A new model for the Hercynian Orogen of Gondwanan France and Iberia

The Hercynian Orogen of Gondwanan France and Iberia is a collage of dispara te terranes separated by faults. Plate reconstructions indicate that the or ogen developed during a massive dextral transpression as Laurentia slid alo ng the boundary of Gondwana, and as Laurentia, Baltica, and East Avalonia r otated clockwise to form Pangea. It is proposed, therefore, that the collag e is the result of this transpression, and that it is an amalgamation of di splaced tectonostratigraphic terranes which represent the dismembering of t he Gondwanan shelf, with its stable platform Ordovician-Devonian sedimentar y sequence, and the neighbouring Rheic Ocean. Specifically, it is proposed that: (1) the slice of the Gondwanan shelf that now forms north Brittany wa s displaced dextrally from NW Africa, around Iberia, by more than 2000 km: (2) the ophiolites, oceanic material, and volcanic arcs of south Armorica a nd the Massif Central represent slices of the Rheic Ocean, displaced dextra lly along the Gondwana margin and shuffled in amongst slices of Gondwanan s helf; (3) the convergent component of the transpression is represented by t hrusts throughout the region, the Leon Terrane of France, and ophiolite-bea ring klippe in NW Iberia. The Ibero-Armorican are was formed by wrapping th e mobile dextral shear belts about a rigid Iberian basement block. The dext ral Porto-Tomar Shear Zone represents the more important shearing in Iberia , and the Iberian sinistral shears are interpreted as bookshelf-type struct ures, subsidiary to the dextral shearing. (C) 2000 Elsevier Science Ltd. Al l rights reserved.