Sr isotope diversity of hot spring and volcanic lake waters from Zao volcano,Japan |
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| Authors: | Hiromasa Ishikawa Tsukasa Ohba Hirokazu Fujimaki |
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| Institution: | 1. Department of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, 6–3 Aramaki, Aoba, Aoba-ku, Sendai 980-8578, Japan;2. School of Geography, Geology & Environmental Science, Faculty of Science, The University of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand |
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| Abstract: | The ratio of 87Sr/86Sr was measured from different water samples of thermal/mineral (hot spring as well as crater lake) and meteoric origins, in order to specify the location and to verify the detailed model of a volcano-hydrothermal system beneath Zao volcano. The ratio showed a trimodal distribution for the case of thermal/mineral water: 0.7052–0.7053 (Type A, Zao hot spring), 0.7039–0.7043 (Type B, Okama crater lake and Shin-funkiko hot spring), and 0.7070–0.7073 (Type C, Gaga, Aone, and Togatta hot springs), respectively. However, in comparison, the ratio was found to be higher for meteoric waters (0.7077–0.7079). The water from the central volcanic edifice (Type B) was found to be similar to that of nearby volcanic rocks in their Sr isotopic ratio. This indicates that the Sr in water was derived from shallow volcanic rocks. The 87Sr/86Sr ratio for water from the Zao hot spring (Type A) was intermediate between those of the pre-Tertiary granitic and the Quaternary volcanic rocks, thus suggesting that the water had reacted with both volcanic and granitic rocks. The location of the vapor–liquid separation was determined as the boundary of the pre-Tertiary granitic and the Quaternary volcanic rocks by comparing the results of this strontium isotopic study with those of Kiyosu and Kurahashi Kiyosu, Y., Kurahashi, M., 1984. Isotopic geochemistry of acid thermal waters and volcanic gases from Zao volcano in Japan. J. Volcanol. Geotherm. Res. 21, 313–331.]. |
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| Keywords: | Zao volcano strontium isotope active volcano&ndash hydrothermal systems hydrothermal fluid water&ndash rock interaction |
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