Transition between Variscan and Alpine cycles in the Pyrenean-Cantabrian Mountains (N Spain): Geodynamic evolution of near-equator European Permian basins

In the northern Iberian Peninsula, the Pyrenean-Cantabrian orogenic belt extends E-W for ca. 1000 km between the Atlantic Ocean and Mediterranean Sea. This orogen developed from the collision between Iberia and Eurasia, mainly in Cenozoic times. Lower-middle Permian sediments crop out in small, elongated basins traditionally considered independent from each other due to misinterpretations on incomplete lithostratigraphic data and scarce radiometric ages. Here, we integrate detailed stratigraphic, sedimentary, tectonic, paleosol and magmatic data from well-dated lithostratigraphic units. Our data reveal a similar geodynamic evolution across the Pyrenean-Cantabrian Ranges at the end of the Variscan cycle. Lower-middle Permian basins started their development under an extensional regime related to the end of the Variscan Belt collapse, which stars in late Carboniferous times in the Variscan hinterland. This orogenic collapse transitioned to Pangea breakup at the middle Permian times in the study region. Sedimentation occurred as three main tectono-sedimentary extensional phases. A first phase (Asselian-Sakmarian), which may have even started at the end of the Carboniferous (Gzhelian) in some sections, is mainly represented by alluvial sedimentation associated with calc-alkaline magmatism. A second stage (late Artinskian-early Kungurian), represented by al-luvial, lacustrine and palustrine sediments with intercalations of calc-alkaline volcanic beds, shows a clear up-ward aridification trend probably related to the late Paleozoic icehouse-greenhouse transition. The third and final stage (Wordian-Capitanian) comprised of alluvial deposits with intercalations of alkaline and mafic beds, rarely deposited in the Cantabrian Mountains, and underwent significant pre-and Early Mesozoic erosion in some segments of the Pyrenees. This third stage can be related to a transition towards the Pangea Supercontinent breakup, not generalized until the Early/Middle Triassic at this latitude because the extensional process stopped about 10 Myr (Pyrenees) to 30 Myr (Cantabrian Mountains). When compared to other well-dated basins near the paleoequator, the tectono-sedimentary and climate evolution of lower-middle Permian basins in Western and Central Europe shows common features. Specifically, we identify coeval periods with magmatic activity, extensional tectonics, high subsidence rates and thick sedi-mentary record, as well as prolonged periods without sedimentation. This comparison also identifies some evolutionary differences between Permian basins that could be related to distinct locations in the hinterland or foreland of the Variscan orogen. Our data provide a better understanding of the major crustal re-equilibration and reorganization that took place near the equator in Western-Central Europe during the post-Variscan period

U–Pb geochronology and geochemistry of late Palaeozoic volcanism in Sardinia (southern Variscides).

The latest Carboniferous to lower Permian volcanism of the southern Variscides in Sardinia developed in a regional continental transpressive and subsequent transtensile tectonic regime. Volcanism produced a wide range of intermediate-silicic magmas including medium- to high-K calc-alkaline andesites, dacites, and rhyolites. A thick late Palaeozoic succession is well exposed in the four most representative Sardinian continental basins (Nurra, Perdasdefogu, Escalaplano, and Seui-Seulo), and contains substantial stratigraphic, geochemical, and geochronological evidence of the area's complex geological evolution from the latest Carboniferous to the beginning of the Triassic. Based on major and trace element data and LA-ICP-MS U-Pb zircon dating, it is possible to reconstruct the timing of post-Variscan volcanism. This volcanism records active tectonism between the latest Carboniferous and Permian, and post-dates the unroofing and erosion of nappes in this segment of the southern Variscides. In particular, igneous zircon grains from calc-alkaline silicic volcanic rocks yielded ages between 299 \ub1 1 and 288 \ub1 3 Ma, thereby constraining the development of continental strike-slip faulting from south (Escalaplano Basin) to north (Nurra Basin). Notably, andesites emplaced in medium-grade metamorphic basement (Mt. Cobingius, Ogliastra) show a cluster of older ages at 332 \ub1 12 Ma. Despite the large uncertainty, this age constrains the onset of igneous activity in the mid-crust. These new radiometric ages constitute: (1) a consistent dataset for different volcanic events; (2) a precise chronostratigraphic constraint which fits well with the biostratigraphic data and (3) insights into the plate reorganization between Laurussia and Gondwana during the late Palaeozoic evolution of the Variscan chain