GEOLOGICAL HISTORY OF THE MORVAN

Late Visean to Namurian

Leucogranitic intrusions


See geologic maps 1/80 000 Avallon, Château-Chinon, Charolles and Autun; 1/50 000 Avallon, Quarré-les-Tombes, Sémur-en-Auxois, Corbigny, Autun, Dompierre-sur-Besbre, Bourbon-Lancy, Fours and Lucenay-l'Evêque; explanatory notes Avallon, Quarré-les-Tombes, Sémur-en-Auxois, Corbigny, Autun, Le Creusot, Dompierre-sur-Besbre, Bourbon-Lancy, Fours and Lucenay-l'Evêque.


The ascending melts of two micas leucogranite (muscovite+biotite) (gg) in the axis of the Late Visean volcano-plutonic trough (Folin massif ) or following the wrench faulting zones inside the granito-gneissic basement (Pierre-qui-Vire massif , Mesvres massif ) outlines the end of the important magmatic activity which characterizes Early Carboniferous times. Like Late Visean rhyodacites and microgranites, leucogranites derive from the anatectic melting of middle layers of the continental crust [REF]. The leucogranite emplacements are coeval or slightly follow the volcanic activity, as indicated by a radiometric age of 327+/-5 Ma obtained on the Pierre-Qui-Vire granite [REF].

Leucogranites

In Late Tournaisian sub-alkaline granites, leucogranites occur also as numerous and relatively small intrusions, stocks and dikes , particularly nearby the Chastellux gneissic domain.

Lamprophyres dikes of vogesite type (biotite-poor) end the magmatism represented by Late Visean volcanic and sub-volcanic rocks and two-micas granites.


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