Structural setting and geodynamics of the foreland domain of Sicily: State of art

In the Central Mediterranean region the Foreland Domain is composed of the undeformed continental areas of the Adriamicroplate, consisting of the Apulian Block, which is separated since the Late Paleozoic from the Pelagian Block, belongingto the Africa Plate, by the oceanic crust of the Ionian Basin.In Sicily and surroundings areas the Foreland is represented by the undeformed portions of the Pelagian Block, and by theIonian Basin.The Pelagian Block is characterized by a 25-35 km thick continental crust including a very thick Mesozoic-Cenozoic marinecarbonates with repeated volcanic intercalations. This sequence crops out in the Sahel region of Tunisia, in Lybia andextends offshore into the Sicily Channel, emerging in Lampedusa and the Malta islands, in the Sciacca area (western Sicily)and in the Hyblean Plateau (SE Sicily).Onshore, the western boundary of the Pelagian Block is represented by a left-lateral transcurrent zone (N-S Axis), separatingthe folded areas of the Tunisia Atlas from the undeformed areas of the Sahel.A similar N-S trending fault zone, the Hyblean-Maltese Escarpment, bounds the Pelagian Block to the east, from the IonianBasin. This prevalently normal fault system partially affected the original margin of the Hyblean continental crust and hasbeen active during the Pliocene and Quaternary.The central portion of the Pelagian Block is represented by the Sicily Channel, which is characterized by a shallow waterepicontinental sea with an irregular bathymetry. This area is affected by intense rifting, which has led to three NW-SEoriented deep troughs since the latest Miocene: the Pantelleria, Linosa and Malta grabens, separated by normal, sub-parallelfaults and filled with 1000-2000 m thick Pliocene-Quaternary turbiditic and hemipelagic sediments. Rift-related alkalicvolcanism is typical of this intraplate rifting. In correspondence with the axis of these tectonic depressions, the “SicilianChannel Rift Zone”, crustal thinning is evident, with the Moho lying at less than 20 km depth.The Hyblean Plateau represents an uplifted element, separated from the flexured areas on its northwestern margin by asystem of NE-SW oriented normal faults, with considerable vertical downthrow. These faults delimit the Gela-CataniaForedeep, which is occupied by allochthonous units of the frontal wedge of the chain, the Gela Nappe. Northwestwards theHyblean carbonates extend beneath the tectonic units of the roof thrust system of the Apenninic-Maghrebian Chain.The sedimentary cover of the Hyblean Plateau has been detected down to the depth of about 6 km, where Middle Triassiclayers have been found, while there is no information about the Permo-Triassic interval, identified in the seismic lines. Thesedimentary succession consists of thick Triassic-Liassic platform carbonates with intercalations of mafic volcanics,overlain by Jurassic-Eocene pelagic carbonates and Tertiary open shelf clastic deposits. On the Hyblean Plateau, exposedsedimentary rocks are mostly of Tertiary age. The Tertiary palaeogeographic picture, unchanged until Messinian times,shows a totally new arrangement after the Pliocene, when the northeastern sector of the Hyblean horst ceased to play the roleof a structural high, and progressively collapsed in connection with the development of the Hyblean-Maltese Escarpment.Early Pleistocene shallow-water bioclastic carbonates and sands with beach conglomerates are located along the margins ofthe plateau.Seismic profiles and well data indicate a lateral facies transition from the Hyblean domain towards the Sciacca domain insouthwestern Sicily. The interpretation of the CROP M23A line shows the continuity between Sciacca area and the HybleanPlateau. The same seismic profile displays flower structures originated by N-S trending trascurrent faults.The northward extent of the foreland below the roof thrust system in Sicily is clear, thanks to geophysical data and indirectgeological reconstructions. Carbonate bodies, connected to the successions of the Hyblean Plateau, but strongly deformedhave been detected below the allochthon of the orogenic belt, as far as the northern Sicilian ridge. There the Pelagian Block isaffected by a deep seated thrust system: the Pelagian-Sicilian Thrust Belt (PSTB). This system originated by the innermostmargins of the carbonate sequences of the Pelagian Block, that have been deforming since Late Miocene times. That iscoeval with the Tyrrhenian Sea opening.In western Sicily the PSTB consists of Triassic-Liassic shallow-water carbonates, Middle Jurassic to Early Oligocenepelagic carbonates and Late Oligocene to Early Tortonian continental shelf to slope, syntectonic terrigenous andbiocalcarenitic deposits. In eastern Sicily the PSTB is not exposed. In the seismic lines a signal interpreted as the top ofcarbonate sequences is clearly identifiable and extends as far as the Tyrrhenian shoreline. Below the northern ridge of Sicily,the seismic lines show a general culmination. This has influenced the geodynamic and the geomorphological evolution ofthe outcropping units of the uppermost roof thrust system.Geophysical data indicate a progressive thinning to the north of the African continental crust, and show a transition to anoriginal mainly consumed slab below the Tyrrhenian shoreline and interpreted like an original sector or branch of thepalaeoionian oceanic crust.The seismogeological data indicate that at the present time the Panormide continental crust is colliding with the PelagianBlock. The geological evidence of this collisional stage is manifested in the NW-SE oriented South Tyrrhenian System(STS), characterized by dextral faults, affecting both the Tyrrhenian offshore and the whole of the Island.In fact such a collisional stage has been recognized along the Tyrrhenian coast of Sicily from the offshore of Palermo town toPatti area, where the Vulcano Line separates the contemporaneous active subduction processes below the Calabrian Arc.The NW-SE oriented STS drives the transfer of the orogenic belt towards the Arc, characterized by the still subductingIonian oceanic crust. Geological mapping, integrated with stratigraphic and structural analysis, widely carried out in Sicilyshow that this area is dominated by a strike-slip tectonics, connected with the geodynamic evolution of the Tyrrhenianorogenic phase (Late Miocene up to Recent). Beside to the NW-SE oriented right lateral faults, antithetical NE-SW system,associated with N-S normal faults and south-verging thrusts, occur. All these structures are compatible with an uniquekinematic picture, but they are the surface expression of main crustal tear faults. An example is the Mt. Etna volcano, whichis located close to the boundary between the collisional area and the still subducting Ionian slab, and it is bounded by twomajor strike-slip shear zones.