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Zircon Lu-Hf and U-Pb isotopic compositions in ultrahigh-pressure eclogite from Dabie orogen, Eastern Central China
Goldschmidt Conference Abstract 2006
Fractionation of Cu, Zn and Fe within the plant–soil environment J.B. CHAPMAN1, K. PEEL1, T. ARNOLD1, J.J. WILKINSON1,2, B.J. COLES1,2, D.J. WEISS1,2 1
Department of Earth Science and Engineering, Imperial College London, South Kensington, London SW7 2AZ, UK ([email protected]) 2 Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5PD, UK The isotope systematics of transition elements offer exiting possibilities to study nutrient cycling in ecosystems and various biogeochemcial processes such as plant uptake. Also possible applications such as screening rice genotypes or tracing of pollutant sources are of great interest. However, a thorough quantitative and qualitative understanding of the various mechanisms that lead to fractionation in the low temperature environment is needed beforehand. Equally key is the development of analytical methods for accurate and high precision isotope ratio measurements in a wide variety of sample types, but particularly for organic samples. We improved the quality of isotopic measurements of Fe, Cu and Zn in a wide variety of challenging matrixes including plants and silicates using a combination of wet and dry ashing, acid digestion and anion exchange chromatography. We obtain clean Fe, Zn and Cu fractions from both matrix types and achieved precisions for d66Zn, d65Cu and d56Fe below ±0.1& in all matrixes using standard-sample bracketing and an IsoProbe MC-ICP-MS. We investigated isotopic fractionation of Fe and Cu during congruent and incongruent dissolution of granites and carbonates using well-constrained batch experiments. We leached malachite (Cu2(OH)2CO3) and commercially available reference granites (G-2 and GS-N) with aqueous solutions and variable pH. The results for malachite show negligible isotopic fractionation of Cu (D65Cu(Cu(II)(aq)–Cumalachite) = 0.03 ± 0.12 (1s, n = 16) during congruent dissolution and in absence of organic ligands. Temperature changes between 4 and 50 °C had no effect. In contrast, significant fractionation of Fe was observed in leached granite with d56Fe values up to 0.35& lighter in solution. This has important implications for the definition of the ‘bulk earth baseline’ (BEB) and for labile Fe in soil (pedogensis vs. plant uptake). Preliminary studies of Fe isotope ratios measured in different grass species showed different d56FeIRMM-014 values ( 0.365 and 0.095&, respectively) and are also significantly fractionated relative to the BEB. This could be, in light of the experimental findings of the leaching experiments, due to weathered labile Fe in the soil solution and/or the plant uptake itself. doi:10.1016/j.gca.2006.06.107
A97
Zircon Lu-Hf and U-Pb isotopic compositions in ultrahigh-pressure eclogite from Dabie orogen, Eastern Central China D. CHEN1, T. NI1, E. DELOULE2, B. LI1 1
School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China (dgchen@ustc. edu.cn) 2 CRPG-CNRS, Nancy 54501, France ([email protected]. fr) The application of Hf isotope in zircon has been well developed to trace rock origin and the evolution of crust and mantle. However, much less attention has been paid on Hf isotopic compositions of zircons presented at ultrahigh-pressure metamorphism. Here we report the combined in situ study of intragrain Lu–Hf and U–Pb isotopic compositions accomplished with CL imaging in zircons from eclogites at Shuanghe and Xingdian from Dabie orogen to understanding the metamorphic affect of Hf isotope compositions during ultrahigh-pressure eclogite-facies metamorphism. The results show systematic change and correlations among 206Pb/238U age, initial Hf isotopic compositions, Th/U and Lu/Hf ratios in zircons from different genetic domains. The metamorphic growth domains are characterized by low Th/ U(<0.1), low Lu/Hf(<0.0005) and low 206Pb/238U ages, but high 176 Hf/177Hf isotopic composition relative to the igneous core and mantle of pre-metamorphic ages. The low Lu/Hf and high initial eHf (t) value of metamorphic growth domain calculated at timing of protolith formation points that the overgrowth was associated with the addition of high 176Hf/177Hf but low 176 Lu/177Hf metamorphic medium. The positive correlation between Th/U and Lu/Hf ratios were observed, implying the similar effect of metamorphism on both U–Th–Pb and Lu–Hf system. Whereas the solid metamorphic re-crystallized domains of zircon have relative high Lu/Hf, low 176Hf/177Hf ratios, distinguished from metamorphic growth, but similar to inherited protolith cores. So, growth and re-crystallization of zircon are two completely different metamorphic processes.
