Thermomechanical evolution of the South Alpine rifted margin (North Italy): Constraints on the strength of passive continental margins

We have reconstructed the kinematic, thermal and rheological evolution of the Triassic-Cretaceous South Alpine passive continental margin (Northern Italy) and estimated lateral strength variations associated with rifting. Rifting initially caused the formation of a roughly symmetrical, ca. 100 km wide graben located 150-200 km away from the future break-up site. 30 Myr after the onset of rifting, the rift axis shifted laterally and eventually led to oceanic crust formation. The thermal evolution of the margin was first controlled by the waning of a thermal anomaly, which was emplaced shortly before rifting and was cooling during the first extensional stages. Numerical modelling of rifting and drifting, constrained by field data, is used to trace thermal and rheological changes affecting the rifted margin. The effects of the thermal anomaly are restricted to the first 10-20 Myr of rifting. Subsequently, isotherms are slightly affected by lithospheric thinning and show very little distortion after break-up. Rheological modelling demonstrates that the South Alpine lithosphere preserved substantial strength even shortly before break-up and became stronger thereafter. The modelling also shows that, at break-up and 100 Myr later, thinned domains of the margin are stronger than the less thinned ones.