Geomorphic Expression of Active Tectonics in a Rapidly-deforming Forearc, Sila Massif, Calabria, Southern Italy

We examine the tectonic geomorphology of La Sila, Calabria, southern Italy, a high-standing (1500 m) plateau surrounded by crustal extension, with map, DEM, and field data. These data are used to constrain a simple geodynamic model that describes short-wavelength deformation of the plateau rim. Topographic metrics including drainage patterns, river longitudinal profiles, and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader, regional uplift that has increased the mean elevation of the Sila Plateau during the Quaternary. The concavity, steepness, and length-gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults. A previously unrecognized horst on the northeastern portion of the plateau was identified with these data. Nevertheless, the core of the Sila Plateau remains relatively undeformed with respect to its flanks which are characterized by steep, fault-bounded escarpments. Active extension has dropped base level for and unloaded the plateau rim, causing deep fluvial incision and associated flexural uplift of the footwall. This footwall uplift helps maintain a separate external, and nearly radial drainage away from the plateau along its flanks, and a nearly closed drainage for the plateau interior. A drainage divide roughly correlates with the plateau rim, inhibiting the process of drainage integration through the Sila interior and subsequent landscape dissection. As a result, geomorphic processes driving erosion of the Sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation. These results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another. We conclude that the Calabrian forearc has a similar geomorphic evolution as the more northern Apennines consistent with the emerging view that growth of Apennine topography has been recent (Quaternary), rapid, and possibly decoupled from rock deformation in the orogenic wedge.