The Pogallo Line is a major crustal shear zone in the crystalline South Alps of northern Italy which separates middle amphibolite–granulite facies rocks of the Ivrea zone from lower–middle amphibolite facies rocks of the Strona-Ceneri zone. U-Pb, Rb-Sr, and K-Ar whole-rock and mineral ages for samples from this region indicate that the two zones pursued different time-temperature paths after Caledonian peak metamorphism. Cooling curves for the two terrains finally converge in the Late Triassic(?)–Early Jurassic, a time of large-scale crustal extension in the South Alps that anticipated the opening of the western Tethys. We suggest that the Pogallo Line may represent a low-angle normal fault that developed at intermediate crustal levels during this period of extension and attained its present subvertical orientation during Alpine deformation.