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Dmitri A. Ionov - One of the best experts on this subject based on the ideXlab platform.
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carbonate bearing mantle peridotite xenoliths from spitsbergen phase relationships mineral compositions and trace element residence
Contributions to Mineralogy and Petrology, 1996Co-Authors: Dmitri A. Ionov, Yury S Genshaft, M G KopylovaAbstract:Carbonates of mantle origin have been found in xenoliths from Quaternary basaltic volcanoes in NW Spitsbergen. The Carbonates range from dolomite to Mg-bearing calcite and have high Mg-numbers [Mg/(Mg+Fe)=(0.92–0.99)]. In some samples they occur interstitially, e.g. at triple junctions of silicate minerals and appear to be in textural and chemical equilibrium with host lherzolite. Most commonly, however, the Carbonates make up fine-grained aggregates together with (Ca,Mg)-rich olivine and (Al,Cr,Ti)-rich clinopyroxene that typically replace spinel, amphibole, and orthopyroxene as well as primary clinopyroxene and olivine. Some lherzolites contain amphibole and apatite that appear to have formed before precipitation of the Carbonates. In situ analyses by proton microprobe show very high contents of Sr in the clinopyroxene, Carbonates and apatite; the apatite is also very rich in LREE, U, Th, Cl, Br. Disseminated amphibole in carbonate-bearing rocks is very poor in Nb and Zr, in contrast to vein amphibole and mica from carbonate-free rocks that are rich in Nb and Zr. Overall, the Spitsbergen xenoliths provide evidence both for the occurrence of primary carbonate in apparent equilibrium with the spinel lherzolites (regardless of the nature of events that emplaced them) and for the formation of carbonate-bearing pockets consistent with metasomatism by carbonate melts. Calcite and amorphous carbonate-rich materials occur in com- posite carbonate-fluid inclusions, veins and partial melting zones that appear to be related to fluid action in the mantle, heating of the xenoliths during their entrainment in basaltic magma, and to decompression melting of the Carbonates. Magnesite is a product of secondary, post-eruption alteration of the xenoliths.
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carbonated peridotite xenoliths from spitsbergen implications for trace element signature of mantle carbonate metasomatism
Earth and Planetary Science Letters, 1993Co-Authors: Dmitri A. Ionov, M G Kopylova, C. Dupuy, Suzanne Y Oreilly, Yury S GenshaftAbstract:Abstract Peridotite xenoliths from basaltic volcanics in NW Spitsbergen contain Carbonates of mantle origin. These occur as pockets of granular dolomite (Mg# 0.95–0.99) accompanied by fine-grained olivine and Al,Cr,Ti-rich clinopyroxene apparently produced by reaction of carbonate-rich fluids with the primary mineral assemblage of coarse spinel peridotites. Accessory apatite occurs in one sample. Most commonly, however, the Spitsbergen xenoliths contain patches and veins of quenched carbonate and silicate melts [1,2]. Our observations suggest that the mantle Carbonates melted shortly before or during the transport of the xenoliths to the surface, which also triggered local melting in the peridotites to produce a Na,Al-rich silicate glass. Four carbonate-bearing peridotite xenoliths were acid leached and the leachates, the residues after leaching and the bulk rocks were analysed for 25 trace elements by ICP-MS. The trace element inventory of the leachates is dominated by dissolved carbonate material. The leachates, and the bulk peridotites, show marked enrichment in LREE, Sr, Ba and Rb and are relatively depleted in Zr, Hf, Nb and Ta. In-situ analyses by proton microprobe show very high contents of Sr in clinopyroxenes, primary Carbonates and accessory apatite; the apatite is also very rich in LREE, U, Th and Br. Relative enrichment in LREE and Sr over HREE and HFSE appears to be characteristic of mantle Carbonates and carbonate-bearing peridotites. High Sr/Sm, Sm/Hf, La/Nb, Zr/Hf and Nb/Ta ratios in mantle peridotites (including basalt source regions) may be a signature of carbonate-related metasomatism.
Ralph P Harvey - One of the best experts on this subject based on the ideXlab platform.
