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The Sheahan Diamond Literature Reference Compilation - Technical, Media and Corporate Articles based on Major Region - Norway
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
Click on icon for details about each occurrence. Works best with Google Chrome.
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]
Compositional variation of some rare earth minerals from the Fen Complex (Telemark, southeast Norway)- implications for the mobilityof rare earths in a carbonatite syste
Mineralogical Magazine, Vol. 50, Sept. pp. 503-509
Compositional variation of some rare earth minerals from the Fen complex(telemark, southeast Norway): implications for the mobility of rare earths in a carbonatite system
Mineralogical Magazine, Vol. 50, No. 357, September pp. 503-509
Mantle and crustal components in a carbonatite complex and the evolution of carbonatite magma: rare earth elements (REE) and isotopic evidence from the Fen complex, southeast Norway
Chemical Geology, Vol. 65, No. 2, May 15, pp. 147-166
Andersen, T.B., Jamveit, B., Dewey, J.F., Swensson, E.
Subduction and education of continental crust: major mechanisms during continent-continent collision and orogenic extensional collapse, a model Based on Norweg
samarium-neodymium (Sm-Nd) and Rubidium-Strontium ages of hornblende clinopyroxenite and metagabbro from the Lillebukt alkaline complex, Seiland Igneous Province.
U Pb geochronology and geochemistry of early Proterozoic rocks of the tectonic basement windows in central Nordland, Caledonides of north central Norway.
Evidence for diamond grade ultra high pressure metamorphism and fluid interaction in the Svartberget Fe Ti garnet peridotite websterite body, western Gneiss region, Norway.
Mineralogy and Petrology, Vol. 88, 1-2, pp. 381-405.
Vrijmoed, J.C., Van Roermund, H.L.M., Davies, G.R.
Evidence for diamond grade ultra high pressure metamorphism and fluid interaction in the Svartberget Fe Ti garnet peridotite websterite body, Western Gneiss
Butler, J.P., Jamieson, R.A., Steenkamp, H.M., Robinson, P.
Discovery of coesite eclogite from the Nordyane UHP domain, Western Gneiss region, Norway: field relations, metamorphic history and tectonic significance.
Journal of Metamorphic Geology, in press available
Abstract: The problem of the existence of the asthenosphere for old Precambrian cratons is still discussed. In order to study the seismic lithosphere-asthenosphere boundary (LAB) beneath the Baltic Shield, we used records of nine local earthquakes with magnitudes ranging from 2.7 to 5.9. To model the LAB, original data were corrected for topography and Moho depth using a reference model with a 46-km-thick crust. For two northern events at Spitsbergen and Novaya Zemlya, we observe a low-velocity layer, 60-70-km-thick asthenosphere, and the LAB beneath Barents Sea was found at depth of c. 200 km. Sections for other events show continuous first arrivals of P-waves with no evidence for "shadow zone" in the whole range of registration, which could either be interpreted as the absence of the asthenosphere beneath the central part of the Baltic Shield, or that the LAB in this area occurs deeper (>200 km). The relatively thin low-velocity layer found beneath southern Sweden, 15 km below the Moho, could be interpreted as small-scale lithospheric heterogeneities, rather than asthenosphere. Differentiation of the lower lithosphere velocities beneath the Baltic Shield could be interpreted as regional heterogeneity or as anisotropy of the Baltic Shield lithosphere, with high velocities approximately in the east-west direction, and slow velocities approximately in the south-north direction.
