Gravimetric evidence of deep structure in mountain building: Subducted Adriatic crust beneath the Tyrrhenian Moho in Central Italy

A possible first-order model of the deep structure underneath Central Italy is provided, taking into account a possible subduction mechanism, by means of updated gravimetric and revised geological and geophysical data. In order to produce a gravimetric model some elements are assumed: the surface geological setting, a deformed basement and the generally accepted depths to the Moho. For the gravimetric model presented here, Bouguer anomaly values (constant density of 2.4 g cm−) from the Italian National Gravimetric Data Base have been used (the data base is on a 3 × 3 km rectangular net). The model has been tested on a geological cross-section and matching calculated gravity and observed gravity. The two curves show a regional negative gradient from the Tyrrhenian towards the Adriatic side, with a minimum central depression corresponding to the core of the Apenninic chain. The general negative slope of the curve suggests mantle densities lower in the western than in the eastern part of the model. This can be justified by taking into account the values of heat flow and the spreading of the Tyrrhenian Sea. The minimum corresponding to the central part of the chain is modelled assuming a wedge of low density in the upper mantle. This wedge is interpreted as part of a slab of Adriatic lithosphere subducting towards the Tyrrhenian Sea.