New field evidence from the eastern margin of the Lepontine Dome: structural constraints for its exhumation

The eastern margin of the Lepontine Dome represents an area of particular interest to understand the geodynamic evolution of the Central Alps. Here, the stack of the lower Penninic units underwent a syn-to post-nappe emplacement regional Barrovian metamorphism and was then exhumed forming a domelike structure. This vertical ascension up to the present-day crustal levels was coeval with the intrusion and exhumation of the Gruf-Bergell system along the Insubric Line and was plausibly affected by buoyancy forces driven by a hot thermal perturbation. The uplift of these units involved the structurally higher Brianҫonnais Tambò and Suretta nappes, that, unlike the Lepontine Dome, did not experience a regional Alpine Barrovian metamorphism. Focusing on the contact between Adula and Tambò nappes, a transition from ductile to brittle deformation behaviour can be observed in the field, along with several kinematic indicators that point to a top to North-NorthEast directed shearing of the southern portion of the Tambò Nappe. The Forcola Line, that separates Adula and Tambò nappes across the Swiss-Italian border, represents the major tectonic lineament that express a syn-collisional orogen-parallel extension within a predominantly brittle regime, active since the Oligocene and directly related to the ascension of the dome. Within this intricated scenario we present several field evidence that will help to shed light on the geodynamic setting and evolution of this area, focusing on the structural relationships between Adula, Tambò and Gruf units and on the role of rigid bodies in the deformation and related metamorphism of the Tambò Nappe.