GEODYNAMIC EVOLUTION OF THE EUROPEAN VARISCAN FOLD BELT: PALAEOMAGNETIC AND GEOLOGICAL CONSTRAINTS

Abstract

The Variscan fold belt of Europe resulted from the collision of Africa, Baltica, Laurentia and the intervening microplates in early Paleozoic times. Over the past few years, many geological, palaeobiogeographic and palaeomagnetic studies have led to significant improvements in our understanding of this orogenic belt. Whereas it is now fairly well established that Avalonia drifted from the northern margin of Gondwana in Early Ordovician times and collided with Baltica in the late Ordovician/early Silurian, the nature of the Gondwana derived Armorican microplate is more enigmatic. Geological and new palaeomagnetic data suggest Armorica comprises an assemblage of terranes or microblocks. Palaeobiogeographic data indicate that these terranes had similar drift histories, and the Rheic Ocean separating Avalonia from the Armorican Terrane Assemblage closed in late Silurian/early Devonian times. An early to mid Devonian phase of extensional tectonics along this suture zone resulted in formation of the relatively narrow Rhenohercynian basin which closed progressively between the late Devonian and early Carboniferous. In this contribution, we review the constraints provided by palaeomagnetic data, compare these with geological and palaeobiogeographic evidence, and present a sequence of palaeogeographic reconstructions for these circum-Atlantic plates and microplates from Ordovician through to Devonian times.