Japan Geoscience Union Meeting 2015

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Symbol S (Solid Earth Sciences) » S-RD Resources, Mineral Deposit & Resource Exploration

[S-RD41] Developments in resource geology: Origin and evolution of ore fluids

Mon. May 25, 2015 9:00 AM - 10:45 AM 106 (1F)

Convener:*Kenzo Sanematsu(Mineral Resource Research Group, Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology), Tatsuo Nozaki(Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology), Tsubasa Otake(Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University), Ryohei Takahashi(Faculty of International Resource Sciences, Akita University), Chair:Kenzo Sanematsu(Mineral Resource Research Group, Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology), Tatsuo Nozaki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology)

10:00 AM - 10:15 AM

[SRD41-04] Li isotopic composition of submarine vent fluids from arc and back-arc hydrothermal systems in the western Pacific

*Daisuke ARAOKA1, Yoshiro NISHIO2, Toshitaka GAMO3, Kyoko YAMAOKA4, Hodaka KAWAHATA3 (1.GSJ, AIST, 2.JAMSTEC, 3.AORI, The Univ. of Tokyo, 4.GSJ, AIST)

Keywords:submarine hydrothermal system, lithium isotope ratio, vent fluid, arc, back-arc basin

Submarine hydrothermal systems significant contribute to heat and elemental fluxes to the ocean. Vent fluid geochemistry in mid-ocean-ridge (MOR) hydrothermal systems were well-studied, while studies on vent fluid geochemistry in arc and back-arc systems with various geological characteristics were insufficient, especially in terms of lithium. To reveal control factors on lithium in arc and back-arc hydrothermal systems and lithium isotopic behavior in water-rock interaction at high temperature, we determined Li contents and its isotopic compositions of 11 vent fluids collected from 5 submarine arc/back-arc hydrothermal systems in the western Pacific.
Based on mass balance calculation, Li in vent fluids are dominated by seawater-rock (seawater-sediment) interaction in sediment-starved (sediment-hosted) hydrothermal systems in arc and back-arc basins at equilibrium. Li contents in vent fluids is also influenced by phase-separated processes, by temperature-related portioning of rock Li into fluid phase, and by host rocks and sediments. In contrast, Li isotopic composition in vent fluids is affected by host rocks and sediments, but not by phase-separated processes. These results demonstrate that lithium is a useful tracer for investigating geological processes occurred underground such as a phase separation process and water-rock/water-sediment interaction at high temperature.