[S-CG54] New Insights of Fluid-Rock Interactions: From Surface to Deep Subduction Zone

[SCG54-07] Geochemical research of volatile element and fluid cycles at plate boundaries

★Invited Papers

*Takanori Kagoshima¹ (1.University of Toyama)

Keywords:plate boundary, geochemical cycle, volatile element, noble gas

Geochemical observations using volatiles (e.g., noble gases) as tracers are useful for investigating material and fluid cycles between the Earth's interior and the surface environment. One of my research projects focused on global fluxes of volatiles at plate boundaries: mid-ocean ridges-subduction zones. Information of volatile global cycles and residence times in terrestrial reservoirs is important for elucidating the Earth's degassing history and evolutions of the atmosphere and the ocean. Chemical and isotopic compositions of samples which preserves mantle-derived components provide crucial information of geochemical cycles between the Earth's interior and the surface. For example, by crushing chilled glassy rims of MORBs, we can measure chemical and isotopic compositions of volatile elements such as helium isotopes extracted from vesicles. Using the obtained data including element/³He ratios, volatile fluxes and cycles may be constrained based on the well-estimated ³He global fluxes. We estimated global fluxes and cycles of sulfur at mid-ocean ridges and subduction zones based on chemical and isotopic compositions of MORBs, hydrothermal fluids and volcanic gases around the world (Kagoshima et al., 2015). The obtained data indicates that sulfur in volcanic gases is mostly derived from subducted materials, and the mantle contribution is small.
My other research projects are focusing on geochemical observations of volcanic and earthquake activity. Chemical and isotopic compositions of gas and groundwater samples released at volcanoes and faults reflect fluid sources, so they are useful for investigating fluid cycles and structures of hydrothermal system. In addition, such chemistry data vary depending on contributions of components derived from different reservoirs such as the mantle and the crust, which is useful for understanding situations and activity of volcanic-hydrothermal system and fluid-related phenomena occurring with earthquake activity (e.g., fluid pathway changes and groundwater mixing). In other sessions, I will give presentations related to seismic swarm activity in the Noto Peninsula and Mt. Ontake volcanic activity. In this presentation, I will introduce topics related to such kind of geochemical observations.

(Reference) Kagoshima et al. (2015) Sci. Rep. 5, 8330.