HR: 1340h
AN: V13A-1442    [Abstracts]
TI: Chemical and isotopic compositions of thermal water related with possible ascending deep fluids in Kii Peninsula, SW Japan
AU: * Morikawa, N
EM: n.morikawa@aist.go.jp
AF: Research Center for Deep Geological Environments, Geological Survey of Japan, AIST, AIST Tsukuba Central 7, 1-1, Higashi 1-Chome, Tsukuba, 305-8567 Japan
AU: Kazahaya, K
AF: Research Center for Deep Geological Environments, Geological Survey of Japan, AIST, AIST Tsukuba Central 7, 1-1, Higashi 1-Chome, Tsukuba, 305-8567 Japan
AU: Takahashi, H A
AF: Research Center for Deep Geological Environments, Geological Survey of Japan, AIST, AIST Tsukuba Central 7, 1-1, Higashi 1-Chome, Tsukuba, 305-8567 Japan
AU: Inamura, A
AF: Research Center for Deep Geological Environments, Geological Survey of Japan, AIST, AIST Tsukuba Central 7, 1-1, Higashi 1-Chome, Tsukuba, 305-8567 Japan
AU: Ohwada, M
AF: Research Center for Deep Geological Environments, Geological Survey of Japan, AIST, AIST Tsukuba Central 7, 1-1, Higashi 1-Chome, Tsukuba, 305-8567 Japan
AU: Yasuhara, M
AF: Research Center for Deep Geological Environments, Geological Survey of Japan, AIST, AIST Tsukuba Central 7, 1-1, Higashi 1-Chome, Tsukuba, 305-8567 Japan
AU: Takahashi, M
AF: Research Center for Deep Geological Environments, Geological Survey of Japan, AIST, AIST Tsukuba Central 7, 1-1, Higashi 1-Chome, Tsukuba, 305-8567 Japan
AU: Ritchie, B E
AF: National Park Service, National Park Service, Grand Teton National Park, P.O. Box 170, Moose, WY 83012, Moose, Wy 83012 United States
AU: Nagao, K
AF: Laboratory for Earthquake Chemistry, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Sumino, H
AF: Laboratory for Earthquake Chemistry, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AB: Kii Peninsula is located in the fore-arc region of SW Japan, where the Philippine Sea plate has been subducting. Although there are no Quaternary volcanic activity, high-temperature thermal brine as well as various kind of hot springs well out in many places. Possible origin of these unusual hot springs is that fluids originated from dehydrated water from subducting slab are incorporated into the surface water (Kazahaya et al., 2003; Matsumoto et al., 2003). Salah and Zhao (2003) suggested the existence of fluids in the crust and the mantle wedge resulting from the dehydration of the subducting slab based on the detailed 3-D P and S wave velocity structures. We examined both chemical and isotopic features of hot springs to make distribution of these unusual hot springs and their relationship with fluids dehydrated from the subducting slab clearer. NaCl-type hot springs were significantly enriched in the heavy isotopes of oxygen and hydrogen, although those of Na(Ca)HCO$_{3}$-type were not shifted from meteoric water line. From helium isotopic compositions, the gas component derived from deeper region including upper mantle is main contributor for both type of hot springs. The $^{20}$Ne concentrations in NaCl-type hot springs are far lower than that in air saturated water (ASW), while most of Na(Ca)HCO$_{3}$-type hot springs have similar or higher $^{20}$Ne concentration level than ASW. From these results, we can get insights into the origin of each type hot spring. High temperature thermal brine with mantle derived component is incorporated into the surface meteoric water and, subsequently, suffered water-gas separation. The gases separated from the thermal brine were rich in noble gas with high $^{3}$He/$^{4}$He ratio and were dissolved into meteoric water. The former may correspond to NaCl-type hot spring, and the latter may correspond to Na(Ca)HCO$_{3}$-type one.
DE: 8135 Hydrothermal systems (8424)
DE: 1040 Isotopic composition/chemistry
DE: 1010 Chemical evolution
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting