Early Palaeozoic geodynamics in NW Gondwana

During Ordovician times, the northwestern margin of Gondwana, in a transect linking the Anti-Atlas, the western and eastern branches of the Ibero-Armorican Arc and the Alps, recorded a stepwise succession of stratigraphic gaps, in some cases linked to magmatism, extensional tectonics, uplift and erosion. The Furongian (Toledanian) and Mid-Ordovician (Sardic) Phases are distinctly separated in time, but share the calc-alkaline-dominant affinities of their involved magmatism and the absence of some typical deformation properties, such as cleavage and metamorphism. The stratigraphic gaps related to uplift events and denudation have been interpreted as break-up (or rift/drift) unconformities, subduction-related orogenies or transpressive-transtensive events associated with hypothetical terranes that have not yet been found amalgamated to other orogens. This geodynamic framework is used to introduce the contributions of this special volume.