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

A joint study of Anisotropy of Magnetic Susceptibility and Shape Preferred 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, has been evidenced. These magnetic structures represent in fact the magmatic 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 emplaced in relation to a NNE-SSW directed opening of the crust. This mechanism is in accordance with the recent models of late Variscan extensional tectonics of the Montagne Noire.