DIAPIRISM RESPONSE TO IMPACTS MAY CAUSE STRESS PERTURBATIONS AROUND CRATERS THAT AFFECT FRACTURE GROWTH ON ENCELADUS

Fractures that interact with craters on Enceladus can create unique deformation patterns that are not observed elsewhere in the solar system. Rather than fractures disrupting older craters, as occurs on Venus, Dione, and Ganymede, some craters on Enceladus appear to cause local perturbations in the regional stress field that cause subsequent fractures to deviate from their growth paths. Addressing why some craters, but not others, affect fractures can provide insights into the causes of local heterogeneities within the regional stress regime. The regional geologic history was established by creating detailed fracture maps within the cratered terrains, revealing four distinctly oriented systematic fracture sets. The four fracture sets indicate a rotation of the stress field through time, possibly caused by nonsynchronous rotation of the ice shell. We examine crater size, fracture spacing, and radius of influence as controls on crater-induced fracture reorientation. Craters of all sizes (>1 km) are found to influence fracture growth but there is a threshold of ~7 km diameter above which craters always reorient fractures. This threshold size likely relates to characteristic fracture spacing, which, in turn, relates to brittle ice thickness. Craters with large diameters relative to fracture spacing cause a more marked fracture reorientation than craters that are small with respect to fracture spacing. Additionally, there appears to be a minimum radius of influence of up to two crater diameters for large craters. These observations will be used to constrain models of the regional stress field around a crater. We consider that localized, thermally mobilized ice beneath the crater causes the perturbation of the stress field, driving crater/fracture interactions. Impact events on Enceladus may create localized disruptions to the thermal regime inducing a diapirism response of the ice shell. This could support the hypothesis that Enceladus has a warm, potentially unstable interior, consistent with a recently hypothesized global ocean model and the development of the south polar thermal anomaly.