Fluorocarbonate is one of the most important RE minerals in the earth With the increment model developed by Zheng, oxygen isotope fractionation of RE fluorocarbonates is discussed and the 18 O enrichment orde...Fluorocarbonate is one of the most important RE minerals in the earth With the increment model developed by Zheng, oxygen isotope fractionation of RE fluorocarbonates is discussed and the 18 O enrichment order is obtained as follows: bastnaesite>cordylite>Ca 0 5 BaCe 2(CO 3) 4F>baiyuneboite>huangheite>cebaite Combining with the calculated equation, the oxygen isotopic compositions in RE fluorocarbonate from Bayan Obo ore deposit is discussed, and a better accordance of 18 O enrichment order with actual data on ore forming temperature with the ore deposit geology are found Because Ba RE fluorocarbonate could be considered as a stacking of CeCO 3F and BaCO 3 layers in the direction c , oxygen isotope fractionation in this stacking is discussed, and I in zhonghuacerite and cordylite is predicted with this model展开更多
The oxygen isotope fractionation equations are calculated for major rare earth oxide minerals by using an increment model. The effects of the variation of RE composition, the isomorphic replacement of Ti 4+ , Nb ...The oxygen isotope fractionation equations are calculated for major rare earth oxide minerals by using an increment model. The effects of the variation of RE composition, the isomorphic replacement of Ti 4+ , Nb 5+ , Ta 5+ , and Th 4+ and the metamictization on the oxygen isotope fractionation in minerals are also discussed. The rare earth oxides are not applicable for geothermometry due to their changeable oxygen isotope fractionation coefficients.展开更多
The increment method is adopted to calculate oxygen isotope fractionation factors for mantle minerals, particularly for the polymorphic phases of MgSiO3 and Mg2SiO4. The results predict the following sequence of18O-en...The increment method is adopted to calculate oxygen isotope fractionation factors for mantle minerals, particularly for the polymorphic phases of MgSiO3 and Mg2SiO4. The results predict the following sequence of18O-enrichment:pyroxene (Mg, Fe, Ca)2Si2O6>olivine (Mg, Fe)2SiO4 > spinel (Mg, Fe)2SiO4> ilmenite (Mg, Fe, Ca) SiO3>perovskite (Mg, Fe, Ca) SiO3. The calculated fractionations for the calcite-perovskite (CaTiO3) System are in excellent agreement with the experimental calibrations. If there would be complete isotopic equilibration in the mantle, the spinel-structured silicates in the transition zone are predicted to be enriched in18O relative to the perovskite-structured silicates in the lower mantle but depleted in18O relative to olivines and pyroxenes in the upper mantle. The oxygen isotope layering of the mantle might result from differences in the chemical composition and crystal structure of mineral phases at different mantle depths. Assuming isotopic equilibrium on a whole earth scale, the chemical structure of the Earth’s interior can be described by the following sequence of18O-enrichment:upper crust>lower crust>upper mantle>transition zone>lower mantle>core.展开更多
This study evaluated the Cretaceous(Campanian–Maastrichtian) kaolinitic sediments of the Ajali/Mamu and Enugu/Nkporo Formations from the Lower Benue Trough of Nigeria. A combined method of inductively coupled plasma...This study evaluated the Cretaceous(Campanian–Maastrichtian) kaolinitic sediments of the Ajali/Mamu and Enugu/Nkporo Formations from the Lower Benue Trough of Nigeria. A combined method of inductively coupled plasma–mass spectrometry and isotope ratio mass spectrometry was used to investigate trace and rareearth element geochemistry and hydrogen and oxygen isotopic compositions. These data were then used to infer the sediments' provenance and paleoclimatic conditions during their deposition. The sediments contained low concentrations of most trace elements, with the exceptions of Zr(651–1352 ppm), Ba(56–157 ppm), V(38–90 ppm),and Sr(15.1–59.6 ppm). Average values of Co and Ni were1.5 and 0.7 ppm, respectively. Trace and rare earth element values were lower than corresponding values for upper continental crust and Post-Archean Australian Shale, with the exception of Zr. The samples showed only slight light rare-earth enrichment and nearly flat heavy rare-earth depletion patterns, with negative Eu and Tm anomalies,typical of felsic sources. Geochemical parameters such as La/Sc, Th/Sc, and Th/Co ratios support that the kaolinitic sediments were derived from a felsic rock source, likely deposited in an oxic environment.^(18 )O values ranged from+ 15.4 to + 21.2% for the investigated samples, consistent with a residual material derived from chemicalweathering of felsic rock and redeposited in a sedimentary basin(typical values of + 19 to + 21.2%). While in the basin, the sediments experienced extended interactions with meteoric water enriched in d D and d16 O. However,the variation in d D and d16 O values for the investigated samples is attributed to the high temperature of formation(54–91 °C). The d D and d^(18 )O values suggest that the sediments, although obtained from different localities within the Lower Benue Trough, formed under similar hot,tropical climatic conditions.展开更多
