts within, an alnöite and olivine melilitite of the Avon Alkalic Igneous Province (AAIP) of Missouri. The AAIP is an ultramafic igneous province consisting of more than 80 known lithologically and texturally diverse intrusions, cropping out in northeastern flank of the St. Francois Mtn. Terrane. 40Ar/39Ar geochronology of biotite phenocrysts constrains emplacement to 386 +/- 1 Ma. Xenocrystic biotite from one sample yields 40Ar/39Ar age spectra characteristic of episodic loss, indicating crystallization at ca. 1.3 Ga followed by partial loss in the ultramafic magma at 386 Ma. Olivines within the alnöite are subhedral, variably serpentinized, and embayed. Olivines within the melilitite are euhedral, but extensively serpentinized. Disequilibrium textures observed in alnöite olivine are consistent with resorption of magmatic olivine as a result of decompression during crystallization. Euhedral olivine within the melilitite appear to have remained in equilibrium with melt, suggesting derivation of alnöite and melilitite from unique magmas. Major and trace elemental abundances of olivine from the alnöite were characterized with electron probe microanalysis. Olivines are Mg-rich (Fo86.9-Fo89.9), and exhibit systematic variation in trace element (e.g., Ni (1627 to 3580 ppm), Cr (97 to 1603 ppm), Co (149 to 259 ppm), Ti (11 to 267 ppm), Al (undetectable to 923 ppm), and P (undetectable to 433 ppm)) abundances with decreasing forsterite content consistent with fractional crystallization. All geothermometers yield a range in temperature, e.g., the Al in olivine (De Hoog et al., 2009) yield temperatures of 1087° to 1313° C at depths of 80 km to 180 km (modern-day midcontinental LAB). Olivine trace element discrimination diagrams indicate AAIP magmas were derived from mantle sources with an alkalic affinity, similar to other continental alkaline rocks and kimberlite. A mantle origin via partial melting of carbonated peridotite mantle is suggested due to the high Mg content, results of geothermometric modeling, and high Ca and Ti abundance within olivine phenocrysts. Melting of the mantle may have ben triggered by "Acadian" tectonic events.
DS1603-0377
2015
Friedman, E., Polat, A., Thorkelson, D.J., Frei, R.Lithospheric mantle xenoliths sampled by melts from upwelling asthenosphere: the Quaternary Tasse alkaline basalts of southeastern British Columbia, Canada.Gondwana Research, In press available 22p.Canada, British ColumbiaAlkaline rocks, basalts

Abstract: The Quaternary Tasse basalts are exposed near the north shore of Quesnel Lake in southeastern British Columbia. They host a variety of mantle xenoliths consisting predominantly of spinel lherzolite with minor dunite and pyroxenite. Mineralogically, the xenoliths are composed of olivine, orthopyroxene, clinopyroxene and spinel characterized by forsterite (Fo87-93), enstatite (En90-92), diopside (En45-50-Wo40-45-Fs5), and Cr-spinel (6 - 11 wt.% Cr), respectively. All of the mantle xenoliths are coarse-grained and show granoblastic textures. Clinopyroxene and spinel display textural evidence for chemical reactions with percolating melts. The mantle xenoliths are characterized by restricted Mg-numbers (89 - 92) and low abundances of incompatible elements (Ba = 2 - 11 ppm; Sr = 3 - 31 ppm) and Yttrium (1 - 3 ppm). On the basis of REE patterns, the xenoliths are divided into three groups reflecting the various degrees of mantle metasomatism: (1) Group 1 consists of concave-up LREE patterns (La/Smcn = 0.48 - 1.16; Gd/Ybcn = 0.71 - 0.92); (2) Group 2 possesses flat to moderately LREE-enriched patterns (La/Smcn = 1.14 - 1.92; Gd/Ybcn = 0.87 - 1.09); and (3) Group 3 is characterized by strongly LREE-enriched patterns (La/Smcn = 1.53 - 2.45; Gd/Ybcn = 1.00 - 1.32). On MORB-normalized trace element diagrams, the majority of the xenolith samples share the enrichment of LILE (Rb, Ba, K), U, Th, Pb, Sr and the depletion of HFSE (Nb, Ta, Ti, Y) relative to REE. These geochemical characteristics are consistent with a compositionally heterogeneous subcontinental lithospheric mantle source that originated as subarc mantle wedge peridotite at a convergent plate margin. The Tasse basalts have alkaline compositions characterized by low SiO2 (44 - 46 wt.%) and high alkali (Na2O + K2O = 5.1 - 6.6 wt.%) contents. They are strongly enriched in incompatible elements (TiO2 = 2.4 - 3.1 wt.%; Ba = 580 - 797 ppm; Sr = 872 - 993 ppm) and, display OIB-like trace element patterns (La/Smn = 3.15 - 3.85; Gd/Ybn = 3.42 - 4.61). They have positive eNd (+ 3.8 to + 5.5) values, with 338 - 426 Ma depleted mantle model ages, and display uniform OIB-like Sr (87Sr/86Sr = 0.703346 - 0.703591) and Pb (206Pb/204Pb = 19.40 - 19.58; 207Pb/204Pb = 15.57 - 15.60; 208Pb/204Pb = 38.99 - 39.14) isotopic compositions. The basalts erupted discontinuously along a > 1000 km long SE-NW-trending linear belt with minimal compositional variation indicative of a homogenous mantle source. The Sr - Nd - Pb isotope and trace element systematics of the alkaline basalts suggests that they originated from partial melting of an upwelling asthenospheric mantle source. Melting of the asthenospheric mantle might have stemmed from extension of the overlying lithosphere in response to the early stages of back-arc basin opening in the Omineca and Intermontane belts. Ridge subduction beneath the Canadian Cordillera might have played an important role in the weakening of the lithospheric mantle prior to its extension. Alternatively, melting of the upwelling asthenosphere in response to the delamination of the lithospheric mantle beneath the Rocky Mountain Trench might have generated the alkaline lavas.
DS1604-0605
2016
Friis, H.First occurrence of moskvinite-(Y) in the Illmaussaq alkaline complex, South Greenland.Mineralogical Magazine, Vol. 80, 1, pp. 31-41.Europe, GreenlandMineralogy

Abstract: Moskvinite-(Y), Na2K(Y,REE)Si6O15, is a rare mineral, which until now has only been described from its type locality Dara-i-Pioz, Tajikistan. At Ilímaussaq moskvinite-(Y) was discovered in a drill core from Kvanefjeld, where it occurs as a replacement mineral associated with a mineral belonging to the britholite group. The composition was determined by a combination of electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry analyses. The empirical formula based on 15 oxygens is Na1.94K0.99(Y0.94Yb0.03Er0.03 Dy0.03Ho0.01Gd0.01) ?1.05Si5.98O15. The coexistence of an almost pure Y and a light rare-earth element (REE) mineral is interpreted as fractionation of REE and Y during the replacement of an earlier formed REE mineral. Theoretical calculations of the observed replacement of feldspathoids by natrolite show that the generated fluid would have pH > 8, which inhibits large scale mobility of REE. In addition, a K-Fe sulfide member of the chlorbartonite-bartonite group is for the first time observed in Ilímaussaq where it occurs where sodalite is replaced by natrolite and arfvedsonite by aegirine. The sulfide incorporates the S and some of the Cl generated by the alteration of sodalite, whereas the K and Fe originates from the replacement of arfvedsonite by aegirine.
DS1608-1403
2016
Fritsch, E.Are near colorless synthetic diamonds truly difficult to identify?GSA Annual Meeting, Abstract, 1p.TechnologySynthetics

Abstract: There is a rising number of near-colorless synthetics diamonds detected in the market, which create concerns for the trade. The recent advent of near-colorless melee size synthetic diamonds has raised the question of how to test large numbers of small stones. Many have turned to specialized sorting machines, which are expensive and difficult to evaluate. The problem arises only within near-colorless type IIa diamond gems. This type is commonly identified by infrared spectroscopy, which is man- or instrument-intensive. For the jeweler-gemologist, this can be identified by UV transparency, which isolates type IIa and also the even rarer type IaB from other types. Then amongst type IIas, one has to determine which are synthetic. One of the most effective sorting methods is anomalous double refringence (ADR) observing between crossed polarizers in a high-index immersion liquid. However, this method finds its limit with very small diameter stones, as then the optical pathlength is so small that no birefringence is perceived. Another approach is luminescence, based on observation of the whole stone; typically synthetics luminesce stronger in shortwave than longwave ultraviolet: this is effective to pinpoint HPHT-grown colorless and yellows, but useless for generally inert CVD-grown ones. Then the observation of luminescence zoning is usually conclusive. It necessitates expensive specialized instruments and also, a good knowledge of the very varied forms of natural diamond growth to avoid mistaking a natural for a synthetic. Finally, the last resort is luminescence spectroscopy. this typically involves laser excitation with several lasers, at low temperature. Further, this implies a very thorough knowledge of natural and synthetic diamond emissions, which limits this approach to a small number of laboratories. In practice, for a small number of stones, the definitive interpretation of spectra may remain a matter of discussion. Thus, the separation of natural from synthetic diamond mélé may appear very difficult. Yet, there are a limited number of simple devices which can help the jeweler-gemologist, even more the diamond professional. The last resort appears to be luminescence spectroscopy, but it is expensive and a great deal of interpretation is required. Automated instruments offer only limited help.
DS1610-1862
2016
Fritsch, E.Are near-colorless synthetic diamonds truly difficult to identify? ( problem type IIa gems)GSA Annual Meeting, 1/2p. abstractTechnologyDouble refringence ADR

Abstract: There is a rising number of near-colorless synthetics diamonds detected in the market, which create concerns for the trade. The recent advent of near-colorless melee size synthetic diamonds has raised the question of how to test large numbers of small stones. Many have turned to specialized sorting machines, which are expensive and difficult to evaluate. The problem arises only within near-colorless type IIa diamond gems. This type is commonly identified by infrared spectroscopy, which is man- or instrument-intensive. For the jeweler-gemologist, this can be identified by UV transparency, which isolates type IIa and also the even rarer type IaB from other types. Then amongst type IIas, one has to determine which are synthetic. One of the most effective sorting methods is anomalous double refringence (ADR) observing between crossed polarizers in a high-index immersion liquid. However, this method finds its limit with very small diameter stones, as then the optical pathlength is so small that no birefringence is perceived. Another approach is luminescence, based on observation of the whole stone; typically synthetics luminesce stronger in shortwave than longwave ultraviolet: this is effective to pinpoint HPHT-grown colorless and yellows, but useless for generally inert CVD-grown ones. Then the observation of luminescence zoning is usually conclusive. It necessitates expensive specialized instruments and also, a good knowledge of the very varied forms of natural diamond growth to avoid mistaking a natural for a synthetic. Finally, the last resort is luminescence spectroscopy. this typically involves laser excitation with several lasers, at low temperature. Further, this implies a very thorough knowledge of natural and synthetic diamond emissions, which limits this approach to a small number of laboratories. In practice, for a small number of stones, the definitive interpretation of spectra may remain a matter of discussion. Thus, the separation of natural from synthetic diamond mélé may appear very difficult. Yet, there are a limited number of simple devices which can help the jeweler-gemologist, even more the diamond professional. The last resort appears to be luminescence spectroscopy, but it is expensive and a great deal of interpretation is required. Automated instruments offer only limited help.
DS1612-2300
2016
Fulop, A., Kurszlaukis, S.Monogenetic v. polygenetic kimberlite volcanism: in-depth examination of the Tango extension super structure, Attawapiskat kimberlite field, Ontario, Canada.Geological Society of London, Special Publication no. 446 on line availableCanada, Ontario, AttawapiskatDeposit - Tango

Abstract: Extensive drilling of the Tango Extension kimberlite pipe resulted in the construction of an emplacement model that revealed the complex architecture of two amalgamated pipes: an older pipe, the Tango Extension Deep, which is cut along its northern margin by the smaller Tango Extension pipe. The resulting volcano forms a complex pipe-in-pipe structure called the Tango Extension Super Structure. The emplacement of the Tango Extension Super Structure sequence indicates prolonged hiatuses, which, similar to other volcanoes classified as monogenetic, puts the classical monogenetic and polygenetic definitions of maar-diatreme volcanoes to the test. Although the Tango Extension and Tango Extension Deep volcanoes could be characterized individually as monogenetic volcanoes, the Tango Extension Super Structure shows evidence of the occurrence of the significant hiatuses typical of polygenetic volcanoes. We suggest that hiatuses that are long enough to consolidate earlier tephra unambiguously differentiate polygenetic from monogenetic maar-diatreme volcanoes.
DS1606-1087
2016
Furman, T., Nelson, W.R., Elkins-Tanton, L.T.Evolution of the East African rift: drip magmatism, lithospheric thinning and mafic volcanism.Geochimica et Cosmochimica Acta, in press availableAfrica, EthiopiaMetasomatism - picrites

Abstract: The origin of the Ethiopian-Yemeni Oligocene flood basalt province is widely interpreted as representing mafic volcanism associated with the Afar mantle plume head, with minor contributions from the lithospheric mantle. We reinterpret the geochemical compositions of primitive Oligocene basalts and picrites as requiring a far more significant contribution from the metasomatized subcontinental lithospheric mantle than has been recognized previously. This region displays the fingerprints of mantle plume and lithospheric drip magmatism as predicted from numerical models. Metasomatized mantle lithosphere is not dynamically stable, and heating above the upwelling Afar plume caused metasomatized lithosphere with a significant pyroxenite component to drip into the asthenosphere and melt. This process generated the HT2 lavas observed today in restricted portions of Ethiopia and Yemen now separated by the Red Sea, suggesting a fundamental link between drip magmatism and the onset of rifting. Coeval HT1 and LT lavas, in contrast, were not generated by drip melting but instead originated from shallower, dominantly anhydrous peridotite. Looking more broadly across the East African Rift System in time and space, geochemical data support small volume volcanic events in Turkana (N. Kenya), Chyulu Hills (S. Kenya) and the Virunga province (Western Rift) to be derived ultimately from drip melting. The removal of the gravitationally unstable, metasomatized portion of the subcontinental lithospheric mantle via dripping is correlated in each case with periods of rapid uplift. The combined influence of thermo-mechanically thinned lithosphere and the Afar plume together thus controlled the locus of continental rift initiation between Africa and Arabia and provide dynamic support for the Ethiopian plateau.
DS1604-0606
2015
G & G Lab notesGraphite inclusions forming octahedral outline in diamond.Gems & Gemology Lab Notes, Vol. 51, 4, winter pp. 428-429.TechnologyDiamond inclusions
DS1604-0607
2015
G & G Lab notesVery large type 1b natural diamond ( yellow)Gems & Gemology Lab notes, Vol. 51, 4, winter pp. 430-431.TechnologyType 1b diamond
DS1607-1346
2016
Gaetani, G.The influence of spinel lherzolite partial melting on oxygen fugacity in the oceanic upper mantle.IGC 35th., Session The Deep Earth 1 p. abstractMantleMelting
DS1606-1088
2016
Gaetani, G.A.The behavior of Fe3/Efe during partial melting of spinel lherzolite.Geochimica et Cosmochimica Acta, in press availableGeothermometry

Abstract: The use of wet chemistry and X-ray absorption near edge structure (XANES) spectroscopy to determine the oxidation state of Fe in submarine glasses and olivine-hosted melt inclusions has provided important new insights into the global systematics of Fe3+/?Fe in mid-ocean ridge basalts (MORB) [1, 2]. Because MORB are aggregates of near-fractional partial melts formed by decompression melting of variably depleted peridotite, it is difficult to judge the extent to which they directly reflect the oxidation state of the oceanic upper mantle. To provide a theoretical framework within which to interpret Fe3+/?Fe in MORB, I have developed a model that describes the behavior of Fe3+/?Fe during spinel lherzolite partial melting in a system closed to oxygen. Modeling is carried out by calculating the Fe3+/?Fe of olivine using the point defect model of [3], and determining Fe3+/?Fe of the bulk peridotite from mineral-mineral partitioning. The inter-mineral Fe3+/Fe2+ exchange coefficients are derived from Mössbauer data on natural spinel peridotites, and are parameterized in terms of oxygen fugacity, temperature, and the Fe content of the olivine. The Fe3+/?Fe of the melt is determined by combining mass-balance with an equation relating the Fe3+/?Fe of the melt to the fugacity of oxygen [4]. Spinel lherzolite partial melting is modeled after [5]. Modeling results indicate that oxygen fugacity does not follow the fayalite-magnetite-quartz (FMQ) buffer during partial melting. For isobaric partial melting, the system becomes reduced relative to FMQ with increasing extent of melting. This results from an increase in the FMQ buffer with increasing temperature, whereas oxygen fugacity in the peridotite remains nearly constant. Conversely, during polybaric partial melting the oxidation state of the residual peridotite increases relative to FMQ. The effective partition coefficient for Fe3+is larger than previously thought, so that a redox couple with S is not required to explain its compatibility during partial melting.
DS1608-1404
2016
Galimov, E.M., Sevastyanov, V.S., Karpova, G.A., Shilobreeva, S.N., Maksimov, A.P.Microcrystalline diamonds in the oceanic lithosphere and their nature. MicrodiamondsDoklady Earth Sciences, Vol. 469, 1, pp. 670-673.RussiaTolbachik Volcano

