Phase evolution and elemental partitioning in impact melts from Meteor Crater, Arizona
The impact of the Canyon Diablo iron meteorite in Arizona ∼61,000 years ago resulted in partial vaporization of the meteorite and target rocks, producing a vapor plume and melt particles with taenite, olivine and clinopyroxene in glassy matrix. The resulting Meteor Crater is ∼1.2 km in diameter and ∼200 m deep. Although the crater has been the natural laboratory for impact cratering, the microstructure and composition of its impact-melt particles remain poorly studied. Here microstructure and composition were investigated using optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, and synchrotron microdiffraction on particles collected from the ejecta blanket to reconstruct their temporal and mineralogical evolution during ultrafast quenching and to explore how mafic minerals form from sedimentary-derived melts. Elemental mapping reveals complex chemical partitioning among glass and mafic phases. Formation of Fe-Ni globules with face-centered cubic (fcc) taenite indicates oxygen fugacity well below atmospheric in the vapor cloud. During rapid cooling, skeletal olivine crystallized, followed by nucleation of clinopyroxenes to form spherical clusters. The glassy matrix contains two glasses separated by sharp boundaries, likely representing immiscible melts derived from different lithologies. The hot particles were deposited on the surface among quartz- and dolomite-rich ejecta, followed by post-depositional precipitation of calcite and barite within glassy nodules. The results demonstrate that mafic minerals can crystallize from melts derived largely from sedimentary target rocks, with Fe supplied by the impactor, and that elemental partitioning and mineral textures record strong disequilibrium crystallization during rapid cooling.