Jurassic rifting evolution of the Apennines and Southern Alps (Italy): Parallels and differences

Jurassic rifting in the Southern Alps and Northern Apennines occurred within a relatively short (2-4 m.y.) interval of tectonic activity (late Hettangian-early Sinemurian) in proximal areas (central-eastern Southern Alps and Northern Apennines), and was followed by calm postrift sedimentation. The main axis of the rift jumped in the late Early Jurassic to the previously unaffected, mostly nonsubsiding and/or uplifted distal areas of southwestern Tuscany and the western Southern Alps. Synchronous stretching occurred in the Helvetic-Brianconnais domains of the Alps and in the Longobucco-Caloveto area (Calabria), here interpreted as the conjugate margin of western Southern Alps and southwestern Tuscany. Major differences occur in the extensional structural style of the Southern Alps and Apennines. The Northern Apennines are characterized by diffuse thin-skinned stretching at shallow depths and by localized thick-skinned stretching at deeper crustal levels. This style contrasts with the well-known thick-skinned nature of extensional tectonics in the Southern Alps, which are also characterized by a larger spacing between major normal faults. It is suggested that these different extensional styles were controlled by contrasting rheologies induced by the different stratigraphies. The strong strain partitioning and the diffuse shallow thin-skinned tectonics of the Northern Apennines basins are here related to the occurrence of thick (up to 2 km) evaporites that underlie a relatively thin (up to 1.3 km) carbonate platform.