Abstract: The petrochemistry of carbonatites of three formation types were studied: (1) ultrahigh-pressure garnet-containing carbonatites (UHPC) of the Caledonian sheet (Tromsö, Norway); (2) rocks of the carbonatite-lkaline-ultrabasic Kovdor massif (the Kola Peninsula); and (3) rocks of the carbonatite-alkaline-gabbroid Tikshozero massif (north of Karelia). The samples of carbonatites were examined and tested with a microprobe; the microelements were determined using the ICP-MS technique at the Institute of Microelectronics Technology and High Purity Materials (Chernogolovka). The carbonatites of the Kovdor and Tikshozero massifs are characterized by similar negative REE trends, with a degree of REE enrichment of the Tikshozero carbonatites. The UHPC from Tromsö are different from those of the Kovdor and Tikshozero massifs in the negative trend along with lower concentrations of light REEs. The Tromsö UHPC are similar to the carbonatites of the Kovdor and Tikshozero massifs in the trend and concentrations of heavy REEs. The carbonatites of the Fennoscandian shield of various formation times and types are characterized by the geochemical similarity to those in different regions of the world with the sources associated to mantle plumes. This similarity might be caused by the formation of the mantle carbonated magmas of carbonatite-containing igneous complexes from a mantle source enriched under either mantle metasomatism or plume-lithosphere interaction, with similar mechanisms of formation. The appearance of the formations as such within a wide time interval points to the long-term occurrence of a superplume at the Fennoscandian shield and to permanent activation of the related processes of magma formation.
Abstract: With convergent plate boundaries at some distance, the sources of the lithospheric stress field of the North Atlantic Realm are mainly mantle tractions at the base of the lithosphere, lithospheric density structure and topography. Given this, we estimate horizontal deviatoric stresses using a well-established thin sheet model in a global finite element representation. We adjust the lithospheric thickness and the sub-lithospheric pressure iteratively, comparing modelled in plane stress with the observations of the World Stress Map. We find that an anomalous mantle pressure associated with the Iceland and Azores melt anomalies, as well as topography are able to explain the general pattern of the principle horizontal stress directions. The Iceland melt anomaly overprints the classic ridge push perpendicular to the Mid Atlantic ridge and affects the conjugate passive margins in East Greenland more than in western Scandinavia. The dynamic support of topography shows a distinct maximum of c. 1000 m in Iceland and amounts <150 m along the coast of south-western Norway and 250 -350 m along the coast of East Greenland. Considering that large areas of the North Atlantic Realm have been estimated to be sub-aerial during the time of break-up, two components of dynamic topography seem to have affected the area: a short-lived, which affected a wider area along the rift system and quickly dissipated after break-up, and a more durable in the close vicinity of Iceland. This is consistent with the appearance of a buoyancy anomaly at the base of the North Atlantic lithosphere at or slightly before continental breakup, relatively fast dissipation of the fringes of this, and continued melt generation below Iceland.
Journal of Metamorphic Geology, in press available
Europe, Sweden, Norway
UHP
Abstract: Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here we present a new occurrence of diamond within the Seve Nappe Complex of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in-situ as single and composite (diamond + carbonate) inclusions within garnet, in kyanite-bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg-rich garnet + phengite + kyanite + rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P-T conditions for this stage are 830-840 °C and 4.1-4.2 GPa, in the diamond stability field. The ultrahigh-pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850-860 °C and 1.0-1.1 GPa, leading to formation of Ca,Mg-poor garnet+biotite+ plagioclase+K-feldspar+sillimanite+ilmenite+quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti-in-quartz thermometry. Chemical Th-U-Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post-UHP exhumation of the diamond-bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh-pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the Seve Nappe Complex, provide compelling arguments for regional (at least 200 km along strike of the unit). UHPM of substantial parts of this far-travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.
