The author calculated the amount of heat supply from the upper mantle and estimated the temperature distribution at the Moho, in and around the Japanese Islands (33°-47°N, 127°-146°E). Although the depth of the Moho is different from place to place, there exists some characteristic tendencies in temperature distribution at the Moho:(A) Low temperature distribution is seen in southwest Japan (except the Green-Tuff region), which corresponds to the geologically non-active area, (B) Low temperature distribution is seen in outer side (Pacific Ocean side) of northeast Japan, which corresponds to the geologically active island arc, (C) High temperature distribution is seen in inner side (Japan Sea side) of northwest Japan, (D) High temperature distribution is seen in the Green-Tuff region, (E) High temperature distribution is seen in the Japan Sea and the Philippine Sea, which are marginal seas of southeastern Japanese Islands arc and the Izu-Bonin arc, respectively. Comparing the Japan Sea with Philippine Sea, large difference in temperature distribution pattern at the Moho can be seen. In the Japan Sea, fluctuation of temperature distribution is relatively small comparing with other regions. However, in the Philippine Sea, very large (about 500°C) fluctuation of temperature at the Moho can be comfirmed in some parts in this region. Obviously, this pattern of thermal state of the Moho in both regions may be caused by the difference of thermal structure in the upper mantle. In the Green-Tuff region, the amount of heat supply from the upper mantle would be estimated between 1.0 HFU and 1.5 HFU. In the areas including west of off Hokkaido, southern part of the Japan Sea, San-in district (Japan Sea side of southwestern part of Honshu), a part of Philippine Sea and west of off Kyushu regions, the temper-ature of the Moho will be exceeded 1000°C. Almost of these regions are located in high heat flow area (Higher than 2.0 HFU) and inner area from the volcanic front. Estimating from temperature distribution pattern in the Moho, the uppermost depth of the partial melting zone will be reached the shallower depth of the upper mantle in the Japan Sea and the Philippine Sea regions than the other regions.
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