CORRELATING CONTRASTING MORPHOLOGY OF LANDSLIDES IN VALLES MARINERIS WITH HYDRATED MINERALS: NEW INSIGHTS FROM DETAILED MORPHOLOGICAL MAPPING AND CRISM SPECTRAL ANALYSIS

Landslides are the most prominent geologic features in the 4000-km long Valles Marineris (VM) trough system. Their occurrences have been variably related to slope instability associated with preexisting weakness, ground shaking by impacts, and seismicity along trough-bounding faults. Transport of long-runout landslides in VM has been related to reduction of basal friction caused by the presence of fluids or trapped air. In order to isolate various competing mechanisms for landslide initiation and transport, we first systematically mapped landslides in VM utilizing multiple orbital imagers. The main finding of this work is that the landslides can be classified into two types: (1) thin-skinned landslides, characterized by thin sheets spreading over 10s of km across the trough floor, and (2) thick-skinned landslides, characterized by fault-bounded rotated blocks with <10 km transport distances from their source regions. To examine the effect of differences in ground surface properties in landslide transport, we also performed visible near-infrared spectral analysis of mineral compositions in the aprons of the two types of landslides with Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Our results indicate that the thin-skinned landslide morphology is associated with the presence of hydrated minerals whereas the thick-skinned morphology is not. As the thin-skinned landslide surfaces display longitudinal grooves, which are typically associated with landsliding over glacial surfaces on Earth, and morphometric data suggest a basal layer of slip as the cause of the long runouts observed, we propose that thin-skinned landslides in the VM troughs were induced by snow-melting due to basal friction along a reactivated normal fault surface during landslide emplacement, as a result of basal erosion and subsequent oversteepening. In this model, in VM, the landslide emplacement style depends on the supply of ground ice along the path of landslide emplacement. The preferential development of thick-skinned landslides in rugged Ius Chasma and wide occurrence of thin-skinned landslides in smooth Coprates Chasma may be related to the east-flowing paleodrainage system along the southern VM trough. Our model has important implications for paleo-climate conditions during the development of VM.