163-12 Multi-episode impact brecciation in lunar highlands meteorite NWA 14657.

Session: Impact Cratering Processes Across the Solar System: In Memory of Dr. Bevan M. French

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Impact reworking of lithologies on the Moon has made it challenging to constrain the evolution of the lunar crust and interior. Lunar meteorites containing evidence of impact brecciation and shock metamorphism can provide insights into lunar cratering processes that affect the occurrence and spatial distribution of diverse lithologies across the lunar surface. Lunar meteorite NWA 14657 has been classified as a feldspathic fragmental breccia, but has not been well studied. In this study, micro-XRF mapping revealed the presence of various highland lithologies, including FAN and MAN suite material. The sample is brecciated, clast rich, and contains areas of vesicular to holohyaline glass as observed through optical and backscattered electron imaging. Fractures in the sample are infilled with terrestrial alteration products. Groundmass major element compositions were measured to investigate the fine scale variations in the glass components. Glass occurs as small pockets and veins throughout the interior of the meteorite. Whereas the sample overall is very clast rich, the glassy veins are surprisingly clast poor, and often highly vesicular. The melt veins in some places contain apparent compositional banding in backscattered electron images, however, individual bands are too thin for precise spot measurements. Despite this apparent banding, the analyzed glassy domains are generally homogeneous in major element compositions, with only slight Fe enrichment along bright wisps in the bands. Some glass veins, along with internal banding, display cryptocrystalline textures at the edges, where the melt is in contact with the clasts. The veins and melt pockets are pervasive throughout the sample and are of feldspathic composition across the sample, likely representing impact melting within a single target region. The feldspathic nature of the clasts and melt indicates that the sample was sourced from a region in the lunar highlands, with the melt potentially derived locally to the clasts. Despite the compositional similarities between the melt veins and the clasts, the textural disparity suggests different timing for the melt/clasts. The presence of vesicular, clast poor melt veins within a generally clast rich, fragmental breccia could suggest that the sample underwent multiple episodes of brecciation.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8875

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