Abstract: The carbon isotope composition of microdiamonds found in products of the Tolbachik Volcano eruption, Kamchatka (porous lavas and ash), was studied. The isotope composition of microdiamonds (with an average value of d13C =-25.05‰) is close to that of microsized carbon particles in lavas (from-28.9 to-25.3‰). The general peculiarities of the diamond-forming environment include (1) no evidence for high pressure in the medium; (2) a reduced environment; and (3) mineralogical evidence for the presence of a fluid. The geochemical data characterizing the type of diamonds studied allow us to suggest that they were formed in accordance with the mechanism of diamond synthesis during cavitation in a rapidly migrating fluid, which was suggested by E.M. Galimov.
DS1611-2109
2016
Ganti, V., Von Hagke, C., Scherler, D., Lamb, M.P., Fischer, W.W., Avouac, J-P.Time scale bias in erosion rates of glaciated landscapes.Science Advances, Vol. 2, 10, 3p.GlobalGlaciology

Abstract: Deciphering erosion rates over geologic time is fundamental for understanding the interplay between climate, tectonic, and erosional processes. Existing techniques integrate erosion over different time scales, and direct comparison of such rates is routinely done in earth science. On the basis of a global compilation, we show that erosion rate estimates in glaciated landscapes may be affected by a systematic averaging bias that produces higher estimated erosion rates toward the present, which do not reflect straightforward changes in erosion rates through time. This trend can result from a heavy-tailed distribution of erosional hiatuses (that is, time periods where no or relatively slow erosion occurs). We argue that such a distribution can result from the intermittency of erosional processes in glaciated landscapes that are tightly coupled to climate variability from decadal to millennial time scales. In contrast, we find no evidence for a time scale bias in spatially averaged erosion rates of landscapes dominated by river incision. We discuss the implications of our findings in the context of the proposed coupling between climate and tectonics, and interpreting erosion rate estimates with different averaging time scales through geologic time.
DS1605-0837
2016
Gao, C., Crabtree, D.C., Dyer, R.D.Indicator mineral and geochemistry data for a till and alluvium sampling survey in the McFaulds Lake ( Ring of Fire) area, northern Ontario. Mentions KIMS.Ontario Geological Survey Report and Data, Report 6309, Data release 322.Canada, OntarioGeochemistry - KIMS
DS1608-1405
2016
Garnero, E.J., McNamara, A.K., Shim, S-H.Continent sized anomalous zones with low seismic velocity at the base of Earth's mantle.Nature Geoscience, Vol. 9, 7, pp. 481-489.MantleGeophysics - seismics

Abstract: Seismic images of Earth's interior reveal two massive anomalous zones at the base of the mantle, above the core, where seismic waves travel slowly. The mantle materials that surround these anomalous regions are thought to be composed of cooler rocks associated with downward advection of former oceanic tectonic plates. However, the origin and composition of the anomalous provinces is uncertain. These zones have long been depicted as warmer-than-average mantle materials related to convective upwelling. Yet, they may also be chemically distinct from the surrounding mantle, and potentially partly composed of subducted or primordial material, and have therefore been termed thermochemical piles. From seismic, geochemical and mineral physics data, the emerging view is that these thermochemical piles appear denser than the surrounding mantle materials, are dynamically stable and long-lived, and are shaped by larger-scale mantle flow. Whether remnants of a primordial layer or later accumulations of more-dense materials, the composition of the piles is modified over time by stirring and by chemical reactions with material from the surrounding mantle, underlying core and potentially from volatile elements transported into the deep Earth by subducted plates. Upwelling mantle plumes may originate from the thermochemical piles, so the unusual chemical composition of the piles could be the source of distinct trace-element signatures observed in hotspot lavas.
DS1608-1406
2015
Garnett, R.H.T.Graphical presentation of production versus estimates in placer mining. Diamonds mentioned.Applied Earth Science Transactions Institute of Mining and Metallurgy, Vol. 124, 3, pp. 175-190.GlobalAlluvials, reserves
DS1605-0838
2016
Gaschnig, R.M., Rudnick, R.L., McDonough, W.F., Kaufman, A.J., Valley, J., Hu, Z., Gao, S., Beck, M.L.Compositional evolution of the upper continental crust through time, as constrained by ancient glacial diamictites.Geochimica et Cosmochimica Acta, in press available 78p.MantleBulk chemistry

Abstract: The composition of the fine-grained matrix of glacial diamictites from the Mesoarchean, Paleoproterozoic, Neoproterozoic, and Paleozoic, collected from four modern continents, reflect the secular evolution of the average composition of the upper continental crust (UCC). The effects of localized provenance are present in some cases, but distinctive geochemical signatures exist in diamictites of the same age from different localities, suggesting that these are global signatures. Archean UCC, dominated by greenstone basalts and less so komatiites, was more mafic, based on major elements and transition metal trace elements. Temporal changes in oxygen isotope ratios, rare earth elements, and high field strength elements indicate that the UCC became more differentiated and that tonalite-trondhjemite-granodiorite suites became less important with time, findings consistent with previous studies. We also document the concentrations of siderophile and chalcophile elements (Ga, Ge, Cd, In, Sn, Sb, W, Tl, Bi) and lithophile Be in the UCC through time, and use the data for the younger diamictites to construct a new estimate of average UCC along with associated uncertainties.
DS1605-0839
2016
Gaudet, M.Renard 65: a multi phase pipe infilled with hypabyssal and Kimberley-type pyroclastic kimberlite.DCO Edmonton Diamond Workshop, June 8-10Canada, QuebecDeposit - Renard65
DS1607-1347
2016
Gee, D.G.Microdiamonds in the Scandinavian Caledonides related to Ordovician continent arc and Siluro-Devonian continent collision.IGC 35th., Session The Deep Earth 1 p. abstractEurope, Scandinavia, SwedenMicrodiamonds
DS1608-1407
2016
Geiger, C.A.A tale of two garnets: the role of solid solution in the development toward a modern mineralogy.American Mineralogist, Vol. 101, pp. 735-1749.TechnologyGarnet classification

Abstract: This article reviews the development of mineralogy as a science by focusing largely on the common silicate garnets of general formula {X3}[Y2](Si3)O12. It tells of important discoveries, analyses, and proposals by various scientists relating to crystallography, crystal structures, isomorphism, and solid solution starting in Europe in the late 1700s. The critical recognition of the importance of ionic size of atoms in determining crystal-chemical properties and solid-solution behavior is emphasized. The two garnet species “pyralspite” and “(u)grandite,” which were considered to represent two independent solid-solution series, were introduced by N.H. Winchell and A.N. Winchell (1927) in their well-known book Elements of Optical Mineralogy. Critical comments on the assumptions behind the classification scheme have been pointed out for at least 50 yr, but it remains in use. There is more, though, behind this garnet classification scheme than just simple terminology. There are a long series of scientific discoveries and advances that are largely forgotten by the broader mineralogical community. They begin, here, with the work of the “father of crystallography,” René-Just Haüy, concerning the microscopic nature of crystals around 1780 and include later discoveries and proposals by Mitscherlich, Beudant, Wollaston, and Kopp relating to isomorphism and solid-solution behavior all before 1850. A second key era started with the discovery of X-ray diffraction in 1912 that allowed the atomic structures of crystals and, furthermore, atomic and ion radii to be determined. In terms of isomorphism and solid solution, the proposals and studies of Vegard, Zambonini, Wherry, A.N. Winchell, and the “father of crystal chemistry” Goldschmidt are briefly discussed. The recognition of the sizes of atoms and ions, along with an understanding of chemical bonding behavior in crystals, was critical in the establishment of what can be termed “modern mineralogy,” a quantitative science as it is largely understood today that emerged by the mid-1930s. The silicate garnet system pyrope-almandine-spessartine-grossular-andradite-uvarovite shows extensive homovalent substitutional solid solution over two structural sites and complete compositional variation between “pyralspite species” and “ugrandite species” has been documented. Thus, the prerequisites behind the terms “pyralspite” and “(u)grandite,” as originally formulated and often accepted even today, are incorrect and use of this classification is not recommended. Diffraction determinations of the volumes of garnet end-members and volumes of mixing of garnet solid solutions give physical insight into solid-solution behavior. Today, investigations of local structural and crystal-chemical properties, together with determinations of lattice strain and thermodynamic mixing properties, of silicate solid solutions are leading to an ever more quantitative understanding of mineral behavior from the microscopic to macroscopic level.
DS1603-0378
2016
Geology InThe largest Tsavorite in the world. 185 grams from Karo area.Gemshare, 1p.Africa, TanzaniaGemstone - Tsavorite
DS1601-0017
2015
Georg, R.B., Shahar, A.The accretion and differentiation of Earth under oxidizing conditions.American Mineralogist, Vol. 100, pp. 2739-2748.MantleCore, formation

Abstract: We present a new approach to model planetary accretion and continuous core formation, and discuss the implications if Earth accreted under conditions initially more oxidized than the modern day mantle. The modified model uses the same partitioning data that were previously used to model accretion under reducing conditions, however, changing the partitioning between accreting metal and silicate mantle means that reducing conditions fail to meet expected core/mantle values. Instead, the model requires conditions more oxidized than the modern day mantle to converge and to yield expected elemental core/mantle distribution values for moderately siderophile elements. The initial oxygen fugacity required to provide the crucial level of oxidation is approximately ?IW ~ -1.2 to -1.7 and thus is in the range of carbonaceous and ordinary chondrites. The range of peak pressures for metal silicate partitioning is 60-6 GPa and oxygen fugacity must decrease to meet modern FeO mantle contents as accretion continues. Core formation under oxidizing conditions bears some interesting consequences for the terrestrial Si budget. Although the presented partitioning model can produce a Si content in the core of 5.2 wt%, oxidizing accretion may limit this to a maximum of ~3.0 to 2.2 wt%, depending on the initial fO2 in BSE, which places bulk earth Mg/Si ratio between 0.98-1.0. In addition, under oxidizing conditions, Si starts partitioning late during accretion, e.g., when model earth reached >60% of total mass. As a consequence, the high P-T regime reduces the accompanied isotope fractionation considerably, to 0.07‰ for 5.2 wt% Si in the core. The isotope fractionation is considerably less, when a maximum of 3.0 wt% in the core is applied. Under oxidizing conditions it becomes difficult to ascertain that the Si isotope composition of BSE is due to core-formation only. Bulk Earth’s Si isotope composition is then not chondritic and may have been inherited from Earth’s precursor material.
DS1604-0608
2016
Gernon, T.M., Hincks, T.K., Tyrell, T., Rohling, E.J., Palmer, M.R.Snowball Earth ocean chemistry driven by extensive ridge volcanism during Rodinia breakup.Nature Geoscience, Vol. 9, 3, pp. 242-248.Gondwana, RodiniaAlkalic

Abstract: During Neoproterozoic Snowball Earth glaciations, the oceans gained massive amounts of alkalinity, culminating in the deposition of massive cap carbonates on deglaciation. Changes in terrestrial runoff associated with both breakup of the Rodinia supercontinent and deglaciation can explain some, but not all of the requisite changes in ocean chemistry. Submarine volcanism along shallow ridges formed during supercontinent breakup results in the formation of large volumes of glassy hyaloclastite, which readily alters to palagonite. Here we estimate fluxes of calcium, magnesium, phosphorus, silica and bicarbonate associated with these shallow-ridge processes, and argue that extensive submarine volcanism during the breakup of Rodinia made an important contribution to changes in ocean chemistry during Snowball Earth glaciations. We use Monte Carlo simulations to show that widespread hyaloclastite alteration under near-global sea-ice cover could lead to Ca2+ and Mg2+ supersaturation over the course of the glaciation that is sufficient to explain the volume of cap carbonates deposited. Furthermore, our conservative estimates of phosphorus release are sufficient to explain the observed P:Fe ratios in sedimentary iron formations from this time. This large phosphorus release may have fuelled primary productivity, which in turn would have contributed to atmospheric O2 rises that followed Snowball Earth episodes.
DS1607-1348
2016
Ghosh, S.REE enriched carbonatite from Kamthai area, Barmer district, Rajasthan, India: imprints of a delta34S depleted mantle source.IGC 35th., Session The Deep Earth 1 p. abstractIndiaCarbonatite
DS1608-1408
2016
GIA LibraryRecommended reading & bibliographiesgia.edu/library, Available as a resourceTechnologyGIA Library
DS1610-1863
2016
Giordano, D., Russell, J.K.The heat capacity of hydrous multicomponent natural melts and glasses.Chemical Geology, In press available 30p.MantleMelting

Abstract: The thermophysical properties of silicate melts and glasses are of fundamental importance for the characterization of the dynamics and energetics of silicate melts on Earth and terrestrial planets. The heat capacity of silicate melts is of particular importance because of its implications for the temperature dependencies of melt enthalpy and entropy and for the potential relationship to melt structure and transport properties. Currently, there are reliable models for predicting the heat capacity of simple and multicomponent silicate glasses (Cpglass) as a function of composition and temperature. Recent differential scanning calorimetry (DSC) measurements of heat capacity for multicomponent silicate liquid (Cpliquid), however, have shown that published models do not accurately reproduce heat capacity measurements on some silicate melts. Here, we have compiled a database of heat capacity values for hydrous and anhydrous multicomponent natural samples. The measurements are on pairs of glasses and melts over the compositional range (wt%) of: SiO2 (44-79), Al2O3 (5-35), TiO2 (0-3), FeOtot (0 - 11); Na2O + K2O (0-27); CaO + MgO (0-39), H2O (0-6.3) and minor oxides. The compiled data show strong correlations between silica content (XSiO2) and the configurational heat capacity (Cpconfig) defined as Cpliquid - Cpglass measured across the glass transition temperature (Tg). This correlation is used to establish an empirical model for predicting Cpliquid as a function of melt composition (i.e. SiO2 content) and values of Cpglass measured at the onset of the glass transition: Cpliquid=52.6-55.88XSiO2+CpglassCpliquid=52.6-55.88XSiO2+Cpglass. The model reproduces values of Cpliquid to within an average relative error of ~ 2.4%. Published models for the heat capacities of silicate melts (e.g., Stebbins, 1984; Richet and Bottinga, 1985; Lange and Navrotsky, 1992) applied to the same dataset have average relative errors in excess of 5.5%.
DS1602-0205
2015
Girard, J., Amulele, G., Farla, R., Mohiuddin, A., Karato, S-i.Shear deformation of bridgmanite and magnesiowustite aggregates at lower mantle conditions.Science, Vol. 351, 6269, pp. 144-147.MantleRheology

Abstract: Rheological properties of the lower mantle have strong influence on the dynamics and evolution of Earth. By using the improved methods of quantitative deformation experiments at high pressures and temperatures, we deformed a mixture of bridgmanite and magnesiowüstite under the shallow lower mantle conditions. We conducted experiments up to about 100% strain at a strain rate of about 3 × 10(-5) second(-1). We found that bridgmanite is substantially stronger than magnesiowüstite and that magnesiowüstite largely accommodates the strain. Our results suggest that strain weakening and resultant shear localization likely occur in the lower mantle. This would explain the preservation of long-lived geochemical reservoirs and the lack of seismic anisotropy in the majority of the lower mantle except the boundary layers.
DS1601-0018
2016
Giuliani, A., Phillips, D., Kamenetsky, V.S., Goemann, K.Constraints on kimberlite ascent mechanisms revealed by phlogopite compositions in kimberlites and mantle xenoliths.Lithos, Vol. 240, pp. 189-201.Africa, South AfricaDeposit - Bultfontein

Abstract: Kimberlite magmas are of economic and scientific importance because they represent the major host to diamonds and are probably the deepest magmas from continental regions. In addition, kimberlite magmas transport abundant mantle and crustal xenoliths, thus providing fundamental information on the composition of the sub-continental lithosphere. Despite their importance, the composition and ascent mechanism(s) of kimberlite melts remain poorly constrained. Phlogopite is one of the few minerals that preserves a history of fluid migration and magmatism in the mantle and crust and is therefore an invaluable petrogenetic indicator of kimberlite magma evolution. Here we present major and trace element compositional data for phlogopite from the Bultfontein kimberlite (Kimberley, South Africa; i.e. the kimberlite type-locality) and from entrained mantle xenoliths. Phlogopite macrocrysts (~ > 0.3-0.5 mm) and microcrysts (between ~ 0.1 and 0.3 mm) in the Bultfontein kimberlite display concentric compositional zoning patterns. The cores of these phlogopite grains exhibit compositions typical of phlogopite contained in peridotite mantle xenoliths. However, the rims of some grains show compositions analogous to kimberlite groundmass phlogopite (i.e. high Ti, Al and Ba; low Cr), whereas other rims and intermediate zones (between cores and rims) exhibit unusually elevated Cr and lower Al and Ba concentrations. The latter compositions are indistinguishable from matrix phlogopite in polymict breccia xenoliths (considered to represent failed kimberlite intrusions) and from Ti-rich overgrowth rims on phlogopite in other mantle xenoliths. Consequently, it is likely that these phlogopite grains crystallized from kimberlite melts and that the high Ti-Cr zones originated from earlier kimberlite melts at mantle depths. We postulate that successive pulses of ascending kimberlite magma progressively metasomatised the conduit along which later kimberlite pulses ascended, producing progressively decreasing interaction with the surrounding mantle rocks. In our view, these processes represent the fundamental mechanism of kimberlite magma ascent. Our study also indicates that, in addition to xenoliths/xenocrysts and magmatic phases, kimberlite rocks incorporate material crystallized at various mantle depths by previous kimberlite intrusions (mantle-derived ‘antecrysts’).
DS1611-2110
2016
Giuliani, A., Soltys, A., Phillips, D., Kamenetsly, V.S., Maas, R., Geomann, K., Woodhead, J.D., Drysdale, R.N., Griffin, W.L.The final stages of kimberlite petrogenesis: petrography, mineral chemistry, melt inclusions and Sr-C-O isotope geochemistry of the Bultfontein kimberlite ( Kimberley, South Africa).Chemical Geology, in press available 15p.Africa, South AfricaDeposit - Bultfontein

