The late- to post-Varsican dioritic dyke swarm of the Argentera-Mercantour Massif and its tectono-metamorphic record

The progressive emplacement of igneous bodies of various sizes was a major process that ruled the renewal of the continental crust after the apex of the Variscan collision. Although late- to post-Variscan magmatic intrusions have been locally reported as intermittent events, if considered at the scale of the whole European Variscan belt, their age range of tens of millions years refects the long lasting perturbed thermo-mechanical state that has been affecting the lithosphere since the end of the Variscan cycle. In the southern Variscan belt, two main magmatic sequences are described, the first of which, markedly calc-alkaline, records Lower Permian ages and has been accommodated by transpressive to transtensive structures, while the second, which comprises alkaline granitoids and lesser tholeiites, has emplaced since the Middle Permian under a pure extensional tectonic regime. Conversely, in most of the External Crystalline massifs (ECMs), which are segments of the southern Variscan belt reworked by the Alpine collision, late- to post-collisional magmatism have ended at the down of Permian time. But there are notable exceptions: in particular, a dioritic dyke swarm crosscuts both migmatitic basement and late- to post-collisional granitoids in the Argentera- Mercantour ECM. These NE-SW trending and steeply dipping dykes display well-developed chilled margins and vesicular texture; within them, soft contacts and magmatic breccias involving different igneous lithotypes are the finnal outcome of complex intrusive processes. WR analyses show that these dykes are magnesian, calc-alkalic to alkali-calcic and peraluminous, while intrusive relationships and igneous textures indicate a shallow emplacement level. The occurrence of these dioritic dykes implies an extension of the magmatic activity in the Argentera-Mercantour ECM beyond the Permo-Carboniferous boundary, in line with what is reported in the southern Variscan belt. Moreover, thermobarometric constrains on their superposed metamorphic assemblages have allowed to dene a complete P-T-t path from the magmatic emplacement to the Alpine exhumation.