A review of the pre-Permian geology of the Variscan French Massif Central

Abstract

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 from six main tectonic-metamorphic events. The first, D 0, is coeval with a Late Silurian (ca 415 Ma) high-pressure (HP) (or ultra high-pressure) metamorphism for which the associated structures are poorly documented. The Early Devonian D 1 event, responsible for top-to-the-southwest nappe displacement, is coeval with migmatization and the exhumation of HP 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 D 2 event involves top-to-the-northwest shearing, coeval with an intermediate pressure-temperature metamorphism dated around 360–350 Ma. The Visean D 3 event is a top-to-the-south ductile shearing, which is widespread in the southern Massif Central. Coevally, in the northern Massif Central, the D 3 event corresponds to the onset of synorogenic extension. The next two events, D 4 and D 5, of Early and Late Carboniferous age, correspond to the syn- and late orogenic extensional tectonic regimes, respectively. The former is controlled by NW–SE stretching whereas the latter is accommodated by NNE–SSW stretching. These structural and metamorphic events are reconsidered in a geodynamic evolution model. The possibilities of one or two cycles involving microcontinent drifting, rewelding and collision are discussed.