摘要：

Submarine hydrothermal systems signicant contribute to heat and elemental uxes to the ocean. Vent uid geochemistry in mid-ocean-ridge (MOR) hydrothermal systems were well-studied, while studies on vent uid geochemistry in arc and back-arc systems with various geological characteristics were insufcient, 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 uids collected from 5 submarine arc/back-arc hydrothermal systems in the western Pacic. Based on mass balance calculation, Li in vent uids 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 uids is also inuenced by phase-separated processes, by temperature-related portioning of rock Li into uid phase, and by host rocks and sediments. In contrast, Li isotopic composition in vent uids 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.

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