TECTONOMETAMORPHIC HISTORY OF THE IVREA ZONE AND ITS RELATIONSHIP TO THE CRUSTAL EVOLUTION OF THE SOUTHERN ALPS

The Ivrea Zone represents a cross-section through the lower continental crust of the Southern Alpine basement. A first long episode with regional metamorphism and associated polyphase deformation ended in the Variscan. Subsequent Late Paleozoic magmatic activity may have occurred during an early stage of crustal attenuation. Late Paleozoic and Early Mesozoic crustal thinning is accommodated by conjugate high-temperature shear zones within the granulite facies Ivrea Zone and by low-angle normal faulting within the Pogallo Ductile Fault Zone, at the base of the intermediate crust. The age and kinematics of the Pogallo Ductile Fault Zone are consistent with the occurrence of Early Mesozoic extensional basins in the Southern Alpine sediments. Exhumation and final steepening of the Ivrea Zone during the Alpine Orogeny did not substantially alter its internal structure exept in the vicinity of the Insubric Line. Thus, the Ivrea Zone and the adjacent Strona-Ceneri Zone represent a good example of highly attenuated lower and intermediate continental crust. © 1990.