The crystal structures of synthetic Re‐ and PGE‐bearing magnesioferrite Spinels: Implications for impacts, accretion and the mantle

Abstract

Re‐ and PGE‐bearing magnesioferrite spinels were synthesized at oxidizing conditions between 0.1 MPa and 5.0 GPa, and 1150 to 1600 °C in equilibrium with Re‐ or PGE‐bearing metals and/or oxides. Electron microprobe analysis and single crystal X‐ray diffraction techniques were employed to determine the composition, crystal structures and site occupancies, indicating that the magnesioferrite structure can accommodate wt% levels of Re and the platinum group elements (PGE) at oxidized conditions. These results suggest that magnesioferrite spinels found in K‐T boundary samples worldwide could be an important host phase for the Ir, Ru, Os, Re, and Rh anomalies found in the boundary layer. Higher Ru/Ir values in Pacific magnesioferrite‐bearing samples may be a reflection of higher condensation temperatures of the oxides. The distribution of PGE's in mantle and magmatic rocks may depend on the stability of spinel‐structure oxides, especially those with a high magnesioferrite component. Finally, magnetite‐rich meteorite fusion crusts may hold PGE' in oxidized form.