Aqueous alteration in Martian meteorite Northwest Africa 11013: an analysis of its extent and origin

Sammanfattning

Nakhlites, which are clinopyroxene-rich cumulate rocks formed from basaltic magma around 1.3 billion years ago, frequently exhibit evidence of aqueous alteration. This study focuses on the extent and origin of aqueous alteration in the nakhlite Martian meteorite Northwest Africa (NWA) 11013, addressing four key research questions: the specific type of alteration, its connection to microstructures, its extent in olivine grains and its connection to Martian geological events. Utilising scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) and 2D-modelling with "Dragonfly 3D World," the mineralogical composition and the extent of alteration were analysed. Results indicate that NWA 11013 is primarily composed of augite and feldspar-rich mesostasis, with Fe-rich olivine, Fe-Ti oxides and pyrite also present. Aqueous alteration, characterised by iron-rich silicate phases and calcium sulphates was predominantly observed along microstructures within olivine grains and in association with mesostasis, but not in contact with augite. Quantitative analysis revealed that the iddingsite alteration in olivine ranges from 5-35%, suggesting localised or limited fluid-rock interaction rather than widespread water saturation. This alteration appears to be structurally controlled by fractures which served as conduits for fluid infiltration. The observed alteration patterns, consistent with findings in other nakhlites, suggest a multi-stage process with potential shifts in environmental conditions on Mars, from reducing to oxidising.