SIMS zircon U-Pb age of the plagiogranites from Kuitun River ophiolite and its tectonic implications
Li Chao1,2,3, Xiao Wenjiao1,3, Han Chunming1,3, Zhou Kefa3, Zhang Zhixin3
1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
2. University of Chinese Academy of Sciences, Beijing 100049;
3. Xinjiang Research Centre for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Vrümqi 830011
As the last suture of the central Asian orogenic belt,the Tianshan-Solonker suture belt the records the evolution of the Paleoasian ocean in its later period of time.This paper carries out SIMS U-Pb chronological and geochemical study of the plagiogranites from the Kuitun River ophiolite within the north Tianshan mélange belt.The plagiogranites are enriched in Na2O and depleted in K2O(<1%)and Al2O3(<15%).Their trace element contents are generally lower than the N-MORB,and REE pattern of the plagiogranites is flat with no distinct Eu anomaly.These features demonstrate that the plagiogranites from the Kuitun River ophiolite are typical plagiogranites generated in the mid-ocean ridge,whose ages could stand for the time of oceanic spreading.24 groups of chronological analysis provide a concordia age of 342.8±2.6 Ma.Combined with previous regional geological study,we conclude that the Junggar ocean was continually spreading and subducting outward beneath its surrounding terranes accompanied by gradual formation of the Kazakhstan orocline,producing the eastern and western Junggar intra-oceanic arcs,and Tianshan and Altai Andes-type continental arcs.