GEOLOGICAL HISTORY OF THE MORVAN

Late Visean

Succession of the volcanic events in the Saint-Honoré-les-Bains (Nièvre) - Lucenay-l'Evêque (Saône-et-Loire) region.


See geologic maps 1/80 000 Château-Chinon and Autun; 1/50 000 Bourbon-Lancy, Fours, Autun, Château-Chinon and Lucenay-l'Evêque; explanatory notes Bourbon-Lancy, Fours, Autun, Château-Chinon and Lucenay-l'Evêque.


Late Visean volcanism

In the Morvan belt, from Saint-Honoré region to Lucenay-l'Evêque region, acidic and aerial volcanic rocks (gg) extend largely and are composed mainly of welded tuffs and ignimbritic rhyodacites , and described previously as Tufs Anthracifères or microgranulitic tuffs [REF]. In some localities (Lucenay-l'Evêque area) sedimentary deposits include anthracite beds and associated silicified vegetal remnants of Late Visean age [REF], [REF].

Late Visean

(gg) Numerous veins and stocks of microgranite and granophyre cut the volcanic rocks [REF]. These cogenetic and coeval hypovolcanic intrusions emplaced about 331+/-10 Ma [REF].

Chemical and mineralogic composition of rhyodacites and microgranites with in addition frequent occurrences in volcanic rocks of garnets with a chemical composition similar to those found in the underlying basement gneisses indicate a probable sialic origin for the magmatic melts [REF].

Leucogranites intrusions emplaced during this period.


Intra-Visean phase HOMEHOME Leucogranites