Late Neoarchean magmatism and Paleoproterozoic metamorphism in the northern Yangtze Craton: Evidence from high-pressure mafic granulites of the Muzidian complex in the Dabie Orogen

Abstract

Deciphering metamorphic evolution of high-pressure granulites developed in Palaeoproterozoic orogenic belt is crucial to understand plate tectonic mechanisms and evolutionary history in ancient cratons. In this study, we reported newly found mafic granulites from the Muzidian outcrop, which preserve a clockwise pressure–temperature-time (P–T–t) path. The prograde stage was suggested by inclusions of amphibole, plagioclase, quartz and clinopyroxene in garnet; the peak high pressure granulite facies stage was evidenced by garnet, clinopyroxene, amphibole, plagioclase, quartz and ilmenite, which was constrained in a P–T regime of 10.5–11.0 kbar/860–890 ℃. An early retrograde stage was recorded by orthopyroxene replacing clinopyroxene at P–T conditions of 5.5–7.0 kbar/820–850 ℃, while a later retrograde stage was revealed by the intergrowth of amphibolite and plagioclase in matrix at P–T conditions of 4.6–6.2 kbar/704–778 ℃. Zircon U-Pb dating for the mafic granulites yielded two age groups of ∼2.5 and 2.0 Ga, representing the formation ages of the magmatic protolith and the high pressure (HP) granulite facies metamorphism, respectively. The magmatic protolith zircons exhibit ɛ_Hf(t) values from −8.3 to −0.9 with single-stage Hf model ages of ca. 3.1–2.8 Ga and high δ¹⁸O values from 9.39 ± 0.18 ‰ to 11.58 ± 0.11 ‰. These suggest the protoliths of the mafic granulites were likely derived from an enriched mantle that had been metasomatized by subducted crusatal materials. The metamorphic zircons have ɛ_Hf(t) values from −8.6 to −0.3 and lower δ¹⁸O values from 8.11 ± 0.11 ‰ to 8.80 ± 0.15 ‰, suggesting that the metamorphosed zircons were formed at the granulite-facies metamorphism stage with external low δ¹⁸O and high ɛ_Hf(t) melt/fluid. The clockwise P–T–t paths of the HP granulites suggest that the ca. 2.0 Ga arc-continent collision in the Yangtze craton has extended northward to the North Dabie Zone (NDZ). The Yangtze Craton might be situated in a key tectonic position between the southern margin of the Siberian Craton and the northern margin of Laurentia during the amalgamation of the Columbia supercontinent.