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The Barrovian metamorphism of the Lepontine dome is manifested by isograds that cross‐cut tectonic nappe contacts, which is commonly interpreted as metamorphism that occurred after nappe emplacement. However, the pervasive mineral and stretching lineation in amphibolite facies, associated with top‐to‐foreland shearing, suggests that peak Barrovian conditions are coeval with nappe‐overthrusting. Here, we combine mapping and U‐Pb zircon dating to better constrain the relation between metamorphism and overthrusting. Metamorphic zircon rims show two age populations at 31–33 and 22–24 Ma. The younger population is locally observed in post‐foliation dikes (and associated metasomatism) likely sourced from deep‐migmatites exhuming along the Alpine backstop. The older population occurs regionally and is found in syn‐kinematic migmatites which occur along a crustal‐scale shear zone. Below this shear zone, magmatic and detrital zircon cores suggest that the Cima Lunga unit, previously interpreted as a tectonic mélange with Mesozoic fragments, was a pre‐Variscan metasedimentary sequence intruded by Permian granitic sills, now orthogneisses. This unit was strongly sheared along the top of the Simano nappe during overthrusting of a rock pile here‐termed Maggia‐Adula nappe. This large‐scale nappe emplacement imprinted the regional lineation and peak temperatures until 31–33 Ma. Péclet (1–10) and Brinkman (0.002–1.8) numbers, estimated for the overthrusting, suggest an advection‐dominated heat transfer caused by rock exhumation, with some diffusion (conduction) during nappe emplacement. Diffusion contributed to Barrovian isograds discordant to the thrust. Shear heating was important if stress times shearing rate >∼5·10−6 W·m−3 within the nappe. The thermal evolution after overthrusting was spatially heterogeneous until ca. 22 Ma. Plain Language Summary: The Lepontine area constitutes the core of the Central European Alps. It has a dome structure and it is internally formed by rock units which register pressure and temperature conditions typical of collisional orogens. The temperatures recorded by minerals are high and the origin of the heat that affected the Lepontine units is still unclear. In this study, we implemented different branches of geology to reveal the age of the Alpine events which juxtaposed the Lepontine units, their provenance and evolution. We performed extensive geological mapping to define the lithologies and structures of rocks. From 13 samples, we extracted 1158 zircon crystals that we analyzed and dated. Fieldwork permitted us to discover new rock units and better characterize the transition between the large‐scale units constituting the Lepontine dome. We propose a geodynamic scenario involving a major large‐scale Alpine unit. The emplacement of this unit generated the main heating event at 31–33 Ma, which is widespread and resulted in peak temperature conditions. The thermal evolution after this event was regionally complex and spatially heterogeneous. Locally in the south we document magmatic/fluid injections at 22–24 Ma, which were sourced from still‐hot regions in the roots of the orogen. Key Points: Geological mapping reveals widespread syn‐tectonic migmatitic rocks along a main crustal‐scale shear zone inside the Lepontine domeAlpine nappe emplacement is regionally recorded at 31–33 Ma, locally overprinted in the south by magmatic/fluid pulses at 22–24 MaMapping and detrital zircon crystals suggest a structurally coherent Cima Lunga unit of pre‐Variscan age, as part of the Simano nappe [ABSTRACT FROM AUTHOR]

Abstract The Barrovian metamorphism of the Lepontine dome is manifested by isograds that cross‐cut tectonic nappe contacts, which is commonly interpreted as metamorphism that occurred after nappe emplacement. However, the pervasive mineral and stretching lineation in amphibolite facies, associated with top‐to‐foreland shearing, suggests that peak Barrovian conditions are coeval with nappe‐overthrusting. Here, we combine mapping and U‐Pb zircon dating to better constrain the relation between metamorphism and overthrusting. Metamorphic zircon rims show two age populations at 31–33 and 22–24 Ma. The younger population is locally observed in post‐foliation dikes (and associated metasomatism) likely sourced from deep‐migmatites exhuming along the Alpine backstop. The older population occurs regionally and is found in syn‐kinematic migmatites which occur along a crustal‐scale shear zone. Below this shear zone, magmatic and detrital zircon cores suggest that the Cima Lunga unit, previously interpreted as a tectonic mélange with Mesozoic fragments, was a pre‐Variscan metasedimentary sequence intruded by Permian granitic sills, now orthogneisses. This unit was strongly sheared along the top of the Simano nappe during overthrusting of a rock pile here‐termed Maggia‐Adula nappe. This large‐scale nappe emplacement imprinted the regional lineation and peak temperatures until 31–33 Ma. Péclet (1–10) and Brinkman (0.002–1.8) numbers, estimated for the overthrusting, suggest an advection‐dominated heat transfer caused by rock exhumation, with some diffusion (conduction) during nappe emplacement. Diffusion contributed to Barrovian isograds discordant to the thrust. Shear heating was important if stress times shearing rate >∼5·10−6 W·m−3 within the nappe. The thermal evolution after overthrusting was spatially heterogeneous until ca. 22 Ma.