Journal of Metamorphic Geology, in press available
Europe, Greenland, Norway
mineral chemistry
Abstract: We present new and compiled whole rock modal mineral, major and trace element data from extremely melt depleted but pyroxenite and garnet(?ite) bearing Palaeoarchaean East Greenland cratonic mantle, exposed as three isolated, tectonically strained orogenic peridotite bodies (Ugelvik, Raudhaugene, Midsundvatnet) in western Norway. The studied lithologies comprise besides spinel? and/or garnet?bearing peridotite (dunite, harzburgite, lherzolite) garnet?clinopyroxenite and partially olivine?bearing garnet?orthopyroxenite and ?websterite. Chemical and modal data and spatial relationships between different rock types suggest deformation to have triggered mechanical mixing of garnet?free dunite with garnet?bearing enclosures that formed garnet?peridotite. Inclusions of olivine in porphyroclastic minerals of pyroxenite show a primary origin of olivine in olivine?bearing variants. Major element oxide abundances and ratios of websterite differ to those in rocks expected to form by reaction of peridotite with basaltic melts or silica?rich fluids, but resemble those of Archaean Al?enriched komatiite (AEK) flows from Barberton and Commondale greenstone belts, South Africa. Websterite GdN/YbN, 0.49-0.65 (olivine?free) and 0.73-0.85 (olivine?bearing), overlaps that of two subgroups of AEK, GdN/YbN 0.25-0.55 and 0.77-0.90, with each of them being nearly indistinguishable from one another in rare earth element fractionation but also concentration. Websterite MgO content is high, 22.7-29.0 wt.%, and Zr/Y is very low, 0.1-1.0. The other, non?websteritic pyroxenites overlap - when mechanically mixed together with garnetite - in chemistry with that of AEK. It follows an origin of websterite and likely all pyroxenite that involves melting of a garnet?bearing depleted mantle source. Pyroxene exsolution lamellae in the inferred solidus garnet in all lithological varieties require the pyroxenites to have crystallised in the majorite garnet stability field, at 3-4 GPa (90-120 km depth) at minimum 1600 °C. Consequently, we interpret the websterites to represent the first recognised deep plutonic crystallisation products that formed from komatiite melts. The other pyroxenitic rocks are likely fragments of such crystallisation products. An implication is that a mantle plume environment contributed to the formation of (one of) the worldwide oldest lithospheric mantle underneath the eastern Rae craton.
Abstract: Carbonatites (sensu stricto) are igneous rocks typically associated with continental rifts, being emplaced at relatively shallow crustal levels or as extrusive rocks. Some carbonatites are, however, related to subduction and lithospheric collision zones, but so far no carbonatite has been reported from ultrahigh-pressure (UHP) metamorphic terranes. In this study, we present detailed petrological and geochemical data on carbonatites from the Tromsø Nappe—a UHP metamorphic terrane in the Scandinavian Caledonides. Massive to weakly foliated silicate-rich carbonate rocks, comprising the high-P mineral assemblage of Mg-Fe-calcite?±?Fe-dolomite?+?garnet?+?omphacitic clinopyroxene?+?phlogopite?+?apatite?+?rutile?+?ilmenite, are inferred to be carbonatites. They show apparent intrusive relationships to eclogite, garnet pyroxenite, garnet-mica gneiss, foliated calc-silicate marble and massive marble. Large grains of omphacitic pyroxene and megacrysts (up to 5?cm across) of Cr-diopside in the carbonatite contain rods of phlogopite oriented parallel to the c-axis, the density of rods being highest in the central part of the megacrysts. Garnet contains numerous inclusions of all the other phases of the carbonatite, and, in places, composite polyphase inclusions. Zircon, monazite and allanite are common accessory phases. Locally, veins of silicate-poor carbonatite (up to 10?cm across) occur. Extensive fenitization by K-rich fluids, with enrichment in phlogopite along contacts between carbonatite and silicate country rocks, is common. Primitive mantle-normalized incompatible element patterns for the carbonatite document a strong enrichment of light rare earth elements, Ba and Rb, and negative anomalies in Th, Nb, Ta, Zr and Hf. The carbon and oxygen isotope compositions of the carbonatite are distinctly different from those of the spatially associated calc-silicate marble, but also from mantle-derived carbonatites elsewhere. Neodymium and Sr isotope data coupled with the trace element distribution indicate a similarity of the Tromsø carbonatite to orogenic (off-craton) carbonatites rather than to anorogenic (on-craton) ones. U-Pb dating of relatively U-rich prismatic, oscillatory-zoned zircon gives an age of 454•5?±?1•1?Ma. We suggest that the primary carbonatite magma resulted from partial melting of a carbonated eclogite at UHP, in a deeply subducted continental slab.
Mineralogical Magazine Open access special publication Critical metal mineralogy and ore genesis, Vol. 82 (S1) pp. S115-S131.
