CORE GROWTH AND SIDEROPHILE ELEMENT DEPLETION OF THE MANTLE DURING HOMOGENEOUS EARTH ACCRETION

Abstract

A simple mechanism is put forward to explain the abundances of siderophile elements in the Earth's mantle. Within the frame of a homogeneous accretion hypothesis, the model involves repeated equilibrium fractionation, in a portion of the mantle, between solid and liquid silicate and metal phases. Fractionation events are followed by segregation of metal phases into the core and extensive mixing of different materials (newly accreted matter, terrestrial unfractionated matter, and silicate mantle material which has undergone fractionation) within the mantle. The time scale of a fractionation and mantle mixing event is very short compared to that of accretion. The process leads to a decrease of the metal fraction in the mantle with time. Therefore, the modelling was done in two stages. In the first, envisaged during accretion, metal fractions around 0.1 were considered. A second stage is set after the completion of accretion and metal fractions modelled are around 0.001.