Hot carbonates deep within the Chicxulub impact structure Kaskes, Pim Marchegiano, Marta Peral, Marion Goderis, Steven Claeys, Philippe Clumped isotopes Chicxulub Decarbonation Constraining the thermodynamic conditions within an impact structure during and after hypervelocity impacts is extremely challenging due to the transient thermal regimes. This work uses carbonate clumped-isotope thermometry to reconstruct absolute temperatures of impact lithologies within and close to the ∼66 Myr old Chicxulub crater (Yucatán, México). We present stable oxygen (δ18O), carbon (δ13C), and clumped-isotope (Δ47) data for carbonate-bearing impact breccias, impact melt rock, and target lithologies from four drill cores on a transect through the Chicxulub structure from the northern peak ring to the southern proximal ejecta blanket. Clumped isotope-derived temperatures (T(Δ47)) are consistently higher than maximum Late Cretaceous sea surface temperatures (35.5°C), except in the case of Paleogene limestones and melt-poor impact breccias outside of the crater, confirming the influence of burial diagenesis and a widespread and long-lived hydrothermal system. The melt-poor breccia unit outside the crater is overlain by melt-rich impact breccia yielding a much higher T(Δ47) of 111 ± 10°C (1 standard error [SE]), which likely traces the thermal processing of carbonate material during ejection. Finally, T(Δ47) up to 327 ± 33°C (1 SE) is determined for the lower suevite and impact melt rock intervals within the crater. The highest temperatures are related to distinct petrological features associated with decarbonation and rapid back-reaction, in which highly reactive CaO recombines with impact-released CO2 to form secondary CaCO3 phases. These observations have important climatic implications for the Cretaceous–Paleogene mass extinction event, as current numerical models likely overestimate the release of CO2 from the Chicxulub impact event. 2024-05-16T10:45:16Z 2024-05-16T10:45:16Z 2024-01-11 journal article Pim Kaskes, Marta Marchegiano, Marion Peral, Steven Goderis, Philippe Claeys, Hot carbonates deep within the Chicxulub impact structure, PNAS Nexus, Volume 3, Issue 1, January 2024, pgad414, https://doi.org/10.1093/pnasnexus/pgad414 https://hdl.handle.net/10481/91872 10.1093/pnasnexus/pgad414 eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional Oxford University Press