Temperature and distribution of radioactive matter in the upper mantle

Abstract

Temperatures of the Earth’s upper mantle, derived from Gutenberg’s seismic velocities, have been revised, using some recent determinations of the clastic constants of dunites. For depths greater than about 50 km the temperature obtained is sufficient to melt the basaltic fraction of a periodotitic mantle (if this low-melting fraction still exists at those depths). The distribution of the radioactive heat sources appears to be fairly uniform down to about 110 km; below this level the radioactive matter is probably absent. This is what would be expected for the upper mantle below the oceans; therefore, Gutenberg’s velocities seem to correspond to oceanic areas, rather than to the mantle below a continental shield.