Hidden tectonism on Miranda's Elsinore Corona revealed by polygonal impact craters

Abstract

We mapped the spatial distribution and orientations of polygonal impact craters (PICs) on the classical Uranian satellite Miranda to gain insight into the complex tectonic history of this moon. PIC straight rim segments in regions without visible fractures can be used to infer sub-regolith and/or sub-resolution fracture orientations. We identified and analyzed 14 PICs on Miranda, nine of which are located on its trailing hemisphere, overprinting Elsinore Corona and the nearby cratered terrain. These PICs do not follow the E-W orientations of the ridges within Elsinore's bounding terrain, indicating that these ridges are not underlain by deep-rooted (at least as deep as the crater bowl), sub-vertical normal or strike-slip faults. Instead, the ridges may be contractional features, consisting of folds and possibly thrust faults, or cryovolcanic features without fault structures. Furthermore, the PICs in this region indicate that a previously undetected NW oriented fracture system is present over much of Miranda's trailing hemisphere. Another PIC, somewhat distal from Elsinore on Miranda's anti-Uranus hemisphere, might be associated with the NW fractures as well. Additionally, three PICs are present proximal to Verona Rupes on Miranda's Uranus-facing hemisphere. These PICs exhibit N-S orientations consistent with the surrounding fractures that make up Miranda's Global Rift System. One other PIC is proximal to Arden and might be associated with the Arden bounding terrain. Identification of the NW fracture system provides new information on Miranda's complex geologic history. Based on cross cutting relationships with Miranda's ancient subdued crater population, the NW fracture system is older than Elsinore. However, this fracture system also overprints Elsinore, suggesting reactivation of the NW fractures after this corona had formed. Along with discussion of Miranda's geologic history, we consider the possibility that Miranda has undergone true polar wander, and we compare its terrains and geologic features to similar features on the Saturnian satellite Enceladus.