Europe, Norway
carbonatite
Abstract: The Fen Complex in Norway consists of a ~583 Ma composite carbonatite-ijolite-pyroxenite diatreme intrusion. Locally, high grades (up to 1.6 wt.% total REE) of rare-earth elements (REE) are found in a hydrothermally altered, hematite-rich carbonatite known as rødbergite. The progressive transformation of primary igneous carbonatite to rødbergite was studied here using scanning electron microscopy and inductively coupled plasma-mass spectrometry trace-element analysis of 23 bulk samples taken along a key geological transect. A primary mineral assemblage of calcite, dolomite, apatite, pyrite, magnetite and columbite with accessory quartz, baryte, pyrochlore, fluorite and REE fluorocarbonates was found to have transformed progressively into a secondary assemblage of dolomite, Fe-dolomite, baryte, Ba-bearing phlogopite, hematite with accessory apatite, calcite, monazite-(Ce) and quartz. Textural evidence is presented for REE fluorocarbonates and apatite breaking down in igneous carbonatite, and monazite-(Ce) precipitating in rødbergite. The importance of micro-veins, interpreted as feeder fractures, containing secondary monazite and allanite, is highlighted. Textural evidence for included relics of primary apatite-rich carbonatite are also presented. These acted as a trap for monazite-(Ce) precipitation, a mechanism predicted by physical-chemical experiments. The transformation of carbonatite to rødbergite is accompanied by a 10-fold increase in REE concentrations. The highest light REE (LREE) concentrations are found in transitional vein-rich rødbergite, whereas the highest heavy REE (HREE) and Th concentrations are found within the rødbergites, suggesting partial decoupling of LREE and HREE due to the lower stability of HREE complexes in the aqueous hydrothermal fluid. The hydrothermal fluid involved in the formation of rødbergite was oxidizing and had probably interacted with country-rock gneisses. An ore deposit model for the REE-rich rødbergites is presented here which will better inform exploration strategies in the complex, and has implications for carbonatite-hosted REE resources around the world.
Abstract: Garnet chemistry provides a well-established tool in the discrimination and interpretation of sediment provenance. Current discrimination approaches, however, (i) suffer from using less variables than available, (ii) subjective determination of discrimination fields with strict boundaries suggesting clear separations where in fact probabilities are converging, and (iii) significant overlap of compositional fields of garnet from different host-rock groups. The new multivariate discrimination scheme is based on a large database, a hierarchical discrimination approach involving three steps, linear discriminant analysis at each step, and the five major host-rock groups to be discriminated: eclogite- (A), amphibolite- (B) and granulite- (C) facies metamorphic rocks as well as ultramafic (D) and igneous rocks (E). The successful application of statistical discrimination approaches requires consideration of the a priori knowledge of the respective geologic setting. This is accounted for by the use of prior probabilities. Three sets of prior probabilities (priors) are introduced and their advantages and disadvantages are discussed. The user is free to choose among these priors, which can be further modified according to the specific geologic problem and the level of a priori knowledge. The discrimination results are provided as integrated probabilities of belonging to the five major host-rock groups. For performing calculations and results a supplementary Excel® spreadsheet is provided. The discrimination scheme has been tested for a large variety of examples of crystalline rocks covering all of the five major groups and several subgroups from various geologic settings. In most cases, garnets are assigned correctly to the respective group. Exceptions typically reflect the peculiarities of the regional geologic situation. Evaluation of detrital garnets from modern and ancient sedimentary settings of the Western Gneiss Region (Norway), Eastern Alps (Austria) and Albertine Rift (Uganda) demonstrates the power to reflect the respective geologic situations and corroborates previous results. As most garnet is derived from metamorphic rocks and many provenance studies aim at reconstructing the tectonic and geodynamic evolution in the source area, the approach and the examples emphasize discrimination of metamorphic facies (i.e., temperature-pressure conditions) rather than protolith composition.