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multi generational carbonate assemblages in martian meteorite allan hills 84001 implications for nucleation growth and alteration
Meteoritics & Planetary Science, 2004Co-Authors: C M Corrigan, Ralph P HarveyAbstract:The carbonate mineralogy of several complex carbonate-rich regions in Allan Hills (ALH) 84001 has been examined. These regions contain familiar forms of carbonate, as well as textural forms previously unreported including carbonate rosettes, planiform "slab" Carbonates, distinct "post-slab" magnesites, and Carbonates interstitial to feldspathic glass and orthopyroxene. Slab Carbonates reveal portions of the carbonate growth sequence not seen in the rosettes and suggest that initial nucleating compositions were calcite-rich. The kinetically controlled growth of rosettes and slab Carbonates was followed by an alteration event that formed the magnesite-siderite layers on the exterior surfaces of the carbonate. Post-slab magnesite, intimately associated with silica glass, is compositionally similar to the magnesite in these exterior layers but represents a later generation of carbonate growth. Feldspathic glasses had little or no thermal effect on Carbonates, as indicated by the lack of thermal decomposition or any compositional changes associated with glass/carbonate contacts.
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evidence for a second generation of magnesite in martian meteorite allan hills 84001
2003Co-Authors: C M Corrigan, Ralph P HarveyAbstract:Single-stage formation mechanisms for carbonate and other secondary minerals in ALH84001 are rapidly being revised to include multiple stages of carbonate growth and later thermal and mechanical events including alteration. In an effort to confirm some of these more complex histories we have been studying carbonate-bearing regions within this meteorite. Magnesitic Carbonates found in contact with unique 'slab' Carbonates in two thin sections of ALH84001 show indications of being of a later generation. The results of our observations help clarify the origins of the carbonate and related minerals in ALH84001, and how these minerals can be used to understand the history of interactions between the martian crust and its volatile inventory.
Didier Bernacheassollant - One of the best experts on this subject based on the ideXlab platform.
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processing of ab type carbonated hydroxyapatite ca10 x po4 6 x co3 x oh 2 x 2y co3 y ceramics with controlled composition
Journal of The European Ceramic Society, 2008Co-Authors: J P Lafon, Eric Champion, Didier BernacheassollantAbstract:Abstract This work is devoted to the preparation of carbonated calcium phosphate apatites. The aim was to produce dense ceramics containing various and precisely controlled amounts of carbonate ions partially substituting either for phosphate (B-type apatites) or for hydroxide ions (A-type apatites). Powders were synthesized by a wet chemical process in aqueous media. Heating carbonated powders above 600 °C in air or neutral atmosphere led to their thermal decomposition. A CO 2 gas partial pressure of 50 kPa in the atmosphere stabilized the carbonated apatites up to temperatures allowing their sintering. But, CO 2 gas induced a carbonation of hydroxide sites (A-site) that was detrimental to the sintering. A low partial pressure of water vapour in the atmosphere proved to be efficient to control A-site carbonation and indirectly favoured the sintering. Dense ceramics made of single phased apatite Ca 10− x (PO 4 ) 6− x (CO 3 ) x (OH) 2− x −2 y (CO 3 ) y , with 0 ≤ x ≤ 1.1 and 0 ≤ y ≤ 0.2 could be produced. The value of x (B-type Carbonates) was controlled by the synthesis process and the value of y (A-type Carbonates) by the sintering atmosphere.
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processing of ab type carbonated hydroxyapatite ca10 x po4 6 x co3 x oh 2 x 2y co3 y ceramics with controlled composition
Journal of The European Ceramic Society, 2008Co-Authors: J P Lafon, Eric Champion, Didier BernacheassollantAbstract:This work is devoted to the preparation of carbonated calcium phosphate apatites. The aim was to produce dense ceramics containing various and precisely controlled amounts of carbonate ions partially substituting either for phosphate (B-type apatites) or for hydroxide ions (A-type apatites). Powders were synthesized by a wet chemical process in aqueous media. Heating carbonated powders above 600 degrees C in air or neutral atmosphere led to their thermal decomposition. A CO2 gas partial pressure of 50 kPa in the atmosphere stabilized the carbonated apatites up to temperatures allowing their sintering. But, CO2 gas induced a carbonation of hydroxide sites (A-site) that was detrimental to the sintering. A low partial pressure of water vapour in the atmosphere proved to be efficient to control A-site carbonation and indirectly favoured the sintering. Dense ceramics made of single phased apatite Ca10-x(PO4)(6-x)(CO3)(x)(OH)(2-x-2y)(CO3)(y), with 0 <= x <= 1.1 and 0 <= y <= 0.2 could be produced. The value of x (B-type Carbonates) was controlled by the synthesis process and the value of y (A-type Carbonates) by the sintering atmosphere.
Akira Yamaguchi - One of the best experts on this subject based on the ideXlab platform.
