Fassaites in compact type A Ca-Al-rich inclusions in the Ningqiang carbonaceous chondrite: Evidence for partial melting in the nebula

Abstract

Fassaite is a major component of Ca-Al-rich inclusions (CAIs) of Types B and degrees C that crystallized from liquids. In contrast, this mineral is rarely reported in Type A inclusions and has been much less studied. In this paper, we report highly Ti-, Al-enriched fassaite that occurs as rims on perovskite in two compact Type A inclusions from the Ningqiang meteorite. In addition, one of the inclusions contains an euhedral grain of Sc-fassaite (16.4 wt% Sc2O3) isolated in melilite. The occurrence and mineral chemistry of the fassaite rims can be explained by a reaction of pre-existing perovskite with CAI melts. Hence, such rims may serve as an indicator for partial melting of Type A inclusions. The Sc-fassaite is probably a relict grain. A third spherical CAI contains several euhedral grains of V-fassaite (4.8-5.4 wt% V2O3) enclosed in a melilite fragment. The high V content of fassaite cannot be related to any Fremdlinge, magnetite, or metallic Fe-Ni, because these phases are absent in the inclusion. In the same CAI, other fassaites intergrow with spinel and minor perovskite, filling voids inside of the melilite and space adjacent to the Wark-Lovering rim. The fassaite intergrown with spinel is almost V-free. The coexistence of two types of fassaite suggests that this CAI has not been completely melted.