Abstract

In the sector NW of the Secchia Valley (Northern Apennines), SW-NE trending folds involve Epiligurian, Subligurian and Modino Units; these are unconformably overlain by late Langhian Epiligurian deposits and seem to be bounded to the SE by displaced Triassic evaporites outcropping northeastward from the Cerreto Pass zone. An interpretation of the tectonic evolution which places both the NE-trending folds and the current position of the Triassic evaporites within a single setting, is proposed. In this interpretation, the early thrusting of the Tuscan Nappe developed along a left-handed oblique footwall ramp, controlled by the Triassic lateral facies variation between the internal Evaporites and the external Dolomites ("Grezzoni" of the Apuane Alps). In this non-cylindrical tectonic frame some transverse transtensive fault systems developed, producing tectonic omissions within the pile of the units and favouring the formation of a second order arc. Thus, in the Langhian the Modino Unit, detached along the incompetent basal complex, the Cervarola Unit was overthrust, forming an archshaped fold system, from the current Mt. Ventasso area to Mt. Cimone. This structure induced the gravity gliding of Ligurian bodies within the Sestola-Vidiciatico Unit overthrusting the Cervarola Sandstone SE of the Secchia Valley. The western arm of the arc would have used the previously transposed evaporites in the NW-verging thrust over the Cervarola Unit. The upper Miocene thrusting of the Cervarola tectonic Unit and the late reactivation of the Macigno frontal thrust produced the dismembering of the middle Miocene arcuate structure.

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