Diffuse mantle upwelling and melts accumulation beneath the Italian Apennines.

The focus of this study is the mantle structure beneath the Apennines, and aims to understanding how deep processes are connected to shallow deformations. We present new observations from a rich receiver function data set from stations located along the North and Central Apennine chain, and use it for comparison and to strengthen the observations of previous seismic tomography images. The two methodologies define a low shear wave velocity zone (decrease of Vs in the order of 5%) and an increase of Vp/Vs (about 3%) in the shallow mantle between 50 and 90 km depth beneath the orogenic belt. The low Vs melt zone is not restricted to the mantle beneath the Quaternary volcanic areas, as previously thought, but is detected under the whole central Apennines suggesting future broad effects on a large scale.  Our interpretation of the teleseismic RFs and tomography, reveals consistently a diffuse mantle upwelling beneath the Apennines, and we hypothesize that slab-derived fluids might interact with the sub-lithospheric mantle generating melts that accumulate at the top of the mantle feeding post-collisional extension. This mechanism can be potentially applied to other cases of extension that spread over wide continental regions.