EBSD Analysis of Iron‐Nickel Metal in L Type Ordinary Chondrites: 1. The Microstructural Shock Signatures

Abstract

AbstractThe diverse microstructures of Fe‐Ni metal in 10 L groups ordinary chondrites that experienced progressive shock alteration were investigated using the electron backscattered diffraction technique. Through a combination of metallography and a silicate‐based shock classification scheme, we established the shock metamorphic features of metal phases corresponding to particular impact stages. In weakly shocked chondrites (S1–S2), the interlaced Neumann bands occur in polycrystalline kamacite, resulting from multiple small impact events on its parent body, and the internal crystallographic orientation difference of each kamacite monocrystal exceeds 5°. In moderately shocked samples (S2–S4), partial austenitization of metal occurs, accompanied by the emergence of net plessite. In strongly shocked samples (S4–S6), the metal has undergone complete austenitization and transformed into a homogenous fcc phase. In subsequent different cooling processes, polycrystalline kamacite with consistent internal crystallographic orientation, martensite, pearlitic plessite, duplex plessite, and acicular plessite form and finally appear in L group chondrites. This study demonstrates the significant utility of the microstructure of metal phases as a valuable tool for both the shock classification of L chondrites and the determination of shock metamorphism stages in iron meteorites.