THE BRACHINITES AND BRACHINITE-LIKE UNGROUPED ACHONDRITES CONNECTION: INSIGHTS FROM SPINELS MINERAL-CHEMISTRY

Among primitive achondrites, brachinites are an olivine-rich meteorites group displaying equilibrated textures and homogenous mineral phase compositions [1]. Brachinite-like ungrouped achondrites (UAB) share many similarities with brachinites [2], although textural and compositional features allow to infer about a different origin for their parent body(ies) [3]. Both represent oxidized meteorite groups and their genetic relationship remains still unknown. In this work we have analyzed 4 brachinites, NWA 4969, NWA 6308, NWA 11756, NWA 12733, and 8 brachinite-like ungrouped achondrites, Al Huwaysah 010, Miller Range 090206-090405, NW A 5400 together with three of its paired (NWA 5363, NWA 6077 and NWA 6292) and NWA 6112. Two more samples are under analyses (the brachinite NWA 13489 and the UAB NWA 14635). For some of these meteorites, a wide literature exists (MIL206-405 and 5400’s group), while for most of remaining few or none works are available. We performed a complete petro-mineralogic survey, focusing on spinels mineral- chemistry, in order to highlight potential relationships between the two achondrite groups. Spinel is a common accessory phase in terrestrial, lunar, martian and asteroidal ultramafic rocks. Moreover, being one of the first phase to crystallize (together olivine) from a basaltic magmas and allowing the incorporation of many multivalent cations (i.e. Fe, Cr, Mn, Ti, V) within its crystalline structure, can provide a useful tool for inspection of pristine source composition and its oxidation state.