Tectonic reconstruction of Sicily in the framework of the Central Mediterranean geological evolution

This PhD thesis is part of a research project focused on the kinematic and tectonic evolution of some key areas of the Western Mediterranean region from the early Cretaceous to present. The aim of this project is to obtain a quantitative model that reconciles the kinematic constraints with the geological-geophysical data recorded in the Mediterranean area. We will provide, using a large amount of data published in many papers in the literature, to develop a coherent reconstruction that will best explain the large scale tectonics of the western Mediterranean region. The kinematic model is obtained taken into account different data derived from various geological datasets, like tectono‐metamorphic events, structural observations, stratigraphic record, magmatic activity distribution and palaeomagnetic data (where available). Reconstruction was carried out using integrated software, PCME 4.0, for the developing of paleogeographic or paleotectonic maps. This software enabled us to create paleotectonic maps by the rotation of all present day tectonic elements to their ancient position by applying rotational motions to numerous microplates and tectonic elements involved in the evolution of the western Mediterranean area. In particular, this PhD thesis is focused on the Neogene evolution of the Sicilian Maghrebian chain. In order to obtain a self-consistent model, it was necessary to reconstruct the Mediterranean evolution, starting from the Mesozoic paleogeography of the western Mediterranean area. The first step was to build a kinematic model that explains the tectonic relation among Western Alps, Alpine Corsica, and Calabrian Arc in the general context of tectonic evolution of the western Mediterranean during the late Cretaceous and the Cenozoic. We propose an alternative model, which overcome the classical models that either interpreting Corsica as the backstop of the Apennine subduction or apply a not easily justified geodynamically model of subduction flip (assuming the detachment of the Ligurian slab following the southeast dipping subduction stage). We suggest that the opposite subduction polarities for Alpine Corsica and for the Calabrian Arc are associated with the occurrence of a transform boundary active since the late Cretaceous. Moreover this new scenario, involving the definition of a new set of plate boundaries for the western Alps–Corsica area, satisfactorily takes into account geological constraints represented by metamorphic ages, stratigraphic record and structural data and also provides useful insights into the geometry of the larger (Africa–Iberia–Eurasia) plate boundary configuration and the original setting of the associated subduction zones. Moreover, the model explains the origin and the structural evolution of the wedge-top deposits, which develops in an extensional context (among Alpine Corsica, Calabria and Kabylies) during the Corsica and Sardinia block rotation, such as “Cilento Unit”, and “Capo d'Orlando Fm. ”. The second step provides a kinematic model of the Tyrrhenian- Apennine system evolution since the early Burdigalian. In this model, we divide the Apennine chain into six deformable sectors, characterized by homogeneous Tyrrhenian extensional deformation, each other separated by the transverse structures of the chain (Ancona-Anzio Line, Sangineto Line, Taormina Line) for which the model explains the origin and evolution. The rotation poles (Euler poles) of each sector are defined through a morfostructural analysis of the tectonic lineament in the Tyrrhenian basin and along the Apennine chain. The ultimate goal of this PhD thesis was the characterization of the tectonic evolution of the Sicilian-Maghrebian chain and Southern Tyrrhenian area in the framework of the Tyrrhenian-Apennine system since the early Oligocene. The main tectono-sedimentary stages of the Caltanissetta foredeep basin and of the Cefalu basin, active from upper Miocene to Plio-Pleistocene, are described from a kinematic point of view through a series of plate reconstructions that show the Caltanissetta basin peculiarity with respect to the Maghrebian chain foredeep. The development of the Neogene systems is deeply controlled by the Mesozoic physiography of the African and European margin: the sinking of the oceanic lithosphere, the thinning of the continental lithosphere, the location, and the structure of the different domains (Imerese, Sicanian, Panormide, and Iblean-Pelagian block) controls the development and the propagation of the foredeep and of the thrust tectonics. Starting from the early Miocene, the foredeep (e.g. the Caltanissetta basin) develops on to the frontal sector of the chain, which is characterized by transversal extension on to the upper plate, while moved towards South-South East involving the Panormide carbonate platform, the basin domains (Imerese-Sicanian domains) and the Iblean-Pelagian domain. This process drives the thinning of the thrusted units whose thickness and elevation decrease toward the south. As a consequence of these coupled processes (E-W extension and contractional deformation in NNW-SSE direction), the geological setting of Sicily is characterized by a deep basin (the Caltanissetta foredeep), evolved since the Tortonian times, and by a chain, which develops in W-E direction, in the northern sector. The thrusting is contemporaneous with lateral movements related to the E-W extension in the basin accompanied by the late Miocene-early Pleistocene clockwise rotations of the extensional structures, undergoing a tectonic inversion, during the progressively deformation of Sicilian margin. This extensional process involves the whole Sicily and it is responsible for the development not only of the Caltanissetta Basin but even of the northern Sicily offshore basins (e.g. the Cefalu basin). More in detail, the continuity of the extensional area is interrupted by an E-W trending regional structure (e.g. the Kumeta-Alcantara fault) that dislocates the different sector (the Caltanissetta Basin to the south and the Cefalu Basin to the north). Along this transpressional structure, which links the two different sector of the basin, the Sicilian Maghrebian chain develops starting from the Tortonian times. The extensional process in the Northern-Central Sicily\Southern Tyrrhenian margin ends in the late Pliocene when this sector of the Sicilian chain welded to Europe with cessation of extension in the southwestern Tyrrhenian Sea and with the formation of the Taormina Line, a major NW-SE boundary between Sicily and Calabrian Arc. From this time, the progressive migration of the thrust front, which is today located in the southern Sicily offshore and, on land, along the Gela-Catania alignment, is controlled by the Africa-Europe movement. Moreover, this model includes a self-consistent reconstruction of the southern Tyrrhenian Sea margin and of the tectonics that led to the formation of structural highs and deep sedimentary basins (Peri–Tyrrhenian basins) and of the Aeolian volcanoes.