Evidence of Tethyan continental break-up and Alpine collision in the Argentera-Mercantour Massif, Western Alps

International audienceIn the Argentera-Mercantour Massif, swarms of high-K calc-alkaline lamprophyres intruded into Carboniferous migmatites and early Permian granites, likely in Permian-Triassic times. The dykes collected multiple magmatic injections, the latest of which of alkaline affinity. Syn-intrusive vesicles and straight chilled margins suggest that the lamprophyres emplaced at a shallow crustal level.Lower greenschist facies mineral assemblages replaced lamprophyre igneous minerals as a result of late-intrusive hydrothermal circulation that occurred soon after the dyke emplacement. The hydrothermal event is constrained at T = 300–350°C and P < 0.1 GPa by matching thermobarometry and pseudosection results. During the Alpine collision, the lamprophyres were intersected by upper greenschist facies mylonitic shear zones developed at T = 420–450°C and P = 0.2–0.4 GPa, which are the metamorphic peak conditions of the Argentera-Mercantour Massif in Alpine times