HTLP metamorphism and fluid‐fluxed melting during multistage anatexis of continental crust (N Sardinia, Italy)

The Variscan high-grade metamorphic basement of northern Sardinia and southern Corsica record lower Carboniferous anatexis related to post-collisional decompression the orogen. Migmatites exposed in Punta Bianca locality (Italy) consist quartz + biotite plagioclase K-feldspar orthogneisses, garnet cordierite-bearing diatexite metatexites, derived from metasediments. Field evidence, petrographic observations, ELA-ICP-MS zircon monazite dating pseudosection modelling suggest that was apparently episodic involving two main stages partial melting. Using modelling, we infer first stage melting is upper amphibolite facies (~0.45 GPa at ~740°C). Cordierite overgrowths replacing sillimanite, combined with composition K-feldspar, followed cooling below solidus low pressures ~0.3 GPa. age anatectic event not precisely constrained because extensive resetting isotopic systems during second stage, yet few zircons preserve a which consistent regional dataset. This migmatitic fabric offset by network pseudotachylyte-bearing faults suggestive greenschist conditions. Garnet/cordierite-bearing diatexites incorporate fragments pseudotachylite-bearing orthogneiss metatexites. Pseudosection indicates nearly isobaric re-heating up ~750°C, further solidus. inferred P–T path crust through extension collapse thickened orogenic crust, (~0.3 GPa) yielding under LP-HT U/Th-Pb ages for migmatites indicate an bound 310–316 Ma suggesting coincident phase crustal shearing. cause high geothermal gradient required unknown but likely requires some heat source probably dissipation mechanical work within crustal-scale shear zones. According this interpretation, peraluminous granite precursors Corsica–Sardinia Batholith could be outcome rather than late-Variscan high-T metamorphism.