Diff-Chrome

Investigation of stable Cr isotopic fractionation during Earth’s silicate differentiation and reassessment of the accurate Bulk Silicate Earth delta53/52Cr value

01.10.2017 bis 01.10.2020

The aim of this project is to investigate possible stable Cr isotopic fracctionation during the silicate differentiation (i.e. partial mantle melting and fractional crystallization) of our planet. In high-T environments with partial pressures for oxygen typical for mantle melt sources significant amounts of chromium will be stable as the reduced Cr2+ as compared to the more common Cr3+ oxidation state. Exchange of Cr2+ with Fe2+, Mg2+ or Ca2+ in the lattice of minerals that crystallize from a magma may lead to significant Cr isotopic fractionation which is linked to the melts Cr2+/Cr3+ ratio and as such to the prevailing oxygen fugacity of the system. If measurable differences are found, the stable Cr isotopic composition of mafic rocks (basalts) may be a direct proxy for the oxygen fugacity of the melt and thus for the partial pressure of oxygen in different mantle melt regimes.