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Field and laboratory structural studies show that the Devonian–Dinantian units of the northeast French Massif Central experienced
a complex and contrasting tectonic–metamorphic evolution during the Hercynian orogeny. The structural analysis of the pre-Middle
Visean Brévenne–Violay–Beaujolais rocks, in the Loire area, shows a polyphase tectonic evolution associated with greenschist
to amphibolite facies metamorphism. The first event, D1, probably occurred in Early Tournaisian or Latest Devonian times.
It is responsible for the flat-lying regional foliation and the NW/SE- to N/S-trending lineation. It is well observed in the
Violay group and corresponds to the NW-vergent emplacement of the Late Devonian units upon their gneissic basement, represented
by the Affoux gneisses. The second event, D2, is responsible for the NE/SW- to E/W-trending lineation. To the south, D2 deformation
is locally reworked by the Grand-Chemin dextral wrench fault, around 345–350 Ma ago. This polyphase deformation is also found
in several Devonian–Dinantian areas of the NE Massif Central, but not in Morvan. This tectonics corresponds to the Tournaisian
closure, by northward thrusting and subsequent intracontinental deformation, of the oceanic Brévenne–Violay–Beaujolais rift
which opened in Devonian times in a back-arc setting.
Received: 4 September 1998 / Accepted: 27 May 1999 相似文献
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