Metamorphic Evolution of Mafic Granulites from the Wuhe Complex at the Southeastern Margin of the North China Craton

Wang Chengcheng; Liu Yican; Yang Yang; Zhang Pingang; Nie Jiazhen

Abstract：Investigations on metamorphic processes of the Wuhe complex provide new insights into the formation and evolution of Precambrian metamorphic basement at the southeastern margin of the North China Craton (NCC).In this paper,three Paleoproterozoic stages of metamorphic assemblages from mafic granulites in the Wuhe complex is recognized and a clockwise P-T-t path characterized by post-peak near-isothermal decompression and subsequent decompression-cooling by conducting detailed petrographic observations,mineral electron microprobe analysis,zircon LA-ICP-MS U-Pb dating and trace element analysis is reconstructed.The peak HP granulite-facies metamorphism (M1) is characterized by high-Ca cores in granet,highAl cores in clinopyrexene,plagioclase,quartz and rutile,yielding P-T conditions of 850-900 ℃ and 1.5 GPa.The mediumpressure (MP) granulite facies assemblage (M2) mainly consists of garnet + orthopyrexene + plagioclase ± clinopyrexene surrounding the amphibole porphyroblasts,recording P-T conditions of ～900 ℃ and 1.1-1.2 GPa.Symplectites or coronas composed of homblende+ plagioclase (M3) surrounding the garnet porphyroblasts indicate garnet decompressional reactions occurred at 600-680 ℃ and 0.65-0.75 GPa.The zircon dating results can be categorized into three groups of ～ 1.90 Ga,～ 1.85 Ga and ～ 1.78 Ga,corresponding to the time of HP granulite facies,MP granulite facies and amphibolite facies metamorphism.The comparable metamorphic evolution of mafic granulites from the Wuhe complex to Jiaobei terrane,combined with previous studies on petrogenesis and U-Pb ages of 2.1 Ga granitic rocks,suggest that the wuhe complex is the west extension of the Jiao-Liao-Ji belt (JLJB) and they constitute a Paleoproterozoic collisional orogen as a whole in the eastern block of the NCC.