Iridium Metal in Chicxulub Impact Melt: Forensic Chemistry on the K-T Smoking Gun

Abstract

Iridium concentrations in successively smaller subsplits of melt rock and melt breccia from the Chicxulub impact basin were tracked to isolate and identify iridium carrier phases. Iridium-rich particles were isolated from two samples, and a micrometer-scale, silicate-enclosed aggregate of subhedral iridium metal grains was identified in one, confirming earlier reports of iridium at ground zero of the impact at the Cretaceous-Tertiary (K-T) boundary. The aggregate may be either a phase formed after the collision or a relict of the Chicxulub basin-forming meteorite. In either case, its presence indicates that even among the largest impact structures on Earth, meteoritic components may be preserved within the crater.