Sr isotopic results for spring water, carbonates, seawater, and rock samples

Slab-fluid is released by dehydration from oceanic crust and overlying sediment in deep subduction zones. Slab-fluid usually triggers arc volcanism, while in the nonvolcanic forearc in western Japan, aqueous fluid migrates to crustal level and appears as spring brine. We analysed new stable Sr isotopes for nonvolcanic spring water with high salinity, called Arima-type, likely originating from slab-fluid that upwelled along major faults. The stable Sr isotope compositions of saline water are similar to those of oceanic carbonates and, in contrast, are clearly different from those of local bed rocks. The light Sr-enriched signature of the saline water reflects the primary signature of slab-fluids without a significant isotopic overprint in the crust. The slab-fluid may acquire light Sr-enriched signature by isotope fractionation during slab-fluid extraction from subducted carbonates and other sediments.