Formation and modification of wrinkle ridges in the central Tharsis region of Mars as constrained by detailed geomorphological mapping and landsystem analysis

Abstract

Wrinkle ridges are common landforms documented on all rocky planets and the Moon in the inner solar system. Despite the long research history, their formation mechanisms remain debated. A key unresolved issue is whether the wrinkle-ridge formation is related to igneous processes. This is because wrinkle ridges are mostly associated in space and possibly in time with the occurrence of flood-basalt volcanism in all cases on the rocky bodies in the inner solar system. To address this issue, we conducted geomorphological mapping, a topographic-data analysis, and a detailed landform analysis of satellite images at a resolution of 25 cm/pixel to 6 m/pixel in the central Tharsis region of Mars. The main results of this work are in the form of (1) a regional geomorphological map at a resolution of 6 m/pixel and (2) a local geomorphological map at a resolution of 50 cm/pixel. Our work suggests the following sequence of geological events in the study area: (1) formation of a northeast-trending mountain range (i.e., the Thaumasia plateau) along the eastern margin of the Tharsis rise resulting from the Himalayan-style crustal-scale thrusting; (2) coeval volcanic-plateau construction west of the thrusting-induced rising mountain range; (3) termination of east-flowing lavas sourced from the volcanic plateau at the rising mountain range to the east; (4) wrinkle-ridge development by folding in recently emplaced warm, ductile volcanic-lava piles; (5) emplacement of a regionally extensive ice sheet over the central Tharsis region that produced extensive boulder-bearing materials, striated surfaces, and boulder-bearing dendritic-ridge networks possibly representing glacial eskers; and (6) deposition of locally highly concentrated glacial flours during deglaciation that resulted in the formation of mantled terrain on plains between wrinkle ridges. Our work supports the early suggestion that the Tharsis wrinkle ridges were created by horizontal shortening induced by crustal-scale tectonic processes. In detail, however, the occurrence of flow-front-like margins of many mapped wrinkle ridges suggests their formation by ductile deformation, which we attribute to the thermally weakened lava piles emplaced during or immediately before the folding event. Our compression-induced wrinkle-ridge model also differs from the early hypotheses in that the thin-skinned folding is associated with basement subduction, which explains the lack of coeval and parallel folding and extensional faulting. Post-folding glacial modification means that the present wrinkle-ridge morphologies may differ significantly from the original fold shapes, which prevents the utility of using present-day topographic profiles across wrinkle ridges for inverting the underlying thrust geometries.