Earth Science Frontiers ›› 2022, Vol. 29 ›› Issue (4): 358-370.DOI: 10.13745/j.esf.sf.2021.10.1

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Late Triassic Mg andesite of Juluotage, eastern Tianshan: Identification and tectonic implications

KANG Huan1,2(), CHEN Yuelong2,*(), LI Dapeng2, ZHANG Huiping1, YANG Yi3, XUE Guoliang4, LIU Wei1   

  1. 1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China
    2. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
    3. Xinjiang Institute of Geological Survey, Ürümqi 050081, China
    4. Key Laboratory of Digital Earth Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China
  • Received:2020-12-31 Revised:2021-05-07 Online:2022-07-25 Published:2022-07-28
  • Contact: CHEN Yuelong


The petrogenesis and sources of Indosinian magmatic rocks and the associated geodynamic settings in eastern Tianshan, Xinjiang have long been debated. In this study, the Aqishan andesites were investigated through integrated petrographic, geochemical and zircon U-Pb-Hf isotopic analyses. The andesites had a typical porphyritic texture and vesicular structure. The porphyritic texture was made of clinopyroxene and plagioclase phenocrysts in a matrix of acicular plagioclase. Zircon U-Pb dating results showed the Mg andesites erupted in ca. 235 Ma (Late Triassic) and contained Carboniferous inherited zircon grains. In-situ Hf isotopic analysis showed the magmatic zircon grains had negative εHf(t) values (-31.7--7.6) and Hf model ages of 2.2-0.7 Ga. The samples were geochemically marked by high MgO contents (3.7%-4.7%) and K2O/Na2O ratios (0.6-1.1) and low TFeO/MgO ratios (1.6-1.8) resembling high-K calc-alkaline Mg andesites. Geochemical characteristics combined with regional tectono-magmatic activities revealed the Aqishan Mg andesites were derived from partial melting of a phlogopite-bearing lithospheric mantle in an intraplate extensional setting. Therefