Strike-slip faults on Mars: Observations and implications for global tectonics and geodynamics

The tectonic evolution of Mars has been driven primarily by the interaction of Tharsis-induced loading stresses with a uniform contractional stress field, leading to global assemblages of graben and wrinkle ridges. Until recently, strike-slip faults have appeared to be largely absent from the tectonic record. We here present evidence for a new set of Noachian to Early Hesperian strike-slip faults southwest of Tharsis. The best-preserved fault in the newly mapped set has a length of similar to 200 km and measured lateral offset of 5-9 km. We use the locations of both previously mapped and newly identified strike-slip faults to investigate the tectonic and geodynamic evolution of Mars. We model the tectonic evolution of the planet in response to the evolving balance between the loading and contractional stresses, finding widespread regions in which strike-slip faulting was favored. The observed tectonic history is consistent with a scenario in which loading-induced stresses peaked early in Mars history, followed by the growth of contractional stresses, leading to a shift in the preferred locus of strike-slip faulting from regions southwest of Tharsis in the Noachian to Early Hesperian, to northwest of Tharsis in the Early Amazonian. The contractional strain history inferred from the ages and locations of the strike-slip faults is consistent with the strains calculated from models of the thermal evolution of Mars in which the gradual secular cooling of the planet over time was augmented by plume-induced contraction during Tharsis formation in the Noachian.