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

In 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 lamprophyreswere intersected by upper greenschist faciesmylonitic shear zones developed at T= 420–450°C and P=0.2–0.4 GPa,which are the metamorphic peak conditions of the Argentera-MercantourMassif in Alpine times.