Abstract: The petrogenesis of kimberlites commonly is obscured by interaction with hydrothermal fluids, including deuteric (late-magmatic) and/or groundwater components. To provide new constraints on the modification of kimberlite rocks during overprinting by such fluids and on the fractionation of kimberlite magmas during crystallisation, we have undertaken a detailed petrographic and geochemical study of a hypabyssal sample (BK) from the Bultfontein kimberlite (Kimberley, South Africa).
DS1608-1409
2016
Glassley, W.Na-P concentrations in high-pressure garnets: a potentially rich, but risky P-T repository.American Mineralogist, Vol. 101, p. 1718.TechnologyUHP - garnets

Abstract: Establishing the history of HP and UHP metamorphic rocks is important for quantifying Earth dynamics. The history of these rocks defines, among other things, paleo-subduction rates, P-T paths, and the kinematics of continent-continent collision. Although the appearance of certain minerals, such as coesite, stishovite, or diamond, provides unequivocal evidence of an HP or UHP component to the history of a rock, they cannot provide details of the P-T-t path a rock has experienced. However, complex solid solutions can. This reflects the fact that solid solutions have the potential to provide a continuous thermodynamically controlled response to evolving P-T conditions. To the extent that such solid-solution characteristics are preserved unmodified in a mineral throughout its history, a detailed description of the trajectory of the rock during burial …
DS1610-1864
2016
Glazner, A.F., Bartley, J.M., Coleman, D.S.We need a new definition of magma.EOS Transaction of AGU, Sept. 22, 3p.TechnologyDefinition of magma
DS1606-1089
2016
Golubkova, A., Schmidt, M.W., Connolly, J.A.D.Ultra reducing conditions in average mantle peridotites and in podiform chromitites: a thermodynamic model for moissanite (SiC) formation.Contributions to Mineralogy and Petrology, in press available, 17p.MantlePeridotite

Abstract: Natural moissanite (SiC) is reported from mantle-derived samples ranging from lithospheric mantle keel diamonds to serpentinites to podiform chromitites in ophiolites related to suprasubduction zone settings (Luobusa, Dongqiao, Semail, and Ray-Iz). To simulate ultra-reducing conditions and the formation of moissanite, we compiled thermodynamic data for alloys (Fe-Si-C and Fe-Cr), carbides (Fe3C, Fe7C3, SiC), and Fe-silicides; these data were augmented by commonly used thermodynamic data for silicates and oxides. Computed phase diagram sections then constrain the P-T-fO2 conditions of SiC stability in the upper mantle. Our results demonstrate that: Moissanite only occurs at oxygen fugacities 6.5-7.5 log units below the iron-wustite buffer; moissanite and chromite cannot stably coexist; increasing pressure does not lead to the stability of this mineral pair; and silicates that coexist with moissanite have X Mg > 0.99. At upper mantle conditions, chromite reduces to Fe-Cr alloy at fO2 values 3.7-5.3 log units above the moissanite-olivine-(ortho)pyroxene-carbon (graphite or diamond) buffer (MOOC). The occurrence of SiC in chromitites and the absence of domains with almost Fe-free silicates suggest that ultra-reducing conditions allowing for SiC are confined to grain scale microenvironments. In contrast to previous ultra-high-pressure and/or temperature hypotheses for SiC origin, we postulate a low to moderate temperature mechanism, which operates via ultra-reducing fluids. In this model, graphite-/diamond-saturated moderately reducing fluids evolve in chemical isolation from the bulk rock to ultra-reducing methane-dominated fluids by sequestering H2O into hydrous phases (serpentine, brucite, phase A). Carbon isotope compositions of moissanite are consistent with an origin of such fluids from sediments originally rich in organic compounds. Findings of SiC within rocks mostly comprised by hydrous phases (serpentine + brucite) support this model. Both the hydrous phases and the limited diffusive equilibration of SiC with most minerals in the rocks indicate temperatures below 700-800 °C. Moissanite from mantle environments is hence a mineral that does not inform on pressure but on a low to moderate temperature environment involving ultra-reduced fluids. Any mineral in equilibrium with SiC could only contain traces of Fe2+ or Cr3+.
DS1608-1410
2015
Gomes dos Santis, E.The Kimberley Process Certification System - KPCS and diamond production changes in selected African Countries.REM: Revista Escola de Minas, Vol. 68, 3, pp. 279-285.AfricaKimberley Process

Abstract: After more than a decade since its creation, the KPCS is undergoing questioning as to efficiency in combating the irregular trade of diamonds, among the countries with significant production for the global market, mainly Angola, the Democratic Republic of the Congo and Zimbabwe. Governments and institutions are considering it to be conducive to serious violations of human rights. In Brazil all activities of the sector have been reduced drastically. It is estimated that there has been a loss in Brazilian production, after implementation of the KPCS rules, in the order of 8.1 million Kts, valued at more than $ 2.0 billion.
DS1603-0379
2015
Goncharov, A.F., Lobanov, S.S., Tan, X., Hohensee, G.T., Cahill, D.G., Lin, J-F., Thomas, S-M., Okuchi, T., Tomioka, N., Helffrich, G.Experimental study of thermal conductvity at high pressures: implication for the deep Earth's interior.Physics of the Earth and Planetary Interiors, Vol. 247, pp. 11-16.MantleExperimental Petrology

Abstract: Lattice thermal conductivity of ferropericlase and radiative thermal conductivity of iron bearing magnesium silicate perovskite (bridgmanite) - the major mineral of Earth’s lower mantle- have been measured at room temperature up to 30 and 46 GPa, respectively, using time-domain thermoreflectance and optical spectroscopy techniques in diamond anvil cells. The results provide new constraints for the pressure dependencies of the thermal conductivities of Fe bearing minerals. The lattice thermal conductivity of ferropericlase Mg0.9Fe0.1O is 5.7(6) W/(m * K) at ambient conditions, which is almost 10 times smaller than that of pure MgO; however, it increases with pressure much faster (6.1(7)%/GPa vs 3.6(1)%/GPa). The radiative conductivity of a Mg0.94Fe0.06SiO3 bridgmanite single crystal agrees with previously determined values for powder samples at ambient pressure; it is almost pressure-independent in the investigated pressure range. Our results confirm the reduced radiative conductivity scenario for the Earth’s lower mantle, while the assessment of the heat flow through the core-mantle boundary still requires in situ measurements at the relevant pressure-temperature conditions.
DS1607-1296
2016
Gonnermann, H.M.Magma fragmentation.Annual Review of Earth and Planetary Sciences, Vol. 43, pp. 431-458.MantleMagmatism

Abstract: Magma fragmentation is the breakup of a continuous volume of molten rock into discrete pieces, called pyroclasts. Because magma contains bubbles of compressible magmatic volatiles, decompression of low-viscosity magma leads to rapid expansion. The magma is torn into fragments, as it is stretched into hydrodynamically unstable sheets and filaments. If the magma is highly viscous, resistance to bubble growth will instead lead to excess gas pressure and the magma will deform viscoelastically by fracturing like a glassy solid, resulting in the formation of a violently expanding gas-pyroclast mixture. In either case, fragmentation represents the conversion of potential energy into the surface energy of the newly created fragments and the kinetic energy of the expanding gas-pyroclast mixture. If magma comes into contact with external water, the conversion of thermal energy will vaporize water and quench magma at the melt-water interface, thus creating dynamic stresses that cause fragmentation and the release of kinetic energy. Lastly, shear deformation of highly viscous magma may cause brittle fractures and release seismic energy.
DS1609-1719
2016
Gonzales, C.M., Gorczyk, W., Gerya, T.V.Decarbonation of subducting slabs: insight from petrological-thermomechanical modeling.Gondwana Research, Vol. 36, pp. 314-332.MantleSubduction

Abstract: Subduction of heterogeneous lithologies (sediments and altered basalts) carries a mixture of volatile components (H2O ± CO2) into the mantle, which are later mobilized during episodes of devolatilization and flux melting. Several petrologic and thermodynamic studies investigated CO2 decarbonation to better understand carbon cycling at convergent margins. A paradox arose when investigations showed little to no decarbonation along present day subduction geotherms at subarc depths despite field based observations. Sediment diapirism is invoked as one of several methods for carbon transfer from the subducting slab. We employ high-resolution 2D petrological-thermomechanical modeling to elucidate the role subduction dynamics has with respect to slab decarbonation and the sediment diapirism hypothesis. Our thermodynamic database is modified to account for H2O-CO2 binary fluids via the following lithologies: GLOSS average sediments (H2O: 7.29 wt.% & CO2: 3.01 wt.%), carbonated altered basalts (H2O: 2.63 wt.% & CO2: 2.90 wt.%), and carbonated peridotites (H2O: 1.98 wt.% & CO2: 1.50 wt.%). We include a CO2 solubility P-x[H2O wt.%] parameterization for sediment melts. We parameterize our model by varying two components: slab age (20, 40, 60, 80 Ma) and convergence velocity (1, 2, 3, 4, 5, 6 cm year- 1). 59 numerical models were run and show excellent agreement with the original code base. Three geodynamic regimes showed significant decarbonation. 1) Sedimentary diapirism acts as an efficient physical mechanism for CO2 removal from the slab as it advects into the hotter mantle wedge. 2) If subduction rates are slow, frictional coupling between the subducting and overriding plate occurs. Mafic crust is mechanically incorporated into a section of the lower crust and undergoes decarbonation. 3) During extension and slab rollback, interaction between hot asthenosphere and sediments at shallow depths result in a small window (~ 12.5 Ma) of high integrated CO2 fluxes (205 kg m- 3 Ma- 1).
DS1607-1349
2016
Goulart, R.Depositional evolution of southwest Gondwana Neoproterozoic paleobasins based on Sr, C and O isotopic compositions of carbonatic rocks from the Sul-Riograndense shield, Brazil.IGC 35th., Session A Dynamic Earth 1p. AbstractSouth America, BrazilCarbonatite
DS1607-1350
2016
Graham, I., Groat, L., Giuliani, G.Gems: bringing the world together,IGC 35th., Session Mineralogy 1 p. abstractTechnologyMineralogy
DS1602-0206
2016
Grakhanov, S.A., Zinchuk, N.N., Sobolev, N.V.The age of predictable primary diamond sources in the northeastern Siberian platform.Doklady Earth Sciences, Vol. 465, 2, pp. 1297-1301.Russia, SiberiaDeposit - Malokuonapskaya

Abstract: The U-Pb (SHRIMP) age was determined for zircons collected from 26 observation and sampling sites of diamonds and index minerals in the northeastern Siberian Platform. This part of the region hosts 15 low-diamondiferous Paleozoic and Mesozoic kimberlite fields, excluding the near economic Triassic Malokuonapskaya pipe in the Kuranakh field. Four epochs of kimberlite formation (Silurian, Late Devonian to Early Carboniferous, Middle to Late Triassic, and Middle to Late Jurassic) of the Siberian Platform, including its northeastern part, are confirmed as a result of our studies. Most observation points, including economic Quaternary diamond placers, contain Middle to Late Triassic zircons, which confirms the abundant Late Triassic volcanism in this region. The positive correlation of diamonds and major index minerals of kimberlites (mostly, garnets) at some observation sites indicates the possible Triassic age of the predictable diamondiferous kimberlites.
DS1603-0380
2010
Grasso, C. B.Petrology of alkaline complex Serra Negra. ( Salitre 1 e Salitre II) Whole rock geochemistry Thesis, Universidade de Brasilia *** IN POR, 164p. Pdf *** In PortugeseSouth America, BrazilCarbonatite
DS1611-2111
2015
Green, D.H.Experimental petrology of peridotites, including effects of water and carbon on melting in the Earth's upper mantle.Physics and Chemistry of Minerals, Vol. 42, pp. 95-102.MantlePeridotite

Abstract: For over 50 years, the use of high-pressure piston/cylinder apparatus combined with an increasing diversity of microbeam analytical techniques has enabled the study of mantle peridotite compositions and of magmas derived by melting in the upper mantle. The experimental studies have been guided by the petrology and geochemistry of peridotites from diverse settings and by the remarkable range of mantle-derived magma types. Recent experimental study using FTIR spectroscopy to monitor water content of minerals has shown that fertile lherzolite (MORB-source upper mantle) at ~1,000 °C can store ~200 ppm H2O in defect sites in nominally anhydrous minerals (olivine, pyroxenes, garnet and spinel). Water in excess of 200 ppm stabilizes amphibole (pargasite) at P < 3 GPa up to the lherzolite solidus. However, at P > 3 GPa, water in excess of 200 ppm appears as an aqueous vapour phase and this depresses the temperature of the upper mantle solidus. Provided the uppermost mantle (lithosphere) has H2O < 4,000 ppm, the mantle solidus has a distinctive P, T shape. The temperature of the vapour-undersaturated or dehydration solidus is approximately constant at 1,100 °C at pressures up to ~3 GPa and then decreases sharply to ~1,010 °C. The strongly negative dT/dP of the vapour-undersaturated solidus of fertile lherzolite from 2.8 to 3 GPa provides the basis for understanding the lithosphere/asthenosphere boundary. Through upward migration of near-solidus hydrous silicate melt, the asthenosphere becomes geochemically zoned with the ‘enriched’ intraplate basalt source (>500 ppm H2O) overlying the ‘depleted’ MORB source (~200 ppm H2O). From the study of primitive MOR picrites, the modern mantle potential temperature for MORB petrogenesis is ~1,430 °C. The intersection of the 1,430 °C adiabat with the vapour-saturated lherzolite solidus at ~230 km suggests that upwelling beneath mid-ocean ridges begins around this depth. In intraplate volcanism, diapiric upwelling begins from shallower depths and lower temperatures within the asthenosphere and the upwelling lherzolite is enriched in water, carbonate and incompatible elements. Magmas including olivine melilitites, olivine nephelinites, basanites, alkali picrites and tholeiitic picrites are consequences of increasing melt fraction and decreasing pressure at melt segregation. Major element, trace element and isotopic characteristics of island chain or ‘hot-spot’ magmas show that they sample geochemically distinct components in the upper mantle, differing from MORB sources. There is no evidence for higher-temperature ‘hot-spot’ magmas, relative to primitive MORB, but there is evidence for higher water, CO2 and incompatible element contents. The distinctive geochemical signatures of ‘hot-spot’ magmas and their ‘fixed’ position and long-lived activity relative to plate movement are attributed to melt components derived from melting at interfaces between old, oxidised subducted slabs (suspended beneath or within the deeper asthenosphere) and ambient, reduced mantle. In convergent margin volcanism, the inverted temperature gradients inferred for the mantle wedge above the subducting lithosphere introduce further complexity which can be explored by overlaying the phase relations of appropriate mantle and crustal lithologies. Water and carbonate derived from the subducted slab play significant roles, magmas are relatively oxidised, and distinctive primary magmas such as boninites, adakites and island arc ankaramites provide evidence for fluxing of melting in refractory harzburgite to lherzolite by slab-derived hydrous adakitic melt and by wedge-derived carbonatite.
DS1611-2112
2015
Green, D.H., Falloon, T.J.Mantle-derived magmas: intraplate, hot spots and mid-ocean ridges.Science Bulletin, Vol. 60, 22, pp. 1873-1900.MantleHotspots

Abstract: Primary or parental magmas act as probes to infer eruption and source temperatures for both mid-ocean ridge (MOR) and ‘hot-spot’ magmas (tholeiitic picrites). The experimental petrogenetic constraints (‘inverse’ experiments) argue for no significant temperature differences between them. However, there are differences in major, minor and trace elements which characterise geochemical, not thermal, anomalies beneath ‘hot-spots’. We suggest that diapiric upwelling from interfaces (redox contrasts) between old subducted slab and normal MOR basalt source mantle is the major reason for the observed characteristics of island chain or ‘hot-spot’ volcanism. Intraplate basalts also include widely distributed volcanic centres containing lherzolite xenoliths, i.e. mantle-derived magmas. Inverse experiments on olivine basalt, alkali olivine basalt, olivine basanite, olivine nephelinite, olivine melilitite and olivine leucitite (lamproite) determined liquidus phases as a function of pressure, initially under anhydrous and CO2-absent conditions. Under C- and H-absent conditions, only tholeiites to alkali olivine basalts had Ol + Opx ± Cpx as high-pressure liquidus phases. Addition of H2O accessed olivine basanites at 2.5-3 GPa, ~1,200 °C, but both CO2 and H2O were necessary to obtain saturation with Ol, Opx, Cpx and Ga at 2.5-3.5 GPa for olivine nephelinite and olivine melilitite. The forward and inverse experimental studies are combined to formulate a petrogenetic grid for intraplate, ‘hot-spot’ and MOR magmatism within the plate tectonics paradigm. The asthenosphere is geochemically zoned by slow upward migration of incipient melt. The solidus and phase stabilities of lherzolite with very small water contents (<3,000 ppm) determine the thin plate behaviour of the oceanic lithosphere and thus the Earth’s convection in the form of plate tectonics. There is no evidence from the parental magmas of MOR and ‘hot-spots’ to support the ‘deep mantle thermal plume’ hypothesis. The preferred alternative is the presence of old subducted slabs, relatively buoyant and oxidised with respect to MORB source mantle and suspended or upwelling in or below the lower asthenosphere (and thus detached from overlying plate movement).
DS1606-1090
2016
Griffin, W.L., Afonso, J.C., Belousova, E.A., Gain, S.E., Gong, X-H., Gonzalez-Jiminez, J.M., Howell, D., Huang, J-X., McGowan, N., Pearson, N.J., Satsukawa, T., Shi R., Williams, P., Xiong, Q., Yang, J-S., Zhang, M., O'Reilly, S.Y.Mantle recycling: transition zone metamorphism of Tibetan ophiolitic peridotites and its tectonic implications.Journal of Petrology, in press available, 30p.Asia, China, TibetPeridotite

