Pogallo Line, South Alps, northern Italy; an intermediate crustal level, low-angle normal fault?

The Pogallo Line is a major crustal shear zone 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. Suggestion 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.--Modified journal abstract.