Evolution Of Eastern Segment Of The Paleo-Asian Ocean In The Late Paleozoic: Geochronology And Geochemistry Constraints Of Granites In Faku Area, North Liaoning, Ne China

To constrain the evolution of the eastern segment of the Paleo-Asian Ocean (PAO), petrography, geochemistry, zircon U-Pb dating and Lu-Hf isotopic analyses were conducted over the Dongxiaoling, Qianjiumen, Hujiatun and Baijiagou plutons in the Faku area, northern Liaoning, in the eastern segment of the northern margin of the North China Craton (NCC). Petrographic characteristics suggest that these plutons are composed mainly of granitic rocks and have widely been remodified by late-stage dynamic metamorphism. Zircon dating results indicate that the Dongxiaoling and the Qianjiumen plutons were formed in the Middle Permian (264.6 +/- 5.9Ma and 262.8 +/- 3.5Ma), the Hujiatun and the Baijiagou plutons were formed in the Late Permian (257.7 +/- 3.1Ma) and the Early Triassic (248.2 +/- 1.5Ma), respectively. Petrogeochemical characteristics indicate that both of the Dongxiaoling and the Hujiatun plutons are metaluminous-weakly peraluminous, high-K calcalkalic A-type granites, and they are formed in a postorogenic extensional environment; the Qianjiumen pluton is of metaluminous-weakly peraluminous, calcalkalic-high-K calcalkalic, highly fractionated I-type granite, and it is formed in a volcanic arc environment; the Baijiagou pluton is of metaluminous-weakly peraluminous, high-K calcalkalic-shoshonitic I-type granite, and formed in a syn-collisional orogenic environment. All granitic plutons of the study area are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs) and heavy rare earth elements (HREEs). Combined with Lu-Hf isotopic characteristics, the initial magma is supposed to be influenced by partial melting of the lithospheric mantle that had been affected by replacement of subducting fluids. Combining with previous studies, we concluded that the study area experienced a subduction-closure process as part of the PAO during the Middle Permian-Early Triassic.