DISTRIBUTION OF RADIOGENIC HEAT-GENERATION IN THE ARCS CRUST OF THE HOKKAIDO-ISLAND, JAPAN

Radiogenic heat generation was measured for rocks collected in the ver tical section of the crust of the are exposed in the Hokkaido island, Japan, Measured heat generation value of metasediments is nearly const ant of similar to 1.0 mu W/m(3) and independent of the metamorphic gra de. Using the measured heat generation value, together with the publis hed heat generation data of a granitic body emplaced in this section, vertical profile of heat generation in the crust is constructed. The e stimated heat generation profile shows steep decrease with depth, but is not lower than a value of similar to 1.0 mu W/m(3) in the upper cru st. In the lower crust metabasites are dominant, and heat generation v alue is one order of magnitude lower than that in the upper crust. Sur face heat flow derived from the crustal heat generation is estimated t o be similar to 25 mW/m(2). When the crustal heat generation is consid ered, temperature at the bottom of the crust estimated from surface he at flow becomes similar to 300 degrees C lower. This temperature diffe rence corresponds to the viscosity variation of more than three orders of magnitude, which is important for understanding lithosphere dynami cs.