Mapping di terreno e digitale: Spunti dal Progetto CARG - F245 Albenga (Liguria, Italia)

The Ligurian Briançonnais represents a key point to unravel the Alpine evolution. Indeed, the Ligurian Alps structure is the result of the staking of paleogeographic domains belonging to a passive margin. The Ligurian Briançonnais represents the innermost portions of the Paleo-European margin. Its intricate framework is interpreted as the result of inherited pre-collisional structures influence and a polyphase deformation. The simpler example is the inversion of pre-Alpine normal faults that could be preferentially reactivated as thrust during the collisional stacking. These occurrences can create three-dimensional elaborate geological patterns. Indeed, it is known that these units are the results of a polyphase deformation. Moreover, to reconstruct the kinematic evolution of this domain, each structure should be analyzed considering the summation of the contribution of overlapping multiple deformation phases, both fragile and ductile, as well as the continuous feedback between pre-existing conditions and changing stress domains. However, how the early fault and fracture network influences the following evolution of brittle structures is poorly quantified. This PhD work presents the main outcomes from the three-year experience of mapping for the CARG 245 – Albenga sheet. The Albenga sheet (located in western Liguria) displays ~ 450 km2 of emerged area hosting a wide variety of rock type, including: i) Paleozoic to Eocene metaintrusive, metavolcanic and metasedimentary sequences that experienced Pre-alpine and/or alpine orogenic deformation and metamorphism; ii) Oligocene to Pliocene post-orogenic sediments and a large Quaternary mixed marine-alluvial fan. The remaining one third (~ 150 km2) of the sheet includes the continental shelf and the upper slope both intersected by well carved submarine canyons. On land survey has been performed through the integration of the classic, field-based approach with the analyses of Digital Outcrop Models (DOM) derived from digital photogrammetry and the use of Unnamed Aircraft Vehicles (UAV). Additionally, this research focused on a tectonic element part of the Monte Carmo unit, Close to Finale Ligure (Monte Caparazoppa), which displays a km-sized recumbent fold characterized by a curvilinear fold axis resulting in a sheath-like fold morphology. These structure records fold imputable to the 2 phase too and it is unconformably covered by post-collisional deposits of Pietra di Finale formation. This peculiar fold is an ideal place to study the influence of the early deformation features (folds and faults/fractures) on the development of the following stages. The aim of the research is to understand if (and how) the early fracture sets, associated with the first folding phases (D1), control the development of the successive fracture orientation. A classic field-based structural investigation has been coupled with the analysis of an Unmanned Aerial Vehicle (UAV)-based Digital Outcrop Model (DOM). The dataset is large and provides a statistically sounding definition of fracture sets, the variation in orientation of which correlates with the different structural locations throughout the fold 3D geometry. This dataset has been also applied to perform a slope stability test, in a tunneling framework. These researches highlighted the importance of integrating the digital workflow with a fully comprehensive field-based characterization of the local litho-stratigraphic and structural setting to prevent misusing of the opportunity to treat large amounts of data with partially automated procedures. Moreover our case history provides new insights for the up-to-date discussion about the methodological approaches in geological mapping applications.