Acknowledgements This research is financial supported by NSFC Grant No. 40573008 and SFRDP Grant No. 20040358050. doi:10.1016/j.gca.2006.06.108
Fractionation of Cu, Zn and Fe within the plant–soil environment J.B. CHAPMAN1, K. PEEL1, T. ARNOLD1, J.J. WILKINSON1,2, B.J. COLES1,2, D.J. WEISS1,2 1
Department of Earth Science and Engineering, Imperial College London, South Kensington, London SW7 2AZ, UK ([email protected]) 2 Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5PD, UK The isotope systematics of transition elements offer exiting possibilities to study nutrient cycling in ecosystems and various biogeochemcial processes such as plant uptake. Also possible applications such as screening rice genotypes or tracing of pollutant sources are of great interest. However, a thorough quantitative and qualitative understanding of the various mechanisms that lead to fractionation in the low temperature environment is needed beforehand. Equally key is the development of analytical methods for accurate and high precision isotope ratio measurements in a wide variety of sample types, but particularly for organic samples. We improved the quality of isotopic measurements of Fe, Cu and Zn in a wide variety of challenging matrixes including plants and silicates using a combination of wet and dry ashing, acid digestion and anion exchange chromatography. We obtain clean Fe, Zn and Cu fractions from both matrix types and achieved precisions for d66Zn, d65Cu and d56Fe below ±0.1& in all matrixes using standard-sample bracketing and an IsoProbe MC-ICP-MS. We investigated isotopic fractionation of Fe and Cu during congruent and incongruent dissolution of granites and carbonates using well-constrained batch experiments. We leached malachite (Cu2(OH)2CO3) and commercially available reference granites (G-2 and GS-N) with aqueous solutions and variable pH. The results for malachite show negligible isotopic fractionation of Cu (D65Cu(Cu(II)(aq)–Cumalachite) = 0.03 ± 0.12 (1s, n = 16) during congruent dissolution and in absence of organic ligands. Temperature changes between 4 and 50 °C had no effect. In contrast, significant fractionation of Fe was observed in leached granite with d56Fe values up to 0.35& lighter in solution. This has important implications for the definition of the ‘bulk earth baseline’ (BEB) and for labile Fe in soil (pedogensis vs. plant uptake). Preliminary studies of Fe isotope ratios measured in different grass species showed different d56FeIRMM-014 values ( 0.365 and 0.095&, respectively) and are also significantly fractionated relative to the BEB. This could be, in light of the experimental findings of the leaching experiments, due to weathered labile Fe in the soil solution and/or the plant uptake itself. doi:10.1016/j.gca.2006.06.107
A97
Zircon Lu-Hf and U-Pb isotopic compositions in ultrahigh-pressure eclogite from Dabie orogen, Eastern Central China D. CHEN1, T. NI1, E. DELOULE2, B. LI1 1
School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China (dgchen@ustc. edu.cn) 2 CRPG-CNRS, Nancy 54501, France ([email protected]. fr) The application of Hf isotope in zircon has been well developed to trace rock origin and the evolution of crust and mantle. However, much less attention has been paid on Hf isotopic compositions of zircons presented at ultrahigh-pressure metamorphism. Here we report the combined in situ study of intragrain Lu–Hf and U–Pb isotopic compositions accomplished with CL imaging in zircons from eclogites at Shuanghe and Xingdian from Dabie orogen to understanding the metamorphic affect of Hf isotope compositions during ultrahigh-pressure eclogite-facies metamorphism. The results show systematic change and correlations among 206Pb/238U age, initial Hf isotopic compositions, Th/U and Lu/Hf ratios in zircons from different genetic domains. The metamorphic growth domains are characterized by low Th/ U(<0.1), low Lu/Hf(<0.0005) and low 206Pb/238U ages, but high 176 Hf/177Hf isotopic composition relative to the igneous core and mantle of pre-metamorphic ages. The low Lu/Hf and high initial eHf (t) value of metamorphic growth domain calculated at timing of protolith formation points that the overgrowth was associated with the addition of high 176Hf/177Hf but low 176 Lu/177Hf metamorphic medium. The positive correlation between Th/U and Lu/Hf ratios were observed, implying the similar effect of metamorphism on both U–Th–Pb and Lu–Hf system. Whereas the solid metamorphic re-crystallized domains of zircon have relative high Lu/Hf, low 176Hf/177Hf ratios, distinguished from metamorphic growth, but similar to inherited protolith cores. So, growth and re-crystallization of zircon are two completely different metamorphic processes.
Acknowledgements This research is financial supported by NSFC Grant No. 40573008 and SFRDP Grant No. 20040358050. doi:10.1016/j.gca.2006.06.108