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The Sheahan Diamond Literature Reference Compilation - Technical Articles based on Major Region - Asia
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 announcements called 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 Region Index
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
Each article reference in the SDLRC is tagged with one or more key words assigned by Pat Sheahan to highlight the main topics of the article. In addition most references have been tagged with one or more region words. In an effort to make it easier for users to track down articles related to a specific region, KRO has extracted these region words and developed a list of major region words presented in the Major Region Index to which individual region words used in the article reference have been assigned. Each individual Region Report contains in chronological order all the references with a region word associated with the Major Region word. Depending on the total for each reference type - technical, media and corporate - the references will be either in their own technical, media or corporate Region Report, or combined in a single report. Where there is a significant number of technical references there will be a technical report dedicated to the technical articles while the media and corporate references are combined in a separate region report. References that were added in the most recent monthly update are highlighted in yellow within the Region Report. The Major Region words have been defined by a scale system of "general", "continent", "country", "state or province" and "regional". Major Region words at the smaller scales have been created only when there are enough references to make isolating them worthwhile. References not tagged with a Region are excluded, and articles with a region word not matched with a Major Region show up in the "Unknown" report.
Kimberlite - diamondiferous
Lamproite - diamondiferous
Lamprophyre - diamondiferous
Other - diamondiferous
Kimberlite - non diamondiferous
Lamproite - non diamondiferous
Lamprophyre - non diamondiferous
Other - non diamondiferous
Kimberlite - unknown
Lamproite - unknown
Lamprophyre - unknown
Other - unknown
Future Mine
Current Mine
Former Mine
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CITATION: Faure, S, 2010, World Kimberlites CONSOREM Database (Version 3), Consortium de Recherche en Exploration Minérale CONSOREM, Université du Québec à Montréal, Numerical Database on consorem.ca. NOTE: This publicly available database results of a compilation of other public databases, scientific and governmental publications and maps, and various data from exploration companies reports or Web sites, If you notice errors, have additional kimberlite localizations that should be included in this database, or have any comments and suggestions, please contact the author specifying the ID of the kimberlite: [email protected]
Constraints on lithospheric structure from satellite potential field at:Africa and Asia. Analysis and interpretation of Magsat anomalies over NorthAfrica
National Technical Information Service, No. N86-21968/0 104p
Magma compositions and genesis of the rocks of the Mushugai Khuduk carbonatite bearing alkalic complex ( southern Mongolia): evidence from melt inclusions.
Periodico di Mineralogia, (in english), Vol. LXX11, 1. April, pp. 95-105.
40 Ar 39 Ar dating of a phlogopite bearing websterite: evidence for ancient metasomatism in the subcontinental lithospheric mantle under the Arabian Shield?
Mineral chemistry of spinel peridotite xenoliths from Baengnyeong Island, South Korea, and its applications for the paleogeotherm of the uppermost mantle.
Limiting effect of UHP metamorphism on length scales of oxygen, hydrogen and argon isotope exchange: an example from the Qinglongshan UHP eclogites, Sulu Terrain.
International Geology Review, Vol. 47, 7, pp. 716-749.
High pressure/ultrahigh pressure eclogites from the Hongan Block, east central China: geochemical characterization, isotope disequilibrium, geochronology
Contributions to Mineralogy and Petrology, Vol. 149, 5, pp. 499-526.
Roy, A., Sarkar, A., Jeyakumar, S., Aggrawal, S.K., Ebihara, M., Satoh, H.
Late Archean mantle metasomatism below eastern Indian craton: evidence from trace elements, REE geochemistry and Sr Nd O isotope systematics of ultramafic dykes.
Proceedings National Academy of Sciences India , Vol. 113, 4, pp. 649-665.
Song, S., Zhang, L., Niu, Y., Su, L., Jian, P., Liu, D.
Geochronology of diamond bearing zircons from garnet peridotite in the North Qaidam UHPM belt, Northern Tibetan Plateau: a record of lithospheric subduction.
Earth and Planetary Science Letters, Vol. 234, 1-2, pp. 99-118.
Wang, Q., Shaocheng, J., Salisbury, M.H., Xia, B., Pan, M., Xu, Z.
Shear wave properties and Poisson's ratios of ultrahigh pressure metamorphic rocks from the Dabie Sulu orogenic belt, China: implications for crustal composition.
Journal of Geophysical Research, Vol. 110, B8, pp. B08411 10.1029/2004 JB003435
Nature of the Mesozoic lithospheric mantle and tectonic decoupling beneath the Dabie Orogen, central China. Evidence from 40Ar 39Ar geochronology, Sr/Nd, Pb
Chemical Geology, Vol. 220, 3-4, pp. 165-189.
Asia, China
Geochronology - early Cretaceous mafic igneous rocks
Using shear wave splitting measurements to investigate the upper mantle anisotropy beneath the North Chin a Craton: distinct variation from east to west.
Geophysical Research Letters, Vol. 32, 10, May 28, DOI 10.1029/2005 GLO22585
Post collisional, potassic and ultrapotassic magmatism of the northern Tibetan Plateau: constraints on characteristics of the mantle source, geodynamic uplift
Petrochemical interpretation of carbonatite-like rocks from the Chagatai Complex of the Tien Shan with appllication to the problem of diamond potential.
Methane rich fluid inclusions from ophiolitic dunite and post collisional mafic/ultramafic intrusion: the mantle dynamics underneath the Paleo-Asian Ocean floor
Earth and Planetary Science Letters, Vol. 242, 3-4, pp. 286-301.
Mesoproterozoic Diamondiferous ultramafic pipes at Majkgawan and Hinota, Panna area, central India: key to the nature of sub-continental lithospheric mantle...
Journal of Earth System Science, Vol. 115, 1m pp. 161-183.
Geochemistry and petrogenesis of neoArchean high Mg low Ti mafic igneous rocks in and intracratonic setting, Central India craton: evidence for boninite magmatism.
Trans Hudson Orogen of North America and Himalaya Karakoram Tibetan Orogen of Asia: structural and thermal characteristics of the lower and upper plates.
Ying, J., Zhang, H., Kita, N., Morishita, Y., Shimoda, G.
Nature and evolution of Late Cretaceous lithospheric mantle beneath the eastern north Chin a craton: constraints from petrology and geochemistry from Junan
Hetenyl, G., Cattin, R., Brunet, F., Bollinger, L., Vergne, J., Nabalek, J.L., Diament, M.
Density distribution of the India plate beneath the Tibetan plateau: geophysical and petrological constraints on kinetics of lower crustal eclogitization
Earth and Planetary Science Letters, Vol. 264, 1-2, pp. 226-244.
Mo, X., Zhao, Z., Deng, J., Flower, M., Yu, X., Luo, Z., Li, Y., Zhou, S., Deng, G., Zhu, D.
Petrology and geochemistry of post collisional volcanic rocks from the Tibetan plateau: implications for lithosphere heterogeneity and collision induced mantle
Geological Society of America, Special Paper, No. 409, pp. 507-530.
Trace elements and volatile components in silicate and silicate salt magmas of the Mushugai Khuduk carbonatite bearing alkaline complex, southern Mongolia.
International Mineralogical Association meeting August Budapest, abstract p. 564.
Ultra high pressure metamorphism and multistage exhumation of eclogite of the Luotian dome, North Dabie Complex Zone: evidence from mineral inclusions -texture
Journal of Asian Earth Sciences, Vol. 42, 4, pp. 607-617.
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.
Abstract: Gem-quality diamonds have been found in several alluvial deposits across central and southern Borneo. Borneo has been a known source of diamonds for centuries, but the location of their primary igneous source remains enigmatic. Many geological models have been proposed to explain their distribution, including: the diamonds were derived from a local diatreme; they were brought to the surface through ophiolite obduction or exhumation of UHP metamorphic rocks; they were transported long distances southward via major Asian river systems; or, they were transported from the Australian continent before Borneo was rifted from its northwestern margin in the Late Jurassic. To assess these models, we conducted a study of the provenance of heavy minerals from Kalimantan's Cempaka alluvial diamond deposit. This involved collecting U Pb isotopic data, fission track and trace element geochemistry of zircon as well as major element geochemical data of spinels and morphological descriptions of zircon and diamond. The results indicate that the Cempaka diamonds were likely derived from at least two sources, one which was relatively local and/or involved little reworking, and the other more distal which records several periods of reworking. The distal diamond source is interpreted to be diamond-bearing pipes that intruded the basement of a block that: (1) rifted from northwest Australia (East Java or SW Borneo) and the diamonds were recycled into its sedimentary cover, or: (2) were emplaced elsewhere (e.g. NW Australia) and transported to a block (e.g. East Java or SW Borneo). Both of these scenarios require the diamonds to be transported with the block when it rifted from NW Australia in the Late Jurassic. The local source could be diamondiferous diatremes associated with eroded Miocene high-K alkaline intrusions north of the Barito Basin, which would indicate that the lithosphere beneath SW Borneo is thick (~ 150 km or greater). The ‘local’ diamonds could also be associated with ophiolitic rocks that are exposed in the nearby Meratus Mountains.
Abstract: Various combinations of diamond, moissanite, zircon, quartz, corundum, rutile, titanite, almandine garnet, kyanite, and andalusite have been recovered from the Dangqiong peridotites. More than 80 grains of diamond have been recovered, most of which are pale yellow to reddish-orange to colorless. The grains are all 100-200 µm in size and mostly anhedral, but with a range of morphologies including elongated, octahedral and subhedral varieties. Their identification was confirmed by a characteristic shift in the Raman spectra between 1325 cm?1 and 1333 cm?1, mostly at 1331.51 cm?1 or 1326.96 cm?1. Integration of the mineralogical, petrological and geochemical data for the Dongqiong peridotites suggests a multi-stage formation for this body and similar ophiolites in the Yarlung-Zangbo suture zone. Chromian spinel grains and perhaps small bodies of chromitite crystallized at various depths in the upper mantle, and encapsulated the UHP, highly reduced and crustal minerals. Some oceanic crustal slabs containing the chromian spinel and their inclusion were later trapped in suprasubduction zones (SSZ), where they were modified by island arc tholeiitic and boninitic magmas, thus changing the chromian spinel compositions and depositing chromitite ores in melt channels.
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?
Earth and Planetary Science Letters, Vol. 430, pp. 284-295.
Asia, Tibet
Luobusa 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 source?C13 values are present in both sets of diamonds. The Tibetan diamonds (n=3n=3) show an exceptionally large range in View the MathML source?N15 (?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 source?N15=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.
Contributions to Mineralogy and Petrology, in press available 19p.
Asia, Tibet
Melting
Abstract: Felsic granulite xenoliths entrained in Miocene (~13 Ma) isotopically evolved, mantle-derived ultrapotassic volcanic (UPV) dykes in southern Tibet are refractory meta-granitoids with garnet and rutile in a near-anhydrous quartzo-feldspathic assemblage. High F-Ti (~4 wt.% TiO2 and ~3 wt.% F) phlogopite occurs as small inclusions in garnet, except for one sample where it occurs as flakes in a quartz-plagioclase-rich rock. High Si (~3.45) phengite is found as flakes in another xenolith sample. The refractory mineralogy suggests that the xenoliths underwent high-T and high-P metamorphism (800-850 °C, >15 kbar). Zircons show four main age groupings: 1.0-0.5 Ga, 50-45, 35-20, and 16-13 Ma. The oldest group is similar to common inherited zircons in the Gangdese belt, whereas the 50-45 Ma zircons match the crystallization age and juvenile character (?Hfi +0.5 to +6.5) of Eocene Gangdese arc magmas. Together these two age groups indicate that a component of the xenolith was sourced from Gangdese arc rocks. The 35-20 Ma Miocene ages are derived from zircons with similar Hf-O isotopic composition as the Eocene Gangdese magmatic zircons. They also have similar steep REE curves, suggesting they grew in the absence of garnet. These zircons mark a period of early Miocene remelting of the Eocene Gangdese arc. By contrast, the youngest zircons (13.0 ± 4.9 Ma, MSWD = 1.3) are not zoned, have much lower HREE contents than the previous group, and flat HREE patterns. They also have distinctive high Th/U ratios, high zircon ?18O (+8.73-8.97 ‰) values, and extremely low ?Hfi (?12.7 to ?9.4) values. Such evolved Hf-O isotopic compositions are similar to values of zircons from the UPV lavas that host the xenolith, and the flat REE pattern suggests that the 13 Ma zircons formed in equilibrium with garnet. Garnets from a strongly peraluminous meta-tonalite xenolith are weakly zoned or unzoned and fall into four groups, three of which are almandine-pyrope solid solutions and have low ?18O (+6 to 7.5 ‰), intermediate (?18O +8.5 to 9.0 ‰), and high ?18O (+11.0 to 12.0 ‰). The fourth is almost pure andradite with ?18O 10-12 ‰. Both the low and intermediate ?18O groups show significant variation in Fe content, whereas the two high ?18O groups are compositionally homogeneous. We interpret these features to indicate that the low and intermediate ?18O group garnets grew in separate fractionating magmas that were brought together through magma mixing, whereas the high ?18O groups formed under high-grade metamorphic conditions accompanied by metasomatic exchange. The garnets record complex, open-system magmatic and metamorphic processes in a single rock. Based on these features, we consider that ultrapotassic magmas interacted with juvenile 35-20 Ma crust after they intruded in the deep crust (>50 km) at ~13 Ma to form hybridized Miocene granitoid magmas, leaving a refractory residue. The ~13 Ma zircons retain the original, evolved isotopic character of the ultrapotassic magmas, and the garnets record successive stages of the melting and mixing process, along with subsequent high-grade metamorphism followed by low-temperature alteration and brecciation during entrainment and ascent in a late UPV dyke. This is an excellent example of in situ crust-mantle hybridization in the deep Tibetan crust.
