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Gondwana-derived microcontinents - The constituents of the Variscan and Alpine collisional orogens
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. (C) 2003 Elsevier Science B.V. All rights
reserved