A non-cylindrical model for the northwest Iberian allochthonous terranes and their equivalents in the Hercynian belt of Western Europe

Abstract

A case is made for a non-cylindrical development of the European Hercynian belt. Far-travelled allochthonous terranes in the belt consist of a mixture of units, including catazonal units, ophiolites and units derived from the continental margin of Gondwana. They often depict a metamorphic history of intermediate to high pressure type and Caledonian to Eo-Hercynian age, and are thought to have been put together in the early stages of the orogeny through a process partly obductive directed onto the continental margin of Gondwana. Considerations upon the disposition of the terranes, their relationships with the paleogeography of the Gondwana realm and the structures in them, suggest that their emplacement took place in an oblique fashion, at a small angle to the margin of the continent. The proposed allochthon could be related to the development of an island arc or a wedge-like subplate in the southern part of the Baltica plate. Later, convergence between Gondwana and Laurussia involving transcurrent, mostly dextral movements, combined with tectonic escape phenomena, would account for the present complexity of the belt and for the narrow strip the allochthonous terranes delineate in westernmost Europe.