Measurement of radioactive heat generation in rocks by means of gamma ray spectrometry - Vertical distribution of heat source in the island arc crust

Terrestrial heat flow is the sum of the radioactive heat generated in the c rust and the heat flow from the mantle. If we can evaluate the radioactive heat generation in the crust more precisely, we can better estimate the hea t flow from the mantle and the thermal state in the earth crust. In this st udy, the authors measured the contents of radioactive elements in rocks of Kohistan volcanic are, Pakistan and Ichinomegata, northeast Japan. We concl ude that low density rocks (rho less than or equal to 2.9) systematically c ontain much more radioactive elements leading to high heat generation compa red with high density rocks (rho greater than or equal to 3.0). In the next step, the vertical distribution of radioactive heat generation in the crus t was estimated, and the heat generation of the lower crust in the two area s was found to be much lower than previously considered. It means, if the s urface heat flow is the same, the estimated temperature at 30 lan depth is about 80 degrees C higher than previous estimates. This temperature change may strongly affect; the seismic activity at the depth.