GNGTS 2013 - Atti del 32° Convegno Nazionale

In contrast, the channels pointing towards the southern sector are channels developed on the steeper cumulative SW-dipping fault slope, locally coincident with the right hillside of the valleys. Furthermore, a morphological local effects of the Late Quaternary tectonic deformation along the studied sector of the PMB is represented by a well defined distribution of the basins extent values (Fig. 3a). In order to carry out this analysis, the III order basins has been taken into account, due to their more homogeneous spatial coverage. In particular, the smaller basins are concentrated close to the faults, in correspondence of their SW-dipping cumulative slope, while the larger III order basins lie on wider and flatter surfaces of the opposite flank of the valleys. These evidences highlight a different significance and evolution history between the two group of basins with the same hierarchical order. The landscape of the studied area, as well as being dominated by the effects of the regional deformation (marine terracing, river entrenching), is characterized by local fault-controlled morphological features connected to the tilting of faulted blocks, such as the diffuse and wide N/NNE-ward fluvial captures. Each captured fluvial channel, flowing from the uplifted sector towards the depressed areas of the tilted blocks, caused a rearrangement of the drainage system. The main effects of this geomorphological processes are represented by an increase in terms of hierarchical orders of the subsequent valleys and the consequent decrease in order of the hosting streams. As a consequence, the forced phase of the drainage system reorganization determined the development of fluvial network anomalies through the tilted blocks, as showed by the distribution of the Hierarchical Anomaly Index ( Da ) (Avena et al. , 1967) calculated for the III order basins (Fig. 3b). Discussion and conclusions. The NE Sicily can be designed as a crustal mobile block ( PMB ) diverging towards the NNE respect to the rest of the Sicilian collision belt (Hollenstein, 2003), disengaging from the rest of the Calabrian Arc. As suggested by the analysis of the marine terraces carved along both the Tyrrhenian and Ionian coasts of NE Sicily, starting to the Middle-Pleistocene the PMB has experienced a huge uplift inferring a difference in uplift-rate of about 0.3-0.4 mm/y between the PMB (~1.1 mm/a) and the surrounding area (~0.75 mm/a). Fig. 3 – a) Map of the distribution of the III order basins extent displaying the NE-ward tilted surfaces. b) Hierarchical Anomaly Index (Da) Map calculated for the III order basins. 180 GNGTS 2013 S essione 1.2