Mineralogy and olivine cooling rate of the Dhofar 019 shergottite

Dhofar 019 is a new basaltic shergottite found in Oman. It is mainly composed of pyroxenes, plagioclase glass, and olivine. Olivine grains show variable size distributions from large (∿1mm) non-euhedral zoned grains with magnesian cores (Fa_) to small euhedral homogeneous grains with variable compositions (Fa_). This may suggest that some of the Dhofar 019 olivines are xenocrysts and others are phenocrysts. The Dhofar 019 olivines are compositionally distinct from those in other shergottites. Pyroxenes are extensively zoned, and pigeonite cores are usually surrounded with augite rims, suggesting undercooling of magma to a similar degree as that of EETA 79001 (lithology A) and Zagami. There appears to be a compositional change in major and minor elements from the magnesian pyroxenes to ferroan pyroxenes for both pigeonite and augite. The magnesian parts have similar compositions to EETA 79001 (lithology A) pyroxenes, and the ferroan parts are similar to Zagami pyroxenes. Plagioclase zoning in Dhofar 019 more closely resembles that of Zagami. Spinel compositions in Dhofar 019 overlap those of EETA79001,and the Dhofar 019 chromite may be a xenocryst like EETA79001. The cooling rate of Dhofar 019 calculated from Fe-Mg zoning profiles of olivine is 0.05-0.1℃/hour. This corresponds to a burial depth of ∿5m from the martian surface, possibly in a lava flow. Thus, the groundmass crystallization of Dhofar 019 occurred near the martian surface, although it is likely that Dhofar 019 has experienced a complex history