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.
Abstract: There exist three mainstream opinions regarding the timing of the initial collision between the Indian and Eurasian continents, namely, 65±5, 45±5, and 30±5 Ma. Five criteria are proposed for determining which tectonic event was related to the initial collision between India and Asia: the rapid decrease in the rate of plate motion, the cessation of magmatic activity originating from the subduction of oceanic crust, the end of sedimentation of oceanic facies, the occurrence of intracontinental deformation, and the exchange of sediments sourced from two continents. These criteria are used to constrain the nature of these tectonic events. It is proposed that the 65±5 Ma tectonic event is consistent with some of the criteria, but the upshot of this model is that the magmatic activity originating from the Tethyan subduction since the Mesozoic restarted along the southern margin of the Asian continent in this time after a brief calm, implying that the subduction of the Neotethys slab was still taking place. The magmatic activity that occurred along the southern margin of the Asian continent had a 7-Myr break during 72-65 Ma, which in this study is interpreted as having resulted from tectonic transformation from subduction to transform faulting, indicating that the convergence between the Indian and Asian continents was once dominated by strike-slip motion. The 30±5 Ma tectonic event resulted in the uplift of the Tibetan Plateau, which was related to the late stage of the convergence between these two continents, namely, a hard collision. The 45±5 Ma tectonic event is in accordance with most of the criteria, corresponding to the initial collision between these two continents.
Abstract: Here, we present studies of natural SiC that occurs in situ in tuff related to the Miocene alkaline basalt formation deposited in northern part of Israel. Raman spectroscopy, SEM and FIB-assisted TEM studies revealed that SiC is primarily hexagonal polytypes 4H-SiC and 6H-SiC, and that the 4H-SiC polytype is the predominant phase. Both SiC polytypes contain crystalline inclusions of silicon (Sio) and inclusions of metal-silicide with varying compositions (e.g. Si58V25Ti12Cr3Fe2, Si41Fe24Ti20Ni7V5Zr3, and Si43Fe40Ni17). The silicides crystal structure parameters match Si2TiV5 (Pm-3 m space group, cubic), FeSi2Ti (Pbam space group, orthorhombic), and FeSi2 (Cmca space group, orthorhombic) respectively. We hypothesize that SiC was formed in a local ultra-reduced environment at respectively shallow depths (60-100 km), through a “desilification” reaction of SiO2 with highly reducing fluids (H2O-CH4-H2-C2H6) arisen from the mantle “hot spot” and passing through alkaline basalt magma reservoir. SiO2 (melt) interacting with the fluids may originate from the walls of the crustal rocks surrounding this magmatic reservoir. The “desilification” process led to the formation of SiC and the reduction of metal-oxides to native metals, alloys, and silicides. The latter were trapped by SiC during its growth. Hence, interplate “hot spot” alkali basalt volcanism can now be included as a geological environment where SiC, silicon, and silicides can be found.
Mantle metasomatism and magma formation in continental lithosphere: dat a on xenoliths in alkali basalts from the Makhtesh Ramon, Negrev Desert, Israel.
Abstract: Microdiamonds ?200 ?m in size, occurring in ophiolitic chromitites and peridotites, have been reported in recent years. Owing to their unusual geological formation, there are several debates about their origin. We studied 30 microdiamonds from 3 sources: (1) chromitite ore in Luobusa, Tibet; (2) peridotite in Luobusa, Tibet; and (3) chromitite ore in Ray-Iz, polar Ural Mountains, Russia. They are translucent, yellow to greenish-yellow diamonds with a cubo-octahedral polycrystalline or single crystal with partial cubo-octahedral form. Infrared (IR) spectra revealed that these diamonds are type Ib (i.e., diamonds containing neutrally charged single substitutional nitrogen atoms, Ns0, known as the C center) with unknown broad bands observed in the one-phonon region. They contain fluid inclusions, such as water, carbonates, silicates, hydrocarbons, and solid CO2. We also identified additional microinclusions, such as chromite, magnetite, feldspar (albite), moissanite, hematite, and magnesiochromite, using a Raman microscope. Photoluminescence (PL) spectra measured at liquid nitrogen temperature suggest that these diamonds contain nitrogen-vacancy, nickel, and H2 center defects. We compare them with high-pressure-high-temperature (HPHT) synthetic industrial diamond grits. Although there are similarities between microdiamonds and HPHT synthetic diamonds, major differences in the IR, Raman, and PL spectra confirm that these microdiamonds are of natural origin. Spectral characteristics suggest that their geological formation is different but unique compared to that of natural gem-quality diamonds. Although these microdiamonds are not commercially important, they are geologically important in that they provide an understanding of a new diamond genesis.
Academia.edu, Supplementary material app. 1 and 2, both 10p.
Asia, Kalimantan
deposit - Kalimantan
Abstract: Diamonds in alluvial deposits in Southeast Asia are not accompanied by indicator minerals suggesting primary kimberlite or lamproite sources. The Meratus Mountains in Southeast Borneo (Province Kalimantan Selatan, Indonesia) provide the largest known deposit of these so-called “headless” diamond deposits. Proposals for the origin of Kalimantan diamonds include the adjacent Meratus ophiolite complex, ultra-high pressure (UHP) metamorphic terranes, obducted subcontinental lithospheric mantle and undiscovered kimberlite-type sources. Here we report results from detailed sediment provenance analysis of diamond-bearing Quaternary river channel material and from representative outcrops of the oldest known formations within the Alino Group, including the diamond-bearing Campanian–Maastrichtian Manunggul Formation. Optical examination of surfaces of diamonds collected from artisanal miners in the Meratus area (247 stones) and in West Borneo (Sanggau Area, Province Kalimantan Barat; 85 stones) points toward a classical kimberlite-type source for the majority of these diamonds. Some of the diamonds host mineral inclusions suitable for deep single-crystal X-ray diffraction investigation. We determined the depth of formation of two olivines, one coesite and one peridotitic garnet inclusion. Pressure of formation estimates for the peridotitic garnet at independently derived temperatures of 930–1250 °C are between 4.8 and 6.0 GPa. Sediment provenance analysis includes petrography coupled to analyses of detrital garnet and glaucophane. The compositions of these key minerals do not indicate kimberlite-derived material. By analyzing almost 1400 zircons for trace element concentrations with laser ablation ICP-MS (LA-ICP-MS) we tested the mineral's potential as an alternative kimberlite indicator. The screening ultimately resulted in a small subset of ten zircons with a kimberlitic affinity. Subsequent U–Pb dating resulting in Cretaceous ages plus a detailed chemical reflection make a kimberlitic origin unfavorable with respect to the regional geological history. Rather, trace elemental analyses (U, Th and Eu) suggest an eclogitic source for these zircons. The age distribution of detrital zircons allows in general a better understanding of collisional events that formed the Meratus orogen and identifies various North Australian Orogens as potential Pre-Mesozoic sediment sources. Our data support a model whereby the majority of Kalimantan diamonds were emplaced within the North Australian Craton by volcanic processes. Partly re-deposited into paleo-collectors or residing in their primary host, these diamond-deposits spread passively throughout Southeast Asia by terrane migration during the Gondwana breakup. Terrane amalgamation events largely metamorphosed these diamond-bearing lithologies while destroying the indicative mineral content. Orogenic uplift finally liberated their diamond-content into new, autochthonous placer deposits.
Abstract: Porphyritic olivine kimberlitic breccia, discovered in the Dörbed Banner of Inner Mongolia, Western China, is referred to as Longtou Shan Kimberlite in our study. This kimberlite occurs as a pipe in the Halahuogete Formation of Bayan Obo Group. Zircon U–Pb ages of Longtou Shan Kimberlite reveals a Mesoproterozoic age of ~1,552 Ma, constraining the deposition age of Halahuogete Formation to the Mesoproterozoic. Compared with Mesoproterozoic kimberlite of the ancient landmass, it can be inferred that the North China Craton is a member of the Ur ancient continent of the Columbia supercontinent. Furthermore, according to the tectonic background of the Bayan Obo Group, we raise this possibility that “Bayan Obo Aulacogen” should be renamed the “Bayan Obo Continental Rift.”
International Journal of Astronomy and Astrophysics, Vol. 1, pp. 98-104.
Asia, Mongolia
astropipes, impact craters
Abstract: In this paper we present summation of eighteen year’s investigation of the all gold and diamond-bearing astropipes of Mongolia. Four astropipe structures are exemplified by the Agit Khangay (10 km in diameter, 470 38' N; 960 05' E), Khuree Mandal (D=11 km; 460 28' N; 980 25' E), Bayan Khuree (D=1 km; 440 06' N; 1090 36' E), and Tsenkher (D=7 km; 980 21' N; 430 36' E) astropipes of Mongolia. Detailed geological and gas-geochemical investigation of the astropipe structures show that diamond genesis is an expression of collision of the lithospheric mantle with the explosion process initiated in an impact collapse meteor crater. The term "astropipes" (Dorjnamjaa et al., 2010, 2011) is a neologism and new scientific discovery in Earth science and these structures are unique in certain aspects. The Mongolian astropipes are genuine "meteorite crater" structures but they also contain kimberlite diamonds and gold. Suevite-like rocks from the astropipes contain such minerals, as olivine, coesite, moissanite (0,6 mm), stishovite, coesite, kamacite,tektite, khamaravaevite (mineral of meteorite titanic carbon), graphite-2H, khondrite, picroilmenite, pyrope, phlogopite, khangaite (tektite glass, 1,0-3,0 mm in size), etc. Most panned samples and hand specimens contain fine diamonds with octahedrol habit (0, 2-2,19 mm, 6,4 mg or 0,034-0,1 carat) and gold (0,1-5 g/t). Of special interest is the large amount of the black magnetic balls (0,05-5,0 mm) are characterized by high content of Ti, Fe, Co, Ni, Cu, Mn, Mg, Cd, Ga, Cl, Al, Si, K. Meanwhile, shatter cones (size approx. 1.0 m) which are known from many meteorite craters on the Earth as being typical of impact craters were first described by us Khuree Mandal and Tsenkher astropipe structures. All the described meteorite craters posses reliable topographic, geological, mineralogical, geochemical, and aerospace mapping data, also some geophysical and petrological features (especially shock metamorphism) have been found, all of which indicate that these structures are a proven new type of gold-diamond-bearing impact structure, termed here "astropipes". The essence of the phenomenon is mantle manifestation and plume of a combined nuclear-magma-palingenesis interaction.
Apatites from Sri Lankan carbonatites: petrogenetic implications.
Carbonatite-alkaline rocks and associated mineral deposits , Dec. 8-11, abstract p. 19.
Asia, Sri Lanka
carbonatites
Abstract: Carbonatite exposures are found near the boundary of Highland and Wanni Complexes that are major lithotectonic units of Precambrian basement of Sri Lanka. Larger bodies of carbonatite are found at Eppawala, in northcentral part of the island and smaller intrusions with associated apatite rich silicate dykes are present at Kawisigamuwa, in the Northwestern part. Both carbonatite complexes appear mostly as dykes and have calcite-dolomite-magnetite-apatite assemblages. The aim of present study is to decipher the petrogenetic history of carbonatite via the compositional and petrographical investigations of apatite. The size of apatite varies from fine grained to mega size (up to 1m). Cathodoluminescence and compositional data of apatite from two carbonatite occurrences and associated dykes are variable. Apatite grains of Eppawala are rich in F and Fe with relatively persistent chemical composition of all sizes. However, over growth zones of crystals show highly variable chemical compositions. Kawisigamuwa apatite is characterized by higher concentrations of Cl, Sr and light rare earth elements (LREE). Higher concentrations of Fe and F with lower Sr levels are measured from apatite crystals in silicate dykes. Results of present study are indicative of composition of parent magma and post magmatic fluid activities on the generation of apatite.
Journal of Asian Earth Sciences, in press availabe, 30p.
Asia, Tien Shan
carbonatites
Abstract: Postorogenic intrusions of essexites and alkaline and nepheline syenites in the Turkestan-Alai segment of the Kyrgyz Southern Tien Shan coexist with dikes and veins of carbonatites dated at ?220?Ma by the Ar-Ar and Rb-Sr age methods. They are mainly composed of calcite and dolomite (60-85%), as well as sodic amphibole, phlogopite, clinopyroxene, microcline, albite, apatite, and magnetite, with accessory niobate, ilmenite, Nb-rutile, titanite, zircon, baddeleyite, monazite-(Ce), barite, and sulfides. The rocks share mineralogical and geochemical similarity with carbonatites that originated by liquid immiscibility at high temperatures above 500?°C. Alkaline silicate and salt-carbonate melts are derived from sources with mainly negative bulk ?Nd(t) ? from ?11 to 0 and high initial 87Sr/86Sr ratios (?0.7061-0.7095) which may be due to mixing of PREMA and EM?type mantle material. Pb isotopic ratios in accessory pyrrhotite (206Pb/204Pb?=?18.38; 207Pb/204Pb?=?15.64; 208Pb/204Pb?=?38.41) exhibit an EM2 trend. The intrusions bear signatures of significant crustal contamination as a result of magma genesis by syntexis and hybridism. Concordant isotope composition changes of ?13C (?6.5 to ?1.9‰), ?18O (9.2-23‰), ?D (?58 to ?41‰), and ?34S (12.6-12.8‰) in minerals and rocks indicate inputs of crustal material at the stage of melting and effect of hot fluids released during dehydration of metamorphosed oceanic basalts or sediments. The observed HFSE patterns of the oldest alkaline gabbro may be due to interaction of the primary mafic magma with IAB-type material. The isotope similarity of alkaline rocks with spatially proximal basalts of the Tarim large igneous province does not contradict the evolution of the Turkestan-Alai Triassic magmatism as the “last echo” of the Tarim mantle plume.
