Polyphase tectonics on Mars: Insight from the Claritas Fossae

Abstract

The Claritas Fossae (CF) is an elongated system of scarps and depressions >900 km long, representing the western boundary of the Thaumasia Region to the south of the Tharsis volcanic province. Although there is general agreement on the tectonic nature of such major physiographic feature, the processes that led to its formation are still debated. This study aims to better understand the tectonic evolution of the CF by combining two methodologies: kinematic numerical modelling and structural mapping. Through kinematic numerical modelling, we reproduce the present-day long-wavelength topography (hundreds of kilometres) at CF along four across-strike topographic profiles through the activity of a crustal listric normal fault. We observe that the modelled fault reaches the base of the crust, located at 80 km of depth, without changes in its listric geometry, suggesting a rather homogeneous thick crust. The accuracy of the results is based on the calculated mean misfit between the Martian and modelled topography. In two of the four profiles, the misfit is locally relatively higher, suggesting that the normal dip-slip component alone hardly explains the entire tectonic setting. Through structural mapping, we explore the depressions and scarps that feature the entire study area. We identify four sets of lineaments with different kinematics. The angular and crosscutting relationships between the sets suggest a Riedel-type arrangement within a dextral strike-slip shear zone. Thus, we propose a tectonic evolutionary model of the CF that involves a polyphase evolution made up of a Noachian-Early Hesperian right-lateral strike-slip phase followed by a Late Hesperian-Early Amazonian transtensional reactivation characterised by a significant normal dip-slip component. Our results suggest that the tectonics on Mars were not exclusively single or long-term deformations and that multiple subsequent tectonic events may have contributed to the present-day setting.