Mississippian synorogenic sedimentation in the Variscan belt: Why are NW and SW Iberia flysch basins so different and yet so similar?

Abstract

Devonian-Carboniferous synorogenic sedimentation is described across the Variscan orogen, as well-preserved exposures in late orogenic structures between continental blocks. Variscan marine sedimentary sequences are described in both colliding continents: Gondwana representative of the southern subducting super-plate, and Laurussia considered as the overriding block. The Variscan synorogenic basin distribution on both sides of the alleged Rheic Ocean suture zone raised questions regarding the basin geodynamic classification and possible geographycal and temporal connections. The Devonian-Carboniferous turbiditic basins of the Variscan belt have been classified as foreland, forearc, or backarc, in line with their relative geographical position in the convergent plate boundary. However, the same Variscan basin may have different classifications depending on the proposed tectonic model and its current geographic position. The standard classification of the Variscan synorogenic basins fails due to a poor understanding of their relationship with the tectono-metamorphic and magmatic evolution of their basement, which means ambiguity and controversy in defining global tectonic models. As a world-class natural laboratory, the Iberian Massif (Portugal and Spain), at the westernmost tip of the Variscan Belt, presents itself as a place to study orogenic processes, from depth (ductile deformation, metamorphism and plutonism) to shallow (synorogenic sedimentation and volcanism) crustal levels. Recent studies in NW and SW Iberia have revealed a regional-scale relationship between Mississippian turbiditic (flysch) basins and magmatic flare-ups.