Abstract

A stratigraphic and structural analysis of the northern border of the Hyblean Plateau (south-eastern Sicily) has been carried out. This area is characterised by the outcropping of Lower Miocene-Quaternary volcanics and sediments (Schmincke et alii, 1997; Grasso et alii, 2004) and by a prominent WSW-ENE striking fault system (Ghisetti & Vezzani, 1980; Grasso et alii, 2000). From a morphological point of view, the study of the area has been supported by the analysis of four 3D-prospective projections obtained by draping a mosaic of aerial photo on DEM (Digital Elevation Model). Stratigraphic sections have been reconstructed in three key areas distributed from the east to the west of the northern margin of Hyblean Plateau, named respectively Monte Ranne-Monte Serravalle, Salto di Primavera-Filidonna and Palagonia-Poggio Forca, where new Quaternary structures have been recognized. Upper Pliocene and Pleistocene volcanism developed in a shallow marine and locally subaerial environment (Schmincke et alii, 1997). Volcanic activity occurred in distinct phases and areas, differing in volume, chemical composition and eruptive mechanism. A detailed stratigraphy of the Plio-Pleistocene volcanism in the Hyblean area is reported in Schmincke et alii (1997). The Authors recognized the presence of three main eruptive cycles named Poggio Pizzuto Formation (Lower Pliocene, basanitic products), Militello Formation (Upper Pliocene, tholeiitic products) and Poggio Vina Formation (Lower Pleistocene alcalic products). Deposition of carbonate sediments occurred during the intervals between of volcanic activity; this is related to a transgressive event which is observed along the marginal areas of Hyblean Plateau. The detailed reconstruction of the stratigraphic succession has provided a valuable contribution to define and constrain the age of the observed tectonic structures. The structural analysis pointed out the occurrence of three tectonic deformation stages characterized by ductile and brittle structures. During the Upper Pliocene-Lower Pleistocene an earlier extensional deformation occurred along the WSW-ENE fault system, induced by a N-S oriented extensional axis. The stratigraphic and tectonic features, broadly along the northern margin of the Hyblean Plateau indicates that these structures are related to the downwarping of this area beneath the front of the Maghrebian Chain. This stage was followed by a contractional deformation event represented by E-W trending brittle and ductile structures affecting Lower Pleistocene carbonate sediments. Structural analysis carried out along these structures pointed out a stress field characterized by a N-S oriented compressive axis, which also generated the contractional tectonic structures occurring to the south of Monte Etna (Lanzafame et alii, 1997; Monaco et alii, 2002; Catalano et alii, 2004). During the last extensional tectonic stage, characterized by a N-S oriented extensional axis, the study area was affected by normal faulting. In fact the observed structures deform Holocene deposits outcropping in Poggio Forca and Monte Ranne areas. Moreover, the recent volcanics observed in Monte Ranne areas. Moreover, the recent volcanics observed in Monte Ranne and Salto di Primavera areas can be related to this stage and could represents the youngest Hyblean volcanic products, probably coeval with the early eruptive event of Monte Etna. In conclusion, during the Lower Pleistocene a compressive event, induced by the migration of the external front of the chain, was recorded in the northern sector of Hyblean Plateau. The contractional deformation can be related to inversion tectonics along the E-W oriented structures coupled with a prominent extensional deformation pattern induced by the collapse of the northern foreland plate margin beneath the front of the thrust belt. This contractional stage is probably induced by frontal thrusting along the northern margin of Hyblean Plateau. In eastern Sicily both axial and frontal areas of the Siculo-Maghrebian Chain have been affected during the Middle Pleistocene contractional deformation processes (Lanzafame et alii, 1997; Monaco et alii, 2002; Catalano et alii, 2004).

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