Abstract: The Central Asian Orogenic Belt (CAOB) is a huge tectonic mélange that lies between the North China Craton and the Siberian Block. It is composed of multiple orogenic belts, continental fragments, magmatic and metamorphic rocks, suture zones and discontinuous ophiolite belts. Although the Hegenshan and Sartohay ophiolites are separated by nearly 3000 km and lie in completely different parts of the CAOB, they are remarkably similar in many respects. Both are composed mainly of serpentinized peridotite and dunite, with minor gabbro and sparse basalt. They both host significant podiform chromitites that consist of high-Al, refractory magnesiochromite with Cr#s [100Cr/(Cr+Al)] averaging >60. The Sartohay ophiolite has a zircon U-Pb age of ca. 300 Ma and has been intruded by granitic plutons of similar age, resulting in intense hydrothermal activity and the formation of gold-bearing listwanites. The age of the Hegenshan is not firmly established but is thought to have formed in the Carboniferous.Like many other ophiolites that we have investigated in other orogenic belts, the chromitites in these two bodies have abundant diamonds, as well as numerous super-reduced and crustal minerals. The diamonds are mostly, colorless to pale yellow, 200-300 ?m across and have euhedral to anhedral shapes. They all have low carbon isotopes (?14C = ?18 to ?29) and some have visible inclusions. These are accompanied by numerous super-reduced minerals such as moissanite, native elements (Fe, Cr, Si, Al, Mn), and alloys (e.g., Ni-Mn-Fe, Ni-Fe-Al, Ni-Mn-Co, Cr-Ni-Fe, Cr-Fe, Cr-Fe-Mn), as well as a wide range of oxides, sulfides and silicates. Grains of zircon are abundant in the chromitites of both ophiolites and range in age from Precambrian to Cretaceous, reflecting both incorporation of old zircons and modification of grains by hydrothermal alteration. Our investigation confirms that high-Al, refractory chromitites in these two ophiolites have the same range of exotic minerals as high-Cr metallurgical chromitites such as those in the Luobusa ophiolite of Tibet. These collections of exotic minerals in ophiolitic chromitites indicate complex, multi-stage recycling of oceanic and continental crustal material at least to the mantle transition zone, followed by uprise and emplacement of the peridotites into relatively shallow ophiolites.
Journal of Asian Earth Sciences, Vol. 153, pp. 252-281.
Asia
carbonatite
Abstract: Postorogenic intrusions of essexites and alkaline and nepheline syenites in the Turkestan-Alai segment of the Kyrgyz Southern Tien Shan coexist with dikes and veins of carbonatites dated at ?220?Ma by the Ar-Ar and Rb-Sr age methods. They are mainly composed of calcite and dolomite (60-85%), as well as sodic amphibole, phlogopite, clinopyroxene, microcline, albite, apatite, and magnetite, with accessory niobate, ilmenite, Nb-rutile, titanite, zircon, baddeleyite, monazite-(Ce), barite, and sulfides. The rocks share mineralogical and geochemical similarity with carbonatites that originated by liquid immiscibility at high temperatures above 500?°C. Alkaline silicate and salt-carbonate melts are derived from sources with mainly negative bulk ?Nd(t) ? from ?11 to 0 and high initial 87Sr/86Sr ratios (?0.7061-0.7095) which may be due to mixing of PREMA and EM?type mantle material. Pb isotopic ratios in accessory pyrrhotite (206Pb/204Pb?=?18.38; 207Pb/204Pb?=?15.64; 208Pb/204Pb?=?38.41) exhibit an EM2 trend. The intrusions bear signatures of significant crustal contamination as a result of magma genesis by syntexis and hybridism. Concordant isotope composition changes of ?13C (?6.5 to ?1.9‰), ?18O (9.2-23‰), ?D (?58 to ?41‰), and ?34S (12.6-12.8‰) in minerals and rocks indicate inputs of crustal material at the stage of melting and effect of hot fluids released during dehydration of metamorphosed oceanic basalts or sediments. The observed HFSE patterns of the oldest alkaline gabbro may be due to interaction of the primary mafic magma with IAB-type material. The isotope similarity of alkaline rocks with spatially proximal basalts of the Tarim large igneous province does not contradict the evolution of the Turkestan-Alai Triassic magmatism as the “last echo” of the Tarim mantle plume.
Mineralogy and geochemistry of Triassic carbonatites in the Matcha alkaline intrusive complex ( Turkestan Alai Ridge, Kyrgyz southern Tien Shan), SW central Asian orogenic belt.
Journal of Asian Earth Sciences, Vol. 153, pp. 252-281.
Journal of Asian Earth Sciences, Vol. 164, pp. 179-193.
Asia, Myanmar
peridotites
Abstract: Peridotites from the Myitkyina ophiolite are mainly composed of lherzolite and harzburgite. The lherzolites have relatively fertile compositions, with 39.40-43.40?wt% MgO, 1.90-3.17?wt% Al2O3 and 1.75-2.84?wt% CaO. They contain spinel and olivine with lower Cr# (12.6-18.2) and Fo values (88.7-91.6) than those of the harzburgites (24.5-59.7 and 89.6-91.6 respectively). The harzburgites have more refractory compositions, containing 42.40-46.23?wt% MgO, 0.50-1.64?wt% Al2O3 and 0.40-1.92?wt% CaO. PGE contents of the peridotites show an affinity to the residual mantle. Evaluation of petrological and geochemical characteristics of these peridotites suggests that the lherzolites and harzburgites represent residual mantle after low to moderate degrees of partial melting, respectively, in the spinel stability field. The U-shaped, primitive mantle-normalized REE patterns and strong positive Ta and Pb anomalies of the harzburgites suggest melt/fluid refertilization in either a MOR or SSZ setting after their formation at a MOR. Mineral separation of the peridotites has yield a range of exotic minerals, including diamond, moissanite, native Si, rutile and zircon, a collection similar to that reported for ophiolites of Tibet and the Polar Urals. The discovery of these exotic minerals in the Myitkyina ophiolite supports the view that they occur widely in the upper oceanic mantle.
PluS One, Vol. 13, 8, doi:10.1371/journal.pone.0200351
Asia, Thailand
garnets
Abstract: Garnets from disparate geographical environments and origins such as oxidized soils and river sediments in Thailand host intricate systems of microsized tunnels that significantly decrease the quality and value of the garnets as gems. The origin of such tunneling has previously been attributed to abiotic processes. Here we present physical and chemical remains of endolithic microorganisms within the tunnels and discuss a probable biological origin of the tunnels. Extensive investigations with synchrotron-radiation X-ray tomographic microscopy (SRXTM) reveal morphological indications of biogenicity that further support a euendolithic interpretation. We suggest that the production of the tunnels was initiated by a combination of abiotic and biological processes, and that at later stages biological processes came to dominate. In environments such as river sediments and oxidized soils garnets are among the few remaining sources of bio-available Fe2+, thus it is likely that microbially mediated boring of the garnets has trophic reasons. Whatever the reason for garnet boring, the tunnel system represents a new endolithic habitat in a hard silicate mineral otherwise known to be resistant to abrasion and chemical attack.
Abstract: Zircon xenocrysts from the kimberlites offer a unique opportunity to identify the cryptic basement components hidden in the deep crust and thus to image lithospheric structure and crustal evolution. Zircon xenocrysts from the Triassic kimberlites, exposed in the Rangrim massif of North Korea, were selected for in situ U-Pb and Hf analyses. These zircon xenocrysts are all crust-derived. Their U-Pb age spectrum is characterized by one prominent age population at ca. 1.9-1.8 Ga without any Archean ages, indicating a Paleoproterozoic-dominated basement in the depth of the Rangrim massif. Archean basement should be very limited or absent at depth. This is different with the previous thought of the Rangrim massif being an Archean terrane. However, most of those Paleoproterozoic zircons display negative ?Hf(t) values (-9.7~+0.7) with the average Hf model age of 2.83 ± 0.09 Ga (2?), implying that protoliths of those zircons were not juvenile but derived from reworking of the pre-existed Archean basement. These observations argue for a strong crustal reworking event occurred in the Rangriam massif during Paleoproterozoic, which exhausted most of the preexisted Archean basement rocks and generated a large abundance of Paleoproterozoic rocks. The 1.9~1.8 Ga thermal event has been well documented in the adjacent Jiao- Liao-Ji orogenic belt of the North China Craton. Both of them are characterized by the widely distributed 1.9~1.8 Ga magmatism and share similar igneous rock assemblage. We suggest that the Rangrim massif may be the eastern extension of the Jiao-Liao-Ji belt in North Korea, constituting part of a huge Paleoproterozoic orogen in the eastern margin of the Sino-Korean craton.
Abstract: The Tethys margin in central and eastern Asia is comprised of continental terranes separated by suture zones, some of which remain cryptic. Determining the crustal architecture, and therefore the geological history, of the Eastern Tethyan margin remains challenging. Sited in the heart of this region, Myanmar is a highly prospective but poorly explored minerals jurisdiction. A better understanding of Myanmar's mineralization can only be realized through a better understanding of its tectonic history, itself reflected in at least four major magmatic belts. The Eastern and the Main Range Provinces are associated with the Late Permian to Early Triassic closure of Palaeo-Tethys. The Mogok-Mandalay-Mergui Belt and Wuntho-Popa Arc are a response to the Eocene closure of Neo-Tethys. However, magmatic ages outside these two orogenic events are also recorded. We present new zircon U-Pb, Lu-Hf and O isotope data from magmatic rocks across Myanmar, which we append to the existing dataset to isotopically characterize Myanmar's magmatic belts. Eastern Province Permian I-type magmatism has evolved eHf (-10.9 to -6.4), whilst Main Range Province Triassic S-type magmatism also records evolved eHf (-13.5 to -8.8). The Mogok-Mandalay-Mergui Belt is here divided into the Tin Province and the Mogok Metamorphic Belt. The Tin Province hosts ca. 77-50 Ma magmatism with evolved eHf (-1.2 to -15.2), and d 18 O of 5.6-8.3‰. The Mogok Metamorphic Belt exhibits a more complex magmatic and metamorphic history, and granitoids record Jurassic, Late Cretaceous, and Eocene to Miocene phases of magmatism, all of which exhibit evolved eHf values between -4.6 and -17.6, and d 18 O between 6.3 and 9.2‰. From the Tagaung-Myitkyina Belt, we report a magmatic age of 172 Ma and eHf of 18.1 to 10.8. To accommodate the geological evidence, we propose a tectonic model for Myanmar involving a greater Sibumasu - where the documented zircon isotopic variations reflect compositional variations in magmatic source - and invoke the role of a Tengchong Block. The Baoshan Block and Greater Sibumasu were likely assembled on or before the Triassic, a former Andean margin and suture which may lie across the Northern Shan Plateau, and reflected in isotopic differences between the northern and southern parts of the Mogok Metamorphic Belt. This contiguous Sibumasu-Baoshan Block then sutured onto the Indochina margin in the Late Triassic. We propose that a Tengchong Block within Myanmar provides for a southerly termination of the Meso-Tethys suture immediately north of the Mogok area. A discrete Tengchong Block may explain a discontinuous arc of Late Triassic to Jurassic I-type magmatism in central Myanmar, representing an Andean-type margin sited above a subducting Meso-Tethys on the margin of Sibumasu. The Tengchong Block sutured onto Greater Sibumasu before the Late Cretaceous, after which subduction of Neo-Tethys drove the magmatism of the Wuntho-Popa Arc and ultimately that of the Tin Province. The metallogenic character of granite belts in Myanmar reflects the crustal architecture of the region, which is remarkable for its prolific endowment of granite-hosted Sn-W mineralization in two quite distinct granite belts related to sequential Indosinian and Himalayan orogenesis.
Geostandards and Geoanalytical Research, http://orchid.org/0000-0002-2701-4635 80p.
Asia, Sri Lanka
geochronology
Abstract: Here we document a detailed characterization of two zircon gemstones, GZ7 and GZ8. Both stones had the same mass at 19.2 carats (3.84 g) each; both came from placer deposits in the Ratnapura district, Sri Lanka. The U-Pb data are in both cases concordant within the uncertainties of decay constants and yield weighted mean ²??Pb/²³?U ages (95% confidence uncertainty) of 530.26 Ma ± 0.05 Ma (GZ7) and 543.92 Ma ± 0.06 Ma (GZ8). Neither GZ7 nor GZ8 have been subjected to any gem enhancement by heating. Structure?related parameters correspond well with the calculated alpha doses of 1.48 × 10¹? g?¹ (GZ7) and 2.53 × 10¹? g?¹ (GZ8), respectively, and the (U-Th)/He ages of 438 Ma ± 3 Ma (2s) for GZ7 and 426 Ma ± 9 Ma (2s) for GZ8 are typical of unheated zircon from Sri Lanka. The mean U concentrations are 680 ?g g?¹ (GZ7) and 1305 ?g g?¹ (GZ8). The two zircon samples are proposed as reference materials for SIMS (secondary ion mass spectrometry) U-Pb geochronology. In addition, GZ7 (Ti concentration 25.08 ?g g?¹ ± 0.18 ?g g?¹; 95% confidence uncertainty) may prove useful as reference material for Ti?in?zircon temperature estimates.
Earth and Planetary Science Letters, Vol. 496, 1, pp. 142-158.
