International audienceLow-angle normal faults accommodate a large part of continental post-orogenic extension. Besides the intrinsic rheological characteristics of the continental crust that may lead to the formation of shallow-dipping shear zones at the brittle–ductile transition, the role of pre-existing low-angle structures such as large thrusts has been proposed by several authors. We explore this question with the example of the North Cycladic Detachment System (NCDS) that is composed of a series of distinct detachments cropping out on the islands of Andros, Tinos and Mykonos, separating the Cycladic Blueschists in the footwall from the Upper Cycladic Nappe in the hanging wall. We show that these extensional structures are part of a single large-scale structure (more than 200 km along strike) that reactivates the Vardar suture zone. It extends eastward on Ikaria and westward offshore Evia and Thessalia where it probably connects to recent shallow-dipping normal faults evidenced on published seismic reflection profiles. The NCDS started its activity in the Oligocene concommitantly with the Aegean extension, and was still active in the Late Miocene. It has exhumed a series of metamorphic domes from southern Evia to Mykonos below low-angle detachment systems, made of low-angle normal faults and low-angle ductile shear zones. The ductile shear zones and the faults were created with a low dip and they kept the same attitude throughout their exhumation. We identify three main detachments that are part of a continuum of extension on the NCDS : Tinos detachment, Livada detachment and Mykonos detachment. A fourth detachment (Vari detachment) is the reactivation of an Eocene exhumation-related structure. Deformation in the footwall is characterized by intense stretching and flattening. Using the spatial evolution observed along strike from Andros to Mykonos we construct a history of formation of the NCDS starting with the reactivation of former thrusts leading to the exhumation of high-temperature metamorphic domes. The Aegean example shows that reactivation of earlier shallow-dipping discontinuities can play a fundamental role in continental post-orogenic extension
International audienceThe Variscan segment of the Pyrenees is well suited to study the timing of crustal-scaledeformations as crustal flow and gneiss dome formation. This has been constrained from a synthesisof available structural and geochronological data of intrusive rocks, as well as new zirconU–Pb age determinations via laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS). After a stage of moderate thickening by fold–thrust belt development in theupper crust between 323 and 308 Ma, the Variscan segment of the Pyrenees experienced crustalflow at c. 306 Ma and then gneiss dome formation at c. 304 Ma. Localization of the deformationalong reverse-dextral shear zones occurred at c. 300 Ma. The Variscan segment of the Pyreneesrecorded a high-temperature regime, which allowed crustal flow of the middle crust, but withlimited amounts of heat which induced rapid cooling. The development of this enigmatic orogenicsegment of the Variscan belt is closely contemporaneous with the formation of the Cantabrian Oroclineand could correspond to a lithospheric-scale shear zone that accommodated buckling of theorocline. Late Variscan lithospheric delamination and asthenospheric upwelling associated withbuckling in the core of the Cantabrian Orocline could explain the short-period high-temperatureregime in the Variscan segment of the Pyrenees
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