When zircon drowns: Elusive geochronological record of water-fluxed orthogneiss melting in the Velay dome (Massif Central, France)

Zircon U-Pb geochronology is routinely performed to unravel the timing and duration of melting events within continental crust. A comprehensive understanding zircon behavior during anatexis therefore paramount accurately assess impact crustal on orogenic processes. We report an anatectic system from southern part Velay dome (Variscan French Massif Central) encompassing late Carboniferous migmatites developed at expense peraluminous orthogneisses associated with (leuco)granite bodies intrusive higher structural levels. Our geochronological survey (494 analyzed grains) evidences a very scant record Variscan event. Indeed, oscillatory-zoned melt-precipitated grains extracted metatexites, leucosomes (leuco)granites almost systematically yielded Neoproterozoic crystallization age felsic igneous protolith. Field petrographic observations, whole-rock geochemical signatures, phase equilibrium thermodynamically-constrained trace element modelling collectively indicate that partial took place T ~ 700 °C was fluxed by ingress external water. The lack new growth ascribed range processes ultimately related low temperature including limited solubility in melt phase, occlusion non-reacting source biotite sluggish dissolution kinetics. Peraluminous orthogneisses, yet highly fusible due their “eutectic” subsolidus mineral assemblage, exhibit water-fluxed melting. Thus, has little potential provide reliable chronological constraints episodes affecting such lithologies.