Crustal shortening and duplication of the Moho in the northern Apennines: A view from seismic refraction data

It has been confirmed that a deep thrust is responsible for Moho doubling in correspondence with the zero-Bouguer anomaly line: the Tuscan Moho overlaps the Umbro-Marchean one for a length of about 30 km. It is hypothesized that another shallower thrust involves upper crust in the Mid-Tuscany Range, Mt. Cetona and Perugia Massifs had their roots in the mantle and that subsequent extensional tectonics obliterated every trace of thrusting in lower crust and mantle rocks.

A reappraisal of the DSS refraction seismic campaigns of 1978 and 1974 in the Northern Apennines and the northern Tyrrhenian Sea, after digitization of the original analog data, and a new interpretation of crustal structures are presented in this paper. The layering of the Adria crust consists of a low-velocity lower crust topped by a 6.7 km/s horizon and an upper crust again formed by a low-velocity layer capped by a faster one. In the Tuscany sector the crust-mantle boundary and lower crust show attenuated velocities and a reduced thickness with respect to the Adriatic counterpart. These differences are due to the extensional tectonics, restricted to Tuscany and occurred in a high heat flow regime related to an uplifting astenosphere.