Abstract
Northwest Africa 1232 (NWA 1232) is a carbonaceous chondrite consisting of two lithologies (A and B) that are separated by a sharp boundary. A petrographic and mineralogical study indicates that both lithologies can be classified as type CO3. However, olivine in lithology B chondrules is more enriched in Fe than in lithology A, whereas olivine in lithology B matrix is more depleted in Fe than in lithology A. Chondrules and Ca-Al-rich inclusions (CAIs) in lithology B show a higher degree of nephelinization than those in lithology A. These differences can be explained by that lithology B has gone through a higher degree of thermal metamorphism than lithology A. These two lithologies probably represent rocks that have been thermally metamorphosed at different locations within a single CO parent body and later mixed to form the present combined rock during a brecciation process.