Asia, Borneo
convection
Abstract: Most, but not all, geodynamic models predict 1-2 km of mantle convective draw-down of the Earth's surface in a region centered on Borneo within southeast Asia. Nevertheless, there is geomorphic, geologic and geophysical evidence which suggests that convective uplift might have played some role in sculpting Bornean physiography. For example, a long wavelength free-air gravity anomaly of +60 mGal centered on Borneo coincides with the distribution of Neogene basaltic magmatism and with the locus of sub-plate slow shear wave velocity anomalies. Global positioning system measurements, an estimate of elastic thickness, and crustal isostatic considerations suggest that regional shortening does not entirely account for kilometer-scale regional elevation. Here, we explore the possible evolution of the Bornean landscape by extracting and modeling an inventory of 90 longitudinal river profiles. Misfit between observed and calculated river profiles is minimized by smoothly varying uplift rate as a function of space and time. Erosional parameters are chosen by assuming that regional uplift post-dates Eocene deposition of marine carbonate rocks. The robustness of this calibration is tested against independent geologic observations such as thermochronometric measurements, offshore sedimentary flux calculations, and the history of volcanism. A calculated cumulative uplift history suggests that kilometer-scale Bornean topography grew rapidly during Neogene times. This suggestion is corroborated by an offshore Miocene transition from carbonate to clastic deposition. Co-location of regional uplift and slow shear wave velocity anomalies immediately beneath the lithospheric plate implies that regional uplift could have been at least partly generated and maintained by temperature anomalies within an asthenospheric channel.
Abstract: With the withdrawal of Soviet troops from Afghanistan, villagers in the Pani- & shir Valley are Lurning their attention to the emerald riches of the nearby Hindu Kush Mountains. Large, dark green crystals have been found in the hundreds of tunnels and shafts dug there. Teams of miners use explosives and drills to remove the limestone that hosts the emerald-bearing quartz and onkerite veins. The gemological properties of Panjshir emeralds are consisrent with those of emeralds from other localities; chemically, they are most similar to emeralds from the Muzo mine in Colombia. "Nodules," previously reported only in tourmaline and morganite, have been found in Panjshir emeralds as well. Approximntely $1 0 million in emeralds were produced in 1990; future prospects ore excellent.
Abstract: Porphyritic olivine kimberlitic breccia, discovered in the Dörbed Banner of Inner Mongolia, Western China, is referred to as Longtou Shan Kimberlite in our study. This kimberlite occurs as a pipe in the Halahuogete Formation of Bayan Obo Group. Zircon U-Pb ages of Longtou Shan Kimberlite reveals a Mesoproterozoic age of ~1,552 Ma, constraining the deposition age of Halahuogete Formation to the Mesoproterozoic. Compared with Mesoproterozoic kimberlite of the ancient landmass, it can be inferred that the North China Craton is a member of the Ur ancient continent of the Columbia supercontinent. Furthermore, according to the tectonic background of the Bayan Obo Group, we raise this possibility that “Bayan Obo Aulacogen” should be renamed the "Bayan Obo Continental Rift."
Abstract: The interaction of hydrous fluids and melts with dry rocks of the lithospheric mantle inevitably modifies their viscoelastic and chemical properties due to the formation of compositionally distinct secondary phases. In addition, melt percolation and the associated metasomatic alteration of mantle rocks may also facilitate modification of the pre-existing rock texture and olivine crystallographic preferred orientation (CPO) and thus seismic properties. Here we explore the relationship between mantle metasomatism, deformation and seismic anisotropy using subduction-related mantle xenoliths from the Penghu Islands, western Taiwan. The investigated xenoliths have equilibrated at upper lithospheric mantle conditions (879?°C to 1127?°C) based on pyroxene geothermometry and show distinct variations in clinopyroxene chemical composition, texture and olivine CPO allowing for the classification of two distinct groups. Group 1 xenoliths contain rare earth element (REE) depleted clinopyroxene, show a porphyroclastic texture and olivine grains are mostly characterized by [100]-axial pattern symmetries. In contrast, REE-enriched clinopyroxene from Group 2 xenoliths occur in a fine-grained equigranular texture and coexisting olivine frequently displays [010]-axial pattern symmetries. The clinopyroxene compositions are indicative of cryptic and modal to stealth metasomatic alteration of Group 1 and Group 2 xenoliths, respectively. Furthermore, the observed olivine [100]-axial pattern of Group 1 xenoliths reflects deformation by dislocation creep at high temperature, low pressure and dry conditions, whereas olivine [010]-axial patterns of Group 2 xenoliths imply activation of olivine [001] glide planes along preferentially wet (010) grain boundaries. This correlation indicates that the variation in olivine CPO symmetry from [100]- to [010]-axial pattern in Penghu xenoliths results from deformation and intra-crystalline recovery by subgrain rotation during metasomatic alteration induced by melt percolation. The microstructural observations and olivine CPO combined with petrological and geochemical data suggest that Group 1 xenoliths preserve microstructural and chemical characteristics of an old, probably Proterozoic lithosphere, while Group 2 xenoliths record localized Miocene deformation associated with wall-rock heating and metasomatism related to melt circulation. Furthermore, the observed transition of olivine CPO from [100]-axial pattern to [010]-axial pattern by deformation in the presence of variable melt fractions and associated metasomatic alteration can be inferred to modify the physical properties of mantle rocks.
Abstract: We present an extensive study of rehomogenized olivine?hosted melt inclusions, olivine phenocrysts, and chromian spinel inclusions to explore the link between geodynamic conditions and the origin and composition of Pliocene-Quaternary intraplate magmatism in Anatolia at Kula, Ceyhan?Osmaniye, and Karacada?. Exceptional compositional variability of these products reveals early and incomplete mixing of distinct parental melts in each volcanic center, reflecting asthenospheric and lithospheric mantle sources. The studied primitive magmas consist of (1) two variably enriched ocean island basalt (OIB)?type melts in Kula; (2) both OIB?type and plume mid?ocean ridge basalt (P?MORB)?like melts beneath Toprakkale and Üçtepeler (Ceyhan?Osmaniye); and (3) two variably enriched OIB?type melts beneath Karacada?. Estimated conditions of primary melt generation are 23-9 kbar, 75-30 km, and 1415-1215 °C for Kula; 28-19 kbar, 90-65 km, and 1430-1350 °C for Toprakkale; 23-18 kbar, 75-60 km, and 1400-1355 °C for Üçtepeler; and 35-27 kbar, 115-90 km, and 1530-1455 °C for Karacada?, the deepest levels of which correspond to the depth of the lithosphere?asthenosphere boundary in all regions. Although magma ascent was likely facilitated by local deformation structures, recent Anatolian intraplate magmatism seems to be triggered by large?scale mantle flow that also affects the wider Arabian and North African regions. We infer that these volcanics form part of a much wider Arabian?North African intraplate volcanic province, which was able to invade the Anatolian upper plate through slab gaps.
Abstract: In situ U-Pb and Hf analyses were used for crustal zircon xenocrysts from Triassic kimberlites exposed in the Rangnim Massif of North Korea to identify components of the basement hidden in the deep crust of the Rangnim Massif and to clarify the crustal evolution of the massif. The U-Pb age spectrum of the zircons has a prominent population at 1.9-1.8 Ga and a lack of Archaean ages. The data indicate that the deep crust and basement beneath the Rangnim Massif are predominantly of Palaeoproterozoic age, consistent with the ages of widely exposed Palaeoproterozoic granitic rocks. In situ zircon Hf isotope data show that most of the Palaeoproterozoic zircon xenocrysts have negative ?Hf ( t ) values (?9.7 to +0.7) with an average Hf model age of 2.86 ± 0.02 Ga (2 ? ), which suggests that the Palaeoproterozoic basement was not juvenile but derived from the reworking of Archaean rocks. Considering the existence of Archaean remanent material in the Rangnim Massif and their juvenile features, a strong crustal reworking event is indicated at 1.9-1.8 Ga, during which time the pre-existing Archaean basement was exhausted and replaced by a newly formed Palaeoproterozoic basement. These features suggest that the Rangnim Massif constitutes the eastern extension of the Palaeoproterozoic Liao-Ji Belt of the North China Craton instead of the Archaean Liaonan Block as previously thought. A huge Palaeoproterozoic orogen may exist in the eastern margin of the Sino-Korean Craton.
Abstract: The role of magmatic differentiation is considered for the formation of the Ulan-Tologoi Ta-Nb-Zr deposit (northwestern Mongolia) related to the eponymous alkali granite pluton. Data are presented on the structure of the pluton, the composition of its rocks, and distribution of rare metal mineralization. The ores of the pluton include alkali granites with contents of ore elements exceeding the normative threshold for Ta (>100 ppm). The rare metal mineralization includes pyrochlore, columbite, zircon, bastnaesite, monazite, and thorite, which are typical of all alkali-salic rocks; however, their amount varies depending on the REE content of the rocks. The pluton was formed ~298 Ma ago under the influence of a mantle-crustal melt source.
Abstract: Identification of the Late Mesozoic carbonatite province in Central Asia is herein discussed. Its regional extent and distribution is investigated, and the areas with manifestations of carbonatite magmatism are described. It is shown that they were developed in terranes with heterogeneous and heterochronous basements: Siberian (Aldan Shield) and North China cratons; Early Paleozoic (Caledonian) and Middle-Late Paleozoic (Hercynian) structures of the Central Asian fold belt (Transbaikal and Tuva zones in Russia; Mongolia). Irrespective of the structural position, the carbonatites were generated within a relatively narrow time interval (150-118?Ma). The geochemical (Sr, LREE, Ba, F and P) specialization of carbonatites of the province is reflected in their mineral composition. Some rocks of the carbonatite complexes always include one or more distinctive minerals: fluorite, Ba-Sr sulfates, Ba-Sr-Ca carbonates, LREE fluorocarbonates, or apatite. Compared to counterparts from other age groups (for example, Maimecha-Kotui group in North Asia), these carbonatites are depleted in Ti, Nb, Ta, Zr and Hf. It is shown that the Sr and Nd isotope composition of carbonatites correlates with the geological age of the host crust. Rocks of carbonatite complexes associated with cratons are characterized by the lowest ?Nd(T) and highest ISr(T) values, indicating that their formation involved an ancient lithospheric material. Carbonatite magmatism occurred simultaneously with the largest plateau basalts 130-120?Ma ago in rift zones in the Late Mesozoic intraplate volcanic province of Central Asia. This interval corresponds to timing of global activation of intraplate magmatism processes, suggesting a link of the carbonatite province with these processes. It is shown that fields with the carbonatite magmatism were controlled by small mantle plumes (“hot fingers”) responsible for the Central Asian mantle plume events.
Geochimica et Cosmochimica Acta, Vol. 248, pp. 1-13.
Mantle, Asia, Mongolia, Russia, Siberia
metasomatism
Abstract: Ca isotopes can be strongly fractionated at the Earth’s surface and thus may be tracers of subducted carbonates and other Ca-rich surface materials in mantle rocks, magmas and fluids. However, the ?44/40Ca range in the mantle and the scope of intra-mantle isotope fractionation are poorly constrained. We report Ca isotope analyses for 22 mantle xenoliths: four basalt-hosted refractory peridotites from Tariat in Mongolia and 18 samples from the Obnazhennaya (Obn) kimberlite on the NE Siberian craton. Obn peridotites are Paleoproterozoic to Archean melting residues metasomatised by carbonate-rich and/or silicate melts including unique xenoliths that contain texturally equilibrated carbonates. ?44/40Ca in 15 Obn xenoliths shows limited variation (0.74-0.97‰) that overlaps the value (0.94?±?0.05‰) inferred for the bulk silicate Earth from data on fertile lherzolites, but is lower than ?44/40Ca for non-metasomatised refractory peridotites from Mongolia (1.10?±?0.03‰). Bulk ?44/40Ca in four Obn peridotites containing metasomatic carbonates ranges from 0.81?±?0.08‰ to 0.83?±?0.06‰, with similar values in acid-leachates and leaching residues, indicating isotopic equilibration of the carbonates with host rocks. We infer that (a) metasomatism tends to decrease ?44/40Ca values of the mantle, but its effects are usually limited (?0.3‰); (b) Ca isotopes cannot distinguish “carbonatite” and “silicate” types of mantle metasomatism. The lowest ?44/40Ca value (0.56‰) was obtained for a phlogopite-bearing Obn peridotite with a very high Ca/Al of 8 suggesting that the greatest metasomatism-induced Ca isotope shifts may be seen in rocks initially low in Ca that experienced significant Ca input leading to high Ca/Al. Two Obn peridotites, a dunite (melt channel material) and a veined spinel wehrlite, have high ?44/40Ca values (1.22‰ and 1.38‰), which may be due to isotope fractionation by diffusion during silicate melt intrusion and percolation in the host mantle. Overall, we find no evidence that recycling of crustal carbonates may greatly affect Ca isotope values in the global mantle or on a regional scale.
