Constraints on the petrologic history of gabbroic shergottite Northwest Africa 6963 from pyroxene zoning profiles and electron backscattered diffraction

Wenzel, Andrea; Filiberto, Justin; Stephen, Natasha; Schwenzer, Susanne P. and Hammond, Samantha J. (2021). Constraints on the petrologic history of gabbroic shergottite Northwest Africa 6963 from pyroxene zoning profiles and electron backscattered diffraction. Meteoritics & Planetary Science, 56(9) pp. 1744–1757.

DOI: https://doi.org/10.1111/maps.13737

Abstract

Northwest Africa 6963 (NWA 6963) is a coarse-grained, gabbroic Martian meteorite that further extends our Martian sample collection, both compositionally and texturally. Gabbroic shergottite NWA 6963 provides direct petrologic evidence of intrusive igneous conditions within the Martian crust. Here, we analyzed geochemical zoning profiles and microstructural-crystallographic information from electron backscattered diffraction of augite and pigeonite to constrain the crystallization history of NWA 6963. Compositional zoning profiles reveal pyroxenes with augite or pigeonite cores mantled by Fe-rich pigeonite rims. Our results suggest complex pyroxene textures and zoning profiles observed in pyroxenes in NWA 6963 are due to pyroxene accumulation from a crystallizing magma in a large intrusive environment (sill or magma chamber); however, without geologic context or companion samples, it is currently impossible to rule out accumulation at the base of a very large (>>100 m) differentiated flow.

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