Zircon U- Pb dating, geochemistry and geological significance of synorogenic- granit in Mutanyao area, eastern Junggar
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    Abstract:

    Mutanyao area is located in east of East Junggar, known as the important tectonic metallogenic belt of the Central Asian Orogenic Belt(CAOB). Through high- precision zircon U- Pb dating and comprehensive research on rock geochemistry, combined with regional comparison, the diagenetic age was determined and its formation environment was discussed to provide chronology and petro- geochemical constraints for the study of Late Paleozoic tectonic magmatism. Methods: The full analysis of the rock was tested in the Aussie Minerals Laboratory in Guangzhou. After the sample was crushed, shrunk and ground to 200 mesh, the content of rare earth elements was determined by ME MS81 fusion inductively coupled plasma mass spectrometry. ME XRF26X fluorescence spectrometer was used for precise analysis. Determination of iron oxide by the main trace element of rock and Fe VOL05 titration. Zircon single minerals were selected in the laboratory of the Institute of Regional Geology and Mineral Resources Research of Hebei Province, and the target, CL photographing, transflective photography, zircon dating and data were carried out in the State Key Laboratory of Mineral Deposits Research Mechanism of Endogenous Metal Deposits, Nanjing University. Correction. The zircon U- Pb test was carried out on an Agilient 7500a ICP- MS connected by a 193 nm laser sampling system. The laser ablation beam spot diameter was 32 μm and the frequency was 6 Hz. He gas was used as the carrier gas for the ablation material, and then mixed with the Ar gas. Analyze. The isotope ratios obtained by the experiment were processed by the GLITTER program and subjected to ordinary lead calibration. The test results are shown in Table 2. The age harmonic curve and the weighted average calculation were processed using Isoplot (3.0) software.Results: Mutanyao syn- orogenic granites are characterized by high SiO2 , high alkaline, low CaO and low TiO2 . Concentration of large ion lithophile element Rb, Ba, K, Th and high field strength element Zr, are relatively deficient in P, Ti, NB, Ta. The total amount of rare earth elements is relatively low, the concentration of light rare earth elements is obvious, and the internal fractionation of light rare earth elements is relatively strong, the internal fractionation of heavy rare earth elements is weak, and the weak negative Eu anomaly (δEu = 0.64~0.95). The saturation temperature of zircon is 740~807℃. It belongs to medium—high pressure when it is put between Zhejiang—Fujian type and Adak type granite in Sr—Yb diagram. Based on petrology and geochemistry, it is considered that the genetic type of granite is I transition type. The diagenetic material mainly comes from partial melting of crustal sandstone and a small amount of argillaceous rock,and a small amount of mantle material is involved. The U- Pb age of LA- ICP- MS zircon shows that its crystallization age is 349.8±3.5 Ma, indicating that it was formed in the Early Carboniferous. Conclusions: The Mutanyao area entered the transition period from subduction to collision orogeny in the early Early Carboniferous (349.8±3.5 Ma), collaged to the Siberian plate, and began the lateral and vertical crustal accretion.

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ZHANG Zhengfeng, XIONG Shuangcai, FAN Xianglian.2021. Zircon U- Pb dating, geochemistry and geological significance of synorogenic- granit in Mutanyao area, eastern Junggar[J]. Geological Review,67(1):231-241.

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History
  • Received:September 24,2019
  • Revised:October 09,2020
  • Adopted:
  • Online: January 19,2021
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