Work

Signatures of vapor evolution in turbulent convection cells recorded by K and Rb isotopes in Chicxulub impact spherules

Year: 2026

Type: article

Abstract: The Cretaceous–Paleogene boundary (~66 Ma) records the Chicxulub asteroid impact, a pivotal event in Earth's history that affected much of the Earth's surface. While products of this impact have been widely studied, the thermodynamics of the plume and formation mechanisms of certain impact materials remain unclear. This study investigates conditions within the intermediate fraction of the Chicxulub impact plume (pyrocloud) using K and Rb isotope signatures of Gorgonilla Island impact spherules with published δ 25 Mg data to trace evaporation and condensation processes during ejecta dispersion. The δ 41 K and δ 87 Rb signatures vary from −1.18 ± 0.04‰ to 0.43 ± 0.09‰ and − 0.35 ± 0.01‰ to 0.07 ± 0.03‰ relative to the UCC, respectively. Combined with δ 25 Mg, these variations indicate evaporation and condensation in the pyrocloud. A fractional condensation model involving Mg and K suggests recondensation of spherules between ~2520–2130 K, with a K- and Rb-saturated vapor at the end of the condensation sequence. The δ 41 K, δ 87 Rb, and δ 25 Mg data imply that spherules formed mainly through recondensation and underwent secondary evaporation due to depressurization and fluctuating temperatures in turbulent convection cells. Decoupled recondensation and evaporation of K and Rb from Mg are required to explain their isotopic signatures. While Mg isotopes trace overall spherule formation, K and Rb isotopes reflect fine-scale physicochemical processes at the end of their formation. These results highlight the thermodynamically complex, yet key effects of turbulent convection cell environments in impact materials and emphasize the need to pair MVE isotope data with refractory element isotopes to better understand the formation of various impacts materials.

Source: Chemical Geology

DOI: 10.1016/j.chemgeo.2026.123309

Authors: Courtney Jean Rundhaug, Martin Schiller, Martin Bizzarro, Zhengbin Deng, Hermann Dario Bermúdez

Institutions: University of Copenhagen, University of Science and Technology of China, Montclair State University, Universidad Nacional de Colombia

Language: English

Topic: Astro and Planetary Science

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $3,550

Funders: Villum Fonden, Carlsbergfondet, European Research Council