Montomoli C. -A multidisciplinary approach to the Crystalline Massifs of Western Alps: a cross-border geological link- Bando "Grant for Internationalization - GFI" - 2022

State of the art The External Crystalline Massifs (ECM) in Western Alps are fragments of the Variscan Belt well preserved within the Mediterranean area. The ECM recorded similar evolution and are composed of a high-to-medium grade metamorphic basement intruded by Permo-Carboniferous granoitoids. ECM have been strongly deformed during the Variscan orogeny and, together with their variably detached post-Variscan sedimentary cover, have been involved in the later Alpine tectonics, but only with localized and low-grade metamorphic overprint. Due to long-term structural geology constraints and recent tectonics and morphoclimatic conditions, ECMs show peculiar geodiversity and valuable geoheritage. We will focus on the Argentera-Mercantour Massif (AM), the southernmost ECM in the belt, at the boundary between Italy and France, where the components of both research units have a long working experience. The AM is constituted by two migmatite-bearing metamorphic complexes (Gesso-Stura-Vésubie and Tinée) (Compagnoni et al., 2010) separated by a Variscan ductile transpressive shear zone (Simonetti et al., 2018). Ferrando et al. (2008) recognized a polyphase Variscan metamorphic evolution starting from HP metamorphic conditions down to LT–LP amphibolite-facies imprint. An Alpine greenschist facies overprint has been related to the development of a system of shear zones affecting the whole AM (Sanchez et al., 2011). The complex shear zone network developed during Variscan and Alpine cycles covers a crucial role also for mining. Indeed, AM is one of the most promising European districts regarding probable “Critical Raw Materials” (CRMs) occurrences but still poorly explored and understood. Besides the area is well known for the occurrences of several hydrothermal mineralized veins, historically exploited for base metals (Cevales, 1961; Martina, 1967; Omenetto and Brigo., 1974), and for accessory Sc, V, Ni, and Co-bearing minerals within fluorite, and carbonate gangue, the relationships with mineralization and the complex structural architecture is still poorly understood. In this framework, the AM represents an invaluable archive of the geological history from Paleozoic to recent times, including the assembly and demise of Pangea and the latest glaciation phases in the Quaternary. The wide cultural heritage represented by a diversity of international known rock units, geological structures and landforms, testifies a very long history and gives the opportunity to identify and describe representative geosites for geo-tourism resources. The latter activities are crucial since the study area is within two National Parks (Parco Naturale Alpi Marittime, Parc National du Mercantour). Research design and objectives: The main goal of this study is to better define the stratigraphic and tectonic-metamorphic evolution of the AM and reconstruct the geological events also leading to the mobilization of metal-bearing fluids within the Variscan basement during Variscan and Alpine orogenic cycles. The CRMs occurrence within polymetallic hydrothermal vein systems hosted in the two different complexes and ductile, brittle-ductile shear zones and faults will also be investigated. In addition, we aim to define, according to international standards, candidate outcrops as suitable geosites for geoeducational activities addressed both to geological and-non geological audience. In line with this purpose, the project will focus on eight specific tasks: Task1. Refining the study of the control of structural inheritance of the Variscan architecture on the subsequent Alpine sedimentary cycle. Task 2. Increasing the knowledge of the Variscan and post-Variscan tectono-metamorphic and magmatic evolution of the Massif, also by comparison between the Gesso-Stura-Vésubie and Tinée terranes. Task 3. Understanding the structural relations among ductile and brittle -ductile shear zones and fault systems developed du