Abstract: The interaction of hydrous fluids and melts with dry rocks of the lithospheric mantle inevitably modifies their viscoelastic and chemical properties due to the formation of compositionally distinct secondary phases. In addition, melt percolation and the associated metasomatic alteration of mantle rocks may also facilitate modification of the pre-existing rock texture and olivine crystallographic preferred orientation (CPO) and thus seismic properties. Here we explore the relationship between mantle metasomatism, deformation and seismic anisotropy using subduction-related mantle xenoliths from the Penghu Islands, western Taiwan. The investigated xenoliths have equilibrated at upper lithospheric mantle conditions (879?°C to 1127?°C) based on pyroxene geothermometry and show distinct variations in clinopyroxene chemical composition, texture and olivine CPO allowing for the classification of two distinct groups. Group 1 xenoliths contain rare earth element (REE) depleted clinopyroxene, show a porphyroclastic texture and olivine grains are mostly characterized by [100]-axial pattern symmetries. In contrast, REE-enriched clinopyroxene from Group 2 xenoliths occur in a fine-grained equigranular texture and coexisting olivine frequently displays [010]-axial pattern symmetries. The clinopyroxene compositions are indicative of cryptic and modal to stealth metasomatic alteration of Group 1 and Group 2 xenoliths, respectively. Furthermore, the observed olivine [100]-axial pattern of Group 1 xenoliths reflects deformation by dislocation creep at high temperature, low pressure and dry conditions, whereas olivine [010]-axial patterns of Group 2 xenoliths imply activation of olivine [001] glide planes along preferentially wet (010) grain boundaries. This correlation indicates that the variation in olivine CPO symmetry from [100]- to [010]-axial pattern in Penghu xenoliths results from deformation and intra-crystalline recovery by subgrain rotation during metasomatic alteration induced by melt percolation. The microstructural observations and olivine CPO combined with petrological and geochemical data suggest that Group 1 xenoliths preserve microstructural and chemical characteristics of an old, probably Proterozoic lithosphere, while Group 2 xenoliths record localized Miocene deformation associated with wall-rock heating and metasomatism related to melt circulation. Furthermore, the observed transition of olivine CPO from [100]-axial pattern to [010]-axial pattern by deformation in the presence of variable melt fractions and associated metasomatic alteration can be inferred to modify the physical properties of mantle rocks.
Geochimica et Cosmochimica Acta, in press available, 32p.
Asia, Tibet, Andes
melting
Abstract: The lithospheric mantle beneath Archean cratons is conspicuously refractory and thick compared to younger continental lithosphere (Jordan, 1988, Boyd, 1989; Lee and Chin, 2014), but how such thick lithospheres formed is unclear. Using a large global geochemical database of Archean igneous crustal rocks overlying these thick cratonic roots, we show from Gd/Yb- and MnO/FeOT-SiO2 trends that crustal differentiation required continuous garnet fractionation. Today, these signatures are only found where crust is anomalously thick (60-70?km), as in the Northern and Central Andes and Southern Tibet. The widespread garnet signature in Archean igneous suites suggests that thickening occurred not only in the lithospheric mantle but also in the crust during continent formation in the late Archean. Building thick crust requires tectonic thickening or magmatic inflation rates that can compete against gravitational collapse through lower crustal flow, which would have been enhanced in the Archean when geotherms were hotter and crustal rocks weaker. We propose that Archean crust and mantle lithosphere formed by thickening over mantle downwelling sites with minimum strain rates on the order of 10?13-10?12 s?1, requiring mantle flow rates associated with late Archean crust formation to be 10-100 times faster than today.
Abstract: The enigmatic appearance of cuboctahedral diamonds in ophiolitic and arc volcanic rocks with morphology and infrared characteristics similar to synthetic diamonds that were grown from metal solvent requires a critical reappraisal. We have studied 15 diamond crystals and fragments from Tolbachik volcano lava flows, using Fourier transform infrared spectrometry (FTIR), transmission electron microscopy (TEM), synchrotron X-ray fluorescence (SRXRF) and laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS). FTIR spectra of Tolbachik diamonds correspond to typical type Ib patterns of synthetic diamonds. In TEM films prepared using focused ion beam technique, we find Mn-Ni and Mn-Si inclusions in Tolbachik diamonds. SRXRF spectra indicate the presence of Fe-Ni and Fe-Ni-Mn inclusions with Cr, Ti, Cu, and Zn impurities. LA-ICP-MS data show variable but significantly elevated concentrations of Mn, Fe, Ni, and Cu reaching up to 70?ppm. These transition metal concentration levels are comparable with those determined by LA-ICP-MS for similar diamonds from Tibetan ophiolites. Mn-Ni (+Fe) solvent was widely used to produce industrial synthetic diamonds in the former USSR and Russia with very similar proportions of these metals. Hence, it appears highly probable that the cuboctahedral diamonds recovered from Kamchatka arc volcanic rocks represent contamination and are likely derived from drilling tools or other hard instruments. Kinetic data on diamond dissolution in basaltic magma or in fluid phase demonstrate that diamond does not form under the pressures and temperature conditions prevalent within the magmatic system beneath the modern-day Klyuchevskoy group of arc volcanoes. We also considered reference data for inclusions in ophiolitic diamonds and compared them with the composition of solvent used in industrial diamond synthesis in China. The similar inclusion chemistry close to Ni70Mn25Co5 for ophiolitic and synthetic Chinese diamonds scrutinized here suggests that most diamonds recovered from Tibetan and other ophiolites are not natural but instead have a synthetic origin. In order to mitigate further dubious reports of diamonds from unconventional tectonic settings and source rocks, we propose a set of discrimination criteria to better distinguish natural cuboctahedral diamonds from those produced synthetically in industrial environments and found as contaminants in mantle- and crust-derived rocks.
Abstract: Dunites in the mantle section of the Oman ophiolite contain olivines which show both a wide range of compositions (Fo86.2 to Fo94) and very high magnesium numbers. These data are combined with experimental liquidus olivine-melt data to show that the range of olivine compositions requires that the dunites formed from a range of melt compositions and that some of these melts were very magnesian, with MgO concentrations up to MgO?=?18-20?wt%. These observations are consistent with the finding of MgO-rich melt inclusions from chromitites in the mantle section of the Oman ophiolite (Rollinson et al., Lithos, 2018). It is proposed that the high Mg-olivines formed in equilibrium with high-Ca boninites, found in the upper section of the pillow lavas sequence of the ophiolite. A model is developed whereby high MgO boninites fractionated olivine through a process of melt-rock reaction/fractionation with the enclosing harzburgite to create a range of dunitic compositions and evolved boninitic lavas. Field evidence shows that the emplacement of boninites was late in the evolution of the Oman ophiolite indicating that the mantle dunites of boninitic origin formed late in the history of the ophiolite. High-Ca boninites form through the shallow, hydrous melting of the mantle wedge in a subduction setting and the presence of boninitic dunites and lavas further supports the view that the Oman ophiolite formed in a fore-arc setting through subduction-induced spreading.
Geostandards and Geoanalytical Research, in press available, 21p.
Asia, Mongolia
olivine
Abstract: A new olivine reference material - MongOL Sh11?2 - for in situ analysis has been prepared from the central portion of a large (20 × 20 × 10 cm) mantle peridotite xenolith from a ~ 0.5 My old basaltic breccia at Shavaryn?Tsaram, Tariat region, central Mongolia. The xenolith is a fertile mantle lherzolite with minimal signs of alteration. Approximately 10 g of 0.5-2 mm gem quality olivine fragments were separated under binocular microscope and analysed by EPMA, LA?ICP?MS, SIMS and bulk analytical methods (ID?ICP?MS for Mg and Fe, XRF, ICP?MS) for major, minor and trace elements at six institutions world?wide. The results show that the olivine fragments are sufficiently homogeneous with respect to major (Mg, Fe, Si), minor and trace elements. Significant inhomogeneity was revealed only for phosphorus (homogeneity index of 12.4), whereas Li, Na, Al, Sc, Ti and Cr show minor inhomogeneity (homogeneity index of 1-2). The presence of some mineral and fluid?melt micro?inclusions may be responsible for the inconsistency in mass fractions obtained by in situ and bulk analytical methods for Al, Cu, Sr, Zr, Ga, Dy and Ho. Here we report reference and information values for twenty?seven major, minor and trace elements.
Abstract: The genesis of Earth’s largest rare earth element (REE) deposit, Bayan Obo (China), has been intensely debated, in particular whether the host dolomite marble is of sedimentary or igneous origin. The protracted (Mesoproterozoic to Paleozoic) and intricate (magmatic to metasomatic) geological processes complicate geochemical interpretations. In this study, we present a comprehensive petrographic and in situ, high-spatial resolution Sr-Pb isotopic and geochemical investigation of the host dolomite from the Bayan Obo marble. Based on petrographic evidence, the dolomite marble is divided into three facies including coarse-grained (CM), fine-grained (FM), and heterogeneous marble (HM). All carbonates are ferroan dolomite with high SrO and MnO contents (>?0.15 wt.%), consistent with an igneous origin. Trace element compositions of these dolomites are highly variable both among and within individual samples, with CM dolomite displaying the strongest LREE enrichment. In situ 206Pb/204Pb and 207Pb/204Pb ratios of the dolomite are generally consistent with mantle values. However, initial 208Pb/204Pb ratios define a large range from 35.45 to 39.75, which may result from the incorporation of radiogenic Pb released from decomposition of monazite and/or bastnäsite during Early Paleozoic metasomatism. Moreover, in situ Sr isotope compositions of dolomite indicate a large range (87Sr/86Sr?=?0.70292-0.71363). CM dolomite is characterized by a relatively consistent, unradiogenic Sr isotope composition (87Sr/86Sr?=?0.70295-0.70314), which is typical for Mesoproterozoic mantle. The variation of 87Sr/86Sr ratios together with radiogenic 206Pb/204Pb signatures for dolomite within FM and HM possibly represents recrystallization during Early Paleozoic metasomatism with the contribution of radiogenic Sr and Pb from surrounding host rocks. Therefore, our in situ geochemical data support a Mesoproterozoic igneous origin for the ore-bearing dolomite marble in the Bayan Obo deposit, which subsequently underwent intensive metasomatism during the Early Paleozoic.
Abstract: We report new ?13C ?values data and N?content and N?aggregation state values for microdiamonds recovered from peridotites and chromitites of the Luobusa ophiolite (Tibet) and chromitites of the Ray?Iz ophiolite in the Polar Urals (Russia). All analyzed microdiamonds contain significant nitrogen contents (from 108 up to 589 ± 20% atomic ppm) with a consistently low aggregation state, show identical IR spectra dominated by strong absorption between 1130 cm?1 and 1344 cm?1, and hence characterize Type Ib diamond. Microdiamonds from the Luobusa peridotites have ?13C ?PDB?values ranging from ?28.7‰ to ?16.9‰, and N?contents from 151 to 589 atomic ppm. The ?13C and N?content values for diamonds from the Luobusa chromitites are ?29‰ to ?15.5‰ and 152 to 428 atomic ppm, respectively. Microdiamonds from the Ray?Iz chromitites show values varying from ?27.6 ‰ to ?21.6 ‰ in ?13C and from 108 to 499 atomic ppm in N. The carbon isotopes values bear similar features with previously analyzed metamorphic diamonds from other worldwide localities, but the samples are characterized by lower N?contents. In every respect, they are different from diamonds occurring in kimberlites and impact craters. Our samples also differ from the few synthetic diamonds; we also analyzed showing enhanced ?13C ?variability and less advanced aggregation state than synthetic diamonds. Our newly obtained N?aggregation state and N?content data are consistent with diamond formation over a narrow and rather cold temperature range (i.e. <950°C), and in a short residence time (i.e. within several million years) at high temperatures in the deep mantle.
www.minsocam.org/ MSA/Centennial/ MSA_Centennial _Symposium.html The next 100 years of mineral science, June 20-21, p. 36. Abstract
Asia, Pakistan, Kashmir, South America, Colombia
sapphire, emerald
Abstract: The geographic origin of gemstones has emerged as one of the major factors affecting their sale on the colored stone market, in large part due to the prestige attributed to certain regions (e.g. sapphires from Kashmir or emeralds from Colombia) but also because of political, environmental and ethical considerations. Identifying the geographic provenance of a colored stone has, therefore, developed into one of the main tasks for gem-testing laboratories, providing a strong motivation to establish accurate scientific methods. The properties and features of individual gemstones reflect the specific geological conditions of their formation and the main challenge of origin determination is to find the link between the two. In addition, access to a complete collection of authentic reference samples and analytical data for all economically relevant mining areas worldwide is key. Different techniques have been developed for determining gemstone provenance, including a range of gemological observations, and spectroscopic, chemical, and isotopic analyses[1]. These have proven useful in distinguishing the origin of gemstones from different geological settings but for many gemstones (including ruby and sapphire) to reliably distinguish between gems from different geographic regions that share a similar geological setting is not always possible. So far, no unique fingerprint exists, and the geographic origin remains a challenge, especially for high-clarity stones, emphasizing the need for a more powerful tool. Here we will give an overview of the current techniques, and outline some of the challenges and limitations of geographical origin determination of colored gemstones. In addition, we present new trace element data and the first radiogenic isotope compositions (Sr and Pb) obtained for ruby and sapphire from several different localities of geologically similar deposits. The acquisition of quantitative data of a range of ultra-trace elements along with the most commonly observed elements in ruby and sapphire (Mg, Fe, Ti, Ca, Ga, V and Cr) makes it possible to explore new elements as potential provenance discriminators. Among the elements consistently above the limits of quantification (Zn, Nb, Ni, and Pb), Ni in particular shows promise as a discriminator for amphibolite-type ruby. Measured 87Sr/86Sr and Pb isotope ratios clearly show distinct ranges for the different localities of amphibolitetype ruby, ranges for marble-related ruby and metamorphic blue sapphires from different geographic regions overlap. These results suggest that radiogenic isotopes potentially offer a powerful means of provenance discrimination for different localities of amphibolite-type ruby, their potential for geographical origin determination among marble-hosted ruby and metamorphic sapphire, however, appears to be limited.
