New temperature and oxygen fugacity data of Martian nakhlite from Northwest Africa (NWA) 5790 and implications for shallow sulphur degassing

Newly analysed titanomagnetite-ilmenite (Tim-Ilm) intergrowths from Martian nakhlite meteorite Northwest Africa (NWA) 5790 yielded crystallisation temperature up to 1032 degrees C and oxygen fugacity (fO(2)) up to Delta QFM + 1.6, notably higher than previous estimates for nakhlite magmas (temperature < 950 degrees C, fO(2) = Delta QFM - 0.5 to Delta QFM + 1). To interpret how the magma was reduced from Delta QFM - 0.5 to Delta QFM + 1.6, we used D-Compress to model the sulphur degassing process within a single thick lava pile. For fO(2) to significantly decrease in this extended range, a sulphur-rich (S content 4000-7000 ppm) Martian lava flow had to degas all the sulphur species at a certain final degassing pressure, which was 2-4 bar for NWA 988 and Lafayette and < 0.7 bar for Y-000593 and Nakhla. These final degassing pressure data are in good agreement with the Martian nakhlite burial depth estimated by other petrological and geochemical methods. These estimates are also comparable with the excavation depth of similar to 40 m based on the small (6.5 km in diameter) impact crater over the Elysium lava plain. The fO(2)-controlled sulphur degassing pressure may constitute a method for estimating the burial depth of sulphur-rich lava flows on Mars.

Automated summary

Newly analyzed titanomagnetite-ilmenite intergrowths from Martian nakhlite meteorite NWA 5790 showed higher crystallization temperature and oxygen fugacity compared to previous estimates. By modeling the sulfur degassing process, it was found that sulfur-rich Martian lava flows degassed sulfur species at specific final degassing pressures, which align with estimates of Martian nakhlite burial depth and excavation depth based on impact craters. This fO(2)-controlled sulfur degassing pressure method may be useful for estimating the burial depth of sulfur-rich lava flows on Mars.