Variscan geology of the Argentera Massif, Western Alps and comparison with the Maures-Tanneron Massifs (France)

This contribution describes the metamorphic and magmatic history of the Argentera Massif, the southernmost of the External Crystalline Massifs of the Western Alps, and compares its evolution to that recorded in the Maures-Tanneron Massifs of Provence, the area of Variscan Europe nearest to Argentera. The Argentera Massif consists of the Gesso-Stura- Vésubie (GSV) Terrane to the NE and of the Tinée Terrane to the SW, which are separated by the Ferriere-Mollières (or La Valletta) shear zone. Both terranes are largely composed of Variscan migmatites with abundant relicts of pre-anatectic rock types, including in the GSV dacite with granulite-facies xenoliths, and contain rare relics of high-pressure (HP) granulite/eclogite facies mineral assemblages. Carboniferous ages at 335-340 Ma were obtained for the HP metamorphism recorded in the granulites of Lago Frisson in the GSV Terrane. A Late- to Mid- Carboniferous age (≤ 323 ± 12 Ma) is likely for the subsequent LP metamorphism (650–700°C; 0.4–0.6 GPa) and partial melting in the GSV Terrane. The LP metamorphism was accompanied and followed by the emplacement in the GSV of small bodies and dykes of Visean metamonzonite (332 ± 3 Ma) and of a post-tectonic Stephanian suite, richer in Fe, mainly represented by the “Central Granite” (~ 295–300 Ma) of the GSV Terrane. Deposition of Westphalian D-Stephanian A continental sediments (conglomerates, sandstones, fossiliferous black schists), preserved in tight synclines inside the GSV gneiss of the Vésubie valley, marks the final exhumation of the GSV Terrane after the Variscan metamorphism.