Topographic and structural response to shallow-crust plutons emplacements: Evidence from the Larderello Swell, Italy

The emplacement of igneous plutons in the middle/shallow crust can affect the topography and trigger crustal deformation. In the framework of the ‘MIGRATE’ project, we explore the potential effect of magmatic intrusions in causing the development of forced folds and associated faults, and in reorganizing rivers dynamics. The Larderello-Travale Topographic Swell (LTS), in central-northern Italy, represents a key study area where multidisciplinary investigations (e.g., geophysical, drilling and thermochronological data) indicate the presence of several shallow magmatic bodies, intruded since the late Pliocene. Preliminary results of structural and topographic analyses suggest that the LTS is an asymmetric sub-circular feature with a steep western flank compared to the eastern one. In the western side of the LTS, the rivers are directly connected to the Tyrrhenian Sea and they show multiple orders of non-lithological knickpoints, for which the above non-equilibrated stream projections indicate at least 200 meters of base level fall. Conversely, the eastern side of the LTS is dominated by long rivers (hundreds of km), which initially drain eastward and then bend before eventually flowing into the Tyrrhenian Sea. Furthermore, these rivers show multiple slope-breaks at increasing elevation that mark the entrance into tectonic depocenters, i.e. the Boccheggiano and Radicondoli Basins, controlled by faults and experienced a previous internal drainage condition. The onset of the Radicondoli Basin is much older with respect to the intrusive system but it is characterized by recent uplift and deformation (e.g., higher elevation compared to coeval basins or increasing in incisions). On the contrary, the Boccheggiano Basin is likely coeval with the magmatic emplacement, and it lays at higher elevation. Moreover, it is bordered by a normal fault striking N130° with a tectonic transport direction of about N230°. Our preliminary findings indicate a positive correlation between the emplacement of a shallow magmatic intrusion beneath the LTS and the topographic uplift, and the development or reactivation of faults in the area. Further analyses will allow to better constraint the timing of deformation and uplift, and they will better estimate the magnitude of the process which, however, appear to be still ongoing.