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Carbonates in fractures of martian meteorite allan hills 84001 petrologic evidence for impact origin
Meteoritics & Planetary Science, 1998Co-Authors: E Scott, Alexander N Krot, Akira YamaguchiAbstract:Carbonates in Martian meteorite Allan Hills 84001 occur as grains on pyroxene grain boundaries, in crushed zones, and as disks, veins, and irregularly shaped grains in healed pyroxene fractures. Some carbonate disks have tapered Mg-rich edges and are accompanied by smaller, thinner and relatively homogeneous, magnesite microdisks. Except for the microdisks, all types of carbonate grains show the same unique chemical zoning pattern on MgCO3-FeCO3-CaCO3 plots. This chemical characteristic and the close spatial association of diverse carbonate types show that all Carbonates formed by a similar process. The heterogeneous distribution of Carbonates in fractures, tapered shapes of some disks, and the localized occurrence of Mg-rich microdisks appear to be incompatible with growth from an externally derived CO2-rich fluid that changed in composition over time. These features suggest instead that the fractures were closed as Carbonates grew from an internally derived fluid and that the microdisks formed from a residual Mg-rich fluid that was squeezed along fractures. Carbonate in pyroxene fractures is most abundant near grains of plagioclase glass that are located on pyroxene grain boundaries and commonly contain major or minor amounts of carbonate. We infer that Carbonates in fractures formed from grain boundary Carbonates associated with plagiociase that were melted by impact and dispersed into the surrounding fractured pyroxene. Carbonates in fractures, which include those studied by McKay et al. (1996), could not have formed at low temperatures and preserved mineralogical evidence for Martian organisms.
Rajdeep Dasgupta - One of the best experts on this subject based on the ideXlab platform.
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The effect of Carbonates on near-solidus melting of pelite at 3 GPa: Relative efficiency of H2O and CO2 subduction
Earth and Planetary Science Letters, 2012Co-Authors: Kyusei Tsuno, Rajdeep DasguptaAbstract:The melting systematics of subducting sediments are important for the cycling of H2O and CO2 to the arc system and to the deep mantle. Several studies have explored melting phase relations of pelitic sediments under wet conditions. However, experiments with mixed COH volatiles, especially under nominally vapor-absent or vapor-poor conditions remain insufficiently investigated. Here we have studied the melting phase relations of water vapor-poor (HPLH1: 1 wt.% bulk H2O), and vapor-poor, carbonated (HPLC2: 1 wt.% bulk H2O and 5 wt.% bulk CO2) pelitic sediments at a single pressure of 3 GPa and temperatures between 770 and 1150 °C. Both the compositions contain trace amount of vapor at subsolidus conditions. For HPLH1, the solidus is ≤ 770 °C, and at 770–800 °C trace hydrous melt is present along with clinopyroxene, garnet, coesite, rutile, and phengite and the complete breakdown of phengite and the appearance of feldspar are observed at 850 °C. For HPLC2, subsolidus phases at 800 °C include clinopyroxene, garnet, coesite, rutile, phengite, and calcitess; the solidus is located between 800 and 850 °C, where the appearance of melt is accompanied by the appearance of feldspar. The melt at near-solidus temperature is rhyodacite for both starting materials, and mass proportion of silicate melt for HPLH1 is higher than that for HPLC2. Comparison of our results with that of a previous study on dry, carbonated metapelite (HPLC1: 5 wt.% bulk CO2), shows the solidus temperature for HPLH1 is the lowest, and that for HPLC1 is the highest of the three starting compositions. The presence of carbonate increases the temperatures of the vapor-present solidus and phengite-out boundary of pelitic sediment, and the addition of water decreases the solidus and the carbonate-out boundary of dry, carbonated pelitic sediment. Comparison of carbonate-free, vapor-poor pelite melting with top-slab P–T paths shows that the phengite-out boundary is encountered in intermediate to hot subductions. This suggests that the deep recycling of water for intermediate to hot subduction may be limited if trace vapor ingress occurs. However, the solidus and phengite-out boundary of vapor-poor pelite are elevated by as much as ~ 50–100 °C in the presence of Carbonates and the complete breakdown of phengite can only occur along the hottest slab–top P–T trajectories for carbonated bulk compositions. The carbonate-out boundary is also located above the hottest estimate of slab–top conditions. This suggests that in mixed COH vapor-poor sediment compositions, most phengite and crystalline carbonate are likely recycled into the deep mantle. One possible scenario for transporting sedimentary carbon from vapor-poor pelite into the arc is via the formation of sediment diapirs, which owing to their low density, will rise to the hotter mantle wedge and undergo partial melting and liberate CO2.
