Core Mantle Interaction

Abstract

During its accretionary phase, planet Earth differentiated into a metallic core and a silicate mantle. This process eventually led to the current structure of Earth's layered interior (inner core, outer core, mantle and crust). Geophysical studies show that the boundary between Earth's metallic core and its silicate mantle is distinct and is characterized by a sharp change in temperature, density and composition. Exchange between core and mantle in the form of thermal and mechanical interaction is a generally accepted process. Chemical interaction, as in the transfer or exchange of elements between the metallic core and silicate mantle, on the other hand, remains a topic of debate. Distinct geochemical signatures have been observed in some plume-derived basaltic rocks, which are interpreted to originate close to or from the core-mantle boundary (CMB). These signatures include ratios of certain elements (e.g., Fe/Mn) and distinct isotopic compositions (182Hf-182W, 190Pt-186Os, 187Re-187Os) and have been used in several studies to infer chemical exchange between core and mantle material. Several mechanisms of core-mantle interaction (CMI) have been proposed and include direct transfer of core metal to the lowermost mantle, as well as transport that is limited to certain elements by processes, such as oxide exsolution, grain-boundary diffusion or liquid metal–liquid silicate chemical reaction. Though some geochemical and isotopic constraints indicate a chemical exchange between core and mantle, the exact mechanism, timing, extent, and consequences of this process are unclear and will remain important topics for future studies.