Stratigraphic and tectonic setting of the southern termination of the Western Alps (Ligurian-Maritime Alps junction): an update

A revision of the stratigraphic and tectonic setting of the southern termination of the Western Alps, at the junction of the Maritime Alps with the westernmost Ligurian Alps, is proposed. In response to the Alpine kinematic evolution a number of tectonic units individuated on the deformed palaeo-European continental margin and were arranged in a NW–SE anastomosed pattern along the NE boundary of the Argentera Massif. These tectonic units often cut across the paleogeographical subdivision of the Alpine literature and show only partial affinity with their distinctive stratigraphic features. The tectono-sedimentary evolution of the studied units is discussed: in the Cretaceous it was characterized by intense tectonic controls on sedimentation inducing lateral variations of stratigraphic features and major hydrothermal phenomena, while since the early Oligocene, a transpressional multistage tectonics induced a NE–SW shortening, together with significant relative left-lateral and then (late Oligocene–middle Miocene) right-lateral movements along E–W to SE–NW direction. This induced the juxtaposition and/or stacking of Briançonnais, Dauphinois and Ligurian tectonic units characterized by different metamorphic histories, from anchizonal to lower greenschist facies. This evolution resulted in the arrangement of the tectono-stratigraphic units in a wide “transfer zone” necessary to allow the Oligocene westward indentation of Adria promontory, the counterclockwise rotations at the south-western termination of Western Alps and the Miocene, SE directed, right-lateral tectonics, coeval with the Argentera Massif uplifting.