53-6 Insights into Lunar Basaltic Regolith Breccia Petrogenesis from the Dominion (DOM) Range 18678 Meteorite

Abstract:

The 2018-2019 NSF-NASA supported Antarctic Search for Meteorites (ANSMET) recovered eight lunar meteorites from the Dominion (DOM) Range. Previous mineralogical and geochemical studies of this lunar DOM suite has classified these samples as polymict regolith breccias composed of multiple clasts, minerals, and glass fragments. They are typically clast-poor with basaltic, gabbroic, granulitic, anorthositic clasts, 3-phase symplectites (fayalite, clinopyroxene, and silica), all ranging from 100µm-1mm in size. 

This study will be the first to conduct a petrological investigation of sample DOM 18678 (mass: 11.6g). Work to date on a single thin section (1.6cm x 2cm) has been conducted via PLM and SEM, including BSE and EDS analyses. Clasts within DOM 18678 are predominantly basaltic, subhedral to anhedral, and vary in size, ranging from 50μm-1mm. These clasts are composed mainly of calcium-rich plagioclase (anorthite), clinopyroxene, iron-rich olivine (fayalite), minor Fe-Ti oxide (ilmenite), silica, and iron sulfide (troilite). Other clasts present include impact melt breccias, microbreccias, and 3-phase symplectites (fayalite, clinopyroxene, silica) consistent with previous work on this lunar DOM suite. These clasts are surrounded by a black to dark gray, fine-grained, glassy matrix. Throughout the brecciated matrix, glass is present in the form of glass spherules, melt veins, and as a variably vesiculated, 10-50μm thick fusion crust surrounding ~55% of the meteorite.

Guided by textural and chemical information acquired via SEM, in-situ analysis via EPMA will quantify major and minor element mineral chemistry to evaluate clast petrogenesis and their potential source regions on the Moon (e.g., plagioclase An# vs. pyroxene Mg#). This will be accompanied by EPMA data from mineral fragments and glass data to further evaluate breccia petrogenesis (e.g., CaO/Al₂O₃ vs. MgO/Al₂O₃ in glasses). Data collected via EPMA will subsequently inform accompanying in-situ trace element data to be acquired via LA-ICP-MS. By analyzing the potential petrogenetic relationships between basaltic components, and comparing clast, mineral, and glass chemistries to other lunar materials, this study will advance understanding of breccia petrogenesis and contribute to knowledge of this relatively new lunar meteorite suite. 

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