Formation and modification of wrinkle ridges in the central Tharsis region of Mars as constrained by detailed geomorphological mapping and landform 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 possible with time to 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, topographic-data analysis, and detailed landform analysis of satellite images at the resolution of 25 cm/pixel to 6 m/pixel in the central Tharsis region of Mars. The main result of this work is in the form of (1) a regional geomorphological map at the resolution 6 m/pixel and (2) a local geomorphological map at the resolution of 50 cm/pixel. Our work suggests the following sequence of events in the study area:(1) the creation of a plateau region along the eastern margin of the Tharsis rise by horizontal shortening, (2) the coeval formation of a western volcanic plateau as the source of east-flowing lavas terminating in the east against the tectonically generated eastern plateau, (3) wrinkle-ridge formation by folding in recently emplaced warm and ductile volcanic-lava piles, (4) emplacement of an ice sheet over the Tharsis region that produced extensive boulder-bearing materials, striated surfaces, and boulder-bearing dendritic ridge networks possibly representing glacial eskers, and(5) deposition of locally highly concentrated glacial flours during deglaciation that resulted in the formation of mantled terrain. 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 ductile folding, which we attribute to the thermally weakened lava piles emplaced during or immediately before the folding event. Post-folding glacial modification means that the present 3 wrinkle-ridge morphologies may differ significantly from the true fold shapes, which prevent their utilities for inverting subsurface thrust geometries. 5 existing fractures formed by earlier impact and tectonic processes. Strom (1972) further suggests that the secondary crenulated ridges are extrusive volcanic landforms emerging from tensile fractures along the ridge crests (also see Guest, 1971).Based on detailed mapping and satellite-image analysis, Bryan (1973) shows that his mapped lunar wrinkle ridges consistently cut across lava-flow-like landforms. This observation rules out the laccolith-dome model of Strom (1972) as a general cause of lunar wrinkle-ridge formation. Mapping by Howard and Muehlberger (1973) simultaneously reaches the same conclusion. The close association of the mapped lunar wrinkle ridges with ridge-bounding scarps leads Howard and Muehlberger (1973) to interpret the ridges and ridge-bounding scarps as folds and thrusts ab...