Abstract: The Fen Complex is a 2 km-wide subcircular intrusion composed mainly of sovite, Fe-dolomite carbonatite, damtjernite (lamprophyre) and minor alkaline rocks such as nepheline syenite and ijolite, emplaced at 580 Ma through Mesoproterozoic orthogneisses forming the Fennoscandian Shield. Previous bulk-rock isotopic study indicates that the carbonatite magma originated in the upper mantle [(87Sr/86Sr)i = 0.7029] and underwent contamination during its ascent throughout the crust. This study focuses on two deep cores (1000 m and 700 m), drilled to assess the distribution of REE mineralizations in the Fe-dolomite carbonatite. Hyperspectral data, allowing investigators to log cores objectively and quantify lithologies, were acquired using a SisuRock Gen 2 system composed of three cameras gathering data in the following wavelengths: RGB, Near-Visible Short-Wave Infrared (VN-SWIR) and Long-Wave Infrared (LWIR). In addition, every meter of the first core and 500 m of the second one were analyzed for bulk-rock geochemistry to characterize the distribution of elements. In this study, we compare the results obtained by the imaging technique with the bulk-rock data and present preliminary results of the textural variations observed in rare-earth mineralizations. Preliminary results indicate that neither of the deep bore holes reached the fenitized host-rock and that the Fe-dolomite carbonatite continues at depth. In both cores, the dominant carbonate is Fe-rich dolomite, although calcite and Fe-Mg carbonate have been observed locally. REE-minerals, composed mainly of bastnäsite, parisite/synchisite and monazite, display variable textural relationships and often occur together in clusters associated with barite and minor Fe-oxides, sulfides (pyrite ± sphalerite) and locally thorite.
Abstract: The first find of microdiamond in the Nordøyane ultra-high-pressure (UHP) domain of the Western Gneiss Region (WGR) of the Scandinavian Caledonides reshaped tectonic models for the region. Nevertheless, in spite of much progress regarding the meaning and significance of this find, the history of rock that the diamonds were found in is complex and still largely ambiguous. To investigate this, we report U-Pb zircon ages obtained from the exact crushed sample material in which metamorphic diamond was first found. The grains exhibit complicated internal zoning with distinct detrital cores overgrown by metamorphic rims. The cores yielded a range of ages from the Archaean to the late Neoproterozoic / early Cambrian. This detrital zircon age spectrum is broadly similar to detrital signatures recorded by metasedimentary rocks of the Lower and Middle allochthons elsewhere within the orogen. Thus, our dating results support the previously proposed affinity of the studied gneiss to the Seve-Blåhø Nappe of the Middle Allochthon. Metamorphic rims yielded a well-defined peak at 447 ± 2 Ma and a broad population that ranges between c. 437 and 423 Ma. The data reveal a prolonged metamorphic history of the Fjørtoft gneiss that is far more complex then would be expected for a UHP rock that has seen a single burial and exhumation cycle. The data are consistent with a model involving multiple such cycles, which would provide renewed support for the dunk tectonics model that has been postulated for the region.
Americam Geophysical Union Fall meeting, 1p. Abstract
Europe, Norway
eclogites, peridotites
Abstract: The preservation of Archean cratons is typically attributed to the presence of a highly-depleted and buoyant sub-continental lithospheric mantle (SCLM) that is equally old or older than its overlying crust. Time constraints on the formation and petrological evolution of the SCLM are key to investigating its long-term evolution and role in the formation and preservation of the continental crust. Nevertheless, such constraints are difficult to obtain as well-preserved samples of the SCLM are rare and typically lack conventional chronometric minerals. The history of SCLM rocks is typically inferred on the basis of model ages, many of which indicate an Archean origin; however, these dates are difficult to link to specific mineral assemblages or chemical signatures, and the petrological and dynamic processes that these represent. Garnet Lu-Hf geochronology is one of the few chronometers that could overcome this limitation. In this study, a refined method in Lu-Hf garnet chronology was applied to fragments of the Laurentian SCLM that are now exposed as orogenic peridotites in the ultrahigh-pressure domains of the Western Gneiss Complex, Norway. The peridotite bodies comprise a variety of unusually well-preserved rock types-from dunites that record decompression and melting at >350 km depth to fertile lithologies produced by melting and fluid metasomatism. Our internal isochron results from pyrope (after exsolution from majorite) in dunite samples yielded identical Neoarchean ages; these are the first-ever obtained for mantle garnet. The ages coincide with a time interval during which there was voluminous juvenile crust formation, indicating a link between this global process and the deeply sourced mantle upwellings that these samples represent. Internal isochrons from websterite-and clinopyroxenite-hosted pyrope yielded Meso-to Neoproterozoic ages that exactly match two distinct supercontinent break-up events in the overlying continental crust. Together, the new Lu-Hf results indicate that since its extraction during a period of widespread Archean crustal growth, the Laurentian SCLM appears to have largely been at petro-physical and chemical stasis and evolved only during short pulses that ran in sync with the supercontinent cycle.
