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

The 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 degrees. 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. L group ordinary chondrite is the most abundant type of meteorite, and the classification of its shock stage based on silicate minerals is well-established. In this manuscript, We have conducted an investigation into the metal in 10 L groups ordinary chondrites of various shock stages by using the Electron Backscattered Diffraction technique. As the intensity of impact increases, the resulting temperature also gradually rises. Due to its high sensitivity to temperature, metal forms a more enriched internal structure compared to silicate minerals. Meanwhile, Our results are also consistent with those observed in several iron meteorites, which may help us to classify the shock metamorphism stages in iron meteorites. The interlaced Neumann bands are a valuable indicator of low-grade shock levels (S1-S2) in L group chondritesThe presence of martensite could be a diagnostic feature for strongly shocked L chondritesThe shock metamorphic features of Fe-Ni metal in chondrite is consistent with that in iron meteorite of the same shock stage