Tectonic evolution of the external zones at the Umbria-Marche Apennines in the Monte San Vicino-Cingoli area

This study summarises the results of a geological survey carried out in the Monte San Vicino-Cingoli area of the Umbria-Marche Apennines. In this area, the axial culmination of the external Apennine ridge and the widespread occurrence of Messinian and Pliocene deposits provide an almost complete record of the deformation history of the external zones of the chain. The prosecution of the Sibillini Thrust North of the Chienti River valley, never previously ascertained, has been identified within the Miocene units exposed in the western limb of the Cingoli anticline, about 4-5 km away from the mountain front. An important role in the tectonic evolution of the study area is also played by inherited (pre-thrusting) structures. These include both those of the rifted continental margin, of Mesozoic age, and those related to Miocene foreland deformation. The former, well known in the geological literature, are organised in two main fault sets (trending NNE-SSW and WNW-ESE). Synsedimentary Miocene faults, mainly trending NNW-SSE, controlled foredeep turbiditic deposition during early (pre-evaporitic) Messinian times. These faults show very limited or no reversal of slip during contractional deformation. In fact, although mild inversion tectonics has produced some uplift and antiformal folding of hanging wall basin fills, only in one instance (i.e. Avenale Fault) has significant fault reactivation occurred. The onset of contractional deformation within the study area coincides with the end of the deposition of the Gessoso-solfifera Fm. Thrusting appears to have migrated in sequence towards the external zones of our study area up to Early Pliocene times (Globorotalia puncticulata biozone).