Origin of metal nodules, veins, and fine‐grained metal in several L and H chondrites

Abstract We investigated the metal nodules, veins, fine‐grained particles of ordinary chondrites (OC) Ash Creek (L6), Ghubara (L5), NWA 6096 (L6), Tsarev (L5), Kunya‐Urgench (H5), NWA 1588 (H3.8), Tamdakht (H5) and Timochin (H5) using optical microscopy, SEM, and LA‐ICP‐MS to determine trace element distributions and understand the origin of these metal components. The metal nodules have a fractionated siderophile element composition differing from OC metal, indicating the elements were distributed during melting. Most nodules and veins are depleted in Cu and the highly refractory siderophile elements (HRSE) Re, Os, Ir, Ru, Pt, and Rh. Nodules and veins are enriched in W, Mo, Ni, Co, Au, As, and Sb compared to OC metal. Kunya‐Urgench metal shows progressive depletion of refractory siderophile elements, likely due to in situ fractionation of liquid metal injected into the chondrite host. We modeled crystallization of L and H chondrite metal melts, producing results similar to the observed compositions, supporting the hypothesis that the metal components may have originated from unfractionated melted in situ primary metal of chondrites. Variations between modeled and observed W, Fe, and Ga abundances suggest varying redox conditions during melting or metamorphism. Tsarev nodule has a unique HRSE zoning recording its high‐temperature thermal history, with modeled cooling to 1300°C in ~1 year, suggesting crystallization in a thermally insulated environment, possibly under a hot layer of impact ejecta. The low‐temperature thermal histories (660–200°C) of investigated meteorites' metal suggest that shock compression and re‐heating may have resulted in a subsolidus decomposition/recrystallization of the metal.