Subduction zone fluids: Chemistry of saline fluids transferring from the ocean to the mantle wedge through the downgoing slab

2015 Fiscal Year Final Research Report

• Project/Area Number: 24340134
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Partial Multi-year Fund
• Section: 一般
• Research Field: Petrology/Mineralogy/Science of ore deposit
• Research Institution: Kyoto University
• Principal Investigator: Kawamoto Tatsuhiko 京都大学, 理学(系)研究科(研究院), 助教 (00303800)
• Co-Investigator(Kenkyū-buntansha): MIBE KENJI 東京大学, 地震研究所, 助教 (10372426) ; YAMAMOTO JUNJI 北海道大学, 総合博物館, 准教授 (60378536) ; ISHIMARU SATOKO 熊本大学, 大学院自然科学研究科, 助教 (60464046)
• Project Period (FY): 2012-04-01 – 2016-03-31
• Keywords: 沈み込み帯 / 水流体 / マグマ / 海水 / 塩水 / 二酸化炭素 / 元素分配 / 高温高圧実験

Outline of Final Research Achievements

1) The inclusions in the Ichinomegata amphibole bearing spinel plagioclase lherzolite xenoliths were found to be composed mainly of CO2-H2O-Cl-S fluids. The salinity of fluid inclusions is 3.7±0.8 wt% NaCl equivalent. The salinity of aqueous fluid inclusions in jadeite-rich rocks in supra subduction zone is 4.3 wt% NaCl equivalent.
2) Partitioning of large ion lithophile elements between aqueous fluids and melts was measured using in-situ synchrotron x-ray fluorescence (XRF) from aqueous fluids and silicate melts at high-temperature and high-pressure conditions. We found a positive correlation between partition coefficients and pressure, as well as between partition coefficients and salinity. Enrichment of large ion lithophile elements in arc basalts relative to mid oceanic ridge basalts has been attributed to the mantle source fertilization by aqueous fluids from dehydrating oceanic plate. Such aqueous fluids are likely to contain Cl, although their amount remains to be quantified.

Free Research Field

固体地球惑星科学