Petrology and oxygen isotopes of NWA 5492, a new metal-rich chondrite

Abstract

Northwest Africa 5492 is a new metal-rich chondrite breccia that may represent a new oxygen reservoir and new chondrite parent body. It has some textural similarities to CB and CH chondrites, but silicates are more reduced, sulfides are more common and not associated with metal, and metal compositions differ from CB and CH chondrites. Oxygen isotope ratios indicate that Northwest Africa (NWA) 5492 components (chondrules and lithic fragments) formed in at least two different oxygen reservoirs. The more common, and presumably host, component plots in a region above the terrestrial fractionation line, below ordinary chondrite compositions, and just above enstatite chondrites in 3-oxygen space. The only other chondritic materials that plot in this region are chondrules from the Grosvenor Mountains (GRO) 95551 ungrouped metal-rich chondrite. The other rare component plots near the CR, CB, and CH chondrites. Based on petrologic characteristics and oxygen isotopic compositions, NWA 5492 appears to be related to the ungrouped metal-rich GRO 95551 chondrite. © 2012 The Meteoritical Society.