Gondwana-derived microcontinents — the constituents of the Variscan and Alpine collisional orogens |
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| Authors: | Jürgen F von Raumer Grard M Stampfli Franois Bussy |
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| Institution: | aDepartment of Sciences Géologiques, Université de Fribourg, CH-1700 Fribourg, Switzerland;bInstitut de Géologie et Paléontologie, Université de Lausanne, UNIL BFSH2 CH-1015 Lausanne, Switzerland;cInstitut de Minéralogie et géochimie, Université de Lausanne, UNIL BFSH2 CH-1015 Lausanne, Switzerland |
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| Abstract: | The European Variscan and Alpine mountain chains are collisional orogens, and are built up of pre-Variscan “building blocks” which, in most cases, originated at the Gondwana margin. Such pre-Variscan elements were part of a pre-Ordovician archipelago-like continental ribbon in the former eastern prolongation of Avalonia, and their present-day distribution resulted from juxtaposition through Variscan and/or Alpine tectonic evolution. The well-known nomenclatures applied to these mountain chains are the mirror of Variscan resp. Alpine organization. It is the aim of this paper to present a terminology taking into account their pre-Variscan evolution at the Gondwana margin. They may contain relics of volcanic islands with pieces of Cadomian crust, relics of volcanic arc settings, and accretionary wedges, which were separated from Gondwana by initial stages of Rheic ocean opening. After a short-lived Ordovician orogenic event and amalgamation of these elements at the Gondwanan margin, the still continuing Gondwana-directed subduction triggered the formation of Ordovician Al-rich granitoids and the latest Ordovician opening of Palaeo-Tethys. An example from the Alps (External Massifs) illustrates the gradual reworking of Gondwana-derived, pre-Variscan elements during the Variscan and Alpine/Tertiary orogenic cycles. |
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| Keywords: | Gondwana-derived terranes Plate-tectonic terminology Polymetamorphic basement relics Collisional orogens Alpine Variscan |
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