Petrogenesis of the Gabbroic Shergottites Northwest Africa 12241: Insights into the Common Intrusive Process of Shergottites

Gabbroic and poikilitic shergottites are intrusive igneous rocks on Mars, providing significant insights into the igneous processes within the Martian crust. However, questions remain regarding the chemical signatures of their source reservoirs and the petrogenesis links among shergottites of different subtypes. In this study, we present petrological and mineralogical analyses of the intermediate shergottite Northwest Africa (NWA) 12241. Quantitative textural analysis and pyroxene chemistry indicate that, despite minor differences such as the accumulation of intermediate-sized olivine and smaller pyroxene oikocrysts, NWA 12241 has experienced a similar emplacement history with typical poikilitic and gabbroic shergottites. The estimated parent melt of NWA 12241 is consistent with an intermediate source reservoir, resulting from mixing of enriched and depleted mantle endmembers at depth, prior to magma ascent. Similar emplacement histories of variable poikilitic and gabbroic shergottites suggest the common presence of multiple staging magma chambers with different compositions at the crust-mantle boundary, coupled with prolonged ponding at this depth. Our study highlights that, in addition to magma mixing and assimilation, magmatic differentiation and cooling conditions at shallow depths are crucial processes leading to textural and compositional variations among shergottites of different subtypes.