Abstract: Large peridotite massifs are scattered along the 1500?km length of the Yarlung-Zangbo Suture Zone (southern Tibet, China), the major suture between Asia and Greater India. Diamonds occur in the peridotites and chromitites of several massifs, together with an extensive suite of trace phases that indicate extremely low fO2 (SiC, nitrides, carbides, native elements) and/or ultrahigh pressures (UHP) (diamond, TiO2 II, coesite, possible stishovite). New physical and isotopic (C, N) studies of the diamonds indicate that they are natural, crystallized in a disequilibrium, high-T environment, and spent only a short time at mantle temperatures before exhumation and cooling. These constraints are difficult to reconcile with previous models for the history of the diamond-bearing rocks. Possible evidence for metamorphism in or near the upper part of the Transition Zone includes the following: (1) chromite (in disseminated, nodular and massive chromitites) containing exsolved pyroxenes and coesite, suggesting inversion from a high-P polymorph of chromite; (2) microstructural studies suggesting that the chromitites recrystallized from fine-grained, highly deformed mixtures of wadsleyite and an octahedral polymorph of chromite; (3) a new cubic Mg-silicate, with the space group of ringwoodite but an inverse-spinel structure (all Si in octahedral coordination); (4) harzburgites with coarsely vermicular symplectites of opx + Cr-Al spinel ± cpx; reconstructions suggest that these are the breakdown products of majoritic garnets, with estimated minimum pressures to?>?13?GPa. Evidence for a shallow pre-metamorphic origin for the chromitites and peridotites includes the following: (1) trace-element data showing that the chromitites are typical of suprasubduction-zone (SSZ) chromitites formed by magma mixing or mingling, consistent with Hf-isotope data from magmatic (375?Ma) zircons in the chromitites; (2) the composition of the new cubic Mg-silicate, which suggests a low-P origin as antigorite, subsequently dehydrated; (3) the peridotites themselves, which carry the trace element signature of metasomatism in an SSZ environment, a signature that must have been imposed before the incorporation of the UHP and low-fO2 phases. A proposed P-T-t path involves the original formation of chromitites in mantle-wedge harzburgites, subduction of these harzburgites at c. 375?Ma, residence in the upper Transition Zone for >200 Myr, and rapid exhumation at c. 170-150?Ma or 130-120?Ma. Os-isotope data suggest that the subducted mantle consisted of previously depleted subcontinental lithosphere, dragged down by a subducting oceanic slab. Thermomechanical modeling shows that roll-back of a (much later) subducting slab would produce a high-velocity channelized upwelling that could exhume the buoyant harzburgites (and their chromitites) from the Transition Zone in?
DS1603-0381
2016
Griffin, W.L., Gain, S.E.M., Adams, D., Huang, J-X., Saunders, M.,Toledo, V., Pearson, N.J., O'Reilly, S.Y.Heaven on Earth: tistarite ( Ti203) and other nebular phases in corundum aggregates from Mt. Carmel volcanic rocks.Israel Geological Society, pp. 85-86. abstractEurope, IsraelMoissanite

Abstract: This ending talk, focused on the ongoing cooperative research of Prof. Griffin and his team at Macquarie University and Shefa Yamim, since January 2014, highlighting unique corundum species characteristics. Preliminary results of this research were presented in the IGS Annual Meeting of 2015, whereas this year Prof. Griffin has shared innovative findings only microscopically tracked within titanium-rich corundum aggregates. One of the more abundant minerals is Tistarite (Ti2O3), previously known only as a single grain in a primitive type of meteorite (!). An article has been submitted to a scientific journal detailing this first terrestrial occurrence. Several other minerals are common in meteorites, but unknown or extremely rare on Earth. About half of these minerals are unknown to science, and will be described as new minerals in the scientific literature. The first of these is a Titanium-Aluminium-Zirconium oxide, informally known as TAZ; it will be submitted to the International Mineralogical Association for recognition as a new mineral, ShefaTAZite. Using state of the art technologies such as Thermal Ionisation Mass Spectrometry (TIMS) and Electron Microscopy Facility (EMF) that has three scanning electron microscopes, all with EBSD capability, and a transmission electron microscope - Prof. Griffin revealed spectacular imagery of minerals and rare compounds associated with titanium rich corundum aggregates.
DS1603-0382
2016
Griffin, W.L., Gain, S.E.M., Adams, D., Toledo, V., Pearson, N.J., O'Reilly, S.Y.Deep-Earth methane, mantle dynamics and mineral exploration: insights from northern Israel, southern Tibet and Kamchatka.Israel Geological Society, pp. 87-88. abstractEurope, Israel, TibetMoissanite
DS1610-1865
2016
Griffin, W.L., Gain, S.E.M., Adams, D.T., Huang, J-X., Saunders, M., Toledo, V., Pearson, N.J., O'Reilly, S.Y.First terrestrial occurrence of tistarite ( Ti2O3): ultra-low oxygen fugacity in the upper mantle beneath Mount Carmel, Israel.Geology, Vol. 44, 10, pp. 815-818.Europe, IsraelMoissanite

Abstract: The minimum oxygen fugacity (fO2) of Earth's upper mantle probably is controlled by metal saturation, as defined by the iron-wüstite (IW) buffer reaction (FeO ? Fe + O). However, the widespread occurrence of moissanite (SiC) in kimberlites, and a suite of super-reduced minerals (SiC, alloys, native elements) in peridotites in Tibet and the Polar Urals (Russia), suggest that more reducing conditions (fO2 = 6-8 log units below IW) must occur locally in the mantle. We describe pockets of melt trapped in aggregates of corundum crystals ejected from Cretaceous volcanoes in northern Israel which contain high-temperature mineral assemblages requiring extremely low fO2 (IW < -10). One abundant phase is tistarite (Ti2O3), previously known as a single grain in the Allende carbonaceous chondrite (Mexico) and believed to have formed during the early evolution of the solar nebula. It is associated with other reduced phases usually found in meteorites. The development of super-reducing conditions in Earth's upper mantle may reflect the introduction of CH4 + H2 fluids from the deep mantle, specifically related to deep-seated volcanic plumbing systems at plate boundaries.
DS1602-0207
2016
Grocholski, B.New crustal clues from old rocks.Science, Vol. 352, 6271, pp. 350-351.MantleGeochronology
DS1607-1297
2016
Grocholski, B.Managing metal the core left behind.Science, Vol. 352, 6291, pp. 1289-1290.MantleGeophysics
DS1605-0840
2016
Grutter, H.Rapid lithosphere scale events constrained by cpx thermobarometry for the Coromandel area, Brazil.DCO Edmonton Diamond Workshop, June 8-10South America, BrazilCoromandel
DS1608-1411
2015
Grynberg, R., Mbayi, L.The Global diamond industry: economics and Development. Vol. I and IIPalgrave Hamilton, Hampshire (Publishers), Two separate Vols. Each $ 75.00 Kindle editionGlobalBook - diamond industry
DS1605-0841
2016
Guiliani, A.Trace element traverses across kimberlite olivine: a new tool to decipher the evolution of kimberlite magmas.DCO Edmonton Diamond Workshop, June 8-10TechnologyMagmatism
DS1607-1351
2016
Guiliani, A.Trace element variations across olivine record the evolution of kimberlite melts: case studies from the Kimberley kimberlites ( South Africa).IGC 35th., Session A Dynamic Earth 1p. AbstractAfrica, South AfricaKimberlite
DS1604-0609
2016
Gwalani, L.G., Jaques, A.L., Downes, P.J., Chalapathi Rao, N.V.Kimberlites, lamproites, carbonatites and associated alkaline rocks: a tribute to the work of Rex T. Prider VolumeMineralogy and Petrology, in press available 5p.MantlePrider volume
DS1607-1298
2016
Hacker, B.R., Kelemen, P.B., Behn, M.D.Continental lower crust.Annual Review of Earth and Planetary Sciences, Vol. 43, pp. 167-205.MantleMagmatism

Abstract: The composition of much of Earth's lower continental crust is enigmatic. Wavespeeds require that 10 -20% of the lower third is mafic, but the available heat-flow and wavespeed constraints can be satisfied if lower continental crust elsewhere contains anywhere from 49 to 62 wt% SiO2. Thus, contrary to common belief, the lower crust in many regions could be relatively felsic, with SiO2 contents similar to andesites and dacites. Most lower crust is less dense than the underlying mantle, but mafic lowermost crust could be unstable and likely delaminates beneath rifts and arcs. During sediment subduction, subduction erosion, arc subduction, and continent subduction, mafic rocks become eclogites and may continue to descend into the mantle, whereas more silica-rich rocks are transformed into felsic gneisses that are less dense than peridotite but more dense than continental upper crust. These more felsic rocks may rise buoyantly, undergo decompression melting and melt extraction, and be relaminated to the base of the crust. As a result of this refining and differentiation process, such relatively felsic rocks could form much of Earth's lower crust.
DS1602-0208
2016
Haggerty, S.E.Spinel in planetary systems.American Mineralogist, Vol. 101, pp. 5-6.TechnologySpinel terminology

Abstract: Spinel is ubiquitous as a rock-forming mineral in terrestrial, lunar, and planetary basalts and closely associated meteoritic equivalents. A major unknown is whether these rocks formed under similar conditions of partial melting of primary or modified mantle, whether redox environments played a role in evolutionary trends, and did mineral crystal chemistry have any influence on elemental partition between solids and liquids? In a novel approach by Papike et al. (2015), spinel is used as an informative, albeit complex indicator of oxygen fugacity, site occupancy of multiple valence elements, and spinel structural types. Planetary basalts may be reduced (IW-3), oxidized (Earth at FMQ), or of intermediate redox state (Mars). Taking an expansive view, the spinel approach holds enormous promise in understanding the magmatic differentiation of asteroids.
DS1610-1866
2016
Hagni, R.D.The alkaline igneous carbonatite complex and fluorspar deposits at Okorusu, north centra Namibia.GSA Annual Meeting, 1/2p. abstractAfrica, NamibiaCarbonatite

Abstract: The Okorusu Alkaline Igneous-Carbonatite Complex is located about 50 km north of Otjiwarongo in North-Central Namibia. The complex was intruded during early Cretaceous into late Precambrian Damaran Series metasedimentary rocks. It is nearly circular in plan view with a diameter of about 8 km. Coarse-grained nepheline syenites and foyaites are exposed in low hills near the northern edge of the complex. Early alkalie-rich fluids pervasively fenitized the metasedimentary rocks along the southern margin of the complex forming an east-west ridge of resistant hills that include Okorusu Mountain. The fenites were subsequently brecciated and intruded by several carbonatites, especially medium-grained iron-rich diopside pyroxene carbonitite and very coarse-grained pegmatitic carbonatite. In addition to predominant calcite, the carbonatites contain titaniferous vanadiferous magnetite crystals and diopside crystals as large as one-third meter and hexagonal pyrrhotite crystals as long as one meter. For the past two decades, Okoruru has been the leading carbonatite-related fluorspar producer in the world. Fluorspar has been mined from five separate ore deposits in open pits A, B, C, D, and E. The deposits formed principally by the replacement of carbonatite as shown by local unreplaced remnants of carbonatite in the fluorspar ores, goethite pseudomorphs in fluorspar ores after carbonatite magnetite, diopside, and pyrrhotite crystals, transitions of the ores into carbonatite, and by elevated phosphorus contents resulting from carbonatite apatite crystals that were incompletely replaced by fluorite. Locally, marbles also are replaced by fluorite to form fluorspar ores that are distinguished from carbonatite-replacement fluorspar ores by their finer grain size and lack of phosphorus contents. Fluid inclusions in the fluorite crystals indicate that the fluorspar ores were deposited from 166 to 128oC from fluids of low salinity with less than 5% NaCl equivalent. The genesis of the fluorspar ores is interpreted to have resulted from deeply circulated ground waters that dissolved fluorine from carbonatite at depth. The fluorine in those ore fluids combined with calcium released during the replacement of calcite in carbonatite and marbles at the sites of the fluorspar ore deposition.
DS1607-1299
2016
Hajjar, Z., Wafik, A., Constantin, M., Bhilisse, M.Process of serpentinization in the ultramafic massif of Beni Bousera ( internal Rift, Morocco).Arabian Journal of Geosciences, Vol. 9, availableAfrica, MoroccoPeridotite
DS1604-0610
2016
Hall, E.M.G., McClenaghan, M.B., Page, L.Application of portable XRF to the direct analysis of till samples from various deposit types in Canada.Geochemistry, Exploration, Environment, Analysis, Vol. 16, pp. 62-84.Canada, Northwest TerritoriesKimberlite - Triple B mentioned

Abstract: In this study, results by direct portable XRF (‘pXRF’) on unsieved till samples were compared with those by established laboratory methods (aqua regia or fusion ICP-MS and ICP-ES) on the <0.063-mm fraction to determine if the application of direct pXRF in the field would serve as an acceptable guide for immediate follow-up work. Four test sites in Canada were chosen: the Halfmile Lake Cu-Pb-Zn VMS deposit; the intrusion-hosted W-Mo Sisson deposit; a Pb-Zn Mississippi Valley-type (MVT) deposit in the Pine Point district; and the Triple B kimberlite. Unsieved till samples from the GSC archive collection were used for this study and included samples from background areas, immediately overlying, and at various distances down-ice of each deposit. Ziploc® and Whirl-Pak® bags that were used to contain the samples in the field were tested for their properties of X-ray attenuation and contamination. In general, the performance of pXRF in the four test areas was very good where concentrations of elements of interest (indicator or pathfinder elements) were substantially above detection limits by this technique (in the low ppm range for many elements). The following elements, shown to be useful indicator elements (important constituents of the ore/commodity) or pathfinder elements (those associated with the commodity elements) by the established methodology, showed similar patterns by pXRF on the unsieved material: Zn, Cu, Pb, and As at Halfmile Lake; W, Mo, Cu, Zn, Pb, and As at the Sisson deposit; Zn, Pb, and Fe at Pine Point; and Ca, Sr, Cr, and Ni at Triple B. Pathfinder elements whose concentrations were too low for determination by pXRF include: Ag and Sb at Halfmile Lake; Ag and Cd at Sisson; Cd, S, and Se at Pine Point; and Co, Mg, P, U, and Th at Triple B. The high background for Bi by pXRF, equivalent to c. 50?ppm, and its noisy signal precluded its use at Halfmile Lake and Sisson. Elements which tended to show poor precision (three analyses each sample) by pXRF in some samples due to sample heterogeneity include Sn, V, and W. Mercury was erroneously reported for the majority of samples in the low ppm range by pXRF whereas its concentration in fact was in the low ppb range. Several Pb-, Zn- (c. 1% Pb, Zn) and Fe-rich (up to 16% Fe) samples demonstrated spectral interferences by: Pb on As, Th and Se; Zn on Cu; and Fe on Co. Results for six till samples analysed in Ziploc® and Whirl-Pak® bags showed that Ziploc® absorbs fewer low-energy photons and hence is preferable for determining light elements such as Si, K and Ca.
DS1603-0383
2016
Hamilton, M.A., Buchan, K.L.A 2169 Ma U-Pb baddeleyite age for the Otish gabbro, Quebec: implications for correlation of Proterozoic magmatic events and sedimentary seuences in the eastern Superior province.Canadian Journal of Earth Sciences, Vol. 53, 2, pp. 119-128.Canada, QuebecGeochronology
DS1611-2113
2016
Happe Kazanzu, C., Linol, B., de Wit, M.J., Brown, R., Persano, R., Stuart, F.M.From source to sink in central Gondwana: exhumation of the Precambrian basement rocks of Tanzania and sediment accumulation in the adjacent Congo basin.Tectonics, Vol. 35, 9, pp. 2034-2051.Africa, TanzaniaGeodynamics

