Structural characterization of the cerberus fossae and implications for paleodischarge of Athabasca Valles, Mars.

摘要

Mechanically interacting fault systems on Earth are often associated with groundwater flow (e.g. Curewitz and Karson, 1997) by facilitating water storage and flow through fracture conduits before, during, and after seismic events (e.g. Sibson, 1975). Similar associations between interacting fault segments and fluid flow are present on Mars (Davatzes and Gulick, 2007a). The Cerberus Fossae compose a system of elongate topographic lows, a portion of which coincides with the source region of the outflow channel Athabasca Valles. The Cerberus Fossae and source area were mapped using Thermal Emission Imaging System (THEMIS) daytime IR mosaics and Context camera (CTX) images to establish spatial relations of structural features. Mars Orbiter Laser Altimeter (MOLA) elevation data were plotted to construct the depth profiles of the fossae to test the hypothesis that the Cerberus Fossae are normal fault-bounded graben. High Resolution Imaging Science Experiment (HiRISE) images were mapped for fractures within the fault damage zones with the degree of fracture plotted as a function of distance along strike. This plot established the spatial relations between fractures, mechanically interacting fossae segments, and Athabasca Valles. The depth profiles of the Cerberus Fossae are consistent with the displacement distribution of terrestrial normal faults with a surface expression consistent with fault propagation from depth and mechanical interaction among segments. Similarly, regions of interpreted mechanical interaction indicated by slip distribution and segment overlap correspond to increased fracture intensity and density. On Earth, such regions of mechanical interaction tend to have high fracture intensity (e.g. Davatzes et al., 2005), are associated with hydrothermal fluid flow (Curewitz and Karson, 1997), and have evidence of extensive long-term fluid flow as evidenced by diagenetic alterations (Eichhubl et al., 2004). Higher fracture intensities and densities near the head of Athabasca Valles as a proxy for increased permeability provide a potential mechanism and a necessary condition for the localized fluid flux necessary to supply the outflow channel. Thus, I conclude the Cerberus Fossae are mechanically interacting normal fault-bounded graben with highly permeable damage zones that would act to quickly dewater an aquifer resulting in the carving of Athabasca Valles.