¹S. A. Singerling
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70177]
¹Schwiete Cosmochemistry Laboratory, Goethe University, Frankfurt, Germany
Published by arrangement with John Wiley & Sons

This study documents micro- to nanoscale observations of primary nebular and secondary parent body iron sulfides in the CR1 GRO 95577. Despite the extensive alteration of the bulk sample, some primary sulfides managed to avoid alteration, having originally formed in the solar nebula during chondrule formation by either fission-sulfidization or crystallization. Secondary sulfides formed by precipitation from a fluid during aqueous alteration on the parent body and show features such as lath-like or euhedral morphologies, fine-scale intergrowths with serpentine, and porosity in pyrrhotite. Microstructures in pentlandite are most consistent with formation via impact-induced shock. Experiments have the potential to better constrain the effects of shock on pentlandite. Given pentlandite’s ubiquity in both minimally and heavily altered meteorites, it has the potential to be used as a shock indicator for samples otherwise ill-suited to shock determination (i.e., heavily aqueously altered materials).

^1,2Jennifer T. Mitchell,^3,4Natasha R. Stephen,¹Zsuzsanna P. Allerton,¹Weiming Ding, Xin-Yuan Zhe
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70181]
¹N.H. Winchell School of Earth & Environmental Sciences, University of Minnesota, 116 Church St SE, Minneapolis,Minnesota, 55455, USA
²Characterization Facility, University of Minnesota, 100 Union St, Minneapolis, Minnesota, 55455, USA
³The Geological Society of London, Burlington House, Picadilly, London, W1J 0BG, UK
⁴Department of Earth Science & Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
Published by arrangement with John Wiley & Sons

This study provides an initial characterization of Stardust Mine, a fresh gabbroic enriched shergottite collected in Arizona, USA, in September 2024 and is the first Martian meteorite to be unequivocably collected on US soil. Analysis was conducted on the type specimen and finds that Stardust Mine is composed of equal proportions of pyroxene and maskelynite, with large Fe-Ti oxides and phosphates. Ti/Al ratios and two-pyroxene thermometry of the most primitive pyroxenes (Mg# >57), inferred to represent preplagioclase pyroxene crystallization, give an estimated minimum initial crystallization depth of ~40 km at ~1140°C. Sector zoning is restricted to these pyroxenes and may have developed through magmatic undercooling in response to magma ascent before storage in a staging chamber in the volcanic system. Pyroxene and plagioclase cocrystallized for almost the entirety of the crystallization sequence with evolving melt compositions, followed by phosphates and Fe-Ti oxides. Ilmenite-titanomagnetite pairs and D(Cr)pyroxene suggest the magma was relatively oxidized (fO2 ΔQFM −1.3) compared with other shergottites. Accumulation and crystal settling in a sill, dyke, or intracrustal magma chamber allowed the development of a shape-preferred orientation and decomposition of metastable pyroxenes to three-phase symplectites. Stardust Mine represents a highly fractionated lithology that extends the range of high-Al basaltic shergottites to ~8 wt% Al. Our analysis does not find a clear pairing with shergottites in literature in lieu of radiogenic isotope data, and Stardust Mine may therefore represent a previously unsampled lithology.