Décollement Rheology Controls Crustal Deformation on Early Mars

Abstract

The circum‐Tharsis wrinkle ridge system represents one of the strongest tectonic imprints of early Mars, formed as the planet's largest volcanic province reshaped the lithosphere and redistributed stresses across thousands of kilometers. The coherent spatial pattern of these ridges suggests deformation governed by a laterally continuous basal décollement, so that their structural wavelength provides a direct constraint on the rheological state of the early Martian crust. We use thermo‐mechanical numerical models to explore two end‐member décollement rheologies and their topographic signatures under early Martian conditions. The spacing and characteristic wavelength of circum‐Tharsis wrinkle ridges, inferred to have formed during the Early Hesperian, constrain the style and scale of compressional deformation. Frictional décollements, even when weakened by high fluid pressures, are mechanically self‐limiting and localize strain, producing only short‐wavelength faults that cannot reproduce the observed ridge system. In contrast, low‐viscosity décollements (<10 18  Pa·s) distribute stress over long distances and generate regularly spaced, long‐wavelength (∼40 km) compressional ridges consistent with the very low surface slopes of Tharsis. These results link volcanic loading and far‐field deformation through ductile flow in a weak basal layer, most plausibly rich in salts. The inferred rheology is consistent with extensive evaporite formation on early Mars during Tharsis construction (Noachian to Hesperian), although hydrothermally altered phyllosilicate sequences cannot be excluded on viscosity grounds alone. Our results provide new constraints on crustal composition and hydrothermal conditions during this major phase of Martian tectonic evolution.