Timing and mechanism of uplift from cosmogenic radionuclides and structural data: a case study from an actively uplifting forearc, Calabria, Southern Italy

Abstract:

The Calabrian Arc is a subduction-rollback system that has experienced remarkably peaceful forearc tectonics during the last 12 My of rollback, even with 780 km of backarc extension. In contrast, during the Middle Pleistocene rollback slowed and the forearc experienced a surge of tectonic activity including 15-20° of clockwise rotation, arc-parallel extension, and widespread uplift. This rapid and continuous uplift (1-1.2 mm/yr) has affected the entire forearc and is striking because subduction is presumed to be ongoing. No discernable structure or mechanism has been identified to account for all phenomena. We combine structural mapping and erosion rates from ¹⁰Be concentrations in river sediment to model river erosion into the Sila Massif, the most prominent highland in northern Calabria. Interfluves between river gorges on the east side of the Sila Massif preserve a tilted paleosurface, which we interpret as subhorizontal until post-Early Pliocene. We reconstruct uplift and river incision using a forward model that is calibrated using the current erosion rates and the elevation of the paleosurface above the Neto River bed. The model tests two end-member structural growth models of uplift: tilting a fixed hinge and tilting from a propagating hinge. The propagating hinge model generates a better fit with the modern river profile and the modern erosion rates. We independently constrain uplift to beginning between 800 ka and 900 ka, consistent with the Late Pleistocene tectonic upheaval. In addition, the results show the Sila Massif grew via tilting with a propagating hinge. This method can be applied to other tectonic regions as a new way to quantify and identify young and active structures.