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Melting phase relation of nominally anhydrous, carbonated pelitic-eclogite at 2.5–3.0 GPa and deep cycling of sedimentary carbon
Contributions to Mineralogy and Petrology, 2011Co-Authors: Kyusei Tsuno, Rajdeep DasguptaAbstract:We have experimentally investigated melting phase relation of a nominally anhydrous, carbonated pelitic eclogite (HPLC1) at 2.5 and 3.0 GPa at 900–1,350°C in order to constrain the cycling of sedimentary carbon in subduction zones. The starting composition HPLC1 (with 5 wt% bulk CO_2) is a model composition, on a water-free basis, and is aimed to represent a mixture of 10 wt% pelagic carbonate unit and 90 wt% hemipelagic mud unit that enter the Central American trench. Sub-solidus assemblage comprises clinopyroxene + garnet + K-feldspar + quartz/coesite + rutile + calcio-ankerite/ankerite_ss. Solidus temperature is at 900–950°C at 2.5 GPa and at 900–1,000°C at 3.0 GPa, and the near-solidus melt is K-rich granitic. Crystalline Carbonates persist only 50–100°C above the solidus and at temperatures above carbonate breakdown, carbon exists in the form of dissolved CO_2 in silica-rich melts and as a vapor phase. The rhyodacitic to dacitic partial melt evolves from a K-rich composition at near-solidus condition to K-poor, and Na- and Ca-rich composition with increasing temperature. The low breakdown temperatures of crystalline carbonate in our study compared to those of recent studies on carbonated basaltic eclogite and peridotite owes to Fe-enrichment of Carbonates in pelitic lithologies. However, the conditions of carbonate release in our study still remain higher than the modern depth-temperature trajectories of slab-mantle interface at sub-arc depths, suggesting that the release of sedimentary Carbonates is unlikely in modern subduction zones. One possible scenario of carbonate release in modern subduction zones is the detachment and advection of sedimentary piles to hotter mantle wedge and consequent dissolution of carbonate in rhyodacitic partial melt. In the Paleo-NeoProterozoic Earth, on the other hand, the hotter slab-surface temperatures at subduction zones likely caused efficient liberation of carbon from subducting sedimentary Carbonates. Deeply subducted carbonated sediments, similar to HPLC1, upon encountering a hotter mantle geotherm in the oceanic province can release carbon-bearing melts with high K_2O, K_2O/TiO_2, and high silica, and can contribute to EM2-type ocean island basalts. Generation of EM2-type mantle end-member may also occur through metasomatism of mantle wedge by carbonated metapelite plume-derived partial melts.
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The effect of bulk composition on the solidus of carbonated eclogite from partial melting experiments at 3 GPa
Contributions to Mineralogy and Petrology, 2005Co-Authors: Rajdeep Dasgupta, Nikki DellasAbstract:To explore the effect of bulk composition on the solidus of carbonated eclogite, we determined near-solidus phase relations at 3 GPa for four different nominally anhydrous, carbonated eclogites. Starting materials (SLEC1, SLEC2, SLEC3, and SLEC4) were prepared by adding variable proportions and compositions of carbonate to a natural eclogite xenolith (66039B) from Salt Lake crater, Hawaii. Near-solidus partial melts for all bulk compositions are Fe–Na calcio-dolomitic and coexist with garnet + clinopyroxene + ilmenite ± calcio-dolomitic solid solution. The solidus for SLEC1 (Ca#=100 × molar Ca/(Ca + Mg + Fe_T)=32, 1.63 wt% Na_2O, and 5 wt% CO_2) is bracketed between 1,050°C and 1,075°C (Dasgupta et al. in Earth Planet Sci Lett 227:73–85, 2004), whereas initial melting for SLEC3 (Ca# 41, 1.4 wt% Na_2O, and 4.4 wt% CO_2) is between 1,175°C and 1,200°C. The solidus for SLEC2 (Ca# 33, 1.75 wt% Na_2O, and 15 wt% CO_2) is estimated to be near 1,100°C and the solidus for SLEC3 (Ca# 37, 1.47 wt% Na_2O, and 2.2 wt% CO_2) is between 1,100°C and 1,125°C. Solidus temperatures increase with increasing Ca# of the bulk, owing to the strong influence of the calcite–magnesite binary solidus-minimum on the solidus of carbonate bearing eclogite. Bulk compositions that produce near-solidus crystalline carbonate closer in composition to the minimum along the CaCO_3-MgCO_3 join have lower solidus temperatures. Variations in total CO_2 have significant effect on the solidus if CO_2 is added as CaCO_3, but not if CO_2 is added as a complex mixture that maintains the cationic ratios of the bulk-rock. Thus, as partial melting experiments necessarily have more CO_2 than that likely to be found in natural carbonated eclogites, care must be taken to assure that the compositional shifts associated with excess CO_2 do not unduly influence melting behavior. Near-solidus dolomite and calcite solid solutions have higher Ca/(Ca + Mg) than bulk eclogite compositions, owing to Ca–Mg exchange equilibrium between Carbonates and silicates. Carbonates in natural mantle eclogite, which have low bulk CO_2 concentration, will have Ca/Mg buffered by reactions with silicates. Consequently, experiments with high bulk CO_2 may not mimic natural carbonated eclogite phase equilibria unless care is taken to ensure that CO_2 enrichment does not result in inappropriate equilibrium carbonate compositions. Compositions of eclogite-derived carbonate melt span the range of natural carbonatites from oceanic and continental settings. Ca#s of carbonatitic partial melts of eclogite vary significantly and overlap those of partial melts of carbonated lherzolite, however, for a constant Ca-content, Mg# of carbonatites derived from eclogitic sources are likely to be lower than the Mg# of those generated from peridotite.
