¹Matthew J. O. Svensson,¹Gordon R. Osinski,¹Fred J. Longstaffe,²Timothy A. Goudge,³Haley M. Sapers
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14330]
¹Department of Earth Sciences, The University of Western Ontario, London, Ontario, Canada
²Department of Earth and Planetary Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas, USA
³Department Astronomy & Planetary Science, Northern Arizona University, Flagstaff, Arizona, USA
Published by arrangement with John Wiley & Sons

Impact-generated hydrothermal systems and postimpact crater lake systems are well-documented geological phenomena; however, evidence of hydrothermal venting into impact crater lake systems has rarely been reported. We investigated the well-preserved contact between hydrothermally altered impact melt-bearing breccia (outer/surficial suevite) and postimpact crater lake deposits sampled by the Wörnitzostheim drill core at the Ries impact structure, Germany. We logged the upper 32 m of core, describing sedimentary structures and general lithological and mineralogical variations. Mineralogy was studied in detail using X-ray diffraction, optical microscopy, backscattered electron imagery, secondary electron imagery, and wavelength-dispersive spectroscopy analyses. Twelve different units were identified in the logged section of drill core, which we broadly separated into four distinct groups: (1) marlstones and limestones, (2) sand/siltstones, (3) conglomerates, and (4) impact melt-bearing breccias. The sedimentary deposits (groups 1–3) likely represent a transition from a back-stepping alluvial fan to a transgressing, shallow lake shoreline. Secondary dolomite, smectitic clay minerals and clinoptilolite occur as void-filling phases in the conglomerates—the earliest sedimentary deposits of the Wörnitzostheim drill core. A potential temperature range of 50–130°C was estimated for these void-filling minerals based on previous mineral synthesis experiments, and the typical mineral assemblages reported for the principal sequence of hydrothermal mineralization in impact craters and argillic alteration. Early postimpact sedimentary deposits likely host limited hydrothermal mineralization, potentially indicating ideal conditions for some microbial life forms during initial crater lake formation.

¹Oliver Christ,²Anna Barbaro,^3,4Ludovic Ferrière,³Lidia Pittarello,¹M. Chiara Domeneghetti,²Frank E. Brenker,^1,5Fabrizio Nestola,¹Matteo Alvaro
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14326]
¹Department of Earth and Environmental Sciences, University of Pavia, Pavia, Italy
²Schwiete Cosmochemistry Laboratory, Department of Geoscience, Goethe-University Frankfurt, Frankfurt, Germany
³Natural History Museum Vienna, Vienna, Austria
⁴Natural History Museum Abu Dabi, Abu Dhabi, United Arab Emirates
⁵Section Alessandro Guastoni, Museum of Nature and Humankind, University of Padova, Padova, Italy
Published by arrangement with John Wiley & Sons

Iron meteorites, originating from the deepest parts of their parent bodies and separated during major break-up events, surprisingly rarely contain diamonds despite experiencing similar pressure–temperature conditions as diamond-bearing ureilites. In this study, graphite from three non-magmatic IAB iron meteorites Canyon Diablo, Campo del Cielo, and Yardymly was analyzed using micro-Raman spectroscopy, revealing the presence of the graphite G-band, the disorder-induced D-band, and occasionally the D′-band. Temperature estimates based on the G-band full width at half maximum (ranging from 1155 to 1339°C) are consistent with those found in ureilites. However, unlike in ureilites, no diamond bands were detected, as confirmed by μ-X-ray diffraction. The absence of diamonds is interpreted to be related to the thermal and mechanical properties of the iron meteorite matrix. Its high thermal diffusivity results in similar temperatures to ureilites, but its ductility dissipates shock-wave energy through plastic deformation, unlike the brittle ureilite matrix, which more effectively transmits the energy. Consequently, graphite in iron meteorites was heated but did not experience the high-pressure conditions required for diamond formation. Thus, we propose that impacts must either involve substantial energy or that graphite must be located close to the impact site, where it can experience high energies before these dissipate.