The classification of Parauapebas Meteorite: Petrological, mineralogical and elemental compositions and physical properties

Abstract

The Parauapebas meteorite, an ordinary chondrite, was investigated through a systematic classification method, applying non-destructive analytical techniques: Electron Microprobe Micro-Analyzer (EPMA), X-Ray Fluorescence (XRF), Proton-Induced X-Ray Emission (PIXE), Cathodoluminescence (CL), and Optical Microscopy (OM). The goal was to achieve a complete and detailed chemical and petrological description of the official Parauapebas meteorite (MB 107). Additionally an inter-technique comparison was included for the bulk chemical composition obtained by means of the X-ray fluorescence PIXE and XRF techniques. The measured elemental compositions were compared to XRF and INAA average values reported in previous works on chondrites. The physical properties, such as density and magnetic susceptibility, of Parauapebas meteorite were also included as a tool for the chemical group classification. The meteorite is rich in iron metal, except into the silicates, thus Parauapebas is an H chemical group chondrite. Nevertheless some elemental compositions were found within the range of L chemical group chondrites. It presents two different lithologies with homogeneous chemistry observed in the analyzed thin sections, which point the meteorite as a genomict breccia (indicated by shock melt veins) formed by petrologic type 4 and 5. A shock stage S3/S4 is indicated by the olivine crystals with undulatory extinction, irregular and some planar fractures and a weak mosaicism, Neumann lines in iron-nickel, in addition to the presence of shock melt veins and pockets. The weathering degree is the lowest (W0), since the fragment was recovered soon after the fall.