Slab retreat, slab tearing and interactions of slabs are first-order drivers of the deformation of the overriding lithosphere. An independent description of the tectonic evolution of the back-arc and peripheral regions is a pre-requisite to test the proposed conceptual, analogue and numerical models of these complex dynamics in 3-D. We propose here a new series of detailed kinematics and tectonic reconstructions from 35 Ma to the Present shedding light on the driving mechanisms of back-arc rifting in the Mediterranean where several back-arc basins all started to form in the Oligocene. The step-by-step backward reconstructions lead to an initial situation 35 Ma ago with two subduction zones with opposite direction, below the AlKaPeCa block (i.e. belonging to the Alboran, Kabylies, Peloritani, Calabrian internal zones). Extension directions are quite variable and extension rates in these basins are high compared to the Africa-Eurasia convergence velocity. The highest rates are found in the Western Mediterranean, the Liguro-Provençal, Alboran and Tyrrhenian basins. These reconstructions are based on shortening rates in the peripheral mountain belts, extension rates in the basins, paleomagnetic rotations, pressure-temperature-time paths of metamorphic complexes within the internal zones of orogens, and kinematics of the large bounding plates. Results allow visualizing the interactions between the Alps, Apennines, Pyrenean-Cantabrian belt, Betic Cordillera and Rif, as well as back-arc basins. These back-arc basins formed at the emplacement of mountain belts with superimposed volcanic arcs, thus with thick, hot and weak crusts explaining the formation of metamorphic core complexes and the exhumation of large portions of lower crustal domains during rifting. They emphasize the role of transfer faults zones accommodating differential rates of retreat above slab tears and their relations with magmatism. Several transfer zones are identified, separating four different kinematic domains, the largest one being the Catalan-Balearic-Sicily Transfer Zone. Their integration in the wider Mediterranean realm and a comparison of motion paths calculated in several kinematic frameworks with mantle fabric shows that fast slab retreat was the main driver of back-arc extension in this region and that large-scale convection was a subsidiary driver for the pre-8 Ma period, though it became dominant afterward. Slab retreat and back-arc extension was mostly NW-SE until ∼ 20 Ma and the docking of the AlKaPeCa continental blocks along the northern margin of Africa induced a slab detachment that propagated eastward and westward, thus inducing a change in the direction of extension from NW-SE to E-W. Fast slab retreat between 32 and 8 Ma and induced asthenospheric flow have prevented the transmission of the horizontal compression due to Africa-Eurasia convergence from Africa to Eurasia and favored instead upper-plate extension driven by slab retreat. Once slab retreat had slowed down in the Late Miocene, this N-S compression was felt and recorded again from the High Atlas to the Paris Basin.
Within deforming continental regions where metamorphic core complexes (MCCs) and synextensional granitoids are closely associated, deciphering the link between detachment faulting and magmatism often remains complex as (1) the rheological weakness of magma may stimulate mechanisms of strain localization, and conversely, (2) tectonic processes may open/close drains where magmas can intrude.Here we tackle this issue by focusing on the Cyclades with the comparison of five granitoid-cored MCCs (Tinos, Mykonos, Ikaria, Naxos, and Serifos) and their flanking detachment systems. In this region, granitoids were emplaced into the middle/upper crust over a relatively short time period (15-9 Ma), while metamorphic domes were largely exhumed after more than 10 Myr of extension. None of those intrusions thereby proves to be a real candidate for the genesis of MCCs but would rather be a consequence of a warmer regime during lithospheric thinning. However, all collected structural and kinematic data converge toward a regional scheme in which magmatic activity played a more pivotal role than previously postulated. Indeed, late evolution stages of MCCs were dynamically impacted by intrusions along which local and transient heterogeneities of the mechanical strength occurred, interfering with the sequential development of detachments. During their tectonically controlled emplacement, magmatic products intruded already formed detachments at depth, locally inhibiting their activity, associated with a contemporaneous upward migration of extensional deformation that tended to localize through time within intrusion roofs along rheological discontinuities. The newly formed detachments are expressed within granitoids through a continuum of deformation from comagmatic to ductile conditions, followed by cataclasis along detachments.Plain Language Summary Tectonics intensely deform continents forming mountains when the crust is thickened or low-standing regions where the sea can invade in the case of extension. Extension is less spectacular as deformation is hidden below sea level, but it involves intense deformations that can be studied when the deep crustal levels are exhumed below extensional faults with low-angle detachments. The portions of exhumed crust reveal deep deformation processes associated with emplacement of magmatic rocks because extension is coeval with heat advection toward the surface. One long pending question is whether or not the evolution of these detachments is influenced by growing granites. Based on a detailed field study of the deformation of five such examples in the Cycladic Archipelago, we show that the granites modify the evolution of the low-angle extensional faults leading to the sequential development and upward migration in the crust of a series of detachments through time. Granites indeed influence the evolution of detachments because they heat the crust in their vicinity and thus modify its mechanical resistance and introduce a mechanical heterogeneity during growth and cooling as the magma is intrinsica...
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