Arima hot spring waters as a deep-seated brine from subducting slab

Chiho Kusuda,Noritoshi Morikawa,Hikaru Iwamori,Kohei Kazahaya,Hitomi Nakamura

doi:10.1186/1880-5981-66-119

Abstract

Abstract Non-volcanic hot springs are generally believed to originate through circulation of meteoric or buried sea water heated at depth. In this study, we report the geochemical characteristics of the Arima and Takarazuka hot spring waters, known as Arima-type deep brine, in a forearc region of southwestern Japan. We examine 14 water samples to determine the levels of 12 solute elements or components and the isotopic ratios of H, He, C, O, and Sr, and we perform correlation analysis of the data to deduce the source materials and origin of the deep brine. Moreover, we perform numerical modeling of oxygen and hydrogen isotopic fractionation along subducting slabs to examine the composition of slab-derived fluid as a possible candidate of the deep brine. The results suggest that the high salinity and solute concentrations with characteristic oxygen, hydrogen, carbon, and strontium isotope compositions, as well as high 3He/4He ratios, can be explained by a dehydrated component of the subducted Philippine Sea slab. Hence, this study may provide an invaluable understanding of geofluid processes over a significant depth range.

Highlights

Various geophysical and geochemical studies suggest that within the mantle wedge and crust in subduction zones, fluid fluxes may trigger seismicity and magmatism throughout the system (e.g., Iwamori 2007; Hasegawa et al 2008)
Masuda et al (1985) argued that the high 3He/4He ratios of the Arima hot spring brines are attributed to deep-lying magma and its interaction with the crustal rocks, together with diluted carbonated waters from the basement Paleozoic sedimentary rocks and the Cretaceous to Paleogene acidic igneous rocks that account for the overall δ18O-δD and solute variations of the Arima hot spring waters
Magmatic activity is certainly important for the origin of deep brines in some geothermal fields such as Salton Sea and Cerro Prieto with high Cl content and high 3He/4He ratios, where heat and material input from subaerial but mid-ocean ridge basalt (MORB)-type magmatism at depth interacts with the overlying thick sedimentary basin (Mazzini et al 2011; Schmitt et al 2013)

Summary

Introduction

Various geophysical and geochemical studies suggest that within the mantle wedge and crust in subduction zones, fluid fluxes may trigger seismicity and magmatism throughout the system (e.g., Iwamori 2007; Hasegawa et al 2008).

Results

Conclusion