Abstract: Apatite fission track (AFT) and (U-Th)/He (AHe) thermochronometry data are reported and used to unravel the exhumation history of crystalline basement rocks from the elevated (>1000?m above sea level) but low-relief Tanzanian Craton. Coeval episodes of sedimentation documented within adjacent Paleozoic to Mesozoic basins of southern Tanzania and the Congo basin of the Democratic Republic of Congo indicate that most of the cooling in the basement rocks in Tanzania was linked to erosion. Basement samples were from an exploration borehole located within the craton and up to 2200?m below surface. Surface samples were also analyzed. AFT dates range between 317?±?33?Ma and 188?±?44?Ma. Alpha (Ft)-corrected AHe dates are between 433?±?24?Ma and 154?±?20?Ma. Modeling of the data reveals two important periods of cooling within the craton: one during the Carboniferous-Triassic (340-220?Ma) and a later, less well constrained episode, during the late Cretaceous. The later exhumation is well detected proximal to the East African Rift (70?Ma). Thermal histories combined with the estimated geothermal gradient of 9°C/km constrained by the AFT and AHe data from the craton and a mean surface temperature of 20°C indicate removal of up to 9?±?2?km of overburden since the end of Paleozoic. The correlation of erosion of the craton and sedimentation and subsidence within the Congo basin in the Paleozoic may indicate regional flexural geodynamics of the lithosphere due to lithosphere buckling induced by far-field compressional tectonic processes and thereafter through deep mantle upwelling and epeirogeny tectonic processes.
DS1605-0842
2016
Hardman, M.Statistical discrimination of mantle eclogitic garnet from crustal garnets.DCO Edmonton Diamond Workshop, June 8-10MantleGarnet
DS1610-1867
2015
Harlow, G.E., Sofianides, A.S.Gems & Crystals from one of the World's great collections. American Museum of Natural HistoryAmerican Mineralogist, Vol. 101, p. 2132.GlobalBook review
DS1607-1300
2016
Harlow, G.E., Tsujimori, T., Sorenson, S.S.Jadeites and plate tectonics.Annual Review of Earth and Planetary Sciences, Vol. 43, pp. 105-138.MantleJadeites

Abstract: Jadeitite is a relatively rare, very tough rock composed predominantly of jadeite and typically found associated with tectonic blocks of high-pressure/low-temperature metabasaltic rocks (e.g., eclogite, blueschist) in exhumed serpentinite-matrix mélanges. Studies over the past ~20 years have interpreted jadeitite either as the direct hydrous fluid precipitate from subduction channel dewatering into the overlying mantle wedge or as the metasomatic replacement by such fluids of oceanic plagiogranite, graywacke, or metabasite along the channel margin. Thus, jadeitites directly sample and record fluid transport in the subduction factory and provide a window into this geochemical process that is critical to a major process in the Earth system. They record the remarkable transport of large ion lithophile elements, such as Li, Ba, Sr, and Pb, as well as elements generally considered more refractory, such as U, Th, Zr, and Hf. Jadeitite is also the precious form of jade, utilized since antiquity in the form of tools, adornments, and symbols of prestige.
DS1610-1868
2016
Harper, D.R., Deangelis, M.T.Examination of mica bearing rocks from the Magnet Cove alkaline intrusive complex, Arkansas.GSA Annual Meeting, 1/2p. abstractUnited States, ArkansasIjolite, carbonatite

Abstract: The Magnet Cove Alkaline Intrusive Complex contains several silica-undersaturated igneous rock types (e.g. nepheline syenite, ijolite, carbonatite) that form a concentric ring map pattern approximately 4.6 square miles in area. These rings, which are likely the result of several nearly contemporaneous magma injection events during the mid Cretaceous, become increasingly silica-undersaturated from rim to core, and have been previously mapped as separate geologic units. The outer ring contains nepheline syenite, the intermediate ring contains both garnet ijolite and garnet biotite ijolite, and the core contains carbonatite. Though the detailed modal mineralogy differs somewhat between the silicate (i.e. syenite and ijolite) rock types, they all have in common the presence of mica group minerals. The purpose of this study is to examine and characterize the diversity of mica group minerals found in the silica-undersaturated rocks of Magnet Cove. Syenite and ijolite rock samples were collected from several locations within the complex, and thin sections were prepared for petrographic and electron microscope analysis using facilities and equipment at the UALR Rock Preparation Laboratory. Overall mineralogy from these samples indicates the presence of potassium feldspar, plagioclase feldspar, several feldspathoid minerals (nepheline, sodalite, altered leucite), amphiboles, pyroxenes (primarily aegerine and aegerine-augite), black Ti-bearing garnets (melanite, schorlomite), and various opaque minerals (e.g. magnetite, pyrite). Previously, micas in these rocks have been labeled simply as “biotite”. However, the ranges of color (yellowish-brown to bluish-green), crystal size (millimeter to several centimeters in diameter), and crystal habit (clusters of euhedral grains) in hand sample and variable pleochroism, ranging interference colors, reaction coronas, and zoning in thin section indicate a more interesting and complex chemical history.
DS1605-0843
2016
Harris, G.Mantle chemistry and age beneath the Darby kimberlite, NW Rae Craton.DCO Edmonton Diamond Workshop, June 8-10Canada, Northwest TerritoriesDeposit - Darby
DS1607-1301
2016
Hart, E., Storey, C., Bruand, E., Schertl, H-P., Alexander, B.D.Mineral inclusions in rutile: a novel recorder of HP-UHP.Earth and Planetary Science Letters, Vol. 446, pp. 137-148.MantleCoesite, subduction

Abstract: The ability to accurately constrain the secular record of high- and ultra-high pressure metamorphism on Earth is potentially hampered as these rocks are metastable and prone to retrogression, particularly during exhumation. Rutile is among the most widespread and best preserved minerals in high- and ultra-high pressure rocks and a hitherto untested approach is to use mineral inclusions within rutile to record such conditions. In this study, rutiles from three different high- and ultrahigh-pressure massifs have been investigated for inclusions. Rutile is shown to contain inclusions of high-pressure minerals such as omphacite, garnet and high silica phengite, as well as diagnostic ultrahigh-pressure minerals, including the first reported occurrence of exceptionally preserved monomineralic coesite in rutile from the Dora -Maira massif. Chemical comparison of inclusion and matrix phases show that inclusions generally represent peak metamorphic assemblages; although rare prograde phases such as titanite, omphacite and corundum have also been identified implying that rutile grows continuously during prograde burial and traps mineralogic evidence of this evolution. Pressure estimates obtained from mineral inclusions, when used in conjunction with Zr-in-rutile thermometry, can provide additional constraints on the metamorphic conditions of the host rock. This study demonstrates that rutile is an excellent repository for high- and ultra-high pressure minerals and that the study of mineral inclusions in rutile may profoundly change the way we investigate and recover evidence of such events in both detrital populations and partially retrogressed samples.
DS1602-0209
2016
Harvey, J., Warren, J.M., Shirey, S.B.Mantle sulfides and their role in Re-Os and Pb isotope geochronology.Reviews in Mineralogy and Geochemistry, Vol. 81, pp. 579-649.MantleGeochronology
DS1602-0210
2016
Harvey, J., Warren, J.M., Shirey, S.B.Mantle sulfides and their role in Re-Os and Pb isotope geochronology.Reviews in Mineralogy and Geochemistry, Vol. 81, pp. 579-649.Geochronology
DS1603-0384
2016
Hasiuk, F., Harding, C.Touchable topography: 3 D printing elevation data and structural models to overcome the issue of scale.Geology Today, Vol. 32, 1, pp. 16-20.TechnologyPrinters - not specific to diamonds
DS1612-2301
2016
Hassan, R., Muller, R.D., Gurnis, M., Williams, S.E., Flament, N.A rapid burst in hotspot motion through the interaction of tectonics and deep mantle flow.Nature, Vol. 533, pp. 239-242.MantleHotspots

Abstract: Volcanic hotspot tracks featuring linear progressions in the age of volcanism are typical surface expressions of plate tectonic movement on top of narrow plumes of hot material within Earth’s mantle1. Seismic imaging reveals that these plumes can be of deep origin2=probably rooted on thermochemical structures in the lower mantle3, 4, 5, 6. Although palaeomagnetic and radiometric age data suggest that mantle flow can advect plume conduits laterally7, 8, the flow dynamics underlying the formation of the sharp bend occurring only in the Hawaiian-Emperor hotspot track in the Pacific Ocean remains enigmatic. Here we present palaeogeographically constrained numerical models of thermochemical convection and demonstrate that flow in the deep lower mantle under the north Pacific was anomalously vigorous between 100 million years ago and 50 million years ago as a consequence of long-lasting subduction systems, unlike those in the south Pacific. These models show a sharp bend in the Hawaiian-Emperor hotspot track arising from the interplay of plume tilt and the lateral advection of plume sources. The different trajectories of the Hawaiian and Louisville hotspot tracks arise from asymmetric deformation of thermochemical structures under the Pacific between 100 million years ago and 50 million years ago. This asymmetric deformation waned just before the Hawaiian-Emperor bend developed, owing to flow in the deepest lower mantle associated with slab descent in the north and south Pacific.
DS1610-1869
2016
Hastie, A.R., Fitton, J.G., Bromiley, G.D., Butler, I.B., Oding, W.A.The origin of Earth's first continents and the onset of plate tectonics.Geology, Vol. 44, 10, pp. 855-858.MantleSubduction

Abstract: The growth and recycling of continental crust has resulted in the chemical and thermal modification of Earth's mantle, hydrosphere, atmosphere, and biosphere for ~4.0 b.y. However, knowledge of the protolith that gave rise to the first continents and whether the environment of formation was a subduction zone still remains unknown. Here, tonalite melts are formed in high P-T experiments in which primitive oceanic plateau starting material is used as an analogue for Eoarchean (3.6-4.0 Ga) oceanic crust generated at early spreading centers. The tonalites are produced at 1.6-2.2 GPa and 900-950 °C and are mixed with slab-derived aqueous fluids to generate melts that have compositions identical to that of Eoarchean continental crust. Our data support the idea that the first continents formed at ca. 4 Ga and subsequently, through the subduction and partial melting of ~30-45-km-thick Eoarchean oceanic crust, modified Earth's mantle and Eoarchean environments and ecosystems.
DS1609-1720
2016
Hawkesworth, C.J., Cawood, P.A., Dhuime, B.Tectonics and crustal evolution.GSA Today, Vol. 26, 9, 9p.MantleStages of subduction

Abstract: The continental crust is the archive of Earth’s history. Its rock units record events that are heterogeneous in time with distinctive peaks and troughs of ages for igneous crystallization, metamorphism, continental margins, and mineralization. This temporal distribution is argued largely to reflect the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly. Isotopic and elemental data from zircons and whole rock crustal compositions suggest that the overall growth of continental crust (crustal addition from the mantle minus recycling of material to the mantle) has been continuous throughout Earth’s history. A decrease in the rate of crustal growth ca. 3.0 Ga is related to increased recycling associated with the onset of plate tectonics. We recognize five stages of Earth’s evolution: (1) initial accretion and differentiation of the core/mantle system within the first few tens of millions of years; (2) generation of crust in a pre-plate tectonic regime in the period prior to 3.0 Ga; (3) early plate tectonics involving hot subduction with shallow slab breakoff over the period from 3.0 to 1.7 Ga; (4) Earth’s middle age from 1.7 to 0.75 Ga, characterized by environmental, evolutionary, and lithospheric stability; (5) modern cold subduction, which has existed for the past 0.75 b.y. Cycles of supercontinent formation and breakup have operated during the last three stages. This evolving tectonic character has likely been controlled by secular changes in mantle temperature and how that impacts on lithospheric behavior. Crustal volumes, reflecting the interplay of crust generation and recycling, increased until Earth’s middle age, and they may have decreased in the past ~1 b.y.
DS1605-0844
2016
Hazen, R.M., Hummer, D.R., Hystad, G., Downs, R.T., Golden, J.J.Carbon mineral ecology: predicting the undiscovered minerals of carbon.American Mineralogist, Vol. 101, pp. 889-906.TechnologyCarbon minerals
DS1605-0845
2016
Hein, K.A.A.West African mineral atlas monograph.Ore Geology Reviews, in press available outline 5p.Africa, West AfricaBook - Atlas
DS1607-1352
2016
Helmstaedt, H.Diamond tectonics and geotectonics - how do they intersect in the Archean.IGC 35th., Session A Dynamic Earth 1p. AbstractGlobalTectonics
DS1602-0211
2015
Henderson, R.The first gravity meter designed, built and used in Australia in the late 1890's and very possibly the first in the world.Preview ( Geophysics), December pp. 53-61.AustraliaHistory - gravity meter
DS1610-1870
2016
Herzberg, C., Vidito, C., Starkey, N.A.Nickel cobalt contents of olivine record origins of mantle peridotite and related rocks.American Mineralogist, Vol. 101, pp. 1952-1966.MantlePeridotite

Abstract: Olivine is distinguished from all other minerals in providing a remarkable chemical narrative about magmatic processes that occurred in Earth’s crust, mantle, and core over the entire age of Earth history. Olivines in mantle peridotite have Ni contents and Mg numbers that were largely produced by equilibrium crystallization in an early turbulently convecting magma ocean; subsequent stages of partial melting operated to slightly elevate Ni and Mg number in residual olivines. Olivines from Archean komatiites from the Abitibi greenstone belt have Ni contents and Mg numbers that are consistent with an extensively melted peridotite source at great depths in the mantle. Olivines from basaltic oceanic crust, the Icelandic mantle plume and other Phanerozoic occurrences have compositions that record magma chamber crystallization, recharge, mixing, and partial melting. Olivines from the present-day Icelandic mantle plume have compositions that are consistent the melting of a peridotite source; unlike Hawaii, the melting of recycled crust as a distinct pyroxenite lithology is not evident in the olivine chemistry of Iceland. Paleocene picrites from Baffin Island and West Greenland from the ancient Icelandic plume have olivines with Ni contents that are consistent with either Ni-rich peridotite that formed by core-mantle interaction or by low-pressure crystallization of hot and deep magmas. In general, hot magma oceans, mantle plumes, and ambient mantle magmatism form in ways that are captured by the compositions of the olivine crystals that they contain.
DS1602-0212
2015
Hirsch, A.C., Dalton, C.A., Ritsema, J.Constraints on shear velocity in the cratonic upper mantle from Rayleigh wave phase velocity.Geochemistry, Geophysics, Geosystems: G3, Vol. 16, 11, Nov. pp. 3982-4005.MantleGeophysics - seismic

Abstract: Seismic models provide constraints on the thermal and chemical properties of the cratonic upper mantle. Depth profiles of shear velocity from global and regional studies contain positive velocity gradients in the uppermost mantle and often lack a low-velocity zone, features that are difficult to reconcile with the temperature structures inferred from surface heat flow data and mantle-xenolith thermobarometry. Furthermore, the magnitude and shape of the velocity profiles vary between different studies, impacting the inferences drawn about mantle temperature and composition. In this study, forward modeling is used to identify the suite of one-dimensional shear-velocity profiles that are consistent with phase-velocity observations made for Rayleigh waves traversing Precambrian cratons. Two approaches to the generation of 1-D models are considered. First, depth profiles of shear velocity are predicted from thermal models of the cratonic upper mantle that correspond to a range of assumed values of mantle potential temperature, surface heat flow, and radiogenic heat production in the lithosphere. Second, shear velocity-depth profiles are randomly generated. In both cases, Rayleigh wave phase velocity is calculated from the Earth models, and acceptable models are identified on the basis of comparison to observed phase velocity. The results show that it is difficult but not impossible to find acceptable Earth models that contain a low-velocity zone in the upper mantle and that temperature structures that are consistent with constraints from mantle xenoliths yield phase-velocity predictions lower than observed. For most acceptable randomly generated Earth models, shear velocity merges with the global average at approximately 300 km.
DS1603-0385
2016
Hirsch, A.C., Dalton, C.A., Ritsema, J.Constraints on shear velocity in the cratonic upper mantle from Rayleigh wave phase velocity.Geochemistry, Geophysics, Geosystems: G3, Vol. 16, 11, pp.MantleGeophysics - seismics
DS1606-1091
2016
Hiyate, A.Tough year tests Dominion.Northern Miner Diamonds in Canada, May pp. 5-7.Canada, Northwest TerritoriesDominion Diamonds
DS1606-1092
2016
Hiyate, A.Rock hounds .. Annual roundup of Canadian listed diamond miners, developers and active juniors.Northern Miner Diamonds in Canada, May pp. 12-17.GlobalDiamond companies
DS1609-1721
2016
Hogberg, K., Stachel, T., Stern, R.A.Carbon and nitrogen isotope systematics in diamond: different sensitivities to isotopic fractionation or a decoupled origin?Lithos, In press available 15p.Canada, Nunavut, Baffin IslandDeposit - Chidliak