Alkaline rocks and carbonatites of the World, Part 4: Antarctica, Asia and Europe ( excluding the former USSR), Australasia and Oceanic Islands.
geolsoc.org.uk, Book MPAR4 approx 150.00
Antarctica, Asia, Europe
carbonatites
Abstract: The alkaline igneous rocks and carbonatites are compositionally and mineralogically the most diverse of all igneous rocks and, apart from their scientific interest, are of major, and growing, economic importance. They are important repositories of certain metals and commodities, indeed the only significant sources of some of them, and include Nb, the rare earths, Cu, V, diamond, phosphate, vermiculite, bauxite, raw materials for the manufacture of ceramics, and potentially Th and U. The economic potential of these rocks is now widely appreciated, particularly since the commencement of the mining of the Palabora carbonatite for copper and a host of valuable by-products. Similarly, the crucial economic dominance of rare earth production from carbonatite-related occurrences in China, has stimulated the world-wide hunt for similar deposits. This volume describes and provides ready access to the literature for all known occurrences of alkaline igneous rocks and carbonatites of Antarctica, Asia and Europe excluding the former USSR, Australasia and oceanic islands. More than 1,200 occurrences from 59 countries are outlined together with those of 57 oceanic islands and island groups. The descriptions include geographical coordinates and information on general geology, rock types, petrography, mineralogy, age and economic aspects with the principal references cited. There are 429 geological and distribution maps and a locality index. As has been demonstrated by the three earlier volumes, the present book is likely to be of considerable interest to mineral exploration companies, as there are no comprehensive published reviews of the economic aspects of the alkaline rocks. It will also interest research scientists in the fields of igneous petrology and volcanology, and geologists concerned with the regional distribution of igneous rocks and their geodynamic relationships.
Abstract: n situ U-Pb and Hf analyses were used for crustal zircon xenocrysts from Triassic kimberlites exposed in the Rangnim Massif of North Korea to identify components of the basement hidden in the deep crust of the Rangnim Massif and to clarify the crustal evolution of the massif. The U-Pb age spectrum of the zircons has a prominent population at 1.9-1.8 Ga and a lack of Archaean ages. The data indicate that the deep crust and basement beneath the Rangnim Massif are predominantly of Palaeoproterozoic age, consistent with the ages of widely exposed Palaeoproterozoic granitic rocks. In situ zircon Hf isotope data show that most of the Palaeoproterozoic zircon xenocrysts have negative ?Hf(t) values (?9.7 to +0.7) with an average Hf model age of 2.86 ± 0.02 Ga (2?), which suggests that the Palaeoproterozoic basement was not juvenile but derived from the reworking of Archaean rocks. Considering the existence of Archaean remanent material in the Rangnim Massif and their juvenile features, a strong crustal reworking event is indicated at 1.9-1.8 Ga, during which time the pre-existing Archaean basement was exhausted and replaced by a newly formed Palaeoproterozoic basement. These features suggest that the Rangnim Massif constitutes the eastern extension of the Palaeoproterozoic Liao-Ji Belt of the North China Craton instead of the Archaean Liaonan Block as previously thought. A huge Palaeoproterozoic orogen may exist in the eastern margin of the Sino-Korean Craton.
Geostandards and Geoanalltical Research, Vol. 43, 3, pp. 543-565.
China, Europe, Sweden, Asia, Mongolia, United States, Africa, Malawi, Madagascar
REE
Abstract: Bastnäsite is the end member of a large group of carbonate-fluoride minerals with the common formula (REE) CO3F•CaCO3. This group is generally widespread and, despite never occurring in large quantities, represents the major economic light rare earth element (LREE) mineral in deposits related to carbonatite and alkaline intrusions. Since bastnäsite is easily altered and commonly contains inclusions of earlier?crystallised minerals, in situ analysis is considered the most suitable method to measure its U?Th?Pb and Sr?Nd isotopic compositions. Electron probe microanalysis and laser ablation (multi?collector) inductively coupled plasma?mass spectrometry of forty?six bastnäsite samples from LREE deposits in China, Pakistan, Sweden, Mongolia, USA, Malawi and Madagascar indicate that this mineral typically has high Th and LREE and moderate U and Sr contents. Analysis of an in?house bastnäsite reference material (K?9) demonstrated that precise and accurate U?Th?Pb ages could be obtained after common Pb correction. Moreover, the Th?Pb age with its high precision is preferable to the U?Pb age because most bastnäsites have relatively high Th rather than U contents. These results will have significant implications for understanding the genesis of endogenous ore deposits and formation processes related to metallogenic geochronology research.
Africa, Madagascar, Zambia, Asia, Sri Lanka, South America, Colombia
emerald
Abstract: The great challenge of geographic origin determination is to connect the properties and features of individual gems to the geology of their deposits. Similar geologic environments can produce gems with similar gemological properties, making it difficult to find unique identifiers. Over the last two decades, our knowledge of corundum and emerald deposit formation has improved significantly. The mineral deposits are classically separated into primary and secondary deposits. Primary corundum deposits are subdivided into two types based on their geological environment of formation: (1) magmatic and (2) metamorphic. Magmatic deposits include gem corundum in alkali basalts as in eastern Australia, and sapphire in lamprophyre and syenite as in Montana (United States) and Garba Tula (Kenya), respectively. Metamorphic deposits are divided into two subtypes (1) metamorphic deposits sensu stricto (in marble; mafic and ultramafic rocks, or M-UMR), and (2) metamorphic-metasomatic deposits characterized by high fluid-rock interaction and metasomatism (i.e., plumasite or desilicated pegmatites in M-UMR and marble, skarn deposits, and shear zonerelated deposits in different substrata, mainly corundum-bearing Mg-Cr-biotite schist). Examples of the first subtype include the ruby deposits in marble from the Mogok Stone Tract or those in M-UMR from Montepuez (Mozambique) and Aappaluttoq (Greenland). The second subtype concerns the sapphire from Kashmir hosted by plumasites in M-UMR. Secondary corundum deposits (i.e., present-day placers) result from the erosion of primary corundum deposits. Here, corundum is found in the following types of deposits: eluvial (derived by in situ weathering or weathering plus gravitational movement), diluvial (scree or talus), colluvial (deposited at the base of slopes by rainwash, sheetwash, slow continuous downslope creep, or a combination of these processes), and alluvial (deposited by rivers). Today, most sapphires are produced from gem placers related to alkali basalts, as in eastern Australia or southern Vietnam, while placers in metamorphic environments, such as in Sri Lanka (Ratnapura, Elahera) and Madagascar (Ilakaka), produce the highest-quality sapphires. The colluvial Montepuez deposit in Mozambique provides a huge and stable supply of clean and very high-quality rubies. Primary emerald deposits are subdivided into two types based on their geological environment of formation: (1) tectonic-magmatic-related (Type I) and (2) tectonic-metamorphic-related (Type II). Several subtypes are defined and especially Type IA, hosted in M-UMR, which accounts for about 70% of worldwide production (Brazil, Zambia, Russia, and others). It is characterized by the intrusion of pegmatites or quartz veins in M-UMR accompanied by huge hydrothermal fluid circulation and metasomatism with the formation of emerald-bearing desilicated pegmatite (plumasite) and biotite schist. Type IB in sedimentary rocks (China, Canada, Norway, Kazakhstan, and Australia) and Type IC in granitic rocks (Nigeria) are of minor importance. The subtype Type IIA of metamorphic deposits is related to hydrothermal fluid circulation at high temperature, in thrust fault and/or shear zones within M-UMR of volcano-sedimentary series, such as at the Santa Terezinha de Goiás deposit in Brazil. The subtype Type IIB is showcased by the Colombian emerald deposits located in the Lower Cretaceous black shales of the Eastern Cordillera Basin. These are related to the circulation of hydrothermal basinal fluids in black shales, at 300330°C, that dissolved evaporites in (1) thrust and tear faults for the deposits of the western emerald zone (Yacopi, Coscuez, Muzo, Peñas Blancas, Cunas, and La Pita mines) and (2) a regional evaporite level intercalated in the black shales or the deposits of the eastern emerald zone (Gachalá, Chivor, and Macanal mining districts). Secondary emerald deposits are unknown because emerald is too fragile to survive erosion and transport in rivers.
Abstract: Over the last several decades, geographic origin determination for fine rubies has become increasingly important in the gem trade. In the gemological laboratory, rubies are generally broken down into two groups based on their trace element chemistry: marble-hosted (low-iron) rubies and high-iron rubies. High-iron rubies are usually a straightforward identification based on their inclusions and trace element profiles. Marble-hosted rubies can be more challenging, with some deposits showing overlap in some of their inclusion scenes. But many marblehosted rubies, especially Burmese stones from Mogok and Mong Hsu, can be accurately identified based on their internal features and trace element profiles. This contribution will outline the methods and criteria used at GIA for geographic origin determination for ruby.
Russia, South America, Brazil, Africa, Tanzania, Zimbabwe, India, Asia, Sri Lanka
alexandrite
Abstract: The gem and jewelry trade has come to place increasing importance on the geographic origin of alexandrite, as it can have a significant impact on value. Alexandrites from Russia and Brazil are usually more highly valued than those from other countries. In 2016, GIA began researching geographic origin of alexandrite with the intent of offering origin determination as a laboratory service. Unfortunately, collecting reliable samples with known provenance can be very difficult. Alexandrite is often recovered as a byproduct of mining for other gemstones (e.g., emerald and corundum), so it can be difficult to secure reliable parcels of samples because production is typically erratic and unpredictable. The reference materials studied here were examined thoroughly for their trace element chemistry profiles, characteristic color-change ranges under daylight-equivalent and incandescent illumination, and inclusion scenes. The data obtained so far allow us to accurately determine geographic origin for alexandrites from Russia, Brazil, Sri Lanka, Tanzania, and India. Future work may help to differentiate alexandrites from other localities.
Abstract: Highly carbonated mantle xenoliths have been found in rift-related alkaline basalts at the Wadi Natash area in the southern part of the Eastern Desert of Egypt. Although all olivine and most orthopyroxene was replaced by carbonate and/or quartz, textural and mineral chemical features show that they are plagioclase-free spinel peridotites (lherzolite to harzburgite). Cr and Mg numbers (Cr#, Mg#) of Cr-spinel vary from 0.06 to 0.45 and 0.73 to 0.81, respectively. The correlation between Cr# and Mg# of the Cr-spinel in the studied xenoliths is weakly negative and its TiO2 content is slightly higher than in abyssal peridotite that was not affected by melt injection. The chemistry of ortho- and clinopyroxene suggests enstatite and chromian diopside compositions, respectively, with distinct signatures of a sub-continental mantle source. In particular, the Na2O contents (>1.0?wt%) and AlVI/AlIV ratios (1.2-2.6) of chromian diopside suggest such an origin. Two-pyroxene geothermometry indicates a temperature of about 900?°C, which is slightly lower than that of ordinary spinel peridotite xenoliths from other rift zones. It is evident that the studied peridotite xenoliths had experienced mantle processes (e.g. decompression melting, magma upwelling and metasomatism) at higher pressure than abyssal peridotites. The trace-element chemistry of clinopyroxene, e.g. high LREE/HREE ratios {(Ce/Yb)n?=?7}, high LREE contents (>3.6?ppm and up to 30.0?ppm Ce) and high Sr between >85.6?ppm and 466?ppm, indicates metasomatic alteration of the peridotite. Clinopyroxene in one sample has very low Ti/Eu and high LREE/HREE ratios. Clinopyroxene with (Ce/Yb)n higher than 3-4 and Ti/Eu ratio lower than 1500 may have experienced carbonatite or carbonate-rich melt metasomatism prior to their incorporation into the host basalt. The basalt itself is almost devoid of any carbonatization and hence the studied mantle peridotites were carbonatized before the generation of the basaltic magma but following an earlier event of K-metasomatism as indicated by the presence of phlogopite. The studied peridotites from the Wadi Natash area were altered by a carbonate-rich melt during a rifting stage. The results of the present paper indicate that the Natash basalts with their peridotite xenoliths extruded along transversal fractures of the NW-trending Nuqra-Kom Ombo-Kharit continental rift on its western shoulder in the south Eastern Desert of Egypt.
Abstract: The redox state of Earth’s upper mantle in several tectonic settings, such as cratonic mantle, oceanic mantle, and mantle wedges beneath magmatic arcs, has been well documented. In contrast, oxygen fugacity (graphic) data of upper mantle under orogens worldwide are rare, and the mechanism responsible for the mantle graphic condition under orogens is not well constrained. In this study, we investigated the graphic of mantle xenoliths derived from the southern Tibetan lithospheric mantle beneath the Himalayan orogen, and that of postcollisional ultrapotassic volcanic rocks hosting the xenoliths. The graphic of mantle xenoliths ranges from ?FMQ = +0.5 to +1.2 (where ?FMQ is the deviation of log graphic from the fayalite-magnetite-quartz buffer), indicating that the southern Tibetan lithospheric mantle is more oxidized than cratonic and oceanic mantle, and it falls within the typical range of mantle wedge graphic values. Mineralogical evidence suggests that water-rich fluids and sediment melts liberated from both the subducting Neo-Tethyan oceanic slab and perhaps the Indian continental plate could have oxidized the southern Tibetan lithospheric mantle. The graphic conditions of ultrapotassic magmas show a shift toward more oxidized conditions during ascent (from ?FMQ = +0.8 to +3.0). Crustal evolution processes (e.g., fractionation) could influence magmatic graphic, and thus the redox state of mantle-derived magma may not simply represent its mantle source.
