Water content and lithium isotope fractionation in subduction-zone mantle olivine

2014 Fiscal Year Final Research Report

• Project/Area Number: 24540513
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Petrology/Mineralogy/Science of ore deposit
• Research Institution: Okayama University
• Principal Investigator: OTA Tsutomu 岡山大学, 地球物質科学研究センター, 助手 (80379817)
• Research Collaborator: MALFAIT WIM J. スイス連邦工科大学, 地球化学研究所, 上級研究員
• Project Period (FY): 2012-04-01 – 2015-03-31
• Keywords: リチウム / 同位体分別 / カンラン石 / 水流体 / 沈み込み帯 / 高温高圧実験 / 二次イオン質量分析計

Outline of Final Research Achievements

In terms of lithium (Li) isotope fractionation between mantle olivine and aqueous fluid, we examined an interaction between mantle and surficial material, which has strongly affected the earth’s chemical evolution.
Combining an experimental study in a simple system with Li-isotope analysis of natural mantle olivine revealed that the mantle olivine yielded Li isotopic abundances that fractionated by an interaction with aqueous fluid is relatively enriched in hydrogen, compared with the less fractionated ones.
This result indicates that mantle materials that interacted with surficial materials have maintained their chemical characteristics including Li isotopic abundance, even under high temperature conditions in mantle on a geologic timescale. The mantle materials, interacted with surficial materials, have been transported back to the mantle by lithospheric plate subduction; such cycling has chemically differentiated the mantle and the surface, that is, the earth’s chemical evolution.

Free Research Field

岩石学、地球化学