Relative Contributions of Uranium, Thorium, and Potassium to Heat Production in the Earth

Abstract

Data from a wide variety of igneous rock types show that the ratio of potassium to uranium is approximately 1 X 10(4). This suggests that the value of K/U approximately 1 X 10(4) is characteristic of terrestrial materials and is distinct from the value of 8 X 10(4) found in chondrites. In a model earth with K/U approximately 10(4), uranium and thorium are the dominant sources of radioactive heat at the present time. This will permit the average terrestrial concentrations of uranium and thorium to be 2 to 4.7 times higher than that observed in chondrites. The resulting models of the terrestrial heat production will be considerably different from those for chondritic heat production because of the longer half-life of U(238) and Th(238) compared with K(40).

Helium, argon and carbon isotopic compositions in diamonds and their implications in mantle evolution.

“…This suggests that the mantle region where diamonds crystallised has remained a closed system with respect to U and K which have the K/U ratio generally considered to represent the average Earth (Wasserburg et al, 1964), being in accordance with the `calm mantle model' inferred from Fig. 2.…”

Potassium isotope cosmochemistry: Genetic implications of volatile element depletion

“…The depletion of alkali elements in the Earth relative to chondrites was noted by Gast ( 1960) and by Wasserburg et al ( 1964). The depletion of volatile elements in all planetary materials is now well established (Wolf and Anders, 1980;Wgnke and Dreibus, 1988;Taylor, 1979Taylor, , 1992Palme and Boynton, 1993).…”

“…This technique was utilized by Wasserburg et al ( 1964) and W&&e et al (1972), and the depletions were reviewed by W&&e and Dreibus ( 1988) and Palme and Boynton ( 1993). An accurate assessment of depletion for volatile elements other than incompatible lithophiles is difficult.…”

Some aspects of core formation in Mercury

“…The details of such a condition are not certain even for the earth (Higgins and Kennedy, 1971;Birch, 1972;Kennedy and Higgins, 1973), but for Mercury about half the heat sources in the planet must be retained in the core, according to Stevenson (1975), for convection to be permitted. If this radioactive heat in the core is provided by K 40 , a roughly chondritic K/U ratio (Wasserburg et al, 1964) is implied. A final possibility to reconcile the postulates of early core formation and a currently fluid core is that in addition to iron and to nickel and other siderophiles, Mercury's core contains one or more additional elements such as a sulfur which substantially lower the solidus temperature of core material (Brett, 1975).…”