Japan Geoscience Union Meeting 2014

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Symbol A (Atmospheric, Ocean, and Environmental Sciences) » A-HW Hydrology & Water Environment

[A-HW25_2AM2] Isotope Hydrology 2014

Fri. May 2, 2014 11:00 AM - 12:45 PM 414 (4F)

Convener:*Masaya Yasuhara(Geological Survey of Japan, AIST), Kohei Kazahaya(Geological Survey of Japan, AIST), Shinji Ohsawa(Institute for Geothermal Sciences, Graduate School of Science, Kyoto University), Masaaki Takahashi(Geological Survey of Japan (GSJ), National Institute of Advanced Industrial Science and Technology (AIST)), YUICHI SUZUKI(Faculty of Geo-Environmental Sience,Rissho University), Futaba Kazama(Social Cystem Engineering, Division of Engineering, Interdiciplinary Graduate School of Medical and Engineering, University of Yamanashi), Kazuyoshi Asai(Geo Science Laboratory), Chair:Kazuyoshi Asai(Geo Science Laboratory), Kazuhiro Amita(Department of Earth Science & Technology Faculty of Engineering and Resource Science Akita University)

12:30 PM - 12:45 PM

[AHW25-14] Genesis of Kashio brine: slab-derived fluid

*Kohei KAZAHAYA1, Hiroshi TAKAHASHI1, Noritoshi MORIKAWA1, Michiko OHWADA1, Akihiko INAMURA1, Masaya YASUHARA1, Masaaki TAKAHASHI1 (1.Geological survey of Japan, AIST)

Keywords:Kashio brine, isotopic ratio, flow rate, slab-derived fluid

In this study, we show the results obtained be investigation of a very saline spring named Kashio brine, central Japan and discuss its genesis and cause of chemical and isotopic features. The brine water is spouting out through the cracks of metamorphic rocks close to Median Tectonic Line (MTL) at 700m asl. The Cl concentration of water is greater than that of the seawater with 18O-shifted isotopic composition. The brine is thought to originate from slab-derived fluid with the chemical and isotopic composition of water like the Arima hot spring, in spite of its low temperature and CO2-less features. The cause of this chemical character might be explained by a reaction with ultramafic rocks existed close to Kashio area which causes high pH condition to deposit all the CO2 as CaCO3. The low temperature may be interpreted by the low upwelling rate because of the low 3He/4He ratio (lower than 2Ra) due to the addition of crustal 4He. The amount of NaCl is finally supplied to the river and is estimated to be 2000kg/day.