Using Relict Landscapes and Cosmogenic 10Be to Constrain Spatial and Temporal Variations in Uplift in Calabria, Southern Italy

Calabria, the toe of Italy, is the emergent part of the active forearc in the Tyrrhenian subduction-rollback system. This system originated along what is now eastern Sardinia with a Serravallian extension and submergence event and has rolled back 600 km in the last 12 My to its present location. During much of its rollback, the forearc remained submerged, recording little deformation, until Pleistocene. Data from uplifted marine terraces and Gilbert-type fan deltas suggest uplift of the forearc began around 1 Ma and progressed at 1.2 mm/yr. The mechanism of this uplift is debated, but coincides with other regional changes, so a deep-rooted transition in Calabrian rollback is hypothesized. Uplift rates show significant spatial and temporal variation across the exposed forearc and are likely to include both orogen-wide and local components. A more detailed, quantitative understanding of the uplift, chiefly in areas of higher elevation, is expected to shed light on the mechanism(s). We explore a new potential to quantify catchment-wide erosion rates on the Sila Plateau, the northernmost of three basement massifs. It has a steep, western flank is not associated with a surficial fault, while the eastern side slopes gently to the Ionian Sea. The basement is unconformably overlain by a Serravallian basal conglomerate and sandstone coeval with the onset of Calabrian rollback. This unconformity has been mostly eroded in the west where subhorizontal Quaternary sediments onlap the basement. On the eastern flank, this unconformity and overlying sediments are tilted 5-10 degrees to the east, developing a structural relief greater than 1 km. We mapped this unconformity throughout the Neto River catchment and found: The thickness of the basal conglomerate is controlled by small and localized syn-depositional extensional faults, but is independent of its position on the massif; the basal conglomerate is remarkably parallel to the unconformity; the unconformity is well preserved on the low relief interfluves of river valleys. The tilted sedimentary section at the base of the massif reaches into the Lower Pliocene, 3.5 Ma, with no evidence of growth; thus, its deposition occurred prior to the rise of the Sila Massif. The deposition of the basal conglomerate preserved a marker horizon to record post-3.5 Ma tilt and uplift. Given the clear morphology of this marker, we can also determine volumetric basement incision for different reaches of the Neto River. If assumed constant, current erosion started at 0.6 Ma, a result of combining incision with 10Be erosion rates. The onset of uplift is likely older since erosion was probably slower at the onset of uplift. Thus, the Sila relief is coeval with the regional, Pleistocene uplift, but requires tilting, not a strictly vertical uplift. Tilting should generate predictable variations in erosion rates around the Sila. The high precision of our 10Be dating enables such a detailed comparison of spatial and temporal variations. We find the highest erosion occurring in the middle reaches of the eastern rivers, while the western rivers have higher erosion further upstream. All the rivers analyzed have their lowest erosion rates near their headwaters.