2:30 PM - 2:45 PM
[SGC40-03] DH partitioning experiment among high-pressure polymorph of olivine
Keywords:mantle transition zone, olivine, wadsleyite, hydrogen isotope
The partitioning experiment was conducted using Kawai-type multianvil press at GRC, Ehime University. Powder of Mg(OH)2 and Mg(OD)2 was mixed with synthetic olivine so that the starting composition is equivalent to Mg1.8Fe0.2SiO4 + 1.0 wt.% HDO. The sample was sealed in the Au75Pd25 capsule and kept at 1300 °C and around 13 GPa, which is the condition of olivine and wadsleyite coexist. The recovered sample was polished and analyzed by micro-focused X-ray diffractometer, Raman spectroscopy and EPMA. Hydrogen isotope composition was determined using SIMS at Kyoto University.
To test for equilibrium, partitioning experiments are made with changing duration times from 1 h to 72 h. The fractionation factor decreases with increasing of duration time. After keeping for 30 h, 1000lnαOlivine-Wadsleyite seems to reach almost equilibrium around -60 ‰. Assuming that the δD of olivine of upper mantle to -80, the δD of wadsleyite at MTZ become -20 to 0, which is more comparable to the composition of the ocean. The present result shows that the depletion of deuterium of upper mantle can be explained as a result of DH fractionation between upper mantle and MTZ.
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