Morphometric evidences of recent tectonic deformation along the southeastern margin of the Hyblean Plateau (SE-Sicily, Italy)

摘要

The present work focuses on the tectonic characterization of the southeastern portion of the Hyblean Plateau (SE Sicily, Italy). Along the southeastern margin of this raised crustal block, a clear recent antiformal deformation, coupled with diffuse landscape rejuvenation, affects the summit surface. Many studies, using merely qualitative geomorphological approach, refer the recent morphotectonic evolution of this region to motion along an active border fault, located at the base of the well-developed, arc-shaped Avola mountain front. This paper provides new insights resulting from the morphometric analysis across the Avola region, in order to detail on the relationships between the landscape geomorphic unsteadiness and the long-term tectonic deformation. We perform both drainage system and relief investigations, consisting of the exploration of different geomorphic indices (e.g. hypsometric integral, topographic relief and dissection, SL index, K-sn), long-profile analysis, marine terraces age model definition, field-based geomorphological and structural surveys. The results and the spatial distribution of morphometric indexes evidence the occurrence of two incipient NNE trending en-echelon fault segments, here named Cassibile-Noto Fault, responsible for the relief building along the southeastern border of the Hyblean Plateau. The northern fault segment directly controls the northern portion of the Avola mountain front, whereas the southern segment diverges from the main scarp, cutting through the low-standing areas of the coastal plain In addition, the centrifugal arrangement of fluvial captures and the half-elliptical envelope of the downstream projections of coeval paleo-long profiles, as well as the distribution of Pleistocene marine terraces, well evidence the long-term WNW-ESE-trending low-amplitude bow-shaped deformation affecting the footwall of the Cassibile-Noto normal fault. We relate this convex-upward trend to the Late Pleistocene (125 ka) tectonic deformation cumulated, at rate of similar to 0.80 +/- 0.05 mm/a, along the active fault. This incipient tectonic structure represents an extensional tectonic boundary that accommodates, together with the lspica Fault, the active NW-ward motion of the entire eastern sector of the Hyblean Plateau. Overall, the proposed updating of the tectonic setting of the study area, framed in the regional geodynamic picture of the eastern Sicily, would contribute to define a more suitable geological risk assessment of the region. (C) 2019 Elsevier B.V. All rights reserved.