Lithospheric Contraction on Mars: A 3D Model of the Amenthes Thrust Fault System

Abstract

Amenthes Rupes is the topographic expression of a main fault belonging to a thrust fault system located parallel to the martian dichotomy boundary. A 3D forward model has been applied to the Amenthes thrust fault system, constraining fault geometries at depth, variations of slip along strike, and structural parameters controlling the formation of fault propagation folds. Our results provide a complex 3D view of the tectonic framework of the area, with implications for tectonic evolution, regional shortening distribution, and the main mechanical discontinuities in the lithosphere. The modeled fault surfaces show planar morphologies combined with listric geometries at depth. The obtained depths of faulting for the major faults of this fault system suggest a depth of the brittle‐ductile transition (at the time of formation) of 20–24 km, somewhat shallower than previous estimates for this area. A possible mechanical discontinuity located at 10.5–13 km deep can be deduced from the faulting depths of the secondary faults. The listric geometries at depth imply that slip is transmitted from the decollement, which, together with the inclusion in the model of secondary and subsidiary faults, allow us to estimate the horizontal shortening recorded in this area ranging from 2–3 km up to ~5.5 km in the southeastern part of the fault system. This range increases the previous shortening estimates in this area between ~60% and ~200%. Consequently, global shortening estimates based on global fault maps are biased by the detail of mapping, and shortening would substantially increase if secondary faults were included.