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Hot-Springs and their Heat Source in Kinki Peninsula,Southwest Japan
Susumu NISHIMURA
Kyoto Institute of Natural History

Abstract
In the Kii Peninsula, there are many famous hot-springs, such as Ryujin, Totsugawa,Tousenji, Yunomine, Watarase, Kawayu, Yukawa, Katsuura, Shirahama hot-springs.
These springs are located mainly along the north-south trends faults near the KumanoOmine acidic intrusions and mineral deposits of which ages are +,ῌ+/ Ma. These ages areoccurred just after the opening of Japan sea, causing of the ./ clockwise rotation ofSouthwest Japan Arc. These bodies have been cooled and could not be the heat sourceof hot-springs.
The sources of these hot-springs might be mixing of the underground water anddehydrated water from subducted slabs of Philippine Sea Plate. These hot-springs arefound along the cracks associated with in these intrusions and dikes. The chemical
characters of hot-springs and geophysical evidences around hot-springs supported theseinterpretation.
Key Words : Kinki Peninsula, heat source of hot-spring, dehydration of subducted slab
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Geological map and localities of hot-springs in Kii Peninsula.

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Fig. . Schematic model of thermal structures of Yunomine, Watarase, Kawayu and drilling well(N.-HG-,), modiﬁed from NEDO (+330).

Fig. / A plausible model for the migration of H, O in subduction zones, modiﬁed from Tatsumi(+33/).

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104

Fig. 1oa The distribution of hypocenters occurred from January +, ,***, toMarch -+, ,**+, in and around Kinki District and the section of thedistribution in the squared area (modiﬁed from Newsletter of theSeismological Society of Japan, ,**+).

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Fig. 1ob The distribution of hypocenters occurred from January +, +322,to May -+,+330, around Geiyo Earthquake and the section of the distribution in the squared
area (Nishimura, +332).

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 !",*** a#$ %%&'()*+,-. - He ῌ . He /+,Furukawa, et al., +332 ; Sano and Wakita, +32-#

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Fig. 3 The - He/ . He proﬁle in the Kinki and Chugoku Districts. The dashed line
shows the atmospheric ratio (modiﬁed from Sano and Wakita, +32-).

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Furukawa, Y., Shinjoe, H. and Nishimura, S. (+332) : Heat ﬂow in the Japan arc and its
implication for thermal processes under arcs, Geophys. Res. Lett., ,/, +*21ῌ+*3*.

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Sano, Y. and Wakita, K. (+32-) : Geographic distributions of the -He/ .He ratios in Japan ;Implications for arc tectonics and incipient magmatism, Jour. Geophys. Res., 3*, 21,3ῌ21.+.

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