UCLA

Wrinkle ridges are common landforms documented on the surface of all rocky planets and the Moon in the inner solar system. Despite the long research history, the origin of this widely occurring class of landforms remains debated. One of the un-resolving issues is whether the formation of the wrinkle ridges were related to igneous processes as the ridges and flood-basalt plains are closely associated in all cases in the solar system. To address this issue, we conducted geomorphologic mapping, topographic-data analysis, and systematic examination of high-resolution satellite images at resolutions of 25 cm/pixel to 6 m/pixel across the central Tharsis region of Mars. The main result of this work is in the form of (1) a regional geomorphological map prepared using a CTX mosaic at a resolution of 6 m/pixel and (2) a local geomorphologic map prepared using a HiRISE image at a resolution of 50 cm/pixel. Our work, when viewed in the context of existing research, suggests that following sequence of events for the landscape evolution of the central Tharsis rise: (1) the creation of a plateau region along the eastern margin of the Tharsis rise by east-directed, crustal-scale thrusting, (2) the coeval formation of a volcanic plateau that acted as the source of east-flowing lavas that filled a basin between the tectonically induced plateau in the east and the volcanically generated plateau, (3) continued east-west crustal shortening during the emplacement of the lava flows favored the formation of wrinkle ridges due to thermal weakening of the uppermost crust, (4) regional glaciation postdating lava emplacement produced extensive boulder-bearing materials, striated surfaces, and glacial eskers that are superposed on top of the earlier formed wrinkle ridges, and (5) deposition of locally highly concentrated glacial flour during deglaciation laid down selectively mantled the tectonically deformed and glacially modified landscape. Our work supports the early suggestion that the Tharsis wrinkle ridges were created by horizontal shortening induced by crustal-scale tectonic processes. However, the occurrence of flow-front-like margins of many mapped wrinkle ridges suggests that the deformation was ductile, at least locally, most likely when the uppermost crust was still hot and weak. Glacial modification of the earlier formed wrinkle ridges means that the present-day wrinkle-ridge morphologies should not be used to invert the geometry of the blind thrust systems below the ridges.