Crustal wedge structure in the Mt. Campo dei Fiori Area (Lugano -Lake Maggiore area): foredeep implication

The geodynamic evolution of the Western (Ivrea - Verbano Zone) and Central (Orobic Alps) part of the South Alpine thrust system have been subjected to deep investigations through years to unravel the deformation and kinematic history of this part of the Alpine Chain (e.g. Brack et al., 2010; D'Adda et al., 2010; Zanchetta et al., 2011; Schmid et al., 2017). Nevertheless, studies on the evolution of their geological knot, the Lake Maggiore - Lugano area, have never been carried out, although it has been the source area of the most part of the synorogenic detritus in the first clastic pulses recorded in the Adriatic Foredeep (Di Capua et al., 2016). This investigational gap created a mismatch between the theoretical models and the buried terminations of the Southern Alps below the Po Plain at the boundary between the chain and the Po Plain. Our study area is focused on the Mt. Campo dei Fiori range, between Lake Maggiore, to the west, and the Mesozoic Generoso basin, to the east. The range is structured into an ENE-WSW striking asymmetric anticline, whose upright northern flank closes against the subparallel and high-dipping Marzio Fault. The latter experienced polyphasic reactivation since the Carboniferous (?) - Permian (Casati, 1978), during the Mesozoic extension and, finally, during the Alpine orogeny. This regional and deeply rooted structure directly lies along the easternmost tip of the Cremosina line, a well-known dextral lineament. Our cross-sections, based on geological mapping and extrapolated at depth thanks to published geophysical data, show that the Mt. Campo dei Fiori Anticline and Marzio Fault are a crustal-rooted break-through faultpropagation fold, connected at depth to a crustal wedge. This interpretation leads to solve this sector in thickskinned view, assuming a fixed-axis fault-propagation folds model (Jamison, 1987; Suppe & Medwedeff ,1990). Conversely, different interpretations have been previously proposed since the 90's for this area: from a pure thin-skinned style (Roeder, 1992), to a basement-involved thin-skinned sheet (Schumacher, 1997; Pfiffner, 2016). The proposed indentation of a crustal wedge could provide a kinematic model to interpret both the retrovergence of the Mt. Campo dei Fiori Anticline and the inception of the shallower Gonfolite back-thrusting, interpreted as mainly active during Burdigalian to Tortonian (Bernoulli et al., 1989).