GEOLOGICAL HISTORY OF THE MORVAN
Middle to Late Visean
Intra-Visean orogenic phase
At the end of the Middle Visean, ca 335 Ma, the epirogenic movements, induced during the Intra-Visean phase, are responsible of the emersion and then erosion of the volcano-sedimentary series.
During this period the subduction plan dipping under the northern part of the Arverno-vosgian zone is still active. In the median depths of the continental crust, anatectic melts generate inside the large thrust zones crossing the crystallophyllian rocks formed during the Meso-Variscan period. These new and essentially acidic and calc-alkaline magmas emplace along the normal faults which relay towards the surface the deep-sited shear-zones. The formation of grabens or volcano-tectonic troughs result from normal faulting. The distribution of these ENE-WSW trending graben structures is related to very local NNW-SSE crustal extensions. Two such and similar structures extend across the northeastern Massif Central, one in the Loire belt [REF], the other in the Morvan belt [REF].
Mise à jour/Last updated: 01/07/08