Pleistocenic tectonic activity in the area to the South of Mt. Etna (Sicily)

The Quaternary sedimentary substratum of Mt. Etna, in Eastern Sicily, crops out in the area to the south of the volcano and is composed of a Lower-Middle Pleistocene foredeep succession of marly clays, up to 600 m thick, which passes upwards to a sequence, some 10 m thick, of coastal sands and fluvio-deltaic conglomerates, unconformably overlain by Middle Pleistocene (-330 ka) alluvial conglomerates. In the area there are evidence of the Etna submarine to subaerial fissural early activity represented by basalts of tholeiitic-transitional affinity (pre-Etnean volcanism, 500-200 ka). This activity is thus almost coeval to the deposition of the Etna substratum deposits. The present volcanic edifice, characterized by alkaline products, started to form 180 ka ago, on the footwall of a Middle-Upper Pleistocene normal faults system, at the boundary between the Ionian and chain-foreland domains. To the South of Mt. Etna, the Lower-Middle Pleistocene deposits are folded in a E-W trending anticline about 10 km long, which has been interpreted as a fault propagation fold at the front of the Maghrebian thrust system. This structure developed about 330 ka ago and warped the Middle Pleistocene alluvial conglomerates. A flight of undeformed coastal alluvial terraces of the Simeto River, related to the time span from 240 and 60 ka and located at altitudes between 250 and 50 m, carve the western extension and the southern limb of the anticline. Therefore, the age of the anticline is confined between 330 and 240 ka and is older than the Etna present edifice, which started to grow 180 ka ago. To the East, beach deposits intercalated with 170-100 ka old alkaline lavas are evidence of the Ionian coast uplift. These deposits, which are at 180 m a.s.l. to the NW of Aci Trezza, can be attributed to the 125 ka Tyrrhenian high-stand. Ancient shorelines, dating to the 200 ka, 100 ka, 80 ka and 60 ka sea level high-stands, were observed in this area at elevations of 230 m, 130 m, 100 m, and 40 m a.s.l., respectively; this fact suggests an uplift-ràte of 1.4 mm/year. This high value of uplift-rate can be explained as the effect of the NNW-SSE trending active normal fault system located at the lower southeastern slope of Mt. Etna, which extends off-shore into the Ionian sea. It can be concluded that the compressive tectonic regime responsible for the evolution of the frontal part of the Maghrebian thrust-system in the Etnean area, ended about 240 ka ago. From that time the uplifting of the eastern Sicily coast has been remarkable and it is attributable to the activity of normal faults related to the regional WNW-ESE extensional tectonic regime. The activity of Mt. Etna volcano, subsequent to the anticline formation, seems to be contemporaneous to the extensional tectonics of the Ionian coast.