Abstract: Using stable isotope data obtained on multiple aliquots of diamonds from worldwide sources, it has been argued that carbon and nitrogen in diamond are decoupled. Here we re-investigate the carbon-nitrogen relationship based on the most comprehensive microbeam data set to date of stable isotopes and nitrogen concentrations in diamonds (n = 94) from a single locality. Our diamond samples, derived from two kimberlites in the Chidliak Field (NE Canada), show large variability in d13C (- 28.4 ‰ to - 1.1‰, mode at - 5.8‰), d15N (- 5.8 to + 18.8‰, mode at - 3.0‰) and nitrogen contents ([N]; 3800 to less than 1 at.ppm). In combination, cathodoluminescence imaging and microbeam analyses reveal that the diamonds grew from multiple fluid pulses, with at least one major hiatus documented in some samples that was associated with a resorption event and an abrupt change from low d13C and [N] to mantle-like d13C and high [N]. Overall, d13C appears to be uncorrelated to d15N and [N] on both the inter- and intra-diamond levels. Co-variations of d15N-log[N], however, result in at least two parallel, negatively correlated linear arrays, which are also present on the level of the individual diamonds falling on these two trends. These arrays emerge from the two principal data clusters, are characterized by slightly negative and slightly positive d15N (about - 3 and + 2‰, respectively) and variable but overall high [N]. Using published values for the diamond-fluid nitrogen isotope fractionation factor and nitrogen partition coefficient, these trends are perfectly reproduced by a Rayleigh fractionation model. Overall, three key elements are identified in the formation of the diamond suite studied: (1.) a low d13C and low [N] component that possibly is directly associated with an eclogitic diamond substrate or introduced during an early stage fluid event. (2.) Repeated influx of a variably nitrogen-rich mantle fluid (mildly negative d13C and d15N). (3.) In waning stages of influx, availability of the mantle-type fluid at the site of diamond growth became limited, leading to Rayleigh fractionation. These fractionation trends are clearly depicted by d15N-[N] but are not detected when examining co-variation diagrams involving d13C. Also on the level of individual diamonds, large (= 5‰) variations in d15N are associated with d13C values that typically are constant within analytical uncertainty. The much smaller isotope fractionation factor for carbon (considering carbonate- or methane-rich fluids as possible carbon sources) compared to nitrogen leads to an approximately one order of magnitude lower sensitivity of d13C values to Rayleigh fractionation processes (i.e. during fractionation, a 1‰ change in d13C is associated with a 10‰ change in d15N). As a consequence, even minor heterogeneity in the primary isotopic composition of diamond forming carbon (e.g., due to addition of minor subducted carbon) will completely blur any possible co-variations with d15N or [N]. We suggest this strong difference in isotope effects for C and N to be the likely cause of observations of an apparently decoupled behaviour of carbon and nitrogen isotopes in diamond.
DS1610-1871
2016
Hogberg, K.,Stachel, T., Stern, R.A.Carbon and nitrogen isotope systematics in diamond: different sensitivities to isotopic fractionation or a decoupled origin?Lithos, in press available 15p.Canada, NunavutDeposit - Chidliak

Abstract: Using stable isotope data obtained on multiple aliquots of diamonds from worldwide sources, it has been argued that carbon and nitrogen in diamond are decoupled. Here we re-investigate the carbon-nitrogen relationship based on the most comprehensive microbeam data set to date of stable isotopes and nitrogen concentrations in diamonds (n = 94) from a single locality. Our diamond samples, derived from two kimberlites in the Chidliak Field (NE Canada), show large variability in d13C (- 28.4 ‰ to - 1.1‰, mode at - 5.8‰), d15N (- 5.8 to + 18.8‰, mode at - 3.0‰) and nitrogen contents ([N]; 3800 to less than 1 at.ppm). In combination, cathodoluminescence imaging and microbeam analyses reveal that the diamonds grew from multiple fluid pulses, with at least one major hiatus documented in some samples that was associated with a resorption event and an abrupt change from low d13C and [N] to mantle-like d13C and high [N]. Overall, d13C appears to be uncorrelated to d15N and [N] on both the inter- and intra-diamond levels. Co-variations of d15N-log[N], however, result in at least two parallel, negatively correlated linear arrays, which are also present on the level of the individual diamonds falling on these two trends. These arrays emerge from the two principal data clusters, are characterized by slightly negative and slightly positive d15N (about - 3 and + 2‰, respectively) and variable but overall high [N]. Using published values for the diamond-fluid nitrogen isotope fractionation factor and nitrogen partition coefficient, these trends are perfectly reproduced by a Rayleigh fractionation model. Overall, three key elements are identified in the formation of the diamond suite studied: (1.) a low d13C and low [N] component that possibly is directly associated with an eclogitic diamond substrate or introduced during an early stage fluid event. (2.) Repeated influx of a variably nitrogen-rich mantle fluid (mildly negative d13C and d15N). (3.) In waning stages of influx, availability of the mantle-type fluid at the site of diamond growth became limited, leading to Rayleigh fractionation. These fractionation trends are clearly depicted by d15N-[N] but are not detected when examining co-variation diagrams involving d13C. Also on the level of individual diamonds, large (= 5‰) variations in d15N are associated with d13C values that typically are constant within analytical uncertainty. The much smaller isotope fractionation factor for carbon (considering carbonate- or methane-rich fluids as possible carbon sources) compared to nitrogen leads to an approximately one order of magnitude lower sensitivity of d13C values to Rayleigh fractionation processes (i.e. during fractionation, a 1‰ change in d13C is associated with a 10‰ change in d15N). As a consequence, even minor heterogeneity in the primary isotopic composition of diamond forming carbon (e.g., due to addition of minor subducted carbon) will completely blur any possible co-variations with d15N or [N]. We suggest this strong difference in isotope effects for C and N to be the likely cause of observations of an apparently decoupled behaviour of carbon and nitrogen isotopes in diamond.
DS1607-1302
2016
Hoggard, M.J., White, N., Al-Attar, D.Global dynamic topography observations reveal limited influences of large scale mantle flow.Nature Geoscience, Vol. 9, 6, pp. 456-463.MantleGeodynamics

Abstract: Convective circulation of the Earth’s mantle maintains some fraction of surface topography that varies with space and time. Most predictive models show that this dynamic topography has peak amplitudes of about ±2?km, dominated by wavelengths of 104?km. Here, we test these models against our comprehensive observational database of 2,120 spot measurements of dynamic topography that were determined by analysing oceanic seismic surveys. These accurate measurements have typical peak amplitudes of ±1?km and wavelengths of approximately 103?km, and are combined with limited continental constraints to generate a global spherical harmonic model, the robustness of which has been carefully tested and benchmarked. Our power spectral analysis reveals significant discrepancies between observed and predicted dynamic topography. At longer wavelengths (such as 104?km), observed dynamic topography has peak amplitudes of about ±500?m. At shorter wavelengths (such as 103?km), significant dynamic topography is still observed. We show that these discrepancies can be explained if short-wavelength dynamic topography is generated by temperature-driven density anomalies within a sub-plate asthenospheric channel. Stratigraphic observations from adjacent continental margins show that these dynamic topographic signals evolve quickly with time. More rapid temporal and spatial changes in vertical displacement of the Earth’s surface have direct consequences for fields as diverse as mantle flow, oceanic circulation and long-term climate change.
DS1603-0386
2015
Hopper, E., Fischer, K.M.The meaning of midlithospheric discontinuities: a case study in the northern U.S. craton.Geochemistry, Geophysics, Geosystems: G3, Vol. 16, 12, pp. 4057-4083.United StatesGeophysics - seismics
DS1607-1353
2016
Hossain, I.Hypabyssal and MARID-type kimberlitic magma signatures at Mithapukur, Rangpur, Bangladesh.IGC 35th., Session The Deep Earth 1 p. abstractIndiaKimberlite
DS1609-1722
2016
Howarth, G.H., Taylor, L.A.Multi-stage kimberlite evolution tracked in zoned olivine from the Benfontein sill, South Africa.Lithos, Vol. 262, pp. 384-397.Africa, South AfricaDeposit - Benfontein

Abstract: Olivine is the dominant mineral present in kimberlite magmas; however, due to the volatile-rich nature of most kimberlites, they rarely survive late-stage serpentinisation. Here we present major and trace element data for a rare example of ultra-fresh olivine in a macrocrystic calcite kimberlite from the Benfontein kimberlite sill complex. Olivines are characterised by xenocrystic cores surrounded by multiple growth zones representing melt crystallisation and late-stage equilibration. Two distinct core populations are distinguished: Type 1) low Fo (88-89), Ni-rich, Ca- and Na-rich cores, interpreted here to be the result of carbonate-silicate metasomatism potentially as part of the earliest stages of kimberlite magmatism, and Type 2) high Fo (91-93), Ni-rich, low-Ca cores derived from a typical garnet peridotite mantle source. In both cases, the cores have transitional margins (Fo89-90) representing equilibration with a proto-kimberlite melt. Trace element concentrations, in particular Cr, of these transition zones suggest formation of the proto-kimberlite melt through assimilation of orthopyroxene from the surrounding garnet peridotite lithology. Trace element trends in the surrounding melt-zone olivine (Fo87-90) suggest evolution of the kimberlite through progressive olivine crystallisation. The final stages of olivine growth are represented by Fe-rich (Fo85) and P-rich olivine indicating kimberlite evolution to mafic compositions. Fine (< 60 µm), Mg-rich olivine rims (Fo94-98) represent equilibration with the final stages of kimberlite evolution back to Fe-poor carbonatitic melts. We present a step-by-step model for kimberlite magma genesis and evolution from mantle to crust tracked by the chemistry of olivines in the Benfontein kimberlite. These steps include early stages of metasomatism and mantle assimilation followed by direct crystallisation of the kimberlite melt and late-stage equilibration with the evolved carbonatitic residual liquids. The Ca contents of the Type 1 xenocrystic olivines are the highest yet measured for mantle olivines, and do not overlap with any known mantle xenolith lithologies. These olivines likely represent an important stage of metasomatism directly related to the early stages of kimberlite melt ponding at the base of the lithospheric mantle.
DS1606-1093
2015
Howell, D., Griffin, W.L., Yang, J., Gain, S., Stern, R.A., Huang, J-X., Jacob, D.E., Xu, X., Stokes, A.J., O'Reilly, S.Y., Pearson, N.J.Diamonds in ophiolites: contamination or a new diamond growth environment?Earth and Planetary Science Letters, Vol. 430, pp. 284-295.Asia, TibetLuobusa Massif Type Iib

Abstract: For more than 20 years, the reported occurrence of diamonds in the chromites and peridotites of the Luobusa massif in Tibet (a complex described as an ophiolite) has been widely ignored by the diamond research community. This skepticism has persisted because the diamonds are similar in many respects to high-pressure high-temperature (HPHT) synthetic/industrial diamonds (grown from metal solvents), and the finding previously has not been independently replicated. We present a detailed examination of the Luobusa diamonds (recovered from both peridotites and chromitites), including morphology, size, color, impurity characteristics (by infrared spectroscopy), internal growth structures, trace-element patterns, and C and N isotopes. A detailed comparison with synthetic industrial diamonds shows many similarities. Cubo-octahedral morphology, yellow color due to unaggregated nitrogen (C centres only, Type Ib), metal-alloy inclusions and highly negative View the MathML sourcedC13 values are present in both sets of diamonds. The Tibetan diamonds (n=3n=3) show an exceptionally large range in View the MathML sourcedN15 (-5.6 to +28.7‰+28.7‰) within individual crystals, and inconsistent fractionation between {111} and {100} growth sectors. This in contrast to large synthetic HPHT diamonds grown by the temperature gradient method, which have with View the MathML sourcedN15=0‰ in {111} sectors and +30‰+30‰ in {100} sectors, as reported in the literature. This comparison is limited by the small sample set combined with the fact the diamonds probably grew by different processes. However, the Tibetan diamonds do have generally higher concentrations and different ratios of trace elements; most inclusions are a NiMnCo alloy, but there are also some small REE-rich phases never seen in HPHT synthetics. These characteristics indicate that the Tibetan diamonds grew in contact with a C-saturated Ni-Mn-Co-rich melt in a highly reduced environment. The stable isotopes indicate a major subduction-related contribution to the chemical environment. The unaggregated nitrogen, combined with the lack of evidence for resorption or plastic deformation, suggests a short (geologically speaking) residence in the mantle. Previously published models to explain the occurrence of the diamonds, and other phases indicative of highly reduced conditions and very high pressures, have failed to take into account the characteristics of the diamonds and the implications for their formation. For these diamonds to be seriously considered as the result of a natural growth environment requires a new understanding of mantle conditions that could produce them.
DS1606-1094
2015
Howell, D., Stern, R.A., Griffin, W.L., Southworth, R., Mikhail, S., Stachel, T.Nitrogen isotope systematics and origins of mixed habit diamonds.Geochimica et Cosmochimica Acta, Vol. 157, pp. 1-12.TechnologyDiamond morphology

Abstract: Nitrogen isotope values from mantle diamonds are a commonly used tracer in the quest to track volatiles within the Earth’s mantle through deep time. Interpretations of this isotope data are valid so long as stable isotope fractionation processes in the mantle are understood. The fractionation of nitrogen isotopes between {1 1 1} and {1 0 0} growth sectors is well documented for high-pressure high-temperature (HPHT) synthetic diamonds, but there is little data on whether it also occurs in natural mixed-habit diamonds. We present 91 in-situ nitrogen isotope (d15N) measurements, along with carbon isotope (d13C) values and nitrogen abundances [N], obtained from three mixed-habit diamonds by secondary ion mass spectrometry (SIMS). While the well-documented enrichment of nitrogen concentrations in octahedral sectors compared to contemporaneous cuboid sectors is observed, a similarly clear disparity is not obvious in the d15N data. Whereas HPHT synthetic diamonds exhibit 15N enrichment in the {1 0 0} sectors by ~+30‰, the mixed-habit diamonds studied here show enrichment of the octahedral sectors in 15N by only 0.4-1‰. This major difference between HPHT synthetic and natural mixed-habit diamonds is proposed to be the result of different physical properties of the growth interfaces. The smooth interfaces of the octahedral sectors are the same in both types of crystal, but the outermost atoms on the smooth cube interfaces of an HPHT synthetic diamond behave differently to those on the rough cuboid interfaces of the natural mixed-habit diamonds, resulting in different d15N values. Both the d13C (average of ~-8.7‰) and d15N (average of ~0‰) data show only minor offsets from the typical mantle values (d13C = -5 ± 3‰, d15N = -5 ± 4‰). This may indicate diamond formation from a mantle derived fluid/melt containing a minor subducted component (lowering d13C values and elevating d15N) or relate to moderate degrees of isotopic fractionation of a pure mantle fluid/melt by prior diamond precipitation. The homogeneous nature of both the carbon and nitrogen isotopic compositions of all three diamonds, however, documents continuous and unlimited supply of diamond forming fluid/melt, with a constant composition. Such homogenous isotopic compositions exclude fluid mixing or isotopic fractionation close to the site of diamond formation and preclude distinguishing between these two processes based on diamond analyses alone.
DS1610-1872
2016
Huang, J-X., Xiang, Y., An, Y., Griffin, W.L., Greau, Y., Xie, L., Pearson, N.J., Yu, H., O'Reilly, S.Y.Magnesium and oxygen isotopes in Roberts Victor eclogites.Chemical Geology, Vol. 438, pp. 73-83.Africa, South AfricaDeposit - Roberts Victor

Abstract: Magnesium and oxygen are critical elements in the solid Earth and hydrosphere. A better understanding of the combined behavior of Mg and O isotopes will refine their use as a tracer of geochemical processes and Earth evolution. In this study, the Mg-isotope compositions of garnet and omphacite separated from well-characterized xenolithic eclogites from the Roberts Victor kimberlite pipe (South Africa) have been measured by solution multi-collector ICP-MS. The reconstructed whole-rock d26Mg values of Type I (metasomatized) eclogites range from - 0.61‰ to - 0.20‰ (Type IA) and from - 0.60‰ to - 0.30‰ (Type IB) (mean - 0.43‰ ± 0.12‰), while d26Mg of Type IIA (fresh, least metasomatized) eclogites ranges from - 1.09‰ to - 0.17‰ (mean - 0.69‰ ± 0.41‰); a Type IIB (fresh, least metasomatized) has d26Mg of - 0.37‰. Oxygen-isotope compositions of garnet were analyzed in situ by SIMS (CAMECA 1280) and cross-checked by laser fluorination. Garnets have d18O of 6.53‰ to 9.08‰ in Type IA, 6.14‰ to 6.65‰ in Type IB, and 2.34‰ to 2.91‰ in Type IIB. The variation of d26Mg and d18O in Type IA and IB eclogites is consistent with the previously proposed model for the evolution of these samples, based on major and trace elements and radiogenic isotopes. In this model, the protoliths (Type II eclogites) were metasomatized by carbonatitic to kimberlitic melts/fluids to produce first Type IA eclogites and then Type IB. Metasomatism has changed the O-isotope compositions, but the Mg-isotope compositions of Type IA are mainly controlled by the protoliths; those of Type IB eclogites reflect mixing between the protoliths and the kimberlitic melt/fluid. The combination of a large range of d26Mg and low d18O in Type II eclogites cannot be explained easily by seawater alteration of oceanic crust, interaction of carbonate/silicate sediments with oceanic crust, or partial melting of mafic rocks.
DS1601-0019
2015
Huang, Yang, J., Zhu, Y., Xiong, F., Liu, Z., Zhang, Z., Xu, W.The discovery of diamonds in chromitite of the Hegenshan ophiolite, Inner Mongolia.Acta Geologica Sinica, Vol. 89, 2, p. 32.Asia, MongoliaOphiolite

