10月13日にOnlineで第８回岩石ー流体セミナーを行いました。講演者は、高知大学橋本研究室の博士課程のWenjing Wang さんで、四万十帯の炭酸塩脈の同位体と構造地質学的解析から、沈み込み帯の流体移動を議論したものです。参加者は27名でした。
Deep fluid migration along a subduction plate interface evidenced from a continuous C-O isotope evolution of carbonic geofluids in the Shimanto belt, SW Japan
Wenjing Wang1,2, Yoshitaka Hashimoto2, Masafumi Murayama2, Takahiro Hosokawa2, Hirokazu Kato3
1. China University of Geoscience; 2. Kochi University; 3. University of Tokyo
Processes of fluid migration along subduction plate interfaces are important to understand the material and heat transportations, friction strength and rock fluid interactions along faults. We focused on syn-tectonic carbonaceous veins filling extensional cracks related to an underplating shear zone in Mugi mélange in the Cretaceous Shimanto Belt. C-O isotope properties of geofluid were examined for the classified veins with normal or reverse stress regimes. The C-O isotope values have obvious positive correlations with its paleo-temperature from clumped isotope (Δ47). The variation in the isotopic values and paleo temperature of the geofluid indicates the existence of hot and external fluid migrated from deeper unit. Moreover, we also evaluated C-O isotope values of geofluids in the other settings with different depths. It showed a continuous C-O isotope evolution from deep (Higuchi serpentinite body) to shallow (~5 km of Mugi). Therefore, we could build a geofluid mixture model for its implication which reflects the migration of deep fluid from mantle wedge to shallow portion along a subduction plate interface.
Ref.
Hosokawa and Hashimoto, 2022. Scientific Report. 12:14789
Okamoto et al., 2021. Communication Earth & Environment. 2:151
Nishiyama et al., 2020. Earth and Planetary Science Letters. 538:116199