a b s t r a c tThe Variscan suture exposed in NW Iberia contains a stack of terranes including two allochthonous units with continental affinity and Gondwanan provenance (Upper and Basal Units), separated by an ophiolite belt where the most common units show protolith ages at c. 395 Ma. Recent Lu-Hf zircon data obtained from these ophiolites indicate interaction between the gabbroic magmas and old continental crust. Hence, the ophiolites could not have originated in a deep ocean basin associated with a mature mid-ocean-ridge or intraoceanic subduction. The tectonothermal evolution of the continental terranes bounding the suture zone records two consecutive events of deep subduction. The Upper Units record an initial high-P/ultra-high-P metamorphic event that occurred before 400-390 Ma, while the Basal Units were affected by a second high-P/low-to-intermediate-T metamorphic event dated at c. 370 Ma. Continental subduction affected the most external margin of Gondwana and developed in a setting of dextral convergence with Laurussia. Development of the two high-P events alternated with the opening of an ephemeral oceanic basin, probably of pull-apart type, in Early Devonian times. This ephemeral oceanic domain is suggested as the setting for the protoliths of the most common ophiolites involved in the Variscan suture. Current ideas for the assembly of Pangea advocate a single collisional event between Gondwana and Laurussia in the Carboniferous. However, the new evidence from the allochthonous terranes of the Variscan belt suggests a more complex scenario for the assembly of the supercontinent, with an interaction between the colliding continental margins that started earlier and lasted longer than previously considered. Based on modern analogs of continental interaction, the development of complex collisions, as here suggested for Gondwana and Laurussia during the assembly of Pangea, could have been the norm rather than the exception throughout Earth history.

Direct dating of brittle structures is challenging, especially absolute dating of diagenesis followed by a series of superimposed brittle deformation events. We report 22 calcite U-Pb ages from tectonites and carbonate host rocks that date 3 diagenetic and 6 brittle deformation events. Results show that U-Pb dating of calcite fibers from these structures is compatible with overprinting relationships. Ages indicate that diagenesis occurred between 147 ± 6 Ma and 103 ± 34 Ma, and was followed by top-to-the-south, layer-parallel shearing due to ophiolite obduction at 84 ± 5 Ma (2σ errors). Sheared top-to-the-northeast, layer-parallel veins were dated as 64 ± 4 Ma and are interpreted to have developed during postobduction exhumation. After this event, a series of strike-slip structures, which crosscut and reactivated older faults due to northwest-southeast horizontal shortening, were dated as 55 ± 22 Ma and 43 ± 6 Ma. Eight ages from strike-slip faults and thrusts resulting from northeast-southwest shortening range from 40.6 ± 0.5 Ma to 16.1 ± 0.2 Ma. The youngest ages are from minor overprinting fibers ranging in age between 7.5 ± 0.9 Ma and 1.6 ± 0.6 Ma. Our results show that U-Pb dating of calcite fibers can be successfully used to constrain a complicated succession of brittle deformation structures that encompasses two orogenies and an intervening extension period. BRITTLE STRUCTURES IN THE AL HAJAR MOUNTAINS Carbonate rocks at the base of the Al Hajar Mountains in Oman (Fig. 1) record several generations of overprinting brittle structures (Fig. 2) containing calcite fibers (Gomez-Rivas et al., 2014), and provide a unique opportunity for dating calcite that crystallized from the Cretaceous to Quaternary. The Al Hajar Mountains, situated on the northeast margin of the Arabian continental plate, consist of a pre-Permian basement that is unconformably covered by a middle Permian to Late Cretaceous carbonate platform (Glennie et al., 1974). In the Late Cretaceous, continental slope-rise sedimentary rocks and the Semail Ophiolite were thrust on top of the carbonate platform (Searle and Cox, 1999). Subsequently, the Al

An integrated interpretation of the late Paleozoic structural and geochronological record of the Iberian Massif is presented and discussed under the perspective of a Gondwana-Laurussia collision giving way to the Variscan orogen. Compressional and extensional structures developed during the building of the Variscan orogenic crust of Iberia are linked together into major tectonic events operating at lithosphere scale. A review of the tectonometamorphic and magmatic evolution of the Iberian Massif reveals backs and forths in the overall convergence between Gondwana and Laurussia during the amalgamation of Pangea in late Paleozoic times. Stages dominated by lithosphere compression are characterized by subduction, both oceanic and continental, development of magmatic arcs, (over-and under-) thrusting of continental lithosphere, and folding. Variscan convergence resulted in the eventual transference of a large allochthonous set of peri-Gondwanan terranes, the Iberian Allochthon, onto the Gondwana mainland. The Iberian Allochthon bears the imprint of previous interaction between Gondwana and Laurussia, including their juxtaposition after the closure of the Rheic Ocean in Lower Devonian times. Stages governed by lithosphere extension are featured by the opening of two short-lived oceanic basins that dissected previous Variscan orogenic crust, first in the Lower-Middle Devonian, following the closure of the Rheic Ocean, and then in the early Carboniferous, following the emplacement of the peri-Gondwanan allochthon. An additional, major intra-orogenic extensional event in the early-middle Carboniferous dismembered the Iberian Allochthon into individual thrust stacks separated by extensional faults and domes. Lateral tectonics played an important role through the Variscan orogenesis, especially during the creation of new tectonic blocks separated by intracontinental strike-slip shear zones in the late stages of continental convergence. Units, (6) Upper Allochthonous Units, (7) Beja-Acebuches Ophiolite, and (8) South Portuguese Zone. Gathering of 4, 5, and 6 will be also referred to as Iberian Allochthon (or simply Allochthon). A simple restoration of the cross-section shown in Figure 3 (Fig. 4a) reveals two major suture zones featured with ophiolitic units with different protolith ages. The NNE-dipping suture represented by the Beja-Acebuches Ophiolite (Bard and Moine, 1979; Munhá et al., 1986; Quesada et al., 1994) cuts the suture marked by the Allochthonous Ophiolitic Units (Arenas et al., 1986) and divides the Iberian Massif in two major blocks. The northern block comprises the Cantabrian Zone, and the Iberian Autochthon, Parautochthon and Allochthon, all of which have Gondwanan affinity