The Lavagna and Antola Nappes in the upper Lavagna and Bisagno Valleys (N. Italy)

Abstract

Comprehensive structural geologic studies reveal a complex tectonic history of the Antola and Lavagna Nappes. Within the slightly metamorphic Lavagna Nappe the effect of five phases of folding have been established. The first phase (F1) is characterized by large isoclinal folds with an originally southwestern vergence. During the second phase (F2) large-scale open folding took place, whereas F3 and F4 produced folds with a northeastern vergence on a regional scale. These first four phases all produced co-axial folds with NW-SE trends. F5-folds are open and have an approximately NE-SW trend. Internal thrusting, associated with F1 and F3 has been established. After a first period of folding, the non-metamorphic rock sequences of the Antola Nappe thrusted over the Lavagna Nappe. Associated with this, thrusting within the S part of the Lavagna Nappe took place. The first four folding phases of the Lavagna Nappe and its metamorphosis were achieved prior to nappe-emplacement. The mutual stacking of the Antola and Lavagna Nappes must have taken place before the Eocene-Oligocene transition. Only F5 postdates the nappe-emplacement.