Science Adavances, Vol. 6, eaba7118 May 27, 9p. Pdf
Asia, Java
geophysics -seismic
Abstract: New passive- and active-source seismic experiments reveal unusually high mantle P-wave speeds that extend beneath the remnants of the world’s largest known large igneous province, making up the 120-million-year-old Ontong-Java-Manihiki-Hikurangi Plateau. Sub-Moho Pn phases of ~8.8 ± 0.2 km/s are resolved with negligible azimuthal seismic anisotropy, but with strong radial anisotropy (~10%), characteristic of aggregates of olivine with an AG crystallographic fabric. These seismic results are the first in situ evidence for this fabric in the upper mantle. We show that its presence can be explained by isotropic horizontal dilation and vertical flattening due to late-stage gravitational collapse and spreading in the top 10 to 20 km of a depleted, mushroom-shaped, superplume head on a horizontal length scale of 1000 km or more. This way, it provides a seismic tool to track plumes long after the thermal effects have ceased.
Abstract: The Mushgai-Khudag alkaline?carbonatite complex, located in southern Mongolia within the Central Asian Orogenic Belt (CAOB), comprises a broad range of volcanic and subvolcanic alkaline silicate rocks (melanephelinite-trachyte and shonkinite-alkaline syenite, respectively). Magnetite-apatite rocks, carbonatites, and fluorite mineralization are also manifested in this area. The complex formed between 145 and 133 Ma and is contemporaneous with late Mesozoic alkaline-carbonatite magmatism within the CAOB. Major and trace element characteristics of silicate rocks in the Mushgai-Khudag complex imply that these rocks were formed by the fractional crystallization of alkaline ultramafic parental magma. Magnetite-apatite rocks may be a product of silicate-Ca-Fe-P liquid immiscibility that took place during the alkaline syenite crystallization stage. The Mushgai-Khudag rocks have variable and moderately radiogenic Sr (87Sr/86Sr(i) = 0.70532-0.70614), ?Nd(t) = ?1.23 to 1.25) isotopic compositions. LILE/HFSE values and SrNd isotope compositions indicate that the parental melts of Mushgai-Khudag were derived from a lithospheric mantle source that was affected by a metasomatic agent in the form a mixture of subducted oceanic crust and its sedimentary components. The ?18OSMOW and ?18CPDB values for calcites in carbonatites range from 16.8‰ to 19.2‰ and from ?3.9‰ to 2.0‰, respectively. CO covariations in calcites of the Mushgai-Khudag carbonatites can be explained by the slight host limestone assimilation.
Nishiyama, T., Ohfuji, H., Fukuba, K., Terauchi, M., Nishi, U., Harada, K., Unoki, K., Moribe, Y., Yoshiasa, A., Ishimaru, S., Mori, Y., Shigeno, M., Arai, S.
Nature Scientific Reports, Vol. 10, 11645 11p. Pdf
Asia, Japan
microdiamond
Abstract: Microdiamonds in metamorphic rocks are a signature of ultrahigh-pressure (UHP) metamorphism that occurs mostly at continental collision zones. Most UHP minerals, except coesite and microdiamond, have been partially or completely retrogressed during exhumation; therefore, the discovery of coesite and microdiamond is crucial to identify UHP metamorphism and to understand the tectonic history of metamorphic rocks. Microdiamonds typically occur as inclusions in minerals such as garnet. Here we report the discovery of microdiamond aggregates in the matrix of a metapelite from the Nishisonogi unit, Nagasaki Metamorphic Complex, western Kyushu, Japan. The Nishisonogi unit represents a Cretaceous subduction complex which has been considered as an epidote-blueschist subfacies metamorphic unit, and the metapelite is a member of a serpentinite mélange in the Nishisonogi unit. The temperature condition for the Nishisonogi unit is 450 °C, based on the Raman micro-spectroscopy of graphite. The coexistence of microdiamond and Mg-carbonates suggests the precipitation of microdiamond from C-O-H fluid under pressures higher than 2.8 GPa. This is the first report of metamorphic microdiamond from Japan, which reveals the hidden UHP history of the Nishisonogi unit. The tectonic evolution of Kyushu in the Japanese Archipelago should be reconsidered based on this finding.
Abstract: Microdiamonds in metamorphic rocks are a signature of ultrahigh-pressure (UHP) metamorphism that occurs mostly at continental collision zones. Most UHP minerals, except coesite and microdiamond, have been partially or completely retrogressed during exhumation; therefore, the discovery of coesite and microdiamond is crucial to identify UHP metamorphism and to understand the tectonic history of metamorphic rocks. Microdiamonds typically occur as inclusions in minerals such as garnet. Here we report the discovery of microdiamond aggregates in the matrix of a metapelite from the Nishisonogi unit, Nagasaki Metamorphic Complex, western Kyushu, Japan. The Nishisonogi unit represents a Cretaceous subduction complex which has been considered as an epidote-blueschist subfacies metamorphic unit, and the metapelite is a member of a serpentinite mélange in the Nishisonogi unit. The temperature condition for the Nishisonogi unit is 450 °C, based on the Raman micro-spectroscopy of graphite. The coexistence of microdiamond and Mg-carbonates suggests the precipitation of microdiamond from C-O-H fluid under pressures higher than 2.8 GPa. This is the first report of metamorphic microdiamond from Japan, which reveals the hidden UHP history of the Nishisonogi unit. The tectonic evolution of Kyushu in the Japanese Archipelago should be reconsidered based on this finding.
Abstract: A new data compilation shows that in intermediate to felsic rocks, zircon Eu/Eu* [chondrite normalized Eu/ graphic] correlates with whole rock La/Yb, which has been be used to infer crustal thickness. The resultant positive correlation between zircon Eu/Eu* and crustal thickness can be explained by two processes favored during high-pressure differentiation: (1) supression of plagioclase and (2) endogenic oxidation of Eu2+ due to garnet fractionation. Here we calibrate a crustal thickness proxy based on Eu anomalies in zircons. The Eu/Eu*-in-zircon proxy makes it possible to reconstruct crustal thickness evolution in magmatic arcs and orogens using detrital zircons. To evaluate this new proxy, we analyzed detrital zircons separated from modern river sands in the Gangdese belt, southern Tibet. Our results reveal two episodes of crustal thickening (to 60-70 km) since the Cretaceous. The first thickening event occurred at 90-70 Ma, and the second at 50-30 Ma following Eurasia-India collision. These findings are temporally consistent with contractional deformation of sedimentary strata in southern Tibet.
Abstract: Swat Valley has become an important source of emeralds, including recently discovered trapiche-type crystals. In this study, emerald samples from Swat were examined by standard gemological testing, UV-Vis-NIR, FTIR, Raman analysis, EDXRF, and LA-ICP-MS. The study found three-phase hexagonal inclusions consisting of water, gaseous carbon dioxide and nitrogen, and a magnesite crystal. The gaseous mixture in two-phase inclusions is characteristic in both trapiche-type (CO2 + N2) and non-trapiche samples (CO2 + N2 + CH4). Mineral inclusions of hematite, magnetite, rutile, graphite, and siderite are reported for the first time. Regular non-trapiche-type Swat emeralds contain high chromium (avg. 7471 ppmw), alkali metal (avg. 21040 ppmw), magnesium (avg. 34263 ppmw), and iron (avg. 9265 ppmw), as well as scandium (avg. 633 ppmw). Infrared spectra show that the absorption of type II H2O is stronger than that of type I H2O. Logarithm plots of trace elements appear to be diagnostic. Based on Raman spectroscopy, the trapiche-type emeralds’ colorless core, light green hexagonal growth zone area, and green rim are emerald, while the six black arms are a mixture of hematite and graphite.
Abstract: Since 2017, a new type of emerald from the Panjshir Valley, Afghanistan, has entered the gem trade. This material is commonly of excellent quality and compares with the finest emeralds from Colombia, not only visually, but also with respect to inclusions, spectral features and chemical composition. As a result, some of these stones have entered the market as Colombian emeralds. This study presents detailed microscopic, spectral and trace-element data for these recently produced Afghan emeralds and compares them to ‘classic’ emeralds from the Panjshir Valley and from Laghman Province in Afghanistan. The samples from each of the three Afghan occurrences showed differences in their UV-Vis-NIR spectra and water-related features in their Raman spectra, and they could also be distinguished from one another-as well as those from other important emerald deposits worldwide- by their trace-element composition. A distinctly higher Fe concentration is the main criterion that separates the recent Panjshir production from Colombian emeralds. This study further shows that it is possible to clearly differentiate emeralds from different localities based on trace-element data using t-SNE statistical processing, which is an unsupervised machine-learning method.
Abstract: From west to east along the Sunda-Banda arc, convergence of the Indo-Australian plate transitions from subduction of oceanic lithosphere to arc-continent collision. This region of eastern Indonesia and Timor-Leste provides an opportunity for unraveling the processes that occur during collision between a continent and a volcanic arc, and it can be viewed as the temporal transition of this process along strike. We collected a range of complementary geological and geophysical data to place constraints on the geometry and history of arc-continent collision. Utilizing ?4 yr of new broadband seismic data, we imaged the structure of the crust through the uppermost mantle. Ambient noise tomography shows velocity anomalies along strike and across the arc that are attributed to the inherited structure of the incoming and colliding Australian plate. The pattern of anomalies at depth resembles the system of salients and embayments that is present offshore western Australia, which formed during rifting of east Gondwana. Previously identified changes in geochemistry of volcanics from Pb isotope anomalies from the inner arc islands correlate with newly identified velocity structures representing the underthrusted and subducted Indo-Australian plate. Reconstruction of uplift from river profiles from the outer arc islands suggests rapid uplift at the ends of the islands of Timor and western Sumba, which coincide with the edges of the volcanic-margin protrusions as inferred from the tomography. These findings suggest that the tectonic evolution of this region is defined by inherited structure of the Gondwana rifted continental margin of the incoming plate. Therefore, the initial template of plate structure controls orogenesis.
Abstract: Alkaline igneous rocks and carbonatites are compositionally and mineralogically the most diverse of all igneous rocks and, apart from their scientific interest, are of major, and growing, economic importance. They are valuable repositories of certain metals and commodities - the only significant sources of some of them - and include Nb, the rare earths, Cu, V, diamond, phosphate, vermiculite, bauxite, raw materials for the manufacture of ceramics, and potentially Th and U. The economic potential of these rocks is now widely appreciated, particularly since the commencement of the mining of the Palabora carbonatite for copper and a host of valuable by-products. Similarly, the crucial economic dominance of rare earth production from carbonatite-related occurrences in China has stimulated the world-wide hunt for related deposits. This volume describes and provides ready access to the literature for all known occurrences of alkaline igneous rocks and carbonatites of Antarctica, Asia and Europe (excluding the former USSR), Australasia and the oceanic islands. More than 1200 occurrences from 59 countries are outlined, together with those of 57 oceanic islands and island groups. The descriptions include geographical coordinates and information on general geology, rock types, petrography, mineralogy, age and economic aspects, with the principal references cited. A brief description is also given of alkaline minerals in meteorites and of alkaline rocks on Mars and Venus. There are 429 geological and distribution maps and a locality index. As has been demonstrated by the three earlier volumes, Alkaline Rocks Part 4 is likely to be of considerable interest to mineral exploration companies, as there are no comprehensive published reviews of the economic aspects of the alkaline rocks. It will also interest research scientists in the fields of igneous petrology and volcanology, and geologists concerned with the regional distribution of igneous rocks and their geodynamic relationships.
Abstract: The small Quaternary volcanic district of Nowbaran (NW Iran) belongs to the Urumieh-Dokhtar Magmatic Arc, a ?1800-km long NW-SE striking Cenozoic belt characterized by the irregular but abundant presence of subduction-related igneous products. Nowbaran rocks are characterized by absence of feldspars coupled with abundance of clinopyroxene and olivine plus nepheline, melilite and other rarer phases. All the rocks show extremely low SiO2 (35.4-41.4?wt%), very high CaO (13.1-18.3?wt%) and low Al2O3 (8.6-11.6?wt%), leading to ultracalcic compositions (i.e. CaO/Al2O3?>?1). Other less peculiar, but still noteworthy, characteristics are the high MgO (8.7-13.3?wt%) and Mg# (0.70-0.75), coupled with a variable alkali content with sodic affinity (Na2O?=?1.8-5.4?wt%; K2O?=?0.2-2.3?wt%) and variably high LOI (1.9-10.4?wt%; average 4.4?wt%). Measured isotopic ratios (87Sr/86Sr?=?0.7052-0.7056; 143Nd/144Nd?=?0.51263-0.51266; 206Pb/204Pb?=?18.54-18.66; 207Pb/204Pb?=?15.66-15.68; 208Pb/204Pb?=?38.66-38.79) show small variations and plot within the literature field for the Cenozoic volcanic rocks of western Iran but tend to be displaced towards slightly higher 207Pb/204Pb. Primitive mantle-normalized multielemental patterns are intermediate between typical subduction-related melts and nephelinitic/melilititic melts emplaced in intraplate tectonic settings. The enrichment in Th, coupled with high Ba/Nb and La/Nb, troughs at Ti in primitive mantle-normalized patterns, radiogenic 87Sr/86Sr and positive ?7/4 anomalies (from +15.2 to +17.0) are consistent with the presence of (old) recycled crustal lithologies in the sources. The origin of Nowbaran magmas cannot be related to partial melting of C-H-free peridotitic mantle, nor to digestion of limestones and marls by ‘normal’ basaltic melts. Rather, we favour an origin from carbonated lithologies. Carbonated eclogite-derived melts or supercritical fluids, derived from a subducted slab, reacting with peridotite matrix, could have produced peritectic orthopyroxene- and garnet-rich metasomes at the expenses of mantle olivine and clinopyroxene. The residual melt compositions could evolve towards SiO2-undersaturated, CaO- and MgO-rich and Al2O3-poor alkaline melts. During their percolation upwards, these melts can partially freeze reacting chromatographically with portions of the upper mantle wedge, but can also mix with melts from shallower carbonated peridotite. The T-P equilibration estimates for Nowbaran magmas based on recent models on ultrabasic melt compositions are compatible with provenance from the lithosphere-asthenosphere boundary at average temperature (?1200°C?±?50°C). Mixing of melts derived from subduction-modified mantle sources with liquids devoid of any subduction imprint, passively upwelling from slab break-off tears could generate magmas with compositions recorded in Nowbaran.