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deep global cycling of carbon constrained by the solidus of anhydrous carbonated eclogite under upper mantle conditions
Earth and Planetary Science Letters, 2004Co-Authors: Rajdeep Dasgupta, Anthony C WithersAbstract:Abstract We present partial melting experiments that constrain the near solidus phase relations of carbonated eclogite from 2 to 8.5 GPa. The starting material was prepared by adding 5 wt.% CO2 in the form of a mixture of Fe–Mg–Ca–Na–K Carbonates to an eclogite from Salt Lake crater, Oahu, Hawaii and is a reasonable approximation of carbonated oceanic crust from which siliceous hydrous fluids have been extracted during subduction. Melt-present versus melt-absent conditions are distinguished based on textural criteria. Garnet and clinopyroxene appear in all the experiments. Between 2 and 3 GPa, the subsolidus assemblage also includes ilmenite±calcio-dolomitess±CO2, whereas above the solidus (1050–1075 °C at 3 GPa) calcio-dolomitic liquid appears. From 3 to 4.5 GPa, dolomitess is stable at the solidus and the near-solidus melt becomes increasingly dolomitic. The appearance of dolomite above 3 GPa is accompanied by a negative Clapeyron slope of the solidus, with a minimum located between 995 and 1025 °C at ca. 4 GPa. Above 4 GPa, the solidus rises with increasing pressure to 1245±35 °C at 8.5 GPa and magnesite becomes the subsolidus carbonate. Dolomitic melt coexists with magnesite+garnet+cpx+rutile along the solidus from 5 to 8.5 GPa. Comparison of our results to other recent experimental studies [T. Hammouda, High-pressure melting of carbonated eclogite and experimental constraints on carbon recycling and storage in the mantle, Earth Planet. Sci. Lett. 214 (2003) 357–368; G.M. Yaxley, G.P. Brey, Phase relations of carbonate-bearing eclogite assemblages from 2.5 to 5.5 GPa: implications for petrogenesis of carbonatites, Contrib. Mineral. Petrol. 146 (2004) 606–619] shows that carbonate minerals are preserved in anhydrous or slightly hydrous carbonated eclogite to temperatures >1100 and >1200 °C at 5 and 9 GPa, respectively. Thus, deep subduction of carbonate is expected along any plausible subduction geotherm. If extrapolated to higher pressures, the carbonated eclogite solidus is likely to intersect the oceanic geotherm at a depth close to 400 km. Carbonated eclogite bodies entering the convecting upper mantle will thus release carbonate melt near the top of the mantle transition zone and may account for anomalously slow seismic velocities at depths of 280–400 km. Upon release, this small volume, highly reactive melt could be an effective agent of deep mantle metasomatism. Comparison of the carbonated eclogite solidus with that of peridotite-CO2 shows a shallower solidus–geotherm intersection for the latter. This implies that carbonated peridotite is a more likely proximal source of magmatic carbon in oceanic provinces. However, carbonated eclogite is a potential source of continental carbonatites, as its solidus crosses the continental shield geotherm at ca. 4 GPa. Transfer of eclogite-derived carbonate melt to peridotite may account for the geochemical characteristics of some oceanic island basalts (OIBs) and their association with high CaO and CO2.
