Bulk Earth Compositional Models Require the Presence of Potassium in Earth's Core

Details Bulk Earth Compositional Models Require the Presence of Potassium in Earth's Core Bulk Earth Compositional Models Require the Presence of Potassium in Earth's Core

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmmr44a..06v&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #MR44A-06

Other

1015 Composition Of The Core, 1027 Composition Of The Planets, 3630 Experimental Mineralogy And Petrology, 5418 Heat Flow

Scientific paper

Constraining the concentration of radioactive potassium-40 as a heat source in Earth's metallic core is crucial for the development of accurate models for the formation and dynamic evolution of the core and lower mantle. A growing body of experimental evidence suggests that significant amounts of potassium can be incorporated into sulphur-bearing iron melts at relatively low pressure (e.g. Rama Murthy et al., Nature 2003), and in sulphur-free iron melts at high pressure (e.g. Lee and Jeanloz, GRL 2003; Hirao et al., GRL 2006), at concentrations consistent with recent core/mantle thermal evolution studies (e.g. Nimmo et al., GJI 2004; Nakagawa and Tackley, G3 2005; Costin and Butler, PEPI 2006). In spite of these studies, the notion of core K has been questioned in the context of current geochemical models for the composition of the bulk silicate Earth (BSE) and Earth's core (e.g. McDonough, Treatise on Geochemistry 2003). Arguments against the presence of potassium in the core are based on: (1) Trends in the elemental composition of the bulk silicate Earth (BSE) compared to the composition of CI carbonaceous chondrite (CC) as a function of element condensation temperatures, (2) Systematics of K/U versus Rb/Sr concentration ratios in BSE and chondrites, and (3) The mantle abundance of Ca relative to other refractory lithophile elements on the presumption that K entry into the core also extracts Ca. Here we show that none of these arguments are valid. Crucially, an updated cosmochemical model of bulk Earth composition, using recent data compilations of CC / BSE compositions and condensation temperatures, requires the presence of ± 250 ppm K in the core, while still being fully consistent with clearly non-linear chondrite K/U - Rb/Sr trends. We conclude that both experimental data and geochemical Bulk Earth models allow for the presence of K in Earth's core.

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