Journal of the Geological Society, Vol. 178, 10.1144/jgs2020-171
Asia, Turkey
deposit - Armutlu
Abstract: Unusual carbonate dykes, which have a thickness of up to 4 m, cross-cut the amphibolites from the high-grade metamorphic rocks in the Armutlu Peninsula (NW Turkey). They are described as carbonatites on the basis of their petrographic, geochemical and isotope-geochemical characteristics. The carbonatites, which commonly show equigranular texture, are composed of calcite and clinopyroxene with other minor phases of plagioclase, mica, garnet, K-feldspar, quartz, epidote, titanite and opaque minerals. They contain abundant xenoliths of pyroxenite and amphibolite. The geochemical characteristics of the carbonatites are significantly different from those of mantle-derived carbonatites. They have remarkably low incompatible element (e.g. Ba, Th, Nb) and total REE (11-91 ppm) contents compared with mantle-derived carbonatites. The high 87Sr/86Sr(i) (0.70797-0.70924) and low ?Nd(t) (?8.08 to ?9.57) of the carbonatites confirm that they were derived from the continental crust rather than from a mantle source. Mica from carbonatite was dated by the 40Ar/39Ar method, yielding a Late Jurassic-Early Cretaceous age (148-137 Ma). This is significantly younger than the age of adjacent amphibolites (Upper Triassic). All data from field studies, as well as petrographic, geochemical and geochronological observations, suggest that these carbonatites were formed from anatectic melting of a carbonated source area in the continental crust.
Abstract: Although a mantle origin of carbonatites has long been advocated, a few carbonatite bodies with crustal fingerprints have been identified. The Eppawala carbonatites in Sri Lanka are more similar to orogenic carbonatites than those formed in stable cratons and within plate rifts. They occur within the Pan-African orogenic belt and have a formation age of ca. 475 Ma newly obtained in this study with no contemporary mantle-related magmatism. These carbonatites have higher (87Sr/86Sr)i ratios (0•70479-0•70524) and more enriched Nd and Hf isotopic compositions than carbonatites reported in other parts of the world. Model ages (1•3-2•0 Ga) of both Nd and Hf isotopes [apatite ?Nd(t)?=??9•2 to ?4•7; rutile ?Hf(t)?=??22•0 to ?8•02] are in the age range of metamorphic basement in Sri Lanka, and the carbon and oxygen isotopic compositions (?13CPDB?=??2•36 to ?1•71; ?18OSMOW?=?13•91-15•13) lie between those of mantle-derived carbonatites and marble. These crustal signatures are compatible with the chemistry of accessory minerals in the carbonatites, such as Ni-free olivine and Al- and Cr-poor rutile. Modeling results demonstrate that the Eppawala carbonatite magmas originated from a mixture of basement gneisses and marbles, probably during regional metamorphism. This interpretation is supported by the occurrence of the carbonatites along, or near, the axes of synforms and antiforms where granitic gneiss and marble are exposed. Therefore, we propose that the Eppawala carbonatites constitute another rare example of a carbonatitic magma that was derived from melting of a sedimentary carbonate protolith. Our findings suggest that other orogenic carbonatites with similar features should be re-examined to re-evaluate their origin.
Abstract: Zircon megacrysts are commonly found in kimberlites and, together with olivine, low-Cr garnet, pyroxene, phlogopite, and ilmenite megacrysts, they constitute a mineral assemblage known as the “low-Cr suite”. The generally close similarity of ages and similar isotope geochemical characteristics of megacrysts and matrix minerals in the host kimberlites support a cognate origin. However, alteration rims commonly develop on zircon and ilmenite megacrysts, providing evidence for a lack of chemical equilibrium between the megacrysts and kimberlitic melts. Here, we report results of a detailed geochronological and geochemical study of zircon megacrysts found in the Middle Devonian Novolaspa kimberlite pipe and dyke located in the Azov Domain of the Ukrainian Shield. The concordia age of zircons is 397.0 ± 2.0 Ma, and it is 14 m.y. older than the age of kimberlite emplacement as defined by a Rb-Sr isochron on phlogopite. The average ?Hf(397) value for unaltered zircon megacrysts is 6.8 ± 0.14, with the alteration rims having similar Hf isotope systematics. These hafnium isotope data indicate a moderately depleted mantle source for zircon. Unaltered megacrystic zircons have low abundances of trace elements and fractionated REE, with pronounced positive Ce/Ce* anomalies and almost no Eu/Eu* anomalies. In contrast, alteration rims have very high and variable concentrations of trace elements, indicating a reaction between zircon and kimberlite melt. The melt or fluid responsible for zircon and ilmenite megacryst formation, in contrast to kimberlitic melt, was poor in incompatible trace elements, except for the HFSE (Zr, Hf, Nb, Ta, and Ti). The oxygen fugacity during crystallization of the megacryst suite was close to the FMQ buffer. Azov zircon megacrysts do not demonstrate close geochronological and isotope-geochemical similarities with their host kimberlites. They are cognate in the broad sense of being related to the same plume event, but their direct affinity is not clearly defined. The megacryst suite may have crystallized from the earliest melts/fluids that separated from the ascending mantle plume, whereas kimberlite magmas were emplaced 14 m.y. after this event.
Abstract: Let us consider a country ruled by a market-friendly dictatorship, which is threatened by a collectivist opposition. The members of the opposition will try to topple the dictatorship, expropriate the returns to the productive capital and distribute the existing resources among the working class. In order to achieve this goal, they need to demonstrate and take to the streets.-
Abstract: Burmese sapphires are among the most coveted colored gemstones in the world. The historical importance of this source and the fine quality of its high-grade material contribute to the legendary status of these gems. Since Mogok is such a long-known source, there are many classic studies available, but modern analytical data are often missing or not up to current standards. This article summarizes the characteristics of Burmese sapphires, including standard gemological properties, inclusion observations, and spectroscopic and trace element analyses. This information was collected from hundreds of blue sapphires that GIA's field gemologists sampled while visiting different mining regions in Mogok over the past decade. Our observations indicate that these sapphires show a wide range of blue color intensities but very consistent inclusion scenes. Trace element chemistry did not show any significant differences between various regions apart from a wider range of Fe concentrations in sapphires from north of Mogok. Rare observations such as orange fluorescence and unusual FTIR spectra can be attributed to the chemical compositions of the sapphires.
Abstract: Harzburgites and dunites forming the base of the Late Cretaceous-Paleocene Papuan Ultramafic Belt (PUB) and Marum ophiolites of Papua New Guinea (PNG) are amongst the most refractory mantle peridotites on Earth. We present a new integrated dataset of major element, bulk plus mineral trace element and Re-Os isotopic analyses aimed at better understanding the genesis of these peridotites. The PUB harzburgites contain olivine (Fo92-93), low-Al enstatite (less than or equal to 0.5 wt. % Al2O3 and CaO), and Cr-rich spinel (Cr# = 0.90-0.95). The Marum harzburgites are less refractory with olivine (Fo91.9-92.7), enstatite (~0.5-1.0 wt. % Al2O3 and CaO), minor clinopyroxene (diopside), and spinel (Cr# = 0.71-0.77). These major element characteristics reflect equivalent or greater levels of melt depletion than that experienced by Archean cratonic peridotites. Whereas bulk-rock heavy rare earth element (HREE) abundances mirror the refractory character indicated by the mineral chemistry and major elements, large-ion lithophile elements (LILEs) indicate a more complex melting and metasomatic history. In-situ olivine and orthopyroxene REE measurements show that harzburgites and dunites have experienced distinct melt-rock interaction processes, with dunite channels/lenses, specifically, showing higher abundances of HREE in olivine. Distinctive severe inter-element fraction of platinum group elements and Re result in complex patterns that we refer to as “M-shaped”. These fractionated highly siderophile element (HSE) patterns likely reflect the dissolution of HSE-rich phases in highly depleted peridotites by interaction with subduction-related melts/fluids, possibly high-temperature boninites. Osmium isotope compositions of the PNG peridotites are variable (187Os/188Os = 0.1204 to 0.1611), but fall within the range of peridotites derived from Phanerozoic oceanic mantle, providing no support for ancient melt depletion, despite their refractory character. This provides further evidence that highly depleted peridotites can be produced in the modern Earth, in subduction zone environments. The complex geochemistry indicates a multi-stage process for the formation of the PNG mantle peridotites in a modern geodynamic environment. The first stage involves partial melting at low-pressure (<2 GPa) and high-temperature (~1250-1350 0C) to form low-K, low-Ti tholeiitic magmas that formed the overlying cumulate peridotite-gabbro and basalt (PUB only) sequences of the ophiolites. This is inferred to have occurred in a fore-arc setting at the initiation of subduction. Later stages involved fluxing of the residual harzburgites with hydrous fluids and melts to form replacive dunites and enstatite dykes, and interaction of the residual peridotites in the overlying mantle wedge with high-temperature hydrous melts from the subducting slab to generate the extremely refractory harzburgites. This latter stage can be linked to the eruption of low-Ca boninites at Cape Vogel, and other arc-related volcanics, in a nascent oceanic island arc. Both ophiolites were emplaced shortly after when the embryonic oceanic island arc collided with the Australian continent.
Abstract: The seismological properties of Earth’s inner core are key to understanding its composition, dynamics and growth history. Within the inner core, fine-scale heterogeneity has previously been identified from backscattering of high-frequency compressional waves. Here we use historical earthquake and explosion data from the Large Aperture Seismic Array, USA, between 1969 and 1975 to build a 3D map of heterogeneity from the inner-core boundary to 500?km depth and determine the geographical distribution of the scatterers across the 40% of the inner core that is visible to the array. Our model has two regions of strong scattering, one beneath eastern Asia and the other beneath South America, both located where past local surveys have identified scattering. We suggest that these loci of strong, fine-scale heterogeneities may be related to random alignments of small, inner-core crystals due to fast freezing. These areas, which have been identified as having high attenuation and lie beneath colder areas of the core-mantle boundary, potentially provide constraints on the dynamics of the inner core and the motions in the outer core, with downwelling in the mantle and outer core possibly associated with strong scattering and inner-core heterogeneity.
Journal of Petrology, 10.1093/petrology/egac014 99p. pdf
Asia, Papua New Guinea
tectonites
Abstract: Harzburgites and dunites forming the base of the Late Cretaceous-Paleocene Papuan Ultramafic Belt (PUB) and Marum ophiolites of Papua New Guinea (PNG) are among the most refractory mantle peridotites on Earth. We present a new integrated dataset of major element, bulk plus mineral trace element and Re-Os isotopic analyses aimed at better understanding the genesis of these peridotites. The PUB harzburgites contain olivine (Fo92-93), low-Al enstatite (less than or equal to 0.5 wt. % Al2O3 and CaO), and Cr-rich spinel (Cr#?=?0.90-0.95). The Marum harzburgites are less refractory with olivine (Fo91.9-92.7), enstatite (~0.5-1.0 wt. % Al2O3 and CaO), minor clinopyroxene (diopside), and spinel (Cr#?=?0.71-0.77). These major element characteristics reflect equivalent or greater levels of melt depletion than that experienced by Archean cratonic peridotites. Whereas bulk-rock heavy rare earth element (HREE) abundances mirror the refractory character indicated by the mineral chemistry and major elements, large-ion lithophile elements indicate a more complex melting and metasomatic history. In situ olivine and orthopyroxene REE measurements show that harzburgites and dunites have experienced distinct melt-rock interaction processes, with dunite channels/lenses, specifically, showing higher abundances of HREE in olivine. Distinctive severe inter-element fraction of platinum group elements and Re result in complex patterns that we refer to as ‘M-shaped’. These fractionated highly siderophile element (HSE) patterns likely reflect the dissolution of HSE-rich phases in highly depleted peridotites by interaction with subduction-related melts/fluids, possibly high-temperature boninites. Osmium isotope compositions of the PNG peridotites are variable (187Os/188Os?=?0.1204 to 0.1611), but fall within the range of peridotites derived from Phanerozoic oceanic mantle, providing no support for ancient melt depletion, despite their refractory character. This provides further evidence that highly depleted peridotites can be produced in the modern Earth, in subduction zone environments. The complex geochemistry indicates a multi-stage process for the formation of the PNG mantle peridotites in a modern geodynamic environment. The first stage involves partial melting at low-pressure (<2 GPa) and high-temperature (~1250°C-1350°C) to form low-K, low-Ti tholeiitic magmas that formed the overlying cumulate peridotite-gabbro and basalt (PUB only) sequences of the ophiolites. This is inferred to have occurred in a fore-arc setting at the initiation of subduction. Later stages involved fluxing of the residual harzburgites with hydrous fluids and melts to form replacive dunites and enstatite dykes and interaction of the residual peridotites in the overlying mantle wedge with high-temperature hydrous melts from the subducting slab to generate the extremely refractory harzburgites. This latter stage can be linked to the eruption of low-Ca boninites at Cape Vogel, and other arc-related volcanics, in a nascent oceanic island arc. Both ophiolites were emplaced shortly after when the embryonic oceanic island arc collided with the Australian continent.
