Distribution of radiogenic heat generation in the arc's crust of the Hokkaido Island, Japan

Abstract

Radiogenic heat generation was measured for rocks collected in the vertical section of the crust of the arc exposed in the Hokkaido island, Japan. Measured heat generation value of metasediments is nearly constant of ∼1.0 µW/m³ and independent of the metamorphic grade. Using the measured heat generation value, together with the published heat generation data of a granitic body emplaced in this section, vertical profile of heat generation in the crust is constructed. The estimated heat generation profile shows steep decrease with depth, but is not lower than a value of ∼1.0 µW/m³ in the upper crust. In the lower crust metabasites are dominant, and heat generation value is one order of magnitude lower than that in the upper crust. Surface heat flow derived from the crustal heat generation is estimated to be ∼25 mW/m². When the crustal heat generation is considered, temperature at the bottom of the crust estimated from surface heat flow becomes ∼300°C lower. This temperature difference corresponds to the viscosity variation of more than three orders of magnitude, which is important for understanding lithosphere dynamics.