地表熱流量からみた日本列島

Abstract

Surface heat flow is observed fairly well at the Japanese Islands area. It is our purpose to utilize the observed heat flow to estimate the thermal condition of the mantle.Two-dimensional heat transfer equation of composite media is solved numerically. The equation is composed of several terms: conductive transport, convective transport, radiogenic heat generation, and metamorphic heat absorption. The boundary conditions are as follows; surface temperature is always equal to zero, and the heat flow at the bottom of the region is kept constant at 0.4×10-6cal/cm2·sec. Crustal structure of the Japanese Islands area is referred from the recent seismological works. The region is devided into square grids. The medium number and the convective vector are specified by two digits for each grid point. Two digits forms a two-dimensional matrix, i. e. Medium Map. Therefore, the Medium Map represents both the crustal structure and the convective current pattern. The convective current is assumed to be stationary where both the current pattern and the velocity are presumed a priori.Several thermal model of the Japanese Islands are discussed and it is concluded that the observed heat flow pattern is explained by the following model: upward mantle convection or large magma reservoir exists under the Japan Sea and no mantle convection or low temperature mantle convection exists under the Pacific Ocean side of the Japanese Islands.