Mantle–melt partitioning of the highly siderophile elements: New results and application to Mars

1K. Righter,2R. Rowland II,2L. R. Danielson,3M. Humayun,3S. Yang,
4N. Mayer (Waeselmann),5K. Pando
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13598]
1NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, Texas, 77058 USA
2Los Alamos National Laboratory, Mail Stop P952, Los Alamos, New Mexico, 87545 USA
3National High Magnetic Field Laboratory, and Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, Florida, 32310 USA
4Mineralogisch‐Petrographisches Institut (MPI), University of Hamburg, Grindelallee, 48, 20146 Hamburg, Germany
5Jacobs JETS, 2101 NASA Parkway, NASA Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

Trace elements and extant and extinct isotopic attributes in Martian meteorites have been used to argue that Mars accreted quickly, differentiated into core and mantle, and established several mantle reservoirs, possibly within 10 Ma of T0. The partitioning of trace elements in the deep mantle has been relatively unstudied, despite the need for such knowledge in understanding magma ocean crystallization and the origin of depleted and enriched mantle reservoirs. The siderophile element composition of the Martian mantle and lithophile isotopic systems such as Sr, Hf, and Nd are thought to record evidence for early metal–silicate equilibrium and deep magma ocean at an intermediate depth and pressure of 800 km or 14 GPa. We have carried out experiments across this pressure range to better understand the mineral/melt partitioning of a wide range of elements. These new data are used to evaluate differentiation models for Mars and to help interpret the available isotopic data. The relatively incompatible nature of Re compared to mildly compatible Os means that the crystallization of a deep magma ocean will lead to residual liquids with superchondritic Re/Os, and solids with subchondritic Re/Os. Such material available in the mantle could be the source of enriched isotopic reservoir that produced shergottites with +γOs values. Slightly subchondritic Re/Os ratios in the crystallizing solids would provide a reservoir that could produce −γOs values. Melting of mixtures of these two enriched and depleted endmembers could explain the Nd‐Os isotopic correlations and systematics of shergottites.

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