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Geoscience ›› 2018, Vol. 32 ›› Issue (02): 289-304.DOI: 10.19657/j.geoscience.1000-8527.2018.02.08

• Petrology • Previous Articles     Next Articles

LA-ICP-MS Zircon U-Pb Dating,Hf Isotopic Composition and Ce4+/Ce3+ Characteristics of the Yanshanian Acid Magma in the Xidamingshan Cluster,Southeastern Margin of the Youjiang Fold Belt,Guangxi

XIAO Changhao1,2(), SHEN Yuke1(), WEI Changshan1, SU Xiaokai1,2, LE Xingwen3, ZHANG Liang2   

  1. 1. Laboratory of Dynamic Digenesis and Metallogenesis,Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China
    2. School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China
    3. Geological Team No.4 of Guangxi Zhuang Autonomic Region,Nanning,Guangxi 530031,China
  • Received:2017-07-12 Revised:2018-01-11 Online:2018-04-10 Published:2018-05-07

Abstract:

The Xidamingshan cluster is located along the southeastern margin of the Youjiang fold belt,South China. LA-ICP-MS zircon U-Pb dating constrains the crystallization of the quartz porphyry,monzogranite and biotite granite at (93.11±0.64) Ma,(92.92±0.69) Ma and (92.5±1.1) Ma,respectively.They have the same ages with each other within errors,suggesting they are magmatism coevally emplaced during the Later Cretaceous.The εHf(t) values of the quartz porphyry vary from -18.4 to -1.2 with an average value of -7.1,with two-stage model Hf ages (TDM2) of 1 236 to 2 326 Ma with an average value of 1 609 Ma. And the values of the monzogranites and biotite granite are from -19.4 to +0.3 with an average value of -5.6 and -12.2 to -3.6 with an average value of -6.7,correspond to two-stage model Hf ages (TDM2) of 1 139 to 2 385 Ma and 1 386 to 1 933 Ma,respectively.It indicates that the source material was derived from the partial melting of the Paleo-and Mesoproterozoic crust.Comparing with Hf isotopic characteristics of the Yan-shanian granites in the boundary of the Youjiang fold belt,we suggest that all of the granites may have the same magma sources.The average Ce(Ⅳ)/Ce(Ⅲ) ratios of monzogranite and biotite granite are 23.65 and 33.76,respectively.It suggests that the Luowei concealed intrusion is with low oxygen fugacity.Combined the results from this study coupled with previous research,we proposed that the magmas formed in a regional extensional setting along the southeastern margin of the Youjiang fold belt in the South China during the Later Cretaceous.This caused the partial melting of the Paleo-and Mesoproterozoic crust due to the lithosphere relaxation and collapse,which meanwhile resulted in the large-scale magmatism in the Xidamingshan cluster.In the light of tectonic settings and geochronology,we deduct that the Yanshanian granites along the margin of the Youjiang fold belt are related to both Pacific and Tethyan tectonic domain.

Key words: zircon U-Pb dating, Hf isotopic composition, Late Yanshanian, Xidamingshan cluster, Youjiang fold belt

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