Mantle Substance and Terrestrial Heat Flow

Abstract

The heat budget of the upper mantle of the earth was recently examined by Tilton and Reed, based on an investigation of the concentration of uranium, thorium and potassium. in ultramafic rocks and eclogites. According to Tilton and Reed, the radioactive heat production rate in ultramafic rocks (olivine nodules from Hualalai, Hawaii; Dreiser Weiher, Germany; Gila, Arizona, USA; and dunite from Twin Sisters Mtn., Washington; St. Pauls Rock, Mid-Atlantic Ridge) and eclogite (from Salt Lake Crater, Hawaii) is 0.38 and 3.25 erg/gr·year respectively.
To account for terrestrial heat flow in oceanic areas (50 erg/cm²·sec), the heat production in ultramafic rocks such as peridotite as a constituent of the outer mantle is too low. The same is true for eclogites, if heat transfer takes place in the mantle solely by thermal conduction. Eclogite could provide a satisfactory heat source, if convection currents exist in the outer mantle as an effective mode of heat transfer. Peridotite may be a major constituent of the outer mantle in continental areas or of the deep mantle underlying continental and oceanic regions.