¹Anna Musolino, ¹Pierre Rochette, ^2,3Jean-Alix Barrat, ⁴Fred Jourdan, ^4,5Bruno Reynard, ¹Bertrand Devouard, ¹Valerie Andrieu, ¹Jérôme Gattacceca, ¹Vladimir Vidal
Earth and Planetary Science Letters 670, 119600 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2025.119600]
¹Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
²Univ Brest, CNRS, Ifremer, IRD, LEMAR, Institut Universitaire Européen de la Mer (IUEM), rue Dumont d’Urville, 29280 Plouzané, France
³Institut Universitaire de France, Paris, France
⁴Western Australian Argon Isotope Facility, School of Earth and Planetary Sciences, John de Laeter Centre for Isotope Research and C-FIGS, Curtin University, GPO Box U1987, Perth WA6845, Australia
⁵Laboratoire de Geologie de Lyon, CNRS UMR 5276, Ecole Normale Superieure de Lyon, 46, Allee d’Italie, 69364 Lyon Cedex 7, France
Copyright Elsevier

This study re-evaluates the anomalous subgroup of australites known as high Na/K (HNa/K) tektites (Chapman and Scheiber, 1969). Although previous compositional and isotopic analyses suggested a distinct origin, the group has never been formally recognized as a separate tektite strewn field. We present new data from six HNa/K tektites, complementing the eight specimens already described. We conducted a comprehensive investigation, including petrographic (optical and electron microscopy, and micro-X-ray tomography), geochemical (major and trace element compositions, Sr-Nd isotopic composition, 40Ar/39Ar dating), and spectroscopic (for the identification of inclusions) analyses. We concluded that the HNa/K tektites originated from a separate impact event compared to Australasian tektites; they have an andesitic to dacitic composition and arc-related trace element signatures. Lechatelierite (and phosphate) inclusions as well as high levels of chondritic contamination support an impact origin, for which we provide a more precise 40Ar/39Ar age: 10.76 ± 0.05 Ma. For now, Sr-Nd isotopic data and trace elements composition point to three possible sources associated with active volcanic arcs: Luzon (Philippines), Sulawesi (Indonesia), and the Bismarck region (Papua New Guinea). Systematic petrographic and geochemical differences observed between tektites from the western and eastern parts of the ∼900-km-wide hypothesized strewn field (located in Southern Australia) may help to constrain the location of the source crater, but they need to be confirmed by the study of more specimens. We propose the name “Ananguite” for this new group of tektites.

¹Courtney Jean Rundhaug, ¹Martin Schiller, ¹Martin Bizzarro, ^1,2Zhengbin Deng, ^3,4,5Hermann Dario Bermúdez
Earth and Planetary Science Letters 670, 119599 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2025.119599]
¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K, Denmark
²Deep Space Exploration Laboratory/CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China
³Department of Earth and Environmental Studies, Montclair State University, Montclair, NJ 07043, USA
⁴Grupo de Investigación Paleoexplorer, 1400-37 Trexlertown Rd, PA 18062, USA
⁵Departamento de Geociencias, Universidad Nacional de Colombia, Bogotá 11001, Colombia
Copyright Elsevier

The Cretaceous-Paleogene boundary (KPB) represents a massive extinction event in Earth’s history, probably triggered by the Chicxulub asteroid impact ∼66 Ma. The event dispersed vast volumes of ejecta materials including exceptionally preserved impact spherules in the Gorgonilla Island KPB section. Previous work identified three populations of spherules at Gorgonilla: 1) ballistically transported molten spherules, 2) a mixture of molten and condensed spherules dispersed by the expansion of a high-temperature, turbulent cloud (the “pyrocloud”), and 3) tiny droplets condensed from the plume (the “fireball layer”). We determine the Mg, Fe, and Ca isotopic compositions of pristine spherules to better understand the evaporation and condensation thermodynamics within the pyrocloud. We detect enrichment in mass bias corrected µ48Ca and µ26Mg* isotope signatures from the terrestrial value corresponding to an impactor contribution of ∼17–25%, most likely from a CM or CO chondrite-like asteroid. The mass-dependent δ25Mg and δ56Fe compositions are generally light or unfractionated, suggesting incomplete recondensation as the pyrocloud cooled and expanded. Combined δ25Mg and δ56Fe signatures reveal decoupling of these isotope systems, likely due to differing condensation rates. Thus, we calculate a higher average condensation rate of Fe than Mg, reflecting the thermodynamic decoupling and more complete recondensation signatures of Fe in the pyrocloud vapor. While we uncover information about the evaporation and condensation thermodynamics in the pyrocloud, the exact formation mechanisms of the complete suite of spherules remain complex with some spherules potentially forming from multiple mechanisms, including recondensation and splash–melting.