The tectonic and volcanic history of Rhea as inferred from studies of scarps, ridges, troughs, and other lineaments

Abstract

Analyses of landforms on Rhea are used to define 13 types of geomorphic features, interpreted to be of tectonic and volcano-tectonic origin. All types except one seem to be extensional in origin. They occurred after the formation of population I craters and are contemporaneous with a major resurfacing event. The troughs, grabens, grooves, pit chains, scarps, and other lineaments vare “pure” extensional features, while the ridges are volcanic features formed in an extensional stress field. This global surface extension was followed by an era of global compression which produced megaridges and megascarps. These compressional features are not numerous enough to fit the theoretical stresses predicted by the typical thermal models of Rhea. All the extensional landforms appear to form a global grid pattern. This planetary wide grid is similar in direction to the theoretical pattern of a tidally distorted planet. That suggests either an orbital variation very early in the history of Rhea or the existence of an unknown process which has oriented the stress field during the extensional period.