Abstract: Investigating the seismic properties of natural eclogite is crucial for identifying the composition, density, and mechanical structure of the Earth’s deep crust and mantle. For this purpose, numerous studies have addressed the seismic properties of various types of eclogite, except for a rare eclogite type that contains abundant olivine and orthopyroxene. In this contribution, we calculated the ambient-condition seismic velocities and seismic anisotropies of this eclogite type using an olivine-rich eclogite from northwestern Flemsøya in the Nordøyane ultrahigh-pressure (UHP) domain of the Western Gneiss Region in Norway. Detailed analyses of the seismic properties data suggest that patterns of seismic anisotropy of the Flem eclogite were largely controlled by the strength of the crystal-preferred orientation (CPO) and characterized by significant destructive effects of the CPO interactions, which together, resulted in very weak bulk rock seismic anisotropies (AVp = 1.0-2.5%, max. AVs = 0.6-2.0%). The magnitudes of the seismic anisotropies of the Flem eclogite were similar to those of dry eclogite but much lower than those of gabbro, peridotite, hydrous-phase-bearing eclogite, and blueschist. Furthermore, we found that amphibole CPOs were the main contributors to the higher seismic anisotropies in some amphibole-rich samples. The average seismic velocities of Flem eclogite were greatly affected by the relative volume proportions of omphacite and amphibole. The Vp (8.00-8.33 km/s) and Vs (4.55-4.72 km/s) were remarkably larger than the hydrous-phase-bearing eclogite, blueschist, and gabbro, but lower than dry eclogite and peridotite. The Vp/Vs ratio was almost constant (avg. ? 1.765) among Flem eclogite, slightly larger than olivine-free dry eclogite, but similar to peridotite, indicating that an abundance of olivine is the source of their high Vp/Vs ratios. The Vp/Vs ratios of Flem eclogite were also higher than other (non-)retrograded eclogite and significantly lower than those of gabbro. The seismic features derived from the Flem eclogite can thus be used to distinguish olivine-rich eclogite from other common rock types (especially gabbro) in the deep continental crust or subduction channel when high-resolution seismic wave data are available.
