Variscan eclogites from the Argentera-Mercantour Massif (External Crystalline Massifs, SW Alps): a dismembered cryptic suture zone

We document structural, geochemical, petrological and 40Ar/39Ar geochronological data performed on Variscan eclogites from the Argentera-Mercantour Massif, southwestern Alps. Based on the high-resolution field mapping, we present new eclogite occurrences and discuss the relationships between eclogites and surrounding migmatites. We recognized for the first time preserved eclogite facies assemblages. Trace elements and REE patterns establish that eclogites protoliths are MORBs contaminated by continental crust. Standard thermobarometry and thermodynamic modeling are consistent with P-T values of 640-740 degrees C for 1.5 +/- 0.25 GPa, coherent with paleo-geotherms predicted for warm subduction of oceanic crust. We interpret these eclogites as a dismembered cryptic suture zone. 40Ar/39Ar dating on amphiboles yields an age of 339.7 +/- 12 Ma for eclogite retrogression under amphibolite facies conditions. All these data are combined to link the Argentera-Mercantour Massif in the tectonic framework of both pre-Mesozoic Alpine basement and European southern Variscides.