EBSD Analysis of Iron‐Nickel Metal in H Chondrites: 1. Evidence for Disruption and Re‐Accretion of Parent Asteroid

Abstract Ordinary chondrites, sourced from S‐type asteroids, provide the most direct documentation of the thermal history of their parent bodies. Current research focuses predominantly on silicates, but early endogenic metamorphism overprinted by impact heating can yield ambiguous silicate records. In contrast, Fe‐Ni metal, also as a major component, exhibits higher strain rates and greater temperature sensitivity than silicates. H‐group ordinary chondrites possess the highest metal content, characterized by thermally informative complex microstructures. In this study, the Electron Backscatter Diffraction technique is employed on 14 H chondrites to constrain their thermal history. Martensite and duplex plessite, microstructures indicative of rapid cooling, are prevalent in the metal. Furthermore, characteristic microstructures formed by martensite tempering under distinct thermal pathways are observed, including polycrystalline martensite (low‐temperature, prolonged heating), net plessite, and acicular plessite (higher‐temperature tempering). Consequently, the metal records a rapid cooling event followed by widespread tempering and thermal annealing. This implies that the H parent body, similar to those of L chondrites, experienced a catastrophic impact, evidenced by their shared quenched metal structure. Subsequent tempering and annealing probably resulted from thermal effects in the re‐accretion of impact debris.