Melt inclusions in chassignite NWA 2737: A link between processes recorded in Martian meteorites and rocks at Gale crater

Abstract

Northwest Africa (NWA) 2737, one of the only three discovered Martian chassignites, provides critical constraints on the evolution of the Martian mantle and crust. Because of chassignites' cumulative nature, they contain abundant melt inclusions (MI). MI are small droplets of melts trapped by crystals during the cooling of magma. They are critical to the study of pre-eruptive parental magma compositions, and thus, provide snapshots of the composition and evolution of Martian magmatic systems. Here, we present fractional crystallization models using parental magma composition calculated from NWA 2737 melt inclusions as starting compositions. We used the thermodynamic modeling software MELTS to model fractional crystallization of NWA 2737 parental magma compositions with a wide range of parameters (pressure, water content, oxygen fugacity). Our models show that the felsic compositions recently analyzed at the Martian surface in Gale crater, especially Sparkle and Angmaat, the two rocks thought to be analogous to the earliest continental crust on Earth, can be obtained by fractional crystallization of chassignite-like parental melts. Our results suggest a link between the processes that resulted in chassignites and the rocks analyzed in situ at Gale crater. To assess the possible scenarios for Martian magma migration and storage processes, we compared chassignites to terrestrial analogs formed via various mechanisms and proposed two mechanisms that may explain the intrusive and effusive rocks found in situ at Gale crater: (1) emplacement and fractionation in a closed-system crustal reservoir and (2) eruption of mafic to intermediate lavas of a relatively open system subject to constant replenishment.

Non‐destructive quantitative analysis of melt inclusions in extraterrestrial samples: Case study of chassignite via nanoscale X‐ray computed tomography

“…Controversy exists regarding the proposed compositions for the chassignite parental magma, as experiments and models utilizing these compositions under various water (dry to 2 wt%) and pressure conditions (up to 15.7 kbar) have been unable to reproduce the commonly found hydrous phase, kaersutite, in NWA 2737 melt inclusions (Filiberto, 2008;Nekvasil et al, 2007). Crystallization paths compared with in situ Martian compositions also suggested that the parental liquid to chassignites could have gone through assimilation and could be more Mg-and Al-rich than previously proposed (Ostwald et al, 2022;Wu et al, 2021). These findings highlight the potential for revised compositions that can accurately reproduce the observed phases in these melt inclusions.…”

“…For cumulate rocks where bulk chemistry cannot be used directly to define their magmatic source compositions, olivine‐hosted melt inclusions (droplets of magmatic liquid trapped inside growing crystals) are used to estimate the parental magma compositions. The study of melt inclusions has been extensively applied in extraterrestrial materials, as demonstrated by classic research on lunar meteorites and chondrites (Roedder, 1981; Roedder & Weiblen, 1971; Sorby, 1864) and in Martian cumulate meteorites (Filiberto, 2008, 2017; Goodrich et al., 2013; He et al., 2013; Johnson et al., 1991; Nekvasil et al., 2007; Ostwald et al., 2022; Wu et al., 2021). Both lunar and Martian meteorites contain crystallized melt inclusions within olivine, varying in size (Johnson et al., 1991; Roedder & Weiblen, 1971).…”