Diverse mineralogical and oxygen isotopic signatures recorded in CV3 carbonaceous chondrites

We describe the petrography and mineralogy of six CV3 carbonaceous chondrites. LAP02206, LAP02228, LAPO4843, and GRA06101 are classified as oxidized Allende-like chondrites (CV3(oxA)). RBT04143 and QUE97186 are classified as members of the reduced subtype (CV3(red)). Chondrules in the CV30(oxA) chondrites show extensive Fe-Mg zoning. Fe-rich olivine in the rims of the CV3(oxA) chondrules are O-16-poor relative to Mg-rich olivine in the cores, suggesting that in addition to Fe and Mg, oxygen was exchanged between chondrules and matrix during weak thermal metamorphism. The CV3(red) chondrites appear to have formed through various processes. QUE97186 shows chondrule flattening with a preferred orientation, which is interpreted to have resulted from shock impact at a pressure of similar to 20 GPa. The post-shock residual heat (similar to 1000 degrees C) is likely to be responsible for the restricted Fe/Mg ratios of matrix olivine. Based on the degree of Fe-Mg homogenization of matrix olivines, we estimate the spatial scale of the shock-heated region to be similar to 1 m. RBT04143 is a breccia containing many clasts of two types of lithologies: reduced-type material and very weakly altered material. (c) 2012 Elsevier B.V. and NIPR. All rights reserved.