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Compositional and structural mapping of Northwest Africa 15507 angrite

July 24, 2024

Angrite meteorites represent interesting sampling of planetary crustal environments. Quench-textured angrites with strong crystal zoning originated from the shallow surface region, with evidence of reducing conditions during solidification. Plutonic angrites have more coarse-grained igneous and metamorphic textures with comparatively less zoning and are interpreted as having equilibrated at greater depth. Plutonic angrites contain the minerals magnetite Fe3O4 comprised of Fe2+ and Fe3+, and rhönite, where Fe3+ is required by inspection of mineral stoichiometry. NWA 15507 is a plutonic angrite with a microgabbroic texture (mean grainsize ∼1.4 mm) composed of zoned Al-Ti-augite, Ca-bearing olivine, anorthite, with accessory kirschsteinite, rhönite, hercynite, low-Ni kamacite, merrillite, Ti-free magnetite and troilite [1]. Rhönite analyzed by electron-probe microanalysis (EPMA) has the formula Ca2.04(Mg0.32Fe2+4.25Fe3+0.47Ti0.33Al0.61)(Si3.74Al2.26)O20, where Fe3+ was estimated by stoichiometric analysis. During preliminary cathodoluminescence (CL) analysis, complex subgrain and oscillatory zoning was observed in the anorthite. In this study we use a combined approach of electron probe microanalysis (EPMA), cathodoluminescence (CL), electron-backscatter diffraction (EBSD), and laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) to further investigate the anorthite and distribution of Fe3+ in NWA 15507.

Publication Year 2024
Title Compositional and structural mapping of Northwest Africa 15507 angrite
DOI 10.1093/mam/ozae044.008
Authors Heather A. Lowers, Paul C. Carpenter, Jay Michael Thompson, Anthony Irving
Publication Type Article
Publication Subtype Journal Article
Series Title Microscopy and Microanalysis
Index ID 70259682
Record Source USGS Publications Warehouse
USGS Organization Central Mineral and Environmental Resources Science Center; Geology, Geophysics, and Geochemistry Science Center
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