GEOCHEMISTRY OF MARTIAN BASALTS WITH CONSTRAINTS ON MAGMA GENESIS (Invited Presentation)

Basaltic rocks analyzed in situ from MER Spirit and Opportunity and MSL Curiosity are more diverse in composition than the rocks represented by the Martian meteorites suggesting they may have tapped a different source region [1, 2]. Surface rocks have more variable Si contents, and higher total alkalis than shergottites [1, 2]. Surface rocks are also ancient while shergottites are young [2, 3]. Therefore, we can use the difference in chemistry and age to constrain the thermal and chemical evolution of the Martian interior.

Petrologic estimates for genesis of Martian magmas come from two main techniques: geochemical modeling and experimental petrology. High-pressure, high-temperature experiments have been conducted on 2 Martian meteorites and 2 surface basalts to reveal their multiple saturation pressure, which has been equated to average melting conditions [4-9]. Geochemical Modeling has been conducted for basalts at Gusev Crater, Merdiani Planum, and Gale Crater, average surface volcanic compositions, as well as some Martian meteorites [10-14].

Combining these results shows a Martian interior that was hotter ~ 150 °C hotter in the Noachian than in the Amazonian and is consistent with convective cooling of the Martian interior [10, 11]. However, mantle temperature estimates for shergottites are significantly (200-300 °C hotter) than the average Amazonian mantle and suggest the possible presence of localized thermal anomalies [10, 11].

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