1ST OCCURRENCE OF PYROPHANITE (MNTIO3) AND BADDELEYITE (ZRO2) IN AN ORDINARY CHONDRITE

A 220 x 430 mum Mg-Al-chromite fragment in the Raguli H3.8 ordinary ch ondrite exhibits distinct optical and compositional zoning. The dark c entral region of the Mg-Al-chromite is enriched in MgO, Al2O3 and ZnO and depleted in TiO2, Cr2O3, FeO and MnO relative to the lighter outer region. A subhedral olivine grain attached to radiating euhedral ilme nites is present in the central region of the fragment. One of the ilm enite crystals contains a tiny grain (0.5 x 5.8 mum) of baddeleyite (Z rO2). Two end-member pyrophanite grains (MnTiO3) occur in the outer po rtion of the fragment. This is the first occurrence of pyrophanite and baddeleyite in an ordinary chondrite. Although it is possible that th e Mg-Al-chromite fragment was derived from an achondritic projectile o f unusual composition, we offer two alternative models for its formati on. These include (a) a multi-stage process involving nebular melting of a chromian-spinel chondrule that had accreted some olivine-bearing, Mn-rich material followed by metamorphism on the parent body, and (b) formation of the fragment on a metamorphosed parent body from an impa ct melt of a chromite-rich assemblage containing Mn-rich ilmenite. We favor the latter alternative.