Paleoproterozoic multiple metamorphic overprinting of granulite facies in the Daqingshan area of the North China Craton and its tectonic implications

Repeated high-grade metamorphic overprinting usually results in incomplete re-equilibrium. This blurs the pressure-temperature-time (P-T-t) information preserved in ancient terranes, complicating the reconstruction of orogenic evolution and tectonics. This study investigated metabasites from the Daqingshan area of the North China Craton, comparing samples distal and proximal to the deformation zone. An undeformed granulite and a plastically deformed amphibolite both record an earlier ultrahigh-temperature (UHT) metamorphism peaking at 950−1000 °C and 8−9 kbar with post-peak cooling ending at fluid-absent solidi, followed by a later granulite-facies overprinting to peak conditions of 8−9 kbar and 870−890 °C, likely driven by prograde hydrational P-T rises. These P-T conditions were reliably constrained by three key factors: tetrahedral Al in clinopyroxene, anorthite in plagioclase, and Ti in amphibole. The overprinting assemblages vary in extent between samples (e.g., local embryos versus widespread neoblasts), suggesting that more complete petrologic records of metamorphic overprinting benefit from deformation and fluid availability. Moreover, zircon and monazite dating show that the earlier UHT metamorphism cooled at 1.94−1.92 Ga, whereas the later overprinting occurred at 1.87−1.83 Ga. The UHT metamorphism is attributed to post-orogenic or backarc extension, preceded by an orogenic event that produced high-pressure granulite-facies metamorphism at ca. 1.96−1.94 Ga. The granulite-facies overprinting is attributed to a separate orogenic event involving typical crustal thickening after the UHT metamorphism, based on its P-T path and nearby geologic data.