古亚洲洋东段晚古生代演化过程:辽宁北部法库地区花岗岩年代学和地球化学的制约

本文对华北克拉通北缘东段辽宁北部法库地区东小陵岩体、前旧门岩体、胡家屯岩体及柏家沟岩体进行了岩相学、地球化学、锆石U-Pb定年以及Lu-Hf同位素研究，以此制约古亚洲洋东段演化过程。岩相学特征表明，本文所研究岩体主要为花岗质岩石，普遍遭受了后期的动力变质作用改造。锆石测年结果显示，东小陵岩体及前旧门岩体形成于中二叠世（264.6±5.9Ma、262.8±3.5Ma），胡家屯岩体及柏家沟岩体分别形成于晚二叠世（257.7±3.1Ma）及早三叠世（248.2±1.5Ma）。岩石地球化学表明，东小陵岩体及胡家屯岩体皆属于准铝质-弱过铝质、高钾钙碱性A型花岗岩，形成于造山后伸展环境；前旧门岩体属于准铝质-弱过铝质、钙碱性-高钾钙碱性高分异I型花岗岩，形成于火山弧环境；柏家沟岩体属于准铝质-弱过铝质、高钾钙碱性-钾玄岩性I型花岗岩，形成于同碰撞造山环境。研究区花岗质岩体皆富集大离子亲石元素（LILEs）和轻稀土元素（LREEs），并且亏损高场强元素（HFSEs）和重稀土元素（HREEs），结合Lu-Hf同位素特征，认为其原始岩浆应受到了俯冲流体交代的岩石圈地幔的影响。综合前人研究，本文认为在中二叠世-早三叠世期间，研究区经历了古亚洲板块的俯冲、闭合过程。

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.