EXHUMATION, DYNAMIC TOPOGRAPHY, AND DRAINAGE DIVIDES IN ACTIVE AND ANCIENT OROGENIC SETTINGS, THE GIBRALTAR ARC AND APPALACHIANS

Erosional exhumation and long­-term landscape evolution of orogens is influenced by unsteady movement of the drainage divide that responds to both deep Earth and surficial processes. Here we explore, compare, and model the dependence of continental-­scale drainage divides on dynamic mantle support for active and post­-orogenic mountain settings. We use published records of exhumation timing and scale to compare against predictions of divide migration and drainage capture. The active tectonic setting for our study is the Alboran Sea, and the surrounding Betic and Rif ranges of the Gibraltar Arc. We low-­pass filter 30 arc­-second GEBCO digital elevation data at wavelengths consistent with crustal, lithospheric, and dynamic mantle­-scale processes to identify high-­standing regional topography. Our analysis identifies several locations where the modern continental divide is mis-­placed with respect to the highest­-standing regional topography. These results are consistent with a proposed model that involves an east­-dipping subduction zone that rolled back to the west across the Alboran Sea during the Late Miocene and is driving asthenospheric return flow. We use the Appalachians as our post­-orogenic setting. Here our analysis shows that the continental divide is again mis­-placed with respect to the highest-­standing regional topography. These results are consistent with recently published models of dynamic mantle support and epierogenic uplift in the past 30 Ma responding to far­field sinking of the Farallon plate. The methods applied in this work, provide a basis under which any topographic feature or region of interest can be evaluated for the feasibility of a dynamic mantle support model.