A Tilted and Dissected Relict Landscape on the east flank of the Sila Massif, Calabria, Southern Italy: Asymmetric Uplift in the Late Quaternary?

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American Geophysical Union
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Calabria, located in Southern Italy, is the emerged part of the forearc in the Ionian/Tyrrhenian subduction-rollback system. Data from uplifted marine terraces and Gilbert-type fan deltas suggest uplift of the forearc began around 1 Ma and progressed at about 1 mm/yr. The uplift is pervasive and spatial variations have not been associated with structural relief that developed earlier during Calabrian rollback (12 My). The onset of uplift coincided with other regional changes and is thought to mark a deep-rooted regime change involving the entire subduction system. Uplift rate at any one place and its evolution through the Quaternary tectonic reorganization is likely to include both orogen-wide and local components. More detailed understanding of the uplift in space and time is expected to shed light on both the nature of the mid-Quaternary tectonic transition and on the cause for the regional uplift that followed. The Sila Massif is the northern-most basement block in Calabria forming a prominent geomorphic and structural high about 50 km long and 30 km wide. It exposes predominantly quartzo-feldspathic crystalline igneous and metamorphic rocks associated with pre-Calabrian, Alpine orogenesis. The basement is unconformably overlain by a basal conglomerate and sandstone deposited at the onset of rollback. These beds are parallel to the unconformity and do not on-lap, thus, the unconformity was sub-horizontal at the time of submergence. Now this unconformity is tilted 5-10 degrees to the east developing a structural relief of more than 1 km. The contact between these units controls the slope of the east flank of the Sila and crops out extensively on the low relief interfluves of river valleys. We, therefore, interpret this unconformity to be a paleolandscape formed at low elevation and preserved only due to recent exposure and river incision. Younger strata (Tortonian to Messinian) are preserved at the base and are parallel to the unconformity. Syn-depositional faults abound, but are relatively small and unrelated (oblique) to this tilting. We mapped the relict surface across the Neto River catchment (a major river that dissects the surface) and found it to be remarkably consistent in areal extent and dip. Catchment-wide erosion rates determined from 10Be concentrations in river sediments offer a new, quantitative analysis of the uplift. We sampled eight locations along the Neto River, measured 10Be concentrations in each, and converted the concentrations to catchment-wide erosion rates. Erosion rates are highest where the Neto River erodes the relict landscape (380 m/My) and lowest on top of the Sila Massif (84 m/My). Assuming the erosion is confined to the canyon, is uniform across the canyon, and is constant through time, the average accumulated erosion in this reach of the Neto River is 165 m. This number, coupled with an erosion rate of 296 m/My for the same reach, yields an age of 0.56 Ma for the uplift of the relict landscape (a minimum age if erosion has increased with tilting). This result suggests that most of the Sila structural high developed since the mid-Quaternary tectonic reorganization.