Reevaluating the impact origin of the Luna Structure in western India using mineralogy, highly siderophile elements, and Re-Os isotopes

The Holocene Luna Structure in western India has been claimed to be the fourth and youngest impact crater on the Indian subcontinent. The circular shape; the unusual mineralogy including high-temperature mineral phases such as kirschsteinite and wüstite; and the elevated abundance of highly siderophile elements (HSE: Os, Ir, Ru, Rh, Pt, and Pd) have been provided as evidence in favor of an impact origin. Here, we present new mineralogical, bulk rock geochemical data including isotope-dilution HSE abundances and ¹⁸⁷Re-¹⁸⁷Os compositions of the suspected Luna impactites. The samples are dense irregular nodules with undulated surface and flow-like structures and are glassy to extremely fine grained, with or without vesicles. The new HSE data show no Ir enrichment compared to upper continental crust. The radiogenic measured ¹⁸⁷Os/¹⁸⁸Os compositions (0.2289–0.7253) further rule out any extraterrestrial contribution in the suspected impactites. The observed high-temperature mineral assemblage shows similarity to that of iron-rich archaeological slags. We reinterpret the Luna Structure materials as slags that are likely associated with the Bronze Age in the Harappan Civilization and may have formed as a byproduct of copper smelting. Considering the new evidence, the Luna Structure of western India is not a meteorite impact crater.