Geo-neutrinos and Silicate Earth Enrichment of U and Th

TL;DR

This paper discusses the distribution of uranium, thorium, and potassium within the Earth, their impact on Earth's thermal evolution, and how geo-neutrino observations can help constrain their mantle abundances for better understanding Earth's history.

Contribution

It introduces a model for estimating U, Th, and K distribution in Earth's crust and mantle using geo-neutrino data, improving understanding of Earth's composition and thermal evolution.

Findings

Enrichment of U and Th in the silicate Earth is estimated to be between 1.5 and 2.8 times the chondritic value.

Geo-neutrino measurements can constrain the mantle's U and Th content.

The model highlights uncertainties in Earth's heat production and composition due to variable element distribution.

Abstract

The terrestrial distribution of U, Th, and K abundances governs the thermal evolution, traces the differentiation, and reflects the bulk composition of the earth. Comparing the bulk earth composition to chondritic meteorites estimates the net amounts of these radiogenic heat-producing elements available for partitioning to the crust, mantle, and core. Core formation enriches the abundances of refractory lithophile elements, including U and Th, in the silicate earth by ~1.5. Global removal of volatile elements potentially increases this enrichment to ~2.8. The K content of the silicate earth follows from the ratio of K to U. Variable enrichment produces a range of possible heat-producing element abundances in the silicate earth. A model assesses the essentially fixed amounts of U, Th, and K in the approximately closed crust reservoir. Subtracting these sequestered crustal amounts from the variable amounts in the silicate earth results in a range of possible mantle allocations, leaving global dynamics and thermal evolution poorly constrained. Terrestrial antineutrinos from {\beta}-emitting daughter nuclei in the U and Th decay series traverse the earth with negligible attenuation. The rate at which large subsurface instruments observe these geo-neutrinos depends on the distribution of U and Th relative to the detector. Geo-neutrino observations with sensitivity to U and Th in the mantle are able to estimate silicate earth enrichment, leading to a more complete understanding of the origin, accretion, differentiation, and thermal history of the planet.