Ab-initio Predictions of Potassium Partitioning Between Lower Mantle Phases
Abstract
The distribution of radioactive isotopes in the Earth's deep interior is of fundamental interest to geophysics, geochemistry and geodynamics as this could potentially influence the distribution of radiogenic heat production and hence the thermal evolution and dynamics of the Earth. 40K is the most abundant long- lived radiogenic isotope in the Earth and as such, where potassium resides in the Earth's interior is of interest. Isolated deep Earth reservoirs of potassium in the core or in Mg-silicate post-perovskite (Mg-ppv) have been previously shown to be unlikely [e.g., Lee et al., 2008]. The lower mantle comprises approximately two-thirds of the Earth's volume, hence the distribution of potassium between the lower mantle phases: iron-bearing Mg silicate perovskite (Mg, Fe)SiO3 (Mg-pv), magnesiowüstite (Mg, Fe)O (mw) and a calcium silicate perovskite CaSiO3 (Ca-pv), is useful to understanding radiogenic heat distribution. The large A-site of Ca-pv provides a potential environment for heat-producing elements [e.g., Kato et al., 1988]. Here we address the partitioning of potassium between iron-bearing Mg-pv and Ca-pv by means density- functional theory-based ab-initio electronic structure computations using a planewave code (VASP). Based on the energetics we compute the equilibrium constant for K distribution between Mg-pv and Ca-pv at lower- mantle conditions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMDI41A1749L
- Keywords:
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- 1025 Composition of the mantle;
- 1040 Radiogenic isotope geochemistry;
- 1042 Mineral and crystal chemistry (3620);
- 1065 Major and trace element geochemistry;
- 3924 High-pressure behavior