The origin of Martian grabens has remained controversial for decades, given the nonuniqueness of graben morphology and conflicting interpretations of dike-induced or faultingbased formation processes. We use measurements from the Mars Orbiter Laser Altimeter to identify the characteristic topographic signature at the surface of an igneous dike beneath a Martian graben. Our results suggest that this subtle but diagnostic signature can be used to test competing interpretations of the formation of grabens and associated fissures and collapse depressions.

The existence of igneous dikes beneath grabens in Tharsis remains contentious due to conflicting observations of Martian geomorphology. We examine the topographic signatures of a Tharsis‐radial graben array in 3 zones south of Arsia Mons. We identify dikes beneath grabens in all of the zones, with fewer dike‐induced grabens closer to Arsia Mons. We infer that a single radial swarm of dikes outside the magmatic source area, central Tharsis, is unlikely. Our observations instead favor a long and varied magmatic history throughout Tharsis with several episodes of dike injection.

[1] The orthogonal pattern of NE and NW striking wrinkle ridges in Hesperia Planum makes this area unique and enigmatic. The wrinkle ridge morphologies revealed in Mars Orbiter Laser Altimeter topography across ridge structures in Hesperia Planum suggest that wrinkle ridges form above thrust faults. The timing relationship among wrinkle ridge sets is evident in the digital elevation models; thrust faults striking NE are older than the NW striking ridges. The NE striking wrinkle ridges show unequal development adjacent to the NW striking wrinkle ridges, and an echelon pattern throughout Hesperia Planum; therefore formation by two independent sequential sets is not likely. Reactivation of the older (NE) thrust faults from the younger (NW) wrinkle ridges, inferred from the observations, is tested by resolving Coulomb failure stress changes along the older thrust faults from slip along the younger thrust faults. We find fault reactivation is likely in Hesperia Planum, regardless of the deposit material (basalt or tuff). Previously, the NE striking wrinkle ridges were interpreted as forming prior to, or contemporaneous to, the Tyrrhena Patera flank flow unit. This observation and the continuation of many of these ridges into the Noachian highlands as thrust fault scarps suggest formation of NE striking thrust faults no later than the late Noachian/early Hesperian. The NW striking wrinkle ridges, forming after the emplacement of the late Hesperian/early Amazonian Tyrrhena Patera deposit, imply geologically recent thrust faulting. The combination of NE and NW structural events implies a stress state rotation in Hesperia Planum of about 90°between the late Noachian and early Amazonian.