Abstract: Diamond, moissanite and a variety of other minerals, similar to those reported from ophiolites in Tibet and northern Russia, have recently been discovered in chromitites of the Hegenshan ophiolite of the Central Asian Orogenic Belt, north China. The chromitites are small, podiform and vein-like bodies hosted in dunite, clinopyroxene-bearing peridotite, troctolite and gabbro. All of the analysed chromite grains are relatively Al-rich, with Cr# [100Cr/(Cr+Al)] of about 47-53. Preliminary studies of mainly disseminated chromitite from ore body No. 3756 have identified more than 30 mineral species in addition to diamond and moissanite. These include oxides (mostly hematite, magnetite, rutile, anatase, cassiterite, and quartz), sulfides (pyrite, marcasite and others), silicates (magnesian olivine, enstatite, augite, diopside, uvarovite, pyrope, orthoclase, zircon, sphene, vesuvianite, chlorite and serpentine) and others (e.g., calcite, monazite, glauberite, iowaite and a range of metallic alloys). This study demonstrates that diamond, moissanite and other exotic minerals can occur in high-Al, as well as high-Cr chromites, and significantly extends the geographic and age range of known diamond-bearing ophiolites.
DS1612-2302
2016
Huangfu, P., Wang, Y., Cawood, P.A., Li, Z-H, Fan, W., Gerya, T.V.Thermo-mechanical controls of flat subduction: insight from numerical modeling.Gondwana Research, Vol. 40, pp. 170-183.MantleSubduction

Abstract: Numerical experiments are used to investigate the thermo-mechanical controls for inducing flat subduction and why flat subduction is rare relative to normal/steep subduction. Our modeling results demonstrate that flat subduction is an end-member of a steady state subduction geometry and is characterized by a curved slab with a nearly-horizontal slab section. Intermediate cases between normal/steep and flat subduction appear to be transient in origin and evolve toward one of the stable end-members. Physical parameters inducing flat subduction can be classified into four categories: buoyancy of the subducting oceanic lithosphere (e.g., slab age, oceanic crustal thickness), viscous coupling between the overriding and downgoing plates (e.g., initial subduction angle), external kinematic conditions, and rheological properties of the subduction zone. On the basis of parameter sensitivity tests and the main characteristics of present-day flat subduction zones, positive buoyancy from either the young slab or the thickened oceanic crust is considered as the primary controlling parameter. Our results show that the possibility of flat subduction is directly proportional to oceanic crustal thickness and inversely proportional to the slab age. Furthermore, oceanic crust must be thicker than 8 km to induce flat subduction, when the slab is older than 30 Ma with an initial subduction angle of = 20° and without absolute trenchward motion of the overriding plate. The lower the initial subduction angle or the thicker the overriding continental lithosphere, the more likelihood for flat subduction. The initial subduction angle is more influential for the development of flat subduction than the overriding lithospheric thickness, and a thick overriding lithosphere induces flat subduction only under the condition of an initial subduction angle of = 25°, with a slab age of = 30 Ma and without absolute trenchward motion of the overriding plate. However, when the initial subduction angle is increased to > 25°, no flat subduction is predicted. All the parameters are evaluated within the constraints of a mechanical framework in which the slab geometry is regarded as a result of a balance between the gravitational and hydrodynamic torques. Any factor that can sufficiently reduce gravitational torque or increase hydrodynamic torque will exert a strong effect on flat subduction development. Our results are consistent with the observations of modern flat subduction zones on Earth.
DS1612-2303
2016
Hulett, S.R.W., Simonetti, A., Rasbury, E.T., Hemming, N.G.Recyclying of subducted crustal components into carbonatite melts revealed by boron isotopes.Nature Geoscience, Nov. 7, on line 6p.GlobalCarbonatite

Abstract: The global boron geochemical cycle is closely linked to recycling of geologic material via subduction processes that have occurred over billions of years of Earth’s history. The origin of carbonatites, unique melts derived from carbon-rich and carbonate-rich regions of the upper mantle, has been linked to a variety of mantle-related processes, including subduction and plume-lithosphere interaction. Here we present boron isotope (d11B) compositions for carbonatites from locations worldwide that span a wide range of emplacement ages (between ~40 and ~2,600?Ma). Hence, they provide insight into the temporal evolution of their mantle sources for ~2.6 billion years of Earth’s history. Boron isotope values are highly variable and range between -8.6 and +5.5, with all of the young (<300?Ma) carbonatites characterized by more positive d11B values (>-4.0‰ whereas most of the older carbonatite samples record lower B isotope values. Given the d11B value for asthenospheric mantle of -7 ± 1‰ the B isotope compositions for young carbonatites require the involvement of an enriched (crustal) component. Recycled crustal components may be sampled by carbonatite melts associated with mantle plume activity coincident with major tectonic events, and linked to past episodes of significant subduction associated with supercontinent formation.
DS1612-2304
2016
Ichikawa, H., Greaux, S., Azuma, S.Subduction of the primordial crust into the deep mantle.Geoscience Frontiers, in press availableMantleSubduction

Abstract: The primordial crust on the Earth formed from the crystallization of the surface magma ocean during the Hadean. However, geological surveys have found no evidence of rocks dating back to more than 4 Ga on the Earth's surface, suggesting the Hadean crust was lost due to some processes. We investigated the subduction of one of the possible candidates for the primordial crust, anorthosite and KREEP crust similar to the Moon, which is also considered to have formed from the crystallization of the magma ocean. Similar to the present Earth, the subduction of primordial crust by subduction erosion is expected to be an effective way of eliminating primordial crust from the surface. In this study, the subduction rate of the primordial crust via subduction channels is evaluated by numerical simulations. The subduction channels are located between the subducting slab and the mantle wedge and are comprised of primordial crust materials supplied mainly by subduction erosion. We have found that primordial anorthosite and KREEP crust of up to ~50 km thick at the Earth's surface was able to be conveyed to the deep mantle within 0.1-2 Gy by that mechanism.
DS1601-0020
2015
ICMMUnderstanding company-community relations toolkit.ICMM, Dec. 1, 72p. PdfGlobalCSR
DS1601-0021
2015
ICMMDemonstrating value: a guide to responsible sourcing for mining companies.ICMM, Dec. 3, 44p. PdfGlobalCSR
DS1601-0022
2015
ICMMLand acquisition and resettlement: lessons learned.ICMM, Dec. 68p.GlobalCSR
DS1606-1095
2016
Ilyina, O.V., Tychkov, N.S., Agashev, A.M., Golovin, A.V., Izokh, A.E., Kozmenko, O.A., Poikilanko, N.P.PGE distribution in deformed lherzolites of the Udachnaya kimberlite pipe ( Yakutia).Doklady Earth Sciences, Vol. 467, 2, pp. 408-411.Russia, YakutiaDeposit - Udachnaya

Abstract: The results of the first study of the PGE distribution in deformed lherzolites of the Udachnaya kimberlite pipe (Yakutia) are presented here. The complex character of evolution of the PGE composition in the Deformed lherzolites is assumed to be the result of silicate metasomatism. At the first stage, growth in the amount of clinopyroxene and garnet in the rock is accompanied by a decrease in the concentration of the compatible PGE (Os, Ir). During the final stage, the rock is enriched with incompatible PGE (Pt, Pd) and Re possible due to precipitation of submicron-sized particles of sulfides in the interstitial space of these mantle rocks.
DS1612-2305
2016
Ingalls, M., Rowley, D.B., Currie, B., Colman, A.S.Large scale subduction of continental crust implied by India-Asia mass balance calculation.Nature Geoscience, Vol.9, 11, pp. 848-853.India, AsiaSubduction

Abstract: Continental crust is buoyant compared with its oceanic counterpart and resists subduction into the mantle. When two continents collide, the mass balance for the continental crust is therefore assumed to be maintained. Here we use estimates of pre-collisional crustal thickness and convergence history derived from plate kinematic models to calculate the crustal mass balance in the India-Asia collisional system. Using the current best estimates for the timing of the diachronous onset of collision between India and Eurasia, we find that about 50% of the pre-collisional continental crustal mass cannot be accounted for in the crustal reservoir preserved at Earth’s surface today—represented by the mass preserved in the thickened crust that makes up the Himalaya, Tibet and much of adjacent Asia, as well as southeast Asian tectonic escape and exported eroded sediments. This implies large-scale subduction of continental crust during the collision, with a mass equivalent to about 15% of the total oceanic crustal subduction flux since 56 million years ago. We suggest that similar contamination of the mantle by direct input of radiogenic continental crustal materials during past continent-continent collisions is reflected in some ocean crust and ocean island basalt geochemistry. The subduction of continental crust may therefore contribute significantly to the evolution of mantle geochemistry.
DS1605-0846
2016
Irving, J.C.E.Imaging the inner core under Africa and Europe.Physics of the Earth and Planetary Interiors, Vol. 254, pp. 12-24.Africa, EuropeGeophysics - seismics, anisotropy, boundary

Abstract: The inner core under Africa is thought to be a region where the nature of inner core texture changes: from the strongly anisotropic ‘western’ part of the inner core to the weakly anisotropic, or isotropic ‘eastern’ part of the inner core. Additionally, observations of a difference in isotropic velocity between the two hemispheres have been made. A very large new dataset of simultaneous PKPdf and PKPbc observations, on which differential travel times have been measured, is used to examine the upper 360 km of the inner core under Europe, Africa and the surrounding oceans. Inversion of the differential travel time data for laterally varying inner core anisotropy reveals that inner core anisotropy is stronger under central Africa and the Atlantic Ocean than under the western Indian Ocean. No hemispherical pattern is present in Voigt isotropic velocities, indicating that the variation in anisotropy is due to differing degrees of crystal alignment in the inner core, not material differences. When anisotropy is permitted to change with depth, the upper east-most part of the study region shows weaker anisotropy than the central and western regions. When depth dependence in the inner core is neglected the hemisphere boundary is better represented as a line at 40°E than one at 10°E, however, it is apparent that the variation of anisotropy as a function of depth means that one line of longitude cannot truly separate the more and less anisotropic regions of the inner core. The anisotropy observed in the part of the inner core under Africa which lies in the ‘western’ hemisphere is much weaker than that under central America, showing that the western hemisphere is not uniformly anisotropic. As the region of low anisotropy spans a significant depth extent, it is likely that heterogeneous heat fluxes in the core, which may cause variations in inner core anisotropy, have persisted for several hundred million years.
DS1608-1412
2016
Irving, J.C.E.Imaging the inner core under Africa and Europe.Physics of the Earth and Planetary Interiors, Vol. 254, pp. 12-24.Africa, EuropeAnisotropy

Abstract: The inner core under Africa is thought to be a region where the nature of inner core texture changes: from the strongly anisotropic ‘western’ part of the inner core to the weakly anisotropic, or isotropic ‘eastern’ part of the inner core. Additionally, observations of a difference in isotropic velocity between the two hemispheres have been made. A very large new dataset of simultaneous PKPdf and PKPbc observations, on which differential travel times have been measured, is used to examine the upper 360 km of the inner core under Europe, Africa and the surrounding oceans. Inversion of the differential travel time data for laterally varying inner core anisotropy reveals that inner core anisotropy is stronger under central Africa and the Atlantic Ocean than under the western Indian Ocean. No hemispherical pattern is present in Voigt isotropic velocities, indicating that the variation in anisotropy is due to differing degrees of crystal alignment in the inner core, not material differences. When anisotropy is permitted to change with depth, the upper east-most part of the study region shows weaker anisotropy than the central and western regions. When depth dependence in the inner core is neglected the hemisphere boundary is better represented as a line at 40°E than one at 10°E, however, it is apparent that the variation of anisotropy as a function of depth means that one line of longitude cannot truly separate the more and less anisotropic regions of the inner core. The anisotropy observed in the part of the inner core under Africa which lies in the ‘western’ hemisphere is much weaker than that under central America, showing that the western hemisphere is not uniformly anisotropic. As the region of low anisotropy spans a significant depth extent, it is likely that heterogeneous heat fluxes in the core, which may cause variations in inner core anisotropy, have persisted for several hundred million years.
DS1610-1873
2016
Ishwar-Kumar, C., Santosh, M., Wilde, S.A., Tsunogae, T., Itaya, T., Windley, B., Sajeev, K.Mesoproterozoic suturing of Archean crustal blocks in western peninsula India: implications for India-Madagascar correlations.Lithos, Vol. 263, pp. 143-160.IndiaGeodynamics

Abstract: The Kumta and Mercara suture zones welding together Archean crustal blocks in western peninsular India offer critical insights into Precambrian continental juxtapositions and the crustal evolution of eastern Gondwana. Here we present the results from an integrated study of the structure, geology, petrology, mineral chemistry, metamorphic P-T conditions, zircon U-Pb ages and Lu-Hf isotopes of metasedimentary rocks from the two sutures. The dominant rocks in the Kumta suture are greenschist- to amphibolite-facies quartz-phengite schist, garnet-biotite schist, chlorite schist, fuchsite schist and marble. The textural relations, mineral chemistry and thermodynamic modelling of garnet-biotite schist from the Kumta suture indicate peak metamorphic P-T conditions of ca. 11 kbar at 790 °C, with detrital SHRIMP U-Pb zircon ages ranging from 3420 to 2547 Ma, eHf (t) values from - 9.2 to 5.6, and TDMc model ages from 3747 to 2792 Ma. The K-Ar age of phengite from quartz-phengite schist is ca. 1326 Ma and that of biotite from garnet-biotite schist is ca. 1385 Ma, which are interpreted to broadly constrain the timing of metamorphism related to the suturing event. The Mercara suture contains amphibolite- to granulite-facies mylonitic quartzo-feldspathic gneiss, garnet-kyanite-sillimanite gneiss, garnet-biotite-kyanite-gedrite-cordierite gneiss, garnet-biotite-hornblende gneiss, calc-silicate granulite and metagabbro. The textural relations, mineral chemistry and thermodynamic modelling of garnet-biotite-kyanite-gedrite-cordierite gneiss from the Mercara suture indicate peak metamorphic P-T conditions of ca. 13 kbar at 825 °C, followed by isothermal decompression and cooling. For pelitic gneisses from the Mercara suture, LA-ICP-MS U-Pb zircon ages vary from 3249 to 3045 Ma, eHf (t) values range from - 18.9 to 4.2, and TDMc model ages vary from 4094 to 3314 Ma. The lower intercept age of detrital zircons in the pelitic gneisses from the Mercara suture ranges from 1464 to 1106 Ma, indicating the approximate timing of a major lead-loss event, possibly corresponding to metamorphism, and is broadly coeval with events in the Kumta suture. Synthesis of the above results indicates that the Kumta and Mercara suture zones incorporated sediments from Palaeoarchean to Mesoproterozoic sources and underwent high-pressure metamorphism in the late Mesoproterozoic. The protolith sediments were derived from regions containing juvenile Palaeoarchean crust, together with detritus from the recycling of older continental crust. Integration of the above results with published data suggests that the Mesoproterozoic (1460-1100 Ma) Kumta and Mercara suture zones separate the Archean (3400-2500 Ma) Karwar-Coorg block and Dharwar Craton in western peninsular India. Based on regional structural and other geological data we interpret the Kumta and Mercara suture zones as extensions of the Betsimisaraka suture of eastern Madagascar into western India.
DS1603-0387
2016
Ivanic, T.J., Harte, B., Gurney, J.J.A discussion of "Mineralogical controls on garnet composition in the cratonic mantle" by Hill et al. 2015Contributions to Mineralogy and Petrology, Vol. 171, 4p.MantleMineralogy
DS1604-0611
2016
Ivanyuk, G.Yu., Kalashnikov, A.O., Pakhomovsky, Ya.A., Mikhailov, J.A., Yakovenchuk, V.N., Konopleva, N.G., Sokharev, V.A., Bazai, A.V., Goryainov, P.M.Economic minerals of the Kovdor baddeleyite apatite magnetite deposit, Russia: mineralogy, spatial distribution and ore processing optimization.Ore Geology Reviews, in press available 73p.RussiaDeposit - Kovdor

Abstract: The comprehensive petrographical, petrochemical and mineralogical study of the Kovdor magnetite-apatite-baddeleyite deposit in the phoscorite-carbonatite complex (Murmansk Region, Russia) revealed a spatial distribution of grain size and chemical composition of three economically extractable minerals — magnetite, apatite, and baddeleyite, showing that zonal distribution of mineral properties mimics both concentric and vertical zonation of the carbonatite-phoscorite pipe. The marginal zone of the pipe consists of (apatite)-forsterite phoscorite carrying fine grains of Ti-Mn-Si-rich magnetite with ilmenite exsolution lamellae, fine grains of Fe-Mg-rich apatite and finest grains of baddeleyite, enriched in Mg, Fe, Si and Mn. The intermediate zone accommodates carbonate-free magnetite-rich phoscorites that carry medium to coarse grains of Mg-Al-rich magnetite with exsolution inclusions of spinel, medium-grained pure apatite and baddeleyite. The axial zone hosts carbonate-rich phoscorites and phoscorite-related carbonatites bearing medium-grained Ti-V-Ca-rich magnetite with exsolution inclusions of geikielite-ilmenite, fine grains of Ba-Sr-Ln-rich apatite and comparatively large grains of baddeleyite, enriched in Hf, Ta, Nb and Sc. The collected data enable us to predict such important mineralogical characteristics of the multicomponent ore as chemical composition and grain size of economic and associated minerals, presence of contaminating inclusions, etc. We have identified potential areas of maximum concentration of such by-products as scandium, niobium and hafnium in baddeleyite and REEs in apatite.
DS1605-0847
2016
Ivanyuk, G.Yu., Kalashnikov, A.O., Pakhomovsky, Ya.A., Mikhailova, J.A., Yakovenchuk, V.N., Konopleva, N.G., Sokharev, V.A., Bazai, A.V., Goryainov, P.M.Economic minerals of the Kovdor baddeleyite apatite magnetite deposit, Russia: mineralogy, spatial distribution and ore procesing optimization.Ore Geology Reviews, Vol. 77, pp. 279-311.RussiaCarbonatite, Kovdor

