[S-GL21] 地球年代学・同位体地球科学

[SGL21-P09] Stable Strontium isotope composition (δ88/86Sr) of Arima-type saline water originated from slab-fluids generated at forearc depth

*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、米田 成一⁵、寺門 靖高⁶ (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.国立科学博物館理工学研究部、6.神戸大学)

キーワード：ストロンチウム安定同位体、スラブ流体、沈み込み、水

Strontium (Sr), its dual isotope systems i.e., radiogenic and mass-dependent isotope systems are useful to understand mass transfer and water budget in the subduction zone. In the southwest Japan forearc, slab-fluid generated from subducted materials migrate up to crustal level and appear as nonvolcanic Arima-type spring water with high salinity. We analyzed stable Sr isotope values (δ88Sr) of Arima-type saline water using by TRITON TIMS with correction of isotope fractionation during mass spectrometry with 87Sr-84Sr double spike. The obtained δ88Sr values of the Arima saline water which range from +0.122‰ to +0.153‰ are lighter than those of local rocks (Rokko granites and Arima rhyolitic welded tuff). Whereas the δ88Sr value of Tansansen spring water as the near-surface water almost identical that of the Rokko granite. These results suggest that the Sr isotope compositions of the Arima saline water should be regarded as those of slab-fluids without significant isotopic disturbances at crustal level. The Sr isotope characteristics of the saline water can be explained by isotope fractionation during fluid extraction from subducted altered oceanic crust and overlying sediments at forearc depth.