Insights into the subsurface structure of wrinkle ridges on Mars

Abstract

Wrinkle ridges are important landforms on Mars and other planetary bodies and result from horizontal tectonic shortening. This study provides insights into the subsurface of selected wrinkle ridge sites, based on exposures provided by steep escarpments and crater slopes that crosscut wrinkle ridges. We mapped the complex fold and fault patterns and measured fault dips, where faults appear planar. The fault pattern underneath wrinkle ridges is diverse and is dominated by reverse faults and thrusts. The predominance of one fault system leads to morphological asymmetries of many wrinkle ridges. The upper tip of the dominant thrust fault is commonly situated beneath the steeper wrinkle ridge slope and may outcrop at its base. Polarity changes of wrinkle ridges along strike go along with a change of the dominant thrust direction. Symmetric wrinkle ridges are formed when a conjugate system of thrusts exists in the subsurface. Several wrinkle ridges display a main thrust fault whose dip angle bends over to a shallower dip at depth. The measurements of average dip for primary thrust and backthrust faults are 37° ± 2° and 28 ± 2°, respectively. In general, most of the examined wrinkle ridges are characterized by a multitude of subsidiary and backthrust faults. With the limitation that the uppermost 500-1000 m of the wrinkle ridges subsurface are accessible in this study and despite the large morphological and structural variability of wrinkle ridges, the kinematics of fault-propagation folds models seem to show a large match to our observations and measurements. Likewise, continuum mechanics models show a good fit to the obtained structural data. Fault-bend fold models and simple buckle folding models seem less compatible with observations.