Abstract: The comprehensive petrographical, petrochemical and mineralogical study of the Kovdor magnetite-apatite-baddeleyite deposit in the phoscorite-carbonatite complex (Murmansk Region, Russia) revealed a spatial distribution of grain size and chemical composition of three economically extractable minerals — magnetite, apatite, and baddeleyite, showing that zonal distribution of mineral properties mimics both concentric and vertical zonation of the carbonatite-phoscorite pipe. The marginal zone of the pipe consists of (apatite)-forsterite phoscorite carrying fine grains of Ti-Mn-Si-rich magnetite with ilmenite exsolution lamellae, fine grains of Fe-Mg-rich apatite and finest grains of baddeleyite, enriched in Mg, Fe, Si and Mn. The intermediate zone accommodates carbonate-free magnetite-rich phoscorites that carry medium to coarse grains of Mg-Al-rich magnetite with exsolution inclusions of spinel, medium-grained pure apatite and baddeleyite. The axial zone hosts carbonate-rich phoscorites and phoscorite-related carbonatites bearing medium-grained Ti-V-Ca-rich magnetite with exsolution inclusions of geikielite-ilmenite, fine grains of Ba-Sr-Ln-rich apatite and comparatively large grains of baddeleyite, enriched in Hf, Ta, Nb and Sc. The collected data enable us to predict such important mineralogical characteristics of the multicomponent ore as chemical composition and grain size of economic and associated minerals, presence of contaminating inclusions, etc. We have identified potential areas of maximum concentration of such by-products as scandium, niobium and hafnium in baddeleyite and REEs in apatite.
DS1608-1413
2016
Ivanyuk, G.Yu., Kalashnikov, A.O., Pakhomovsky, Ya.A., Mikhailova, J.A., Yakovenchuk, V.N., Konopleva, N.G., Sokharev, V.A., Bazai, A.V., Goryainov, P.M.Economic minerals of the Kovdor baddeleyite apatite magnetite deposit, Russia: mineralogy, spatial distribution and ore processing optimization.Ore Geology Reviews, Vol. 77, pp. 279-311.RussiaDeposit - Kovdor

Abstract: The comprehensive petrographical, petrochemical and mineralogical study of the Kovdor magnetite-apatite-baddeleyite deposit in the phoscorite-carbonatite complex (Murmansk Region, Russia) revealed a spatial distribution of grain size and chemical composition of three economically extractable minerals — magnetite, apatite, and baddeleyite, showing that zonal distribution of mineral properties mimics both concentric and vertical zonation of the carbonatite-phoscorite pipe.The marginal zone of the pipe consists of (apatite)-forsterite phoscorite carrying fine grains of Ti-Mn-Si-rich magnetite with ilmenite exsolution lamellae, fine grains of Fe-Mg-rich apatite and finest grains of baddeleyite, enriched in Mg, Fe, Si and Mn. The intermediate zone accommodates carbonate-free magnetite-rich phoscorites that carry medium to coarse grains of Mg-Al-rich magnetite with exsolution inclusions of spinel, medium-grained pure apatite and baddeleyite. The axial zone hosts carbonate-rich phoscorites and phoscorite-related carbonatites bearing medium-grained Ti-V-Ca-rich magnetite with exsolution inclusions of geikielite-ilmenite, fine grains of Ba-Sr-Ln-rich apatite and comparatively large grains of baddeleyite, enriched in Hf, Ta, Nb and Sc. The collected data enable us to predict such important mineralogical characteristics of the multicomponent ore as chemical composition and grain size of economic and associated minerals, presence of contaminating inclusions, etc. We have identified potential areas of maximum concentration of such by-products as scandium, niobium and hafnium in baddeleyite and REEs in apatite.
DS1605-0848
2016
Jacob, D.Insights into subcratonic lithosphere development from banded eclogite xenoliths.DCO Edmonton Diamond Workshop, June 8-10MantleXenoliths
DS1607-1303
2016
Jacob, D.E., Piazolo, S., Screiber, A., Trimby, P.Redox-freezing and nucleation of diamond via magnetite formation in the Earth's mantle.Nature Communications, Vol. 7, June 21, 7p.Africa, BotswanaDeposit - Orapa

Abstract: Diamonds and their inclusions are unique probes into the deep Earth, tracking the deep carbon cycle to >800?km. Understanding the mechanisms of carbon mobilization and freezing is a prerequisite for quantifying the fluxes of carbon in the deep Earth. Here we show direct evidence for the formation of diamond by redox reactions involving FeNi sulfides. Transmission Kikuchi Diffraction identifies an arrested redox reaction from pyrrhotite to magnetite included in diamond. The magnetite corona shows coherent epitaxy with relict pyrrhotite and diamond, indicating that diamond nucleated on magnetite. Furthermore, structures inherited from h-Fe3O4 define a phase transformation at depths of 320 -330?km, the base of the Kaapvaal lithosphere. The oxidation of pyrrhotite to magnetite is an important trigger of diamond precipitation in the upper mantle, explaining the presence of these phases in diamonds.
DS1605-0849
2016
Jacob, J.Using the proportion of barren samples as a proxy for minimum grade in a diamondiferous linear beach deposit - an application of the Nachman model.Diamonds Still Sparkling SAIMM 2016 Conference, Mar. 14-17, pp. 47-56.Africa, NamibiaGeostatistics
DS1612-2306
2016
Jacob, J.Using the proportion of barren samples as a proxy for minimum grade in a diamondiferous linear beach deposit - an application of the Nachman model.Journal of South African Institute of Mining and Metallurgy, Vol. 116, Aug. pp. 731-737.Africa, NamibiaDeposit - marine placers

Abstract: Over the past 80 years, the Namibian diamondiferous marine placer has been studied extensively to develop solutions for mining and sampling challenges. The types of studies include the statistical modelling of the distributions of the stone counts per sample; investigating the relationship between geology and the grade distribution; assessing the quality potential of the entrapment of the available diamond pulse; using predetermined acceptability of barren samples (zero proportion (Zp) samples) to model distributions; optimal sample sizes; and more. During early-stage project evaluation it is more important to find out if a particular area is likely to be above a specific cut-off grade than to focus on sampling for the purpose of accurate resource estimation. Previous work using mixed Poisson and Sichel distributions to model the abundant onshore diamond data has been very successful in modelling the long-tailed nature of these linear beach deposits. The means of these distributions are, however, sensitive to extreme values. Technical and cost constraints prevent a similar scale of sample collection in an adjacent, geologically equivalent, submerged beach environment. A method not sensitive to extreme values is thus required to make early-stage assessments of the likelihood that the grade of a particular target is above a minimum cut-off grade. The Nachman model describes the functional relationship between the mean population density and proportion of barren patches ( Zp) in a patchy environment. A prerequisite for using the Nachman model is that the underlying data must be modelled using a negative binomial distribution (NBD). The case study data is from an analogous area adjacent to the exploration target and meets the NBD requirement. It is thus appropriate to apply the Nachman model. The Nachman model provides an opportunity to use the observed Zpto predict the mean grade for an area at the very early stage of an exploration project. In future, early-stage exploration data from a homogenous geological zone exhibiting characteristics of the Nachman model assumptions can thus be used to rank and target those areas that show potential to be above the minimum required grade cut-off for follow-up sampling and inclusion in the mine planning cycle.
DS1612-2307
2016
Jacob, J., Prins, C.Construction of an expert opinion based virtual orebody for a diamondiferous linear beach deposit.Journal of South African Institute of Mining and Metallurgy, Vol. 116, July pp. 629-635.Africa, NamibiaDeposit - marine placers

Abstract: During early-stage diamond exploration projects, hard data underpinning spatial continuity is often very limited. An extreme example of this is a submerged diamondiferous marine placer target area alongside a current onshore mining area in southwestern Namibia. Although an abundance of geological and grade data exists for the adjacent onshore mining area, the target area itself contains no such information. Despite this apparent abundance of data, it is extremely difficult to obtain a variogram (Prins and Jacob, 2014) for use in this study area. The use of traditional simulation techniques is further hindered by the fact that diamond entrapment within the highly gullied footwall is non-stationary. An alternative approach for creating a simulated virtual orebody (VOB) is thus required in order to enable the assessment of sampling strategies. This paper demonstrates how expert opinion is used to generate a composite probability map for diamond concentration using a greyscale hand-sketching technique. The probability map is subsequently calibrated and populated using the diamond distribution for different raised beaches obtained from analog data based on sample results adjacent to the target area. The resultant grade simulation is used to test different sample scenarios and is a first step towards determining an appropriate sampling strategy for the target area. The VOB is used to analyse and rank the efficiency of different sampling strategies for grade determination of submerged diamondiferous linear beach exploration targets.
DS1605-0850
2016
Jacobsen, S.Earth's deep mantle water cycle: what diamond inclusions might be telling us.DCO Edmonton Diamond Workshop, June 8-10MantleDiamond Inclusions
DS1611-2114
2016
Jadamec, M.A.Insights into slab-driven mantle flow from advances in three-dimensional modelling.Journal of Geodynamics, Vol. 100, pp. 51-70.MantleSubduction

Abstract: The wealth of seismic observations collected over the past 20 years has raised intriguing questions about the three-dimensional (3D) nature of the mantle flow field close to subduction zones and provided a valuable constraint for how the plate geometry may influence mantle flow proximal to the slab. In geodynamics, there has been a new direction of subduction zone modelling that has explored the 3D nature of slab-driven mantle flow, motivated in part by the observations from shear wave splitting, but also by the observed variations in slab geometries worldwide. Advances in high-performance computing are now allowing for an unprecedented level of detail to be incorporated into numerical models of subduction. This paper summarizes recent advances from 3D geodynamic models that reveal the complex nature of slab-driven mantle flow, including trench parallel flow, toroidal flow around slab edges, mantle upwelling at lateral slab edges, and small scale convection within the mantle wedge. This implies slab-driven mantle deformation zones occur in the asthenosphere proximal to the slab, wherein the mantle may commonly flow in a different direction and rate than the surface plates, implying laterally variable plate-mantle coupling. The 3D slab-driven mantle flow can explain, in part, the lateral transport of geochemical signatures in subduction zones. In addition, high-resolution geographically referenced models can inform the interpretation of slab structure, where seismic data are lacking. The incorporation of complex plate boundaries into high-resolution, 3D numerical models opens the door to a new avenue of research in model construction, data assimilation, and modelling workflows, and gives 3D immersive visualization a new role in scientific discovery.
DS1607-1304
2016
Jagoutz, O., Kelemen, P.B.Role of arc progresses in the formation of continental crust.Annual Review of Earth and Planetary Sciences, Vol. 43, pp. 363-404.MantleMagmatism

Abstract: We review data and recent research on arc composition, focusing on the relatively complete arc crustal sections in the Jurassic Talkeetna arc (south central Alaska) and the Cretaceous Kohistan arc (northwest Pakistan), together with seismic data on the lower crust and uppermost mantle. Whereas primitive arc lavas are dominantly basaltic, the Kohistan crust is clearly andesitic and the Talkeetna crust could be andesitic. The andesitic compositions of the two arc sections are within the range of estimates for the major element composition of continental crust. Calculated seismic sections for Kohistan and Talkeetna provide a close match for the thicker parts of the active Izu arc, suggesting that it, too, could have an andesitic bulk composition. Because andesitic crust is buoyant with respect to the underlying mantle, much of this material represents a net addition to continental crust. Production of bulk crust from a parental melt in equilibrium with mantle olivine or pyroxene requires processing of igneous crust, probably via density instabilities. Delamination of dense cumulates from the base of arc crust, foundering into less dense, underlying mantle peridotite, is likely, as supported by geochemical evidence from Talkeetna and Kohistan. Relamination of buoyant, subducting material—during sediment subduction, subduction erosion, arcarc collision, and continental collision—is also likely.
DS1607-1354
2016
Janney, P.A hidden mantle reservoir in the continental lithosphere? Evidence from Hf-Sr-Nd-Pb isotopes in megacrysts and kimberlites.IGC 35th., Session A Dynamic Earth 1p. AbstractMantleKimberlite
DS1602-0213
2016
Jaques, A.L.Major and trace element variations in oxide and titanate minerals in the West Kimberley lamproites, Western Australia.Mineralogy and Petrology, In press available, 39p.AustraliaLamproite

Abstract: New data are presented for groundmass chromian spinel, perovskite, ilmenite, and K-Ti-Ba-rich phases from the Miocene olivine and leucite lamproites of the West Kimberley region. The spinels range from early Ti-Al-Mg chromite through Ti-Mg chromite to Ti-chromite and, in Ellendale 4 and 9, Ti-Cr magnetite and Ti-magnetite. Most crystallized at 850-1220 °C and fO2 ~ MW + 1-2 log units except for Ellendale 4 and 9 spinels which underwent marked late oxidation at ~650-750 °C with fO2 increasing sharply to ~FMQ + 2-3 log units. Perovskite is ubiquitous in the olivine lamproites and the Walgidee Hills (WH) lamproite. Compositional features of the perovskite are a wide range in Cr, and high Sr, Nb, Th, and LREE contents with highly fractionated REE patterns (La/YbCN ~ 750-3000). Perovskite from WH defines an evolutionary trend of enrichment in Na, Sr, Y, Nb, U and REE, and depletion in Cr, Fe, and Th with magma fractionation. Late crystallizing WH perovskite shows a decrease in LREE due to relative depletion of LREE in residual magma by extended crystallization of perovskite (and apatite). Priderite ((K,Ba)(Ti,Fe3+)8O16) has low Mg and V, and a range in Cr contents which decrease with magma evolution. Jeppeite ((K,Ba)2(Ti,Fe)6O13), has higher Sr and Nb content than priderite. Both contain low Y and REEs. Wadeite (K2ZrSi3O9), a ubiquitous groundmass phase, has high Sc, Rb and Hf contents, and strongly LREE-depleted REE patterns with positive Ce anomalies. Noonkanbahite, a late crystallizing phase in WH, has low Cr and Ni, and high Sr, Nb and Y contents. REE patterns for noonkanbahite display high HREE, depleted MREE, enriched La-Ce-Pr, and a positive Eu anomaly.
DS1609-1723
2016
Jaupart, C., Mareschal, J-C., Iarotsky, L.Radiogenic heat production in the continental crust.Lithos, Vol. 262, pp. 398-427.MantleThermometry

Abstract: Heat flow and heat production data complement seismic information and provide strong constraints on crustal composition, thickness and evolution. They have helped understand the nature of the Mohorovicic discontinuity and the variations in seismic velocities below the Moho. Notably, heat flow studies have delineated the vertical distribution of heat producing elements throughout the crust and in the upper most mantle lithosphere. Analysis of global data sets on heat flow and crustal thickness demonstrate that there is no correlation between these two variables. This is due to the large spatial variations in crustal composition and heat production that exist within a single geological province. For a given crustal thickness, the Moho temperature varies within a wide range (˜ 300 K) depending on surface heat flux and crustal heat production. Thus one cannot use generic models based on a “type” crustal column to calculate crustal geotherms. In stable regions, lower crustal temperatures depend on the amount and vertical distribution of heat producing elements in the crust. These temperatures determine the conditions of crustal stability and impose a limit on the maximum thickness of a stabilized crust.
DS1610-1874
2016
Jean, M.M., Taylor, L.A., Howarth, G.H., Peslier, A.H., Fedele, L., Bodnar, R.J., Guan, Y., Doucet, L.S., Ionov, D.A., Logvinova, A.M., Golovin, A.V., Sobolev, N.V.Olivine inclusions in Siberian diamonds and mantle xenoliths: contrasting water and trace -element contents.Lithos, in press available 11p.Russia, SiberiaDiamond inclusions
DS1602-0214
2016
Jenkins, J., Cottaar, S., White, R.S., Deuss, A.Depressed mantle discontinuities beneath Iceland: evidence of a garnet controlled 660 km discontinuity?Earth and Planetary Science Letters, Vol. 433, pp. 159-168.Europe, IcelandMantle - 660 km

Abstract: The presence of a mantle plume beneath Iceland has long been hypothesised to explain its high volumes of crustal volcanism. Practical constraints in seismic tomography mean that thin, slow velocity anomalies representative of a mantle plume signature are difficult to image. However it is possible to infer the presence of temperature anomalies at depth from the effect they have on phase transitions in surrounding mantle material. Phase changes in the olivine component of mantle rocks are thought to be responsible for global mantle seismic discontinuities at 410 and 660 km depth, though exact depths are dependent on surrounding temperature conditions. This study uses P to S seismic wave conversions at mantle discontinuities to investigate variation in topography allowing inference of temperature anomalies within the transition zone. We employ a large data set from a wide range of seismic stations across the North Atlantic region and a dense network in Iceland, including over 100 stations run by the University of Cambridge. Data are used to create over 6000 receiver functions. These are converted from time to depth inc