地殻内発熱を考慮した場合の東北日本島弧地殻の温度構造

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Thermal structure beneath subduction zones plays a key role in understanding their tectonic activities, such as seismicity, volcanism, arc formation and genesis of back-arc basins. In this study, thermal structure in the crust of Northeast Japan was investigated to account for the surface heat flow data. To estimate the contribution of the heat generation in the crust to the surface heat flow, heat production rate was obtained on granitic rocks collected from the Hidaka terrain, Hokkaido, where the crustal section of an island arc is supposed to be exposed. INNA method was adopted to analyze the concentration of heat producing elements. The obtained rate of heat generation and its decrease with increasing depth for the Hidaka terrain were found to be similar to those estimated for stable continental areas. The vertical distribution of heat production rate in the crust of the Northeastern Japan arc was estimated from the present results and previous estimates of heat production rates of different rocks, using crustal structure determined by explosion seismology. The total heat generation in the crust thus estimated is about 30 mW/m^2. With the surface heat flow data and estimated heat generation distribution in the crust, the thermal structure in the crust was simulated numerically. Modeling calculations were made on a cross section along the line from a Japan trench to the Japan Sea of which direction is parallel to the direction of convergence of the Pacific and Eurasian plates. The models were two-dimensional and included the frictional heating at the upper surface of the slab. Calculated thermal structure in the crust shows that the temperature at the Moho is about 850℃ and almost about 250℃ lower than previous estimates. The magnitude of the interplate stress was derived by considering the rate of frictional heating at the interface between the plates. In order to explain the surface heat flow between the trench and aseismic front, the interplate stress should be less than 200 bars.
1986-04-30

地殻内発熱を考慮した場合の東北日本島弧地殻の温度構造

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