Hydrogen and oxygen isotope compositions of eclogites from the Dabie Mountains and geodynamic implications |
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Authors: | Yongfei Zheng Bin Fu Bing Gong Yilin Xiao Ningjie Ge Shuguang Li |
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Affiliation: | (1) Department of Earth and Space Sciences, University of Science and Technology of China, 230026 Hefei, China;(2) Advanced Center for Earth Science and Astronomy, The Third World Academy, University of Science and Technology of China, 230026 Hefei, China |
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Abstract: | Heterogeneous δ18O values as low as - 2.6‰ to+7.0% are observed for ultrahigh pressure eclogites from the Dabie Mountains in East China. Oxygen isotope equilibrium has been approached between the eclogite minerals, suggesting that the rocks would have acquired the unusual δ18O values prior to ultrahigh pressure metamorphism by interaction with18O-depleted fluid. δD values of hydroxyl-bearing are between — 51% and - 83‰, precluding the possibility of paleoseawater involvement. The only likely fluid is ancient meteoric water that exchanged oxygen isotopes with the eclogite precursor (a kind of basaltic rocks) formerly resident on the continental crust. This suggests a crustal recycling process in the suture zone of late subduction. Because silicate minerals undergo rapid oxygen isotope exchange at mantle pressures, preservation of the isotopic signature of meteoric water in the eclogites indicates limited crust-mantle interaction and thus a short residence time (<20 Ma) when the plate containing the eclogite precursor was subducted to mantle depths. The agreement in oxygen isotope temperatures for different mineral pairs suggests a rapid cooling and ascent process for the eclogites subsequent to their formation at mantle depths. Project supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences. |
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Keywords: | ultrahigh pressure eclogite meteoric water oxygen isotopes hydrogen isotopes geodynamies the Dabie Mountains |
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