Abstract: New petrographic, geochemical, and isotopic (Sr, Nd, and ?18?) data on olivine and pyroxene phenocrysts provide constraints on the composition and crustal evolution of primary melts of Paleoproterozoic (2.40 Ga) picrodoleritic sills in the northwest Kola province, Fennoscandian Shield. The picrodolerites form differentiated sills with S-shaped compositional profiles. Their chilled margins comprise porphyritic picrodolerite (upper margin) and olivine gabbronorite (bottom) with olivine and clinopyroxene phenocrysts. Analysis of the available data allows us to recognize three main stages in the crystallization of mineral assemblages. The central parts of large (up to 2 mm) olivine phenocrysts (Ol-1-C) crystallized at the early stage. This olivine (Mg# 85-92) is enriched in Ni (from 2845 to 3419 ppm), has stable Ni/Mg ratio, low Ti, Mn and Co concentrations, and contains tiny (up to 10 ?m) diopside-spinel dendritic lamella that probably originated due to the exsolution from high Ca- and Cr- primary magmatic olivine. All these features of Ol-1-C are typical of olivine from primitive picritic and komatiitic magmas (De Hoog et al., 2010; Asafov et al., 2018). Ol-1-C contains large (up to 0.25 mm) crystalline inclusions of high-Al enstatite (Mg# 80-88) and clinopyroxene (Mg# 82-90), occasionally in association with Ti-pargasite and chromian spinel (60.4 wt.% Al2O3). These inclusions are regarded as microxenoliths of wall rock that were captured by primary melt at depths more than 30 km and preserved due to the conservation in magmatic olivine. The second stage was responsible for the crystallization of Ol-1 rim (Ol-1-R), small (up to 0.3 mm) olivine (Ol-2, Mg# 76-85) grains, and central parts of large (up to 1.5 mm) clinopyroxene (Cpx-C) phenocrysts in the mid-crustal transitional magma chamber (at a depth of 15-20 km) at 1160-1350°C. At the third stage, Cpx-C phenocrysts were overgrown by low-Mg rims (Mg# 70-72) similar in composition to the groundmass clinopyroxene from chilled picrodolerite and gabbro-dolerite in the central parts of the sills. This stage likely completed the evolution of picrodoleritic magma and occurred in the upper crust at a depth of about 5 km. All stages of picrodoleritic magma crystallization were accompanied by contamination. Primary melts were contaminated by upper mantle and/or lower crust as recognized from xenocrystic inclusions in Ol-1-C. The second contamination stage is supported by the negative values of ?Nd(2.40) = -1.1 in clinopyroxene phenocrysts. At the third stage, contamination likely occurred in the upper crust when ascending melts filled gentle fractures. This caused vertical whole-rock Nd heterogeneity in the sills (Erofeeva et al., 2019), and difference in Nd isotopic composition of clinopyroxene phenocrysts and doleritic groundmass. It was also recognized that residual evolved melts are enriched in radiogenic strontium but have neodymium isotopic composition similar to other samples. It could be explained by the interaction of the melts with fluid formed via decomposition of biotite from surrounding gneisses under the effect of high-temperature melts.
Mineralogy and Petrology, doi.org/10.1007/ s00710-021-00736-0 11p. Pdf
Europe, Norway
carbonatite
Abstract: Carbonatites in the Fen intrusive complex (southern Norway) contain abundant burbankite (confirmed by Raman microspectroscopy) as inclusions in calcite, dolomite and, less commonly, fluorapatite and pyrochlore. Typically the inclusions occur in the core of calcite or dolomite grains relatively unaffected by subsolidus processes, and are associated with Fe-poor dolomite or Sr-rich calcite, respectively. Burbankite does not exceed 30?×?50 ?m in size and is characteristically absent from the peripheral areas of carbonate grains affected by recrystallization or interaction with fluids. Compositionally, the mineral falls within the following range: (Na1.51-2.16Ca0.58-1.21)(Sr1.50-2.42Ca0.28-0.57LREE0.05-0.64Ba0.06-0.41)(CO3)5 and contains low Th, but no detectable Mg, Fe or F (LREE?=?light rare-earth elements: Ce?>?La?>?Nd?>?Pr?>?Sm). Burbankite inclusions at Fen are interpreted as primary and indicative of Na enrichment in their parental carbonatitic magma. Dissociation of burbankite during subsolidus re-equilibration of its host phases with fluids undoubtedly served as one of the sources of LREE for the development of late-stage mineralization in the Fen complex.
