Evidence for pre-orogenic,Early Devonian rifting in the Variscan belt: stratigraphy and structure of the Palaeozoic cover of the Mauges Unit (Upper Allochthon,Armorican massif,France) |
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Authors: | Céline Ducassou Michel Ballèvre Hubert Lardeux Cécile Robin |
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Institution: | 1.Géosciences Rennes,Université de Rennes 1,Rennes Cedex,France;2.LeVerger-Beaucé,Mélesse,France;3.Applied Geosciences,German University of Technology in Oman (GUtech),Muscat,Sultanate of Oman |
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Abstract: | The Palaeozoic sediments from the Mauges Unit (Armorican Massif, France) are the best-preserved pre-orogenic sequences belonging
to the Upper Allochthon. Two coherent sequences are identified. The southern unit (Chateaupanne Unit) represents the cover
of the Proterozoic basement and consists of Ordovician sediments unconformably overlain by Emsian carbonates followed by Emsian
to earliest Eifelian immature sandstones. The northern unit (Tombeau Leclerc Unit) consists of an Hirnantian to Emsian condensed
sequence, in reverse position, that has been thrust over the southern unit. The Devonian unconformity is interpreted as evidence
for an Early Devonian extension, recorded by normal faults affecting both the Early Devonian limestones and the underlying
Ordovician series. This crustal extension, recorded here for the first time, is possibly related to the opening of a back-arc
basin (Saint-Georges-sur-Loire) associated with the subduction of an ocean located further south (Galicia-Brittany-Massif
Central Ocean). |
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