Rochechouart Hydrothermal Overprint: Disentangling the Timing of Events through Ar-ar Dating

Introduction: There is a growing interest in the thermal evolution and fluid behavior of impact structures in the context of their possible influence on emergence of life both in the Early Earth and on other Planetary Bodies. This is largely related to hydrothermal mechanisms at work during the cooling of the hot materials produced and deposited in impact craters. Yet most of the research in this field is focused on theoretical approaches and mathematical models. Ground truth data of terrestrial craters are limited, despite the fact that they are by far the most accessible reservoir for testing models. Even on Earth, few of the 185 impact sites are sufficiently well preserved to yield material that can constrain the key processes of temperature evolution and water availability. The Rochechouart impact crater in the Massif Central region of France exposes rocks that recorded the hydrothermal system. Target rocks immediately below the crater floor are widely exposed within the ~24 km Rochechouart impact structure overlaid by the complete sequence of crater fill deposits in an inner zone ~15 km [1]. The post-impact hydrothermal system has recently been explored [2] and shows three main impactgenerated hydrothermal alteration assemblages; argillic-like, carbonate, and oxide dominated, based on SEM investigation of ejecta. However, the duration of the post-impact heating is critically important. Post-