A review of the pre-Permian geology of the Variscan French Massif Central
Résumé
The Massif Central, like the southern part of the Massif Armoricain, belongs to the North Gondwana margin. The Massif Central consists of a stack of nappes resulting of six main tectonic-metamorphic events. The first one, D0, is coeval with an Early Late Silurian (ca 415 Ma) high-pressure (or ultra high-pressure) metamorphism for which the associated structures are poorly documented. The Early Devonian D1 event, responsible for top-to-the-SW nappe displacement, is coeval with migmatization and exhumation of high-pressure rocks around 385-380 Ma. In the northern part of the Massif Central, metamorphic rocks with retrogressed eclogites are covered by Late Devonian undeformed sedimentary rocks. The Late Devonian-Early Carboniferous D2 event is a top-to-the-NW shearing coeval with an intermediate pressure-temperature metamorphism dated around 360-350 Ma. The Visean D3 event is a top-to-the-south ductile shearing widespread in the southern Massif Central. Coevally, in the northern Massif Central, the D3 event corresponds to the onset of synorogenic extension. The next two events, D4 and D5, of Early and Late Carboniferous age, correspond to the syn and late orogenic extensional tectonics, respectively. The former is controlled by NW-SE stretching whereas the later is accommodated by a NNE-SSW stretching. These structural and metamorphic events are replaced in a geodynamic evolution model. The possibilities of one or two cycles involving microcontinent drifting, rewelding and collision are discussed.
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