MAGMATIC STRUCTURES OF THE SIDOBRE GRANIT E PLUTON (TARN, FRANCE) - FROM THE MASSIF SCALE TO THE SPECIMEN SCALE

A joint study of Anisotropy of Magnetic Susceptibility and Shape Prefe rred Orientations (SPO) of the principal mineral phases of the Sidobre granite has been performed. A remarkable organization of the magnetic foliations and lineations, oblique to the long axis of the pluton, ha s been evidenced. These magnetic structures represent in fact the magm atic ones as proved by the SPO of biotite, plagioclase and K-feldspar megacrysts. NNE-SSW striking lineations, systematically orthogonal to the trends of aplo-pegmatitic dykes, suggest that the pluton was empla ced in relation to a NNE-SSW directed opening of the crust. This mecha nism is in accordance with the recent models of late Variscan extensio nal tectonics of the Montagne Noire.