Ground-based geological mapping integrated by UAs in the Chiavenna area (Central Alps): examples of application in the frame of the CARG project

Ground-based geological mapping integrated by UAs in the Chiavenna area (Central Alps): examples of application in the frame of the CARG project Tartarotti P.*1, Apuani T.', Arrigoni F.', Conforto A.', Pigazzi E.', Tantardini D.' & Toffolon G.? 1 Dipartimento di Scienze della Terra "A. Desio", Università di Milano. 2 Contractor CARG-Valchiavenna Project. Corresponding author e-mail: paola.tartarotti@unimi.it Traditional ground-based mapping of cry stalline basements is essential to unravel their tectono-metamorphic evolution. However, the structural setting of metamorphic terranes is most of the time complicated by the polyphase history, not least by neotectonics. Many scientific difficulties can be overcome by implementing the field work with analytical investigations, such as chemical or geochronological analyses, that may solve several geological issues as long as the structural and microstructural features are well constrained. Recently, an interest has been growing in advanced technologies dedicated to data acquisition and applications in geological mapping. Nowadays, unmanned aerial systems (UASs) such as drones are more and more utilised, especially in mineral exploration and mine exploitation (.g., Honarmand & Shahriari, 2021). Drone photogrammetry is particularly useful in inaccessible areas, opening a new perspective for all kinds of ground operators. We used DJI Mavic 2 Pro and DJI Mavic Mini drones to implement the traditional field work on crystalline basements in the Chiavenna area (Central Alps), within the frame of the project ' "Carta Geologica d'Italia at scale 1:50.000 - CARG', covering ca. 700 kmq. This area is characterized by altitudes ranging between 200 and 3300 m a.s.l., and by a hostile topography with steep slopes and few road access that make many outcrops scarcely or not reachable. Most of the territory sees the exposure of polymetamorphic basements of the Penninic Suretta, Tambò, and Adula Nappes, separated by sheets of Mesozoic metasedimentary rocks, the Chiavenna unit, interpreted as a remnant of the Valais Ocean, and the Gruf Complex, whose attribution is still uncertain, intruded in the southeastern portion by the Bergell pluton (Schmid et al., 1996). UAS tools turn to be fundamental in such kind of terrains, whose applications regard the recognition of different lithologies on exposed surfaces, structures, morphologies, and landslides. Reiteration of field and intermediate laboratory work, with UAS-assisted surveys is necessary to finalise the geological mapping and its interpretation. Honarmand M. & Shahriari H. (2021) - Geological Mapping Using Drone-Based Photogrammetry: An Application for Exploration of Vein-Type Cu Mineralization. Minerals, 11(6), 585. Schmid S. M., Pfiffner O. A., Froitzheim N., Schönborn G. & Kissling E. (1996) - Geophysical-geological transect and tectonic evolution of the Swiss-Italian Alps. Tectonics, 15(5), 1036-1064.