Neogene mantle delamination beneath the Northern Apennines: Insights from thermo-mechanical modelling

Mantle delamination postdating continental collision has been conceptually proposed in previous studies for the Northern Apennines. Here we use 2D thermo-mechanical modelling to quantitively explore the consequences of delamination along a NE-SW-trending section crossing the Northern Apennines. We constrain the model by geological reconstructions and recent results on the present-day lithosphere and upper mantle structure. The results show that the combination of a weak lower crust and the negative buoyancy of the slab promotes the progressive detachment of the Adria lithospheric mantle from the upper crust since the Middle Miocene. This modelling accounts for the northeastward migrating pattern of extension and crustal and lithospheric thinning in the Tyrrhenian Sea and Tuscany, and simultaneous compression and crustal thickening in the eastern Apennines. A similar migrating pattern is obtained for the topographic uplift of the orogen and subsidence at the Adriatic foredeep. The topography in the western Apennines is sustained by lithospheric mantle thinning due to asthenospheric upwelling, while the moderate topography in the eastern Apennines results from the opposing effects of a thick crust, up to 80 km, and the negative buoyancy of the sinking Adria lithosphere. This modelling quantitatively explains the occurrence of magmatism and high heat flow beneath the Tyrrhenian Sea and Tuscany, as well as the first order features of the lithospheric and upper mantle structure in the region. We suggest that the findings of this study can be extended to other orogenic belts where continental delamination has been proposed.