DID VARISCAN EUROPE BEHAVE AS AN OROCLINALLY BENT RIBBON CONTINENT DURING THE LATEST CARBONIFEROUS?

Any pre-Carboniferous paleogeographic reconstruction involving NW Iberia must take into account the pre-orocline geometry of the Western European Variscan Belt (WEVB). The present-day arcuate geometry of the WEVB curves around, concave towards the east, through Brittany, the British Isles, into NW Iberia where it curves around and terminates in southern Iberia, and potentially continues into Morocco. Overall the WEVB describes ~180o of curvature. Several hundred paleomagnetic sites have been collected from the inner core of the WEVB, which demonstrably show that the present-day curvature, of at least the inner core, is mainly secondary in nature and is a consequence of a protracted two-phase oroclinal model. Closure of the Rheic Ocean resulted in E-W shortening (in present-day coordinates) in the Carboniferous, which produced a near linear N-S trending, east verging, fold-thrust belt. Subsequent N-S shortening near the Carb-Perm boundary resulted in oroclinal bending. This late-stage orogenic event remains an enigmatic part of the final amalgamation of Pangea. Originally thought of as strictly a thin-skinned fold-thrust belt, geodynamic models of late Variscan tectonics suggest that oroclinal bending of the WEVB was lithospheric in scale and resulted in thickening and eventual detachment of the lithospheric root of the orogen. This hypothesis is consistent with the chronology of tectonic, metamorphic, magmatic, and hydrothermal events in the WEVB. Assuming the results from the core of the WEVB are representative of the entire belt, it is mandatory to palinspastically restore the WEVB to a linear pre-Stephanian configuration to understand the tectonic evolution of Variscan convergent margins in SW Europe. Such large-scale rotations require significant lithospheric buckling synonymous with recently proposed ribbon continents in the Mediterranean, SW Pacific and Western Cordillera. These lithospheric rotations necessitate major crustal detachments on the eastern and western flanks of the WEVB during oroclinal bending that would coincide with the recently generated paleo-Tethys Ocean and the Rheic suture respectively. Moreover, a major dextral strike-slip fault must have existed between present-day North Africa and Iberia to allow for the truncation of the WEVB north of the modern Rif-Betic ranges.