Crustal tectono-stratigraphic setting and geodynamics of the Corso-Sardinian Block from new CROP seismic data

Based on new CROP lithospheric seismic data integrated with other geophysical and geological data, a well controlled crustal setting for the Corso-Sardinian Block (CSB) has been reconstructed, and an innovative constrained geodynamic evolution is proposed. A continuous marine CROP section passing between Corsica and Sardinia and crossing the CSB from the Balearic Sea to the Tyrrhenian back-arc basin exhibits the tectono-stratigraphy of the block, which is thus fully explored for the first time by transcrustal seismic reflection data. On the western margin, listric faults connected to the Balearic basin opening and CSB rotation are clearly shown. The CSB axial mainland is characterized by thrust faults which thicken a crust previously stretched during the early Balearic stage (Oligocene) and successively recompacted in the late Balearic stage when collisions of Corsica with the NW Adria margin to the north of the block, and of SE Sardinia with the NW Panormid Promontory to the south took place. The CROP section M10, running from the Tuscan Archipelago to the Ligurian sphenochasm, exhibits an Alpine Tethys slab subducted laterally beneath Adria in the Eo-Alpine stage (Upper Cretaceous–Lower Eocene) and a W-dipping slab subducted beneath the southern European margin (Corsica) in the Balearic stage (Oligocene–Lower Miocene). CROP section M12B illustrates the lithospheric tectono-stratigraphy of the southern Corsica basin where it was closed by eastward-pulled CSB units along the Augustus Line (41◦ parallel, northern boundary of the Ionian Tethys), just at the NW Adria plate corner (Etrurian Promontory). Clear seismic imaging of the subducted Alpine Tethys slab is visible. On the Adria-verging frontal thrusts of the CSB, at the southern closure of the Corsica basin, Europe-verging thrusts associated with high mag anomalies are present. They are attributed to ophiolite-bearing units of Eo-Alpine obduction. These ophiolites are the southeastern continuation of those outcropping in NE Corsica and, with the exception of some dispersed fragments, are the last to connect those of the Coastal Chain segment in northern Calabria. The CROP section M28B images the stretched and delaminated eastern Sardinian margin very well. In the Cornaglia terrace, the Sardinian (Europe) crust is four times thinner than on the island’s coast. Over the delaminated crustal Sardinian units, thin Europe-verging thrust units associated with high mag anomalies are identified. On the basis of their tectonic framework, associated high mag anomaly, and characteristic seismic facies, we attribute these units to the SE Sardinian segment of the ophiolite-bearing units. With the discovery of this last segment, and by inverting the migration of all known ophiolites to their original position of Eo-Alpine obduction, it is now possible to reassemble an almost complete belt of ophiolites from the Betic zone to the Alps. From specific new geological-geophysical investigations, a detailed study of Sardinian rift activity has been performed, providing also an explanation of related magmatic activities. The ensemble of all relevant new data allows us to reconstruct a time–space evolution of the CSB. At the end of the Lower Cretaceous, the paleogeography of the central Mediterranean consisted of two intercommunicating ocean basins (Ionian Neotethys opened in Permo- Triassic times, and Alpine Neotethys opened in Middle Jurassic–Lower Cretaceous times), interposed between Europe to the north and Adria–Africa to the south. Two promontories (Etrurian Promontory to the north and Panormid Promontory to the south) delimited the Alpine Tethys crust from the Ionian. In the Eo-Alpine geodynamic stage (Upper Cretaceous–Lower Eocene) the joint convergence of Africa–Adria and interposed Ionian with Europe determined the closure of the Alpine Tethys and continental collision in the sector of the Alps, leaving a wide remnant of the Alpine Tethys west of the Alps unsubducted. In the Balearic stage (Oligocene–Lower Miocene), within the remnant Alpine Tethys, the CSB rotated, closing the Tethyan basin, and opening the Balearic back-arc basin. The Corsica block collided with NW Adria (Etrurian Promontory) and SE Sardinia collided with the NW Panormid Promontory, arresting the CSB rotation. The W-dipping subduction continued without stop in the Ionian Tethys (Tyrrhenian stage), and connected mantle flux dynamics gave origin to the Southern Apennine–Calabrian Arc–Sicilian Apennine thrust belt system, delaminating the Sardinian margin and opening the Tyrrhenian back-arc basin.