[S-GL34] 地球年代学・同位体地球科学

[SGL34-P03] Stable Sr isotopes of saline water from non-volcanic Arima-type spring in Japan: Sr isotope fractionation during fluid generation from subducting carbonate?

*可児 智美¹、三澤 啓司²、森川 徳敏³、風早 康平³、楠原 文武⁴、寺門 靖高⁵ (1.熊本大学大学院先端科学研究部理学系、2.極地研究所、3.地質調査所、4.電力中央研究所、5.神戸大学)

キーワード：スラブ流体、沈み込み、地殻流体、水

Stable Sr isotope values (δ⁸⁸Sr) of saline water, which were sampled from Arima-type springs in Japan, were analyzed by TRITON TIMS with correction of isotope fractionation during mass spectrometry with ⁸⁷Sr-⁸⁴Sr double spike. The saline water samples were collected from Arima hot spring in Hyogo prefecture and Kashio mineral spring in Nagano prefecture. The Arima-type saline water possibly originated deep fluids derived from subducting slab rather than palaeoseawater buried in an aquifer, based on oxygen, hydrogen, helium and carbon isotopic compositions. The new obtained δ⁸⁸Sr values (0.11) of the saline water samples from Arima hot spring in this work are lower than those of surrounding Rokko granitoids and tuff (0.2) and the Phanerozoic mean of carbonates (0.16). The obtained δ⁸⁸Sr value (0.13) of the Kashio saline water is low as much as that of Arima saline water. The low δ⁸⁸Sr of Arima-type saline water indicate Sr isotope fractionation during fluid extraction from subducting oceanic plate with marine carbonates.