文摘Fluorocarbonate is one of the most important RE minerals in the earth With the increment model developed by Zheng, oxygen isotope fractionation of RE fluorocarbonates is discussed and the 18 O enrichment order is obtained as follows: bastnaesite>cordylite>Ca 0 5 BaCe 2(CO 3) 4F>baiyuneboite>huangheite>cebaite Combining with the calculated equation, the oxygen isotopic compositions in RE fluorocarbonate from Bayan Obo ore deposit is discussed, and a better accordance of 18 O enrichment order with actual data on ore forming temperature with the ore deposit geology are found Because Ba RE fluorocarbonate could be considered as a stacking of CeCO 3F and BaCO 3 layers in the direction c , oxygen isotope fractionation in this stacking is discussed, and I in zhonghuacerite and cordylite is predicted with this model
文摘The oxygen isotope fractionation equations are calculated for major rare earth oxide minerals by using an increment model. The effects of the variation of RE composition, the isomorphic replacement of Ti 4+ , Nb 5+ , Ta 5+ , and Th 4+ and the metamictization on the oxygen isotope fractionation in minerals are also discussed. The rare earth oxides are not applicable for geothermometry due to their changeable oxygen isotope fractionation coefficients.
文摘The increment method is adopted to calculate oxygen isotope fractionation factors for mantle minerals, particularly for the polymorphic phases of MgSiO3 and Mg2SiO4. The results predict the following sequence of18O-enrichment:pyroxene (Mg, Fe, Ca)2Si2O6>olivine (Mg, Fe)2SiO4 > spinel (Mg, Fe)2SiO4> ilmenite (Mg, Fe, Ca) SiO3>perovskite (Mg, Fe, Ca) SiO3. The calculated fractionations for the calcite-perovskite (CaTiO3) System are in excellent agreement with the experimental calibrations. If there would be complete isotopic equilibration in the mantle, the spinel-structured silicates in the transition zone are predicted to be enriched in18O relative to the perovskite-structured silicates in the lower mantle but depleted in18O relative to olivines and pyroxenes in the upper mantle. The oxygen isotope layering of the mantle might result from differences in the chemical composition and crystal structure of mineral phases at different mantle depths. Assuming isotopic equilibrium on a whole earth scale, the chemical structure of the Earth’s interior can be described by the following sequence of18O-enrichment:upper crust>lower crust>upper mantle>transition zone>lower mantle>core.
文摘This study evaluated the Cretaceous(Campanian–Maastrichtian) kaolinitic sediments of the Ajali/Mamu and Enugu/Nkporo Formations from the Lower Benue Trough of Nigeria. A combined method of inductively coupled plasma–mass spectrometry and isotope ratio mass spectrometry was used to investigate trace and rareearth element geochemistry and hydrogen and oxygen isotopic compositions. These data were then used to infer the sediments' provenance and paleoclimatic conditions during their deposition. The sediments contained low concentrations of most trace elements, with the exceptions of Zr(651–1352 ppm), Ba(56–157 ppm), V(38–90 ppm),and Sr(15.1–59.6 ppm). Average values of Co and Ni were1.5 and 0.7 ppm, respectively. Trace and rare earth element values were lower than corresponding values for upper continental crust and Post-Archean Australian Shale, with the exception of Zr. The samples showed only slight light rare-earth enrichment and nearly flat heavy rare-earth depletion patterns, with negative Eu and Tm anomalies,typical of felsic sources. Geochemical parameters such as La/Sc, Th/Sc, and Th/Co ratios support that the kaolinitic sediments were derived from a felsic rock source, likely deposited in an oxic environment.^(18 )O values ranged from+ 15.4 to + 21.2% for the investigated samples, consistent with a residual material derived from chemicalweathering of felsic rock and redeposited in a sedimentary basin(typical values of + 19 to + 21.2%). While in the basin, the sediments experienced extended interactions with meteoric water enriched in d D and d16 O. However,the variation in d D and d16 O values for the investigated samples is attributed to the high temperature of formation(54–91 °C). The d D and d^(18 )O values suggest that the sediments, although obtained from different localities within the Lower Benue Trough, formed under similar hot,tropical climatic conditions.
