Mineralogy of the Martian mantle inferred from bulk chemical compositions

Understanding the mineralogy of the Martian mantle is essential for constructing geochemical and geophysical models of Mars. This study employs the pMELTS program to determine the mineralogy at the solidus from 11 published bulk silicate Mars (BSM) compositions, within a pressure range of 2–5 GPa. The pMELTS results align with experimental data and calculations from another thermodynamic program (Perple_X/stx11). Mineral modes from compositional models based on Martian meteorite geochemistry show relatively consistent abundances modes (olivine: 48–56 wt%, orthopyroxene: 20–25 wt%, clinopyroxene: 15–17 wt%, garnet: 6–9 wt%). In contrast, mineral modes from compositional models that are not based on Martian meteorite geochemistry exhibit a wider range of olivine and garnet abundances. Additionally, we constrained the mineral modes of the Martian mantle using trace element partitioning and partial melting models. Our calculations indicate that melts derived from mantle sources with a hypothesized garnet content of 5–10 wt% closely match the analyzed compositions of shergottites, validating the garnet mode (6–9 wt%) constrained in our pMELTS calculations. Extracting low-degree (<4 wt%) melts from a BSM to form depleted Martian mantle (DMM) does not significantly alter the mineralogical modes of solid residues, but it does lead to substantial trace elemental depletion in the DMM. Therefore, enriched, intermediate, and depleted shergottite sources are likely characterized by similar mineral modes yet differ in incompatible element abundances.