Petrology, Metamorphic P-T Paths and Zircon U-Pb Ages for Paleoproterozoic Mafic Granulites from Xuanhua, North China Craton

摘要: The studied mafic granulites are located at Xiwangshan, Xuanhua region in the north of Trans-North China Orogen (TNCO), occurring as lens within tonalite-trondhjemite-granodiorite (TTG) gneisses eastern part Xiwangshan area. rocks contain representative granulite-facies minerals such garnet, clinopyroxene, orthopyroxene, plagioclase, amphibolite, rutile and quartz, also well-developed melt pseudomorph antiperthite. Although prograde metamorphic stage (M1) cannot be retrieved due to rare preservation pre-peak-stage mineral associations, three distinct assemblages that formed different stages can identified, based on petrography mineralogy characteristics. peak (M2) is characterized by Grt2+Cpx2+Amp2+Pl2+Rt+melt pseudomorphs, a post-peak decompression (M3) contains assemblage Grt3+Opx3+ Cpx3+Amp3+Pl3, while later-retrogression (M4) featured coronas Amp4+Pl4 surrounding garnet. By calculating P-T conditions using THERMOCALC, M2 was constrained 13.2–14.8 kbar 1 050–1 080 °C, M3 recorded 5.7–7.3 825–875 M4 yielded P ~5 T ~660 consistent with amphibolite facies metamorphism. Taking into account all these petrological data, we propose granulite experienced high-pressure (HP) ultra-high temperature (UHT) metamorphism during metamorphism, which accompanied clockwise path. U-Pb dating zircons yields two groups ages 853±14 744±44 Ma, respectively. We suggest older age corresponded HP-UHT younger represented an retrograde event cooling.