The role of structural inheritance in continental break-up and exhumation of Alpine Tethyan mantle(Canavese Zone,Western Alps)

The Canavese Zone(CZ)in the Western Alps represents the remnant of the distal passive margin of the Adria microplate,which was stretched and thinned during the Jurassic opening of the Alpine Tethys.Through detailed geological mapping,stratigraphic and structural analyses,we document that the continental break-up of Pangea and tectonic dismemberment of the Adria distal margin,up to mantle rocks exhumation and oceanization,did not simply result from the syn-rift Jurassic extension but was strongly favored by older structu ral inheritances(the Proto-Canavese Shear Zone),which controlled earlier lithospheric weakness.Our findings allowed to redefine in detail(i)the tectono-stratigraphic setting of the Variscan metamorphic basement and the Late Carbonife rous to Early Cretaceous CZ succession,(ii)the role played by inherited Late Carboniferous to Early Triassic structures and(iii)the significance of the CZ in the geodynamic evolution of the Alpine Tethys.The large amount of extensional displacement and crustal thinning occurred during different pulses of Late Carbonife rous-Early Triassic strike-slip tectonics is wellconsistent with the role played by long-lived regional-scale wrench faults(e.g.,the East-Variscan Shear Zone),suggesting a re-discussion of models of mantle exhumation driven by low-angle detachment faults as unique efficient mechanism in stretching and thinning continental crust.

Multistage tectono-stratigraphic evolution of the Canavese Intracontinental Suture Zone:New constraints on the tectonics of the Inner Western Alps

The Canavese Intracontinental Suture Zone(CISZ) within the Inner Western Alps represents the remnant of a long-lived minor subduction zone involving a narrow, thinned continental crust/oceanic lithosphere seaway between two continental domains of the Adria microplate(i.e., the Sesia Zone and the IvreaVerbano Zone). As opposed to many suture zones, the CISZ mostly escaped pervasive tectonic deformation and metamorphism, thus preserving the original stratigraphy and allowing the relationships between tectonics and sedimentation to be defined. Through detailed geological mapping(1:5000 scale),structural analysis, stratigraphic and petrographic observations, we document evidences for the late Paleozoic to late Cenozoic tectonic evolution of the CISZ, showing that it played a significant role in the context of the tectonic evolution of the Inner Western Alps region from the early to late Permian Pangea segmentation, to the Jurassic Tethyan rifting, and up to the subduction and collisional stages,forming the Western Alps. The site of localization/formation of the CISZ was not accidental but associated with the re-use of structures inherited from regional-scale wrench tectonics related to the segmentation of Pangea, and from the subsequent extensional tectonics related to the Mesozoic rifting, as documented by crosscutting relationships between stratigraphic unconformities and tectonic features. Our findings document that evidences derived from stratigraphy, facies indicators, and relationships between tectonics and sedimentation in the shallow crustal portions of suture zones, such in the CISZ, are important to better constrain the tectonic history of those metamorphic orogenic belts around the world in which evolutionary details are commonly complicated by high-strain deformation and metamorphic transformations.