Study of fusion crust in ureilite and H-chondrites

Fusion crust forms during the atmospheric entry of meteoroids. A large part of it is ablated, but commonly a thin layer is preserved and quenched, coating the meteorites surface (e.g., [1]). Fusion crust forms in all kind of meteorites, but generally it is thicker on iron meteorites than on stony chondrites possibly due to the high heat conductivity of the metal [2]. In iron meteorites, enrichment in Ni and Co in the metal in the quenched fusion crust is observed and interpreted as the result of oxidation [2]. In stony meteorites, even though fusion crust results from melting, its bulk composition differs slightly from that of the original material [1], because of melt evolution or reflecting the local mineral composition [3]. This difference in bulk composition is obvious for volatiles, which are depleted in the fusion crust with respect to the original bulk composition [1; 3]. Recently fusion crust raised new interest because a possible analogue for chondrule formation [4] and for comparison with cosmic spherules (ongoing work).
Among stony meteorites, ureilites are believed to produce thin fusion crust and entirely consisting of glass [1]. However, sample A 09368, an Antarctic meteorite collected during joint Japanese-Belgian missions to Antarctica and classified as ureilite [5], exhibits a thick and well-developed fusion crust. In this work we focus on this sample, particularly investigating the change in composition of olivine through the fusion crust, comparing the results with those from the fusion crust of two H-chondrites (A 09004 and A 09502; [5]), in the framework of progressive oxidation of the material.