Geometric forward modeling of thrust systems underlying shortening landforms on Mercury

Abstract

Mercury hosts thousands of shortening landforms that are widespread across the entire planet. The shortening is widely accepted to be caused by a combination of thrust faulting and folding, resulting from the global contraction of Mercury caused by long, sustained cooling. Most shortening landforms on Mercury's surface have been classified into one of two groups: lobate scarps or wrinkle ridges. There is no distinct statistical difference in the surface morphology of these shortening landform classifications. Only a small subset of shortening landforms are clear-endmember wrinkle ridges and lobate scarps. The difference between geomorphic manifestations of shortening landforms may be governed entirely by the thrust systems and associated folding that form them. We therefore model thrust systems associated with 55 lobate scarp and wrinkle ridge endmember shortening landforms found across the surface of Mercury. Structures were modeled in 2D sections below the topographic profiles of landforms with the greatest structural relief. Models utilized the fault-bend fold algorithm in the MOVE geologic modeling software. Once models matched the observed topography and shortening strain, fault geometric parameters, such as number of structures, dip, depth extent of faulting, height, etc., were extracted and compiled for all structures. Our modeling shows that Mercury hosts a wide range of complex thrust systems, including single, listric faults, imbricate thrusts, and pop-up structures. In particular, the morphologies of lobate scarps endmember structures are best explained by models of a single, listric fault, whereas most wrinkle ridge endmember structures require more than one fault. We identify a large overlap in the variation of fault geometric parameters for both wrinkle ridge and lobate scarp archetypes, confirming the results of our previous geomorphic analysis that shortening landforms do not comprise two distinct categories. The overlap in geometric parameters suggests that the formation mechanisms of lobate scarp and wrinkle ridge endmember structures are the same.