Experimentally melting a Mg# 80 Martian Mantle at 0.5 to 1.5 GPa: Implications for basalt genesis

The most widely used and accepted composition for the Martian mantle in experimental petrology is the Dreibus and Wänke (1985) proposed composition based on only eight SNC meteorites. This composition is enriched in iron with respect to the Earth, which follows what we see from samples of Mars. The magnesium number (Mg#=Mg/Mg+Fe) of the Dreibus and Wänke (1985) composition is Mg#75, which is iron rich compared to Earth’s Mg# of around 90. However, when experimentally melted as a source for generating Martian basalts, the melt concentrates iron further, higher than the Mars basalt compositions, and requires melting a large percentage of the mantle to reach a composition that is comparable to known Martian basalts. Partial melting experiments of an Mg# 80 mantle composition produced shergottite-like melts with a lower percentage of partial melting than with the Mg#75 compositions. This would be more likely since the Martian mantle would have cooled considerably by the time it would have produced the shergottites, which was only approximately 180 million years ago. The reprised composition is Mg#80 and less iron rich than the DW composition, but more iron-rich than Earth