Geochemistry International, Vol. 59, 8, pp. 801-812. pdf
Europe, Norway
deposit - Tromso Nappe
Abstract: The paper presents data on phase relations in garnet-bearing carbonatite from the Tromsø Nappe, Norway. The carbonatite matrix consists of calcite-dolomite carbonate with three generations of garnet inclusions (up to 15-20%). The relics of the primary garnets (Grt1) are depleted (<10-2 wt %) in the rare earth elements (REE). The garnet of the second and third generations (Grt2-3) is anomalously enriched (up to 10-15 wt %) in the light REE (LREE), and the carbonates are depleted in these elements. The distribution of REE between the garnet and carbonate indicates the absence of equilibrium. The melting of the carbonatite at T = 950-1400°C, P = 4.0 GPa showed that the “dry” solidus temperature is 1150°C, and the liquidus temperature is >1300°C. In the experiment with H2O + CO2 fluid, the solidus and liquidus temperatures are ?950 and 1250°C, respectively. The subsolidus association is calcite, garnet, clinopyroxene, biotite, and accessory minerals: apatite, ilmenite, rutile, and titanite. The garnet and carbonatite melt occur in reaction relationships, as is evident from the garnet zoning with a decrease in the FeO and increase in the MgO, CaO, TiO2, and LREE concentrations. The geological setting, phase relationships, and experimental data indicate that the garnet-bearing carbonatites in the Tromsø area were formed in relation to the carbonatization and melting of upper mantle material at high pressures during the collision of the Baltica and Laurentia plates in the course of the Caledonian orogenesis, with subsequent intrusion and crystallization of silicate-carbonate magmas.
Geochimica et Cosmochimica Acta, Vol. 312, pp. 158-179. pdf
Europe, Norway
deposit - Spitzbergen
Abstract: Enrichments in light REE without concomitant enrichments in high-field-strength elements in mantle peridotites are usually attributed to inputs from carbonate-rich melts and referred to as ‘carbonatite’ metasomatism as opposed to interaction with evolved silicate melts. Alternatively, both enrichment types are ascribed to percolating volatile-bearing mafic liquids whose chemical signatures evolve from ‘silicate’ to ‘carbonatite’. Here we compare these models for peridotites in which these enrichment types are combined, as may be common in the mantle. We report new Ca-Sr-Nd isotope and chemical data for lherzolite and harzburgite xenoliths from Spitsbergen that were metasomatized, first, by silicate, then by carbonate-rich melts that formed carbonate-bearing pockets replacing earlier minerals. Seven crushed samples were treated with acetic acid that dissolved carbonates formed in the latest event, but not silicates. The leachates (acid-removed carbonates making up 0.6-1.4% of total sample mass) contain much more Sr than the residues after leaching (277-2923 vs. 16-60 ppm), have a greater overall 87Sr/86Sr range (0.7049-0.7141 vs. 0.7036-0.7055) and higher 87Sr/86Sr in each sample than the residues. The leachates have lower ?44/40Ca range (0.17-0.68‰) than the residues (0.78-1.00‰), as well as lower ?44/40Ca than the residues in all samples but one. By and large, the carbonates are out of Ca-Sr isotope equilibrium with the host peridotites implying that the older silicate and younger carbonatite metasomatism were produced by different parental melts, thus supporting the existence of distinctive carbonate-rich metasomatic media in the lithospheric mantle, possibly including recycled materials. The ?44/40Ca in the leachates (i.e. carbonates, 0.17-0.68‰) are well below bulk silicate Earth (BSE) estimates (0.94 ± 0.05‰) and ?44/40Ca in non-metasomatized melt-depleted mantle. Yet, ?44/40Ca in the non-leached whole rock (WR) carbonate-bearing samples (0.75-0.95‰) fall within, or are only slightly lower than, the BSE range. The 87Sr/86Sr range in these WR samples (0.7030-0.7112) includes very high values for peridotites with large aggregates of dolomite and Mg-calcite. It appears that both carbonatite and silicate metasomatism may produce ?44/40Ca values lower than the BSE such that Ca-isotope data cannot robustly tell apart these two enrichment types, yet carbonatite metasomatism may yield the lowest ?44/40Ca. Carbonates, even at small mass fractions, are significant hosts of Sr in the WR Spitsbergen peridotites (8-51 wt.% of Sr mass) because of very high Sr concentrations, but add little to WR Ca balance (3-12 wt.%). As a result, high Sr content and 87Sr/86Sr ratios may be indices (though not definitive proofs) of carbonatite metasomatism in mantle rocks.
