The extremely reduced silicate-bearing iron meteorite Northwest Africa 6583: Implications on the variety of the impact melt rocks of the IAB-complex parent body

Northwest Africa (NWA) 6583 is a silicate-bearing iron meteorite with Ni=18wt%. The oxygen isotope composition of the silicates (O-17=-0.439 parts per thousand) indicates a genetic link with the IAB-complex. Other chemical, mineralogical, and textural features of NWA 6583 are consistent with classification as a new member of the IAB-complex. However, some unique features, e.g., the low Au content (1.13gg(-1)) and the extremely reducing conditions of formation (approximately -3.5 IW), distinguish NWA 6583 from the known IAB-complex irons and extend the properties of this group of meteorites. The chemical and textural features of NWA 6583 can be ascribed to a genesis by impact melting on a parent body of chondritic composition. This model is also consistent with one of the most recent models for the genesis of the IAB-complex. Northwest Africa 6583 provides a further example of the wide lithological and mineralogical variety that impact melting could produce on the surface of a single asteroid, especially if characterized by an important compositional heterogeneity in space and time like a regolith.