Revisiting the Rochechouart impact structure, France

Abstract

AbstractThe Rochechouart impact structure, south‐central France (45o50′N, 0o46′E), is a partly eroded, approximately 200 Myr, complex impact structure. The impactite suite at Rochechouart provides an excellent example of gradational boundaries and transitional lithologies that have been historically difficult to classify with standard impactite nomenclature. Here, we present the first detailed scanning electron microscopy‐based description of the Rochechouart impactites integrated with hand‐sample and petrographic observations with the goal of understanding the clast‐matrix relationships of transitional lithologies. Three main impact‐generated hydrothermal alteration assemblages are also recognized: (1) argillic‐like, (2) carbonate, and (3) oxide. Our results support the existence of a continuum between clast‐rich impact melt rocks and glass‐rich clastic breccias (suevites) that must be represented in universal classification schemes. This suite of impactites from the Rochechouart impact structure is used as a test case for a recently published classification scheme based on the nature of the groundmass setting a precedent for classification of impactites with limited to no geological context such as deeply eroded terrestrial impact structures and future sample return missions. The re‐evaluation of the melt‐bearing Rochechouart impactites questions the currently accepted size of the crater, suggesting a much larger original crater diameter.