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- Title
Strontium Isotope Characteristics (δ<sup>88/86</sup>Sr, <sup>87</sup>Sr/<sup>86</sup>Sr) of Arima‐Type Brines Originated From Slab‐Fluids.
- Authors
Kani, T.; Misawa, K.; Morikawa, N.; Kazahaya, K.; Kusuhara, F.; Yoneda, S.; Terakado, Y.
- Abstract
In the southwest Japan forearc, slab‐fluids produced from subducted materials migrate to crustal levels and appear as deep‐seated brine. We have analyzed for the first‐time stable strontium isotopes in non‐volcanic spring water with high salinity, referred to as Arima‐type saline water that likely originate from slab‐fluid that upwelled along major faults. The stable strontium isotope compositions of the saline water are isotopically light (δ88/86Sr = 0.122–0.157‰) and different from those of local bedrock and near‐surface water. The light strontium‐enriched and radiogenic signature of the saline water reflects the primary characteristic of slab‐fluids without an isotopic overprint in the crust. The Arima‐type brines show signatures of slab‐fluids at forearc depth, which is different from the slab‐fluids at subarc depth estimated from arc lavas. The characteristic features of the Arima‐type brines are explained by a larger contribution of subducted sediments and strontium isotope fractionation during fluids generation at shallower depth. Plain Language Summary: Slab‐fluids are likely sourced from oceanic crust and sediments, such as carbonate, chert, and clay, materials that are subducting into the mantle at convergent boundaries, which is a process that triggers arc volcanism and transports elements/water. The fluids released in the deep subduction zone appear to migrate to the Earth's surface and upwell along major faults in western Japan as spring water with high salinity, referred to as Arima‐type saline water. The stable strontium isotope compositions of the Arima‐type saline water are different from those of surrounding rocks, interpreted as reflecting the isotopically light signature as geochemical characteristics of slab‐fluid. The lighter strontium enrichments are thought to be the result of involvement of subducted crust and sediments, and likely reflect the mass dependent isotope fractionation with a preferential extraction of the lighter isotopes during slab‐fluid generation. Key Points: The stable strontium isotopes for the Arima‐type saline water show light isotope enrichment and are different from those of local rocksThe strontium isotopes of the saline water reflect the primary characteristics of slab‐fluids without an isotopic overprint in the crustThe light strontium isotope‐enriched signature of the saline water suggests isotope fractionation associated with slab‐fluid generation
- Subjects
SUBDUCTION zones; STRONTIUM isotopes; SALINE waters; SURFACE of the earth; STABLE isotopes; STRONTIUM ions; ISOTOPE separation
- Publication
Geophysical Research Letters, 2023, Vol 50, Issue 8, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2022GL100309