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Weibiao Hsu - One of the best experts on this subject based on the ideXlab platform.
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Rare Earth Element geochemistry and petrogenesis of miles (IIE) silicate inclusions
Geochimica et Cosmochimica Acta, 2003Co-Authors: Weibiao HsuAbstract:An ion probe study of Rare Earth Element (REE) geochemistry of silicate inclusions in the Miles HE iron meteorite was carried out. Individual mineral phases among inclusions have distinct REE patterns and abundances. Most silicate grains have homogeneous REE abundances but show considerable intergrain variations between inclusions. A few pyroxene grains display normal igneous REE zoning. Phosphates (whitlockite and apatite) are highly enriched in REEs (50 to 2000 X CI) with a relatively light Rare Earth Element (LREE)-enriched REE pattern. They usually occurred near the interfaces between inclusions and Fe host. In Miles, albitic glasses exhibit two distinctive REE patterns: a highly fractionated LREE-enriched (CI normalized La/Sm similar to 15) pattern with a large positive Eu anomaly and a relatively heavy Rare Earth Element (HREE)-enriched pattern (CI-normalized Lu/Gd similar to4) with a positive Eu anomaly and a negative Yb anomaly. The glass is generally depleted in REEs relative to CI chondrites.
Shaojun Dong - One of the best experts on this subject based on the ideXlab platform.
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The direct electrochemistry of cytochrome c at the nanometer-sized Rare Earth Element oxide particle-modified gold electrodes
Journal of Molecular Catalysis A: Chemical, 1996Co-Authors: Xiangting Dong, Ziyong Cheng, Shaojun DongAbstract:The direct electrochemistry of cytochrome c was studied at nanometer-sized Rare Earth Element dioxide particle-modified gold electrodes. It was demonstrated that Rare Earth Element oxides can accelerate the electrochemical reaction of cytochrome c and the reversibility of the electrochemical reaction of cytochrome c was related to the size of Rare Earth Element oxide particles.
Jianxin Zhao - One of the best experts on this subject based on the ideXlab platform.
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Rare Earth Element geochemistry of scleractinian coral skeleton during meteoric diagenesis a sequence through neomorphism of aragonite to calcite
Sedimentology, 2009Co-Authors: Gregory E Webb, Luke D Nothdurft, Balz S Kamber, J T Kloprogge, Jianxin ZhaoAbstract:Rare Earth Element geochemistry in carbonate rocks is utilized increasingly for studying both modern oceans and palaeoceanography, with additional applications for investigating water–rock interactions in groundwater and carbonate diagenesis. However, the study of Rare Earth Element geochemistry in ancient rocks requires the preservation of their distribution patterns through subsequent diagenesis. The subjects of this study, Pleistocene scleractinian coral skeletons from Windley Key, Florida, have undergone partial to complete neomorphism from aragonite to calcite in a meteoric setting; they allow direct comparison of Rare Earth Element distributions in original coral skeleton and in neomorphic calcite. Neomorphism occurred in a vadose setting along a thin film, with degradation of organic matter playing an initial role in controlling the morphology of the diagenetic front. As expected, minor Element concentrations vary significantly between skeletal aragonite and neomorphic calcite, with Sr, Ba and U decreasing in concentration and Mn increasing in concentration in the calcite, suggesting that neomorphism took place in an open system. However, Rare Earth Elements were largely retained during neomorphism, with precipitating cements taking up excess Rare Earth Elements released from dissolved carbonates from higher in the karst system. Preserved Rare Earth Element patterns in the stabilized calcite closely reflect the original Rare Earth Element patterns of the corals and associated reef carbonates. However, minor increases in light Rare Earth Element depletion and negative Ce anomalies may reflect shallow oxidized groundwater processes, whereas decreasing light Rare Earth Element depletion may reflect mixing of Rare Earth Elements from associated microbialites or contamination from insoluble residues. Regardless of these minor disturbances, the results indicate that Rare Earth Elements, unlike many minor Elements, behave very conservatively during meteoric diagenesis. As the meteoric transformation of aragonite to calcite is a near worst case scenario for survival of original marine trace Element distributions, this study suggests that original Rare Earth Element patterns may commonly be preserved in ancient limestones, thus providing support for the use of ancient marine limestones as proxies for marine Rare Earth Element geochemistry.
M. Lesourd - One of the best experts on this subject based on the ideXlab platform.
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Strontium isotopes and Rare-Earth Element geochemistry of hydrothermal carbonate deposits from Lake Tanganyika, East Africa
Geochimica et Cosmochimica Acta, 2000Co-Authors: Jean-alix Barrat, Jacques Boulègue, Jean-jacques Tiercelin, M. LesourdAbstract:At Cape Banza (North Tanganyika Lake), fluids and aragonite chimneys have been collected many times since the discovery of this sublacustrine field in 1987. This sampling has been investigated here for the Sr isotopic compositions and the Rare-Earth Element features of the carbonates and a few fluid samples. The 87Sr/86Sr ratios of the chimneys indicate that they have precipitated from a mixture of lake water (more than 95%) and hydrothermal fluids. No zoning in the chimneys was detected with our Sr data. For the Rare-Earth Elements, the situation is more complex. The external walls of the chimneys are Rare-Earth-Element-poor (La ≈ 500 ppb, Yb ≈ 200 ppb, La/Yb = 2 to 3.4). Their shale normalised Rare-Earth Element patterns suggest that they are in equilibrium with the inferred carbonate-depositing fluids. The Rare-Earth Element concentrations of the internal walls of the chimneys are significantly light Rare Earth Elements (LREE)-enriched with La contents sometimes up to 5 ppm. We suggest that they contain more vent-fluid Rare-Earth Elements than the external wall samples, possibly adsorbed on the surface of growing crystals or simply hosted by impurities. It was not possible to constrain the nature of these phases, but the variations of the compositions of the internal wall materials of the active chimneys with time, as well as data obtained on an inactive chimney indicate that this Rare-Earth Element excess is mobile. Partition coefficients were calculated between the external wall aragonite and carbonate-depositing fluid. The results are strikingly similar to the values obtained by Sholkovitz and Shen (1995) on coral aragonite, and suggest that there is no significant biologic effect on the incorporation of Rare-Earth Elements into coral aragonite and that the various carbonate complexes involved Me(CO3+) complexes are the main LREE carriers in seawater (Cantrell and Byrne, 1987) instead of Me(CO3)2− in Banza fluids) have the same behaviour during aragonite precipitation.
Wolfgang Jeitschko - One of the best experts on this subject based on the ideXlab platform.
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equiatomic quaternary Rare Earth Element zinc pnictide oxides rznpo and rznaso
Inorganic Chemistry, 1998Co-Authors: Andre T Nientiedt, Wolfgang JeitschkoAbstract:The twelve phosphide oxides RZnPO (R = Y, La−Nd, Sm, Gd−Tm) and the nine arsenide oxides (R = Y, La−Nd, Sm, Gd−Dy) have been prepared by reaction of the Rare Earth Elements, ZnO, and phosphorus or arsenic, respectively, in a NaCl/KCl flux. The compounds RZnPO (R = Y, Pr, Nd, Sm, Gd−Tm) crystallize with a new trigonal rhombohedral structure type, determined from single-crystal X-ray diffractometer data of NdZnPO: R3m, a = 397.7(1) pm, c = 3097.5(5) pm, Z = 6. The other eleven compounds are isotypic with ZrCuSiAs (P4/nmm, Z = 2). This tetragonal structure was refined from single-crystal X-ray data of LaZnPO (a = 404.0(1) pm, c = 890.8(2) pm) and NdZnAsO (a = 403.0(1) pm, c = 894.9(4) pm). In both structure types Rare Earth Element−oxygen layers alternate with zinc−pnictogen layers. The Rare Earth Element atoms have four oxygen and three (NdZnPO) or four (LaZnPO, NdZnAsO) pnictogen neighbors. The zinc atoms have tetrahedral pnictogen coordination. The arsenide oxides as well as the tetragonal phosphide oxi...
