VARISCAN P-T DEFORMATION PATHS FROM THE SOUTHWESTERN AIGUILLES-ROUGESMASSIF (EXTERNAL MASSIF, WESTERN ALPS) AND THEIR IMPLICATION FOR ITS TECTONIC EVOLUTION

Petrological and structural investigations in metapelites and amphibol ites were undertaken to unravel the Variscan tectonic and metamorphic evolution of the southwestern Aiguilles Rouges massif. The geometry of planar and linear structures indicates a transpressive deformation re gime with a change from predominantly subhorizontal to subvertical mov ements during its evolution. In metapelite samples from gneiss areas, garnet zonation trends have been correlated with chemical variations i n plagioclase and biotite by microstructural observations. Applied con ventional cation-exchange and net-transfer geothermobarometers yielded anti-clockwise P-T-deformation paths. Clockwise P-T-deformation paths resulted from (Na, Ca)-amphibole zonations of amphibolite samples fro m a different lithotectonic unit. Notable differences in P-T condition s and the general shape of P-T paths for the gneisses and amphibolites indicate that the units do not represent a continuous metamorphic zon ation and underwent no common tectono-metamorphic evolution throughout the entire deformation. The combination of P-T-deformation paths and structural investigations revealed first-stage thrust tectonics follow ed by a transpressive deformation which was responsible for the uplift of the southwestern Aiguilles Rouges massif.