Distinguishing Volcanic and Fluvial Activity in Mangala Valles, Mars via Geomorphic Mapping

Introduction: Mangala Valles is a 900 km-long outflow system extending from the martian southern highlands toward the northern lowlands just west of the Tharsis rise. Until recently, it was widely accepted that the flow features observed in Mangala Valles were the result of one or more catastrophic flooding events, likely by igneous disturbance of massive aquifer sources [1,2,4]. Such ideas have been supported by the presence of obvious streamlined features that can be easily identified using relatively low-resolution images such as those returned by Viking [1]. Subsequent studies focused on the number of flooding events, the amount of time separating each event, whether they shared a common source, and whether intermittent volcanism took place between flooding events [e.g., 1,3,4]. Recently, Leverington [5,6] introduced the idea that the system could have been carved solely by thermo-mechanical erosion by voluminous lava flows, or a hybrid hypothesis where the valley was initially carved by aqueous processes and later modified by volcanic erosion and deposition. McEwen et al. [10] also suggested that rather than being a strictly fluvial or strictly volcanic system, Mangala Valles was formed by fluvial incision followed by large-scale volcanic activity. To investigate this hypothesis, we composed a detailed geomorphic map of the Mangala Valles area using primarily MRO CTX images [9] and evaluated age estimates calculated using crater counting methods [16]. Although Mangala Valles has been previously mapped [1,3,4,17], CTX images provide resolution and coverage not available to previous authors, who relied on HRSC, MOC, MOLA, and Viking imagery for map production and analysis. Consequently, these maps either focus on a very small area or lack sufficient detail to make complete interpretations of the area as a whole.