TECTONOTHERMAL EVOLUTION ASSOCIATED WITH VARISCAN CRUSTAL EXTENSION IN THE TORMES GNEISS DOME (NW SALAMANCA, IBERIAN MASSIF, SPAIN)

The tectonothermal Variscan evolution of the Tormes Gneiss Dome is con trolled by a subhorizontal ductile shear zone of crustal scale and ext ensional characteristics that induced a quick exhumation of the deep p arts of the metamorphic complex during crustal thinning. The shearing affected a broad band of metamorphic rocks but, as the temperature dec reased, became progressively concentrated in a low-grade ductile detac hment that separates two distinct units, characterized by their lithol ogy and different tectonothermal evolution. Kinematic indicators in no n-coaxial fabrics show a displacement of the hanging wall to the south east, i.e., parallel to the trend of the foldbelt. The subhorizontal s hearing is related to the extensional collapse of the variscan crust, previously thickened during the collision tectonics.