Thrust faulting as the origin of dorsa in the trailing hemisphere of Enceladus

Abstract

Several large ridges, termed dorsa, stand over 800 m above their surroundings in a region centered on the trailing hemisphere of Saturn's icy moon Enceladus. In map view, these dorsa are linear to curvilinear, 20 km to more than 50 km long, and display near-orthogonal trends. They cross-cut (are younger than) most other geological features in the region. High-resolution limb profiles show the dorsa to be asymmetric in cross-sectioned profile and 5–6 km in width, and high-resolution images show striations along their crests. The structure and morphology of the dorsa suggest they are thrust blocks, possibly analogous to lobate scarps or wrinkle-ridges found on the terrestrial planets. The low slopes of their backlimbs and steeper forelimbs, suggest the dorsa were formed as wrinkle ridges or lobate scarps overlying thrust faults that penetrate 1–4 km deep to a detachment, most likely at the brittle-ductile transition (BDT). Their near-orthogonal trends are consistent with biaxial horizontal shortening. These relationships suggest that the central trailing hemisphere was recently subjected to a relatively high heat flow at the time that deformation occurred.