PETROLOGICAL ARGUMENTS FOR HIGH-TEMPERATURE EXTENSIONAL DEFORMATION IN THE PYRENEAN VARISCAN CRUST (SAINT-BARTHELEMY MASSIF, ARIEGE, FRANCE)

The Saint Barthélémy Massif is one of the Variscan massifs of the North Pyrenean Zone. Thermobarometric analysis has been completed across a sequence comprising (from bottom to top) basal granulitic gneisses, the Main Mylonite Band, and migmatites. PT estimates are correlated with textures which represent progressive stages of gneissification and mylonitization. The main foliation and the mylonitic textures were developed during the retrogressive evolution of the LP-HT granulitic metamorphism. Retrogressive conditions are characterized by high heat flow associated with a pressure reduction. The main penetrative deformation of the Saint Barthélémy Massif is interpreted as resulting from a continuous extensional event. © 1990.