QUANTIFYING THE STRUCTURES RESPONSIBLE FOR DIFFERENTIAL UPLIFT OF THE CALABRIAN FOREARC (SOUTHERN ITALY) USING GEOMORPHIC CONSTRAINTS FROM RECENT DEFORMATION OF THE LANDSCAPE

The Sila Massif is an uplifted block located in the forearc of the active Calabrian subduction zone, southern Italy. Uplift of the forearc began about 1 Ma, following a long period of tectonic quiescence despite hundreds of kilometers of horizontal translation. Correlation and dating of marine terraces throughout the forearc have constrained the vertical uplift rates to 1-1.2 mm/yr. These rates assume a vertical block uplift, however, which restricts possible mechanisms of uplift. In addition to the uplifted marine terraces, the forearc has rotated clockwise 15-20º since the Late Pleistocene and arc parallel extension, forming arc normal basins have dissected the arc. A vertical uplift cannot also explain these phenomena. We quantify spatial variations in uplift around the Sila Massif by comparing quantitative and qualitative geomorphology data of river drainages. Variations in river profile data and drainages reveal abrupt and gradual morphologic changes that occur across blind faults. Rivers eroding the flanks of the Sila Massif show high steepness indices. The regions of high steepness on the west side of the Sila Massif correspond to high concavities and sharp knickpoints, while the regions of high steepness on the east side correspond to low concavities and broad knickzones. Erosion rates determined from ¹⁰Be concentrations in river sediments are relatively consistent between the knickpoint and the mouth of rivers on the west side of the Sila Massif, but show significant increases from the mouth to the flanks on the east side. Lastly, river captures are occurring on the eastern part of the Sila Massif, but not the western part. These comparisons show a strong asymmetry in uplift of the Sila Massif from east to west, even though the overall uplift rates on both sides are about equal. We infer that uplift on each side of the Sila Massif must be controlled by different and unique structures. We propose a normal fault on the west side and a reverse fault with folding in the hanging wall to account for the morphology of the uplifted region. We show that these two structures fit into a broader picture of the subduction system and provide a framework in which we can interpret all the Pleistocene deformation.