Crevassed Craters on Mars: Detection of Ancient Volatile Rich Crust

Introduction: Xanthe Terra region on Mars is known as a site of most drastic evolution related to the formations of extensive chaotic terrains and multiple outflow channels. Chaotic terrains are thought to have been the source of gigantic flooded water [1,2], and several models which fundamentally consider the chaotic terrain as a site of disruption of the aquifer in consequence of groundwater emanation, have been proposed [3,4,5,6,7,8,9,10]. Here we present geomorphological evidences which show the evolution of chaotic terrains and their association with the presence and distribution of subsurface volatiles. We examined a particular type of craters, which are called here crevassed craters (Fig.1) which dominantly exist inside and around the chaotic terrains. Crevassed craters have been already examined by several studies [11,12,8]. In [11] they were described and interpreted as a kind of thermokarst consequently formed by permafrost melting over the intruded magmatic body. Recently the morphology of chaotic terrains and outflow channels was again examined [8]. It was suggested that the crevassed craters resulted from localization of ground water paths through connected fractures systems related to the impacts. We report here new statistical observations on (1) crevassed crater sizes distribution and (2) crevassed craters excavation and present depths. These observations lead us to conclude about the presence of a critical depth for the formation crater crevasses overall the region. In consequence, we propose a volatile distribution in the Martian crust at the time of outflow channels event which explains the crevassed craters characteristics. We also suggest plausible models for the crevasses formation within the craters.