On the age of mylonites within the Mont Blanc massif

AbstractThree generations of mylonites occur in the Mont Blanc Massif :— the first one has produced mylonitic schists trending N20°E, of regional extension; the late Variscan Mont Blanc granite intruded these mylonites;— the second one has affected large areas in the Mont Blanc granite, with the same N20°E direction;— the third one is located along rather narrow bands N45°E, in the granite as well as in the older mylonitic schists.All theses mylonites have been generated under (Bi) - greenschist facies conditions. They exhibit steeply plunging schistosity and lineation. They are all ante-Alpine; paradoxically, Alpine structures within the massif do not exhibit a striking appearence.