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Geochronology, Geochemistry, Hf Isotope of Xiaojinggou Pluton in the Northern Margin of North China Craton and Its Tectonic Implications
MO Nan,GUO Lei,TONG Ying,WANG Tao,LIU Jiang,LI Jianbo
Acta Scientiarum Naturalium Universitatis Pekinensis
In order to enhance the understanding of the late Paleozoic tectonic settings of northern margin of the north China craton (NNCC) and closure time of the Paleo-Asian Ocean, the zircon U-Pb age, geochemistry and zircon Hf isotope of the Xiaojinggou granite are conducted by LA-MC-ICP-MS, ICP-AES and ICP-MS. The zircon U-Pb dating results indicate that the Xiaojinggou pluton was intruded at Permian (275±1 Ma, MSWD=0.93). All the granite have high contents of SiO2 (70.72%?to?72.64%), K2O (4.19% to 4.23%) with moderate A/CNK values (averaged at 1.1), suggesting that Xiaojinggou pluton is slightly peraluminous and belongs to the high-K calc-alkaline series. The concentrations of rare earth elements (ΣREE) varies in the range of 87.67 to 101.51 μg/g. The Xiaojinggou pluton is characterized by enriched LREE patterns with slightly negative Eu anomalies. It is enriched in large ion lithophile elements (LILE, e.g. Rb, Ba, K, Sr), but depleted in high field strength elements (HFSEs, e.g. Nb, Ta, Y, Yb, Lu), which suggest this plutou may be derived from partial melting of the lower crust. Zircon εHf(t) value varies from -9.56 to -5.00 and TDM2 varies in the range of 1.91 to 1.61 Ga. All these characters indicates that the Xiaojinggou pluton is probably generated by partial melting of Lower Proterozoic crust of the NNCC, accompanied by the possible assimilation of mantle-derived magmas. In view of the evolution of the Permian granitic magmatism in the NNCC, middle Permian Xiaojinggou pluton formes in the transition period from subduction to collision/post-collision, and the Paleo-Asian Ocean should close before late Permian.
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