Progressive Evolution of the Valles Marineris Fault Zone and its Role in Controlling Interior Layered Deposits and Outflow Channels

Most recent studies of Valles Marineris concluded that its interior layered deposits (ILDs) were accumulated after the formation of the Valles Marineris trough system. Some workers also suggest that the ILDs originated from sedimentation in lakes within the Valles Marineris troughs, and that the sudden release of lake waters to the northern lowlands created the spectacular outflow channels at the eastern end of the Valles Marineris trough zone, leaving mounds of ILD sediments exposed within the troughs. The sudden release of water has been commonly related to erosion of damming of the troughs induced by glacial or mass-wasting depositional processes. In all existing models linking the ILDs to the outflow channels, the shape of the Valles Marineris trough system upon deposition of the ILDs was regarded to be constant. However, this notion is at odds with the new observation that the development of the Valles Marineris fault zone, a left-slip transtensional structure, continued to be dynamic throughout at least part of the sedimentation of the ILDs. This conflict prompts analysis of the role of the progressive opening of the Valles Marineris trough system in controlling the spatial and temporal evolution of ILDs and their relationship to the formation of the circum-Chryse outflow channels. Here, we test the hypothesis that the Valles Marineris trough system was a single intra-canyon lake and its outlet was progressively opened by normal faulting at the eastern end of the trough zone, releasing the floodwaters that formed the equatorial outflow channels. Our model sharply contrasts alternative mechanisms for producing the outflow channels such as progressive overtopping of structurally isolated lakes, rapid release of a subsurface groundwater aquifer, rapid release of stored ice, and episodic flooding. This tectonic damming makes specific predictions on the spatial relationships among (1) the evolution of the Valles Marineris fault zone, (2) the deposition and development of the ILDs, and (3) the timing and location of major outflow channels. Systematic geologic and geomorphic mapping of these relationships at locations of possible tectonic dams in northeastern Valles Marineris is currently in progress.