Evaluating Potential Alteration Products of Nwa7034: Expanding Our Knowledge of Martian Crustal Alteration Assemblages

Introduction: NWA 7034 is a monomict breccia of volcanic [1] or impact [2,3] origin. Interestingly, the oldest zircon ages in the paired NWA7533 meteorite point at an ancient formation age (~4.43 Gyr, [3]), while disturbed younger zircon ages are observed [3], and the Rb/Sr age of NWA7034 is ~2.1 Gyr [1]. According to the initial study by Agee and co-workers [1], NWA7034 shares features with the SNC meteorites and with compositions measured by MER. NWA7034 consists of a variety of clasts [4] some of which show similarities to the Gale Crater rock Jake_M [5]. It is the most oxidized of all SNCs and has the highest water content [1]. Besides high magnetite contents [1], the only potential alteration phase observed to date is terrestrial Ca-carbonate [1]. However, the above mentioned young ages [3] might indicate Martian alteration processes. NWA7034 potentially is a volcanic [1] or impact breccia [2,3] exposing it to hydrothermal alteration. But because of the potential near-surface nature, NWA7034 might have been exposed to changing surface and subsurface conditions since its formation, thus a complex and multi-stage alteration history of the rock is possible. In addition, it is a terrestrial desert find, which calls for understanding the terrestrial alteration products to be able to disentangle them from potential Martian assemblages. The aim of this study is to investigate potential alteration scenarios of NWA7034 to give insights into Martian volcanic and post-impact hydrous and hydrothermal alteration, and secondary mineral formation during Martian and terrestrial weathering. Alteration scenarios: ‘Pure water’ explores the alteration through a dilute fluid, such as meteoric water or ice melt water (‘pure water’, PW, see also [6] for details), for which an overall dilute water scenario and a CO2-rich fluid (0.5 mole H2CO3) are considered. Subsurface brine alteration could happen through a brine in equilibrium with underground rocks, such as a pore fluid (‘adapted water’, AW). In this scenario I use the same fluid used in previous impact-generated hydrothermal and Martian weathering studies [6–9], whereby a CO2-poor and CO2-enriched (0.5 mole H2CO3) cases are considered. Acidic fluids: Acid weathering is a widely discussed topic [10], especially late in Martian history. In particular, it has been modeled in the light of the MER findings [11,12]. If the NWA7034 breccia is of volcanic nature, the rock could have been in direct contact with the (hot) acidic volcanic exhalation, too. Because experiments have demonstrated the buffering capabilities of basaltic Martian rocks [13], as much as 0.5 mole of H2SO4 were added to PW or AW.