Local stratigraphic relations at Sandel crater, Venus: Possible evidence for recent volcano-tectonic activity in Imdr Regio

Abstract Imdr Regio is a volcano dominated young topographic rise of Venus whose most prominent volcanic structure, Idunn Mons, shows indications of being recently active. Despite its scientific relevance, this region has been poorly studied to date. Idunn Mons is spatially related to a rift system, Olapa Chasma, which dominates the topographic rise. The rift fractures around Idunn Mons form an “hourglass” pattern indicating a close tectonic interaction between the volcano and Olapa Chasma. The principal aim of this work is to understand whether Olapa Chasma has been tectonically active in the recent geologic past. For this purpose, we analyzed Sandel crater (45.7°S/211.7°E), an impact structure 17.9 km in diameter situated NW of Idunn Mons, and we used it as a local stratigraphic marker. Observing the variations in the radar brightness and crosscutting relationships, we produced a local geologic map of impact deposits, volcanic materials and tectonic structures surrounding the crater. Then, we used the map to reconstruct the local stratigraphy and relative ages of the materials for deciphering the temporal relations between the crater and volcano-tectonic activity. Following the existing degradation models for Venusian craters we could also estimate a time range for the formation of Sandel crater. The results show that its formation convincingly occurred during the period between 0.5 T and 0.15 T, where T is the average age of the surface of Venus. We present here a line of evidence that, at least in its last stage, the tectonic activity characterizing Olapa Chasma and Idunn Mons postdate the formation of Sandel crater. Building on the findings from previous studies, we hypothesize that not only volcanism but also the tectonic processes behind the formation of Idunn Mons and Olapa Chasma are geologically recent. For this reason, we refer to Olapa Chasma and Idunn Mons as a recently active volcano-tectonic system of Venus, which deserves to be a potential target site for future missions to Venus, including investigations of surface volcanism and seismicity.