Oxybarometry constrains through multivalent cation XANES study on primitive achondrite spinels

Our purpose is to measure Ti, V, Cr and Fe valences in chromites in a set of olivine-rich primitive achondrite meteorites, namely brachinites and ungrouped achondrites with brachinite affinity, to obtain fO2 estimations. Spinel is a common accessory phase in terrestrial, lunar, martian and asteroidal ultramafic rocks. Moreover, being one of the first phases to crystallize from basaltic magmas and allowing the incorporation of many multivalent cations, it can provide insights on the pristine source composition and fO2 degree. Both brachinites and brachinite-like ungrouped achondrites represent oxidized meteorite groups and their genetic relationship remains still unknown. Although both groups share many similarities, textural and compositional features allow to infer about a different origin for their parent body(ies). A large and complete fO2 dataset could shed a new light on their genetic relationships and improve our knowledge about pristine parent body (ies) composition(s).