Behaviour of lower continental plate associated to a collisional orogen: structures, seismic-stratigraphy, deformations timing and local geophysical characters of foreland area with examples from Sicily channel and Adriatic region (Central Mediterranean).

Subduction zones are crucial for Earth’s dynamics and are characterized by the convergence of tectonic plates with one of it diving down the other; the subducting plate, or lower plate, is governed by flexural subsidence and extensional stresses which keep on migrating towards the orogenic wedge where it experiences the thrust sheet loading. When the two continental plates converge and collide (continent-continent collision), the lower plate is characterized by a foreland basin which preserves the evidence of extensional tectonics as well as the deformation signs caused by the loading of the orogenic wedge. For this PhD research, the aim is to investigate and characterize the geometry of the deformation timing and the geophysical characters in the foreland area of the Sicily Channel which belongs to the northern margin of the subducting African plate under the European plate to constrain the underlying mechanism and their variation through space and time. The intricate relation of the extensional and compressional tectonic settings ahead of the Sicily–Maghrebian orogenic system has been documented. The areas close to this orogenic wedge show complexity in the tectono-stratigraphic framework due to the migration of extensional stresses on the forebulge more towards the orogenic wedge which acts as a load on the bending lower plate. The confluence of the opposing extensional and compressional tectonic regimes occurs giving rise to structural and stratigraphic complexities. The analysis was performed with the aid of subsurface data and the satellite gravity and heat flow measurements which were complemented by high-resolution bathymetric data across the focused region. The anomalous behavior of geophysical and heat flow characters through depth crustal models of the focused region presented in this thesis confirms the presence of volcanic bodies and change in the lithospheric thickness with the migration of extensional stress that affects also the orogenic wedge. The Sicily Channel serves as a natural laboratory, revealing that this foreland region has preserved the record of dynamic processes (extension and compression), controlling lithosphere deformation in the lower plate. Thus, compressive deformations have extended far beyond the major orogenic front and affected a vast region of the subducting lower plate which otherwise has been under extension due to its bending. But, this work revealed that extension can propagate inside the orogenic wedge orthogonal to the trends of its major folds and thrusts which are both extended/dismembered and again compressed (causing positive inversion) in a short period of time (Pleistocene-Holocene – about 2 Ma). This envisages a more complex geodynamic relationship between the lower plate and the associated orogenic wedge in a collisional mountain chain.