Spinel-Bearing Spherules Condensed from the Chicxulub Impact-Vapor Plume

TL;DR

This study predicts the sequential condensation of spinel-bearing spherules from vapor plumes generated by the Chicxulub impact, explaining their composition and global variation in the boundary layer.

Contribution

It is the first to model the condensation process of impact vapor plumes and link spinel composition variations to condensation temperatures and geographic location.

Findings

Spinel-bearing spherules form from impact vapor plumes.

Global compositional variations correlate with condensation temperatures.

Predicted compositions match those found at the K-T boundary.

Abstract

Formation of the giant Chicxulub crater off Mexico's Yucatan Peninsula coincided with deposition of the global Ir-rich Cretaceous-Tertiary (K-T) stratigraphic boundary layer at ca. 65 Ma. The boundary is marked most sharply by abundant spherules containing unaltered grains of magnesioferrite spinel. Here we predict for the first time the sequential condensation of solids and liquids from the plume of vaporized rock expected from oblique K-T impacts. We predict highly oxidizing plumes that condense silicate liquid droplets bearing spinel grains whose compositions closely match those marking the actual boundary. Systematic global variations in spinel composition are consistent with higher condensation temperatures for spinels found at Atlantic and European sites than for those in the Pacific.