Zircon and Monazite in Bohemian Felsic Granulite Record Multiple Metamorphic and Anatectic Events in Continental Collisional Orogens

Understanding monazite and zircon behavior during high- to ultrahigh-pressure eclogite-granulite facies metamorphism and anatexis remains limited. This study investigates evolution of monazite and zircon in metasedimentary rocks during continental collision. Their growth is linked to specific metamorphic reactions and to melting processes occurring in felsic granulites from the Bohemian massif. We establish a complete P-T-t path for these rocks, documenting (1) peak UHP eclogite-facies metamorphism (3.4-5.0 GPa/875-1039°C; 340±6 Ma by zircon), (2) subsequent near-isothermal decompression to HP eclogite-facies (2.8-2.3 GPa/980°C) and further decompression-cooling to UHT/HP granulite-facies (2.3-1.3 GPa/880-980°C) recorded by monazite and zircon (331±7–341±4 Ma), (3) final cooling crystallization stage (0.4-1.3 GPa/730-830°C) at 337±5~335±15 Ma. Monazite and zircon forming at distinct stages exhibit diagnostic trace element compositions primarily controlled by metamorphic and anatectic reactions as well as coexisting mineral assemblages. Geochronology constrains the interval between ultrahigh-pressure (UHP) and ultrahigh-temperature (UHT) metamorphic events to be only 3-5 Myr. This finding corroborates petrological and phase equilibrium modeling results and provides direct geological evidence for the breakoff of subducted slab. It demonstrates that slab breakoff at the lithosphere-asthenosphere boundary depth, triggering asthenospheric upwelling, is a fundamental mechanism enabling the coeval development of UHP and UHT metamorphism in continental collision orogens.