53-5 Insights into Lunar Basaltic Magmatism and Regolith Composition from Dominion Range (DOM) Meteorite 18262

Abstract:

        Repeated bombardment, melting, and fragmentation of the lunar surface over billions of years has established a lunar regolith which dominates the Moon’s surface environment. As these regolith materials comprise the ground over which rovers and astronauts will explore, characterization of regolith materials is crucial for supporting future surface exploration missions. One approach to advancing understanding of lunar regolith composition and evolution is through the study of regolith breccias. 

        Dominion Range (DOM) 18262 is one of eight lunar basaltic regolith breccias returned from the 2018-2019 Antarctic Search for Meteorites (ANSMET) season. Through a detailed textural, mineralogical, and geochemical analysis of DOM 18262, this study aims to investigate the petrogenesis of its regolith components while contributing to the knowledge of the Moon’s geological evolution.

        Work to date on a 1.2cm by 1.2cm thin section of DOM 18262 has involved characterization via microscopy: PLM, and SEM-EDS. Meteorite DOM 18262 is a clast-poor (<10%) breccia where a glassy matrix surrounds clasts, mineral fragments, glass spherules, melt pockets, and melt veins. A glassy, variably vesiculated fusion crust surrounds ~90% of the sample with some segments texturally akin to lunar agglutinates. The clast inventory includes basalts, impact melt breccias, microbreccias, and 3-phase symplectites. Basaltic clasts are the most common and are characterized primarily by unzoned plagioclase and variably zoned clinopyroxene with variable proportions of minor fayalitic olivine and ilmenite in addition to accessory troilite, apatite, silica, spinel, and alkali feldspar. These basaltic components also characterize the mineral fragment population found throughout the matrix. Collectively, these petrographic observations are consistent with the samples’ basaltic regolith classification and are similar to those reported for select paired stones (e.g., DOM 18543, 18666).

        Electron MicroProbe data will quantify the chemical composition of the meteorite’s components (clasts, fragments, glass) identified via microscopy, guided by spatial context provided via SEM-EDS. Chemical data will evaluate if DOM 18262 shares a similar lunar provenance to that of its paired stones, for which a comparative dataset exists. This includes assessing 1) the potential derivation of basaltic components from an ancient, highly fractionated, Fe-rich and low-Ti magma, and 2) the delivery of anorthositic material to the site of regolith breccia petrogenesis and the development of potential cryptomare.

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