Japan Geoscience Union Meeting 2016

Presentation information


Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG57] Geofluids and dynamics in subduction zones

Tue. May 24, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Ikuo Katayama(Department of Earth and Planetary Systems Science, Hiroshima University), Atsushi Okamoto(Graduate School of Environmental Studies), Tatsuhiko Kawamoto(Institute for Geothermal Sciences, Graduate School of Science, Kyoto University), Junichi Nakajima(Department of Earth and Planetary Sciences, Tokyo Institute of Technology)

5:15 PM - 6:30 PM

[SCG57-P04] Experimental constraints on the serpentinization rate of fore-arc peridotites: implications for the welling condition of the "Arima-type" hydrothermal fluids

*Takayuki Nakatani1, Michihiko Nakamura1 (1.Division of Earth and Planetary Materials Science Department of Earth Science Graduate School of Science, TOHOKU Univ.)

Keywords:hydration reaction, slab-fluid, serpentine, fore-arc mantle

In order to palce a constraint on the water circulation in subduction zones, hydration rates of peridotites have been investigated experimentally in fore-arc mantle conditions. Experiments were conducted at 400–580°C and 1.3 and 1.8 GPa, where antigorite was expected to form as a stable serpentine phase. Crushed powders of olivine ± orthopyroxene and orthopyroxene + clinopyroxene were reacted with 15 wt% distilled water for 4–19 days. The synthesized serpentine was lizardite in all experimental conditions except that of 1.8 GPa and 580°C in the olivine + orthopyroxene system, in which antigorite was formed. In the olivine + orthopyroxene system, the reactions were interface-controlled except for the reaction at 400°C, which was diffusion-controlled. Corresponding reaction rates were 7.0 × 10-12–1.5 × 10-11 m·s-1 at 500–580°C and 7.5 × 10-16 m2·s-1 at 400°C for the interface- and diffusion-controlled reactions, respectively. Based on a simple reaction-transport model with these hydration rates, we infer that leakage of the slab-derived fluid from an water-unsaturated fore-arc mantle is allowed only when focused flow occurs with a spacing larger than 77–229 km in hot subduction zones like Nankai and Cascadia, whereas the necessary spacing is just 2.3–4.6 m in intermediate-temperature subduction zones like Kyushu and Costa Rica. These calculations suggest that fluid leakage in hot subduction zones may occur after the fore-arc mantle is totally hydrated, while in intermediate-temperature subduction zones, leakage through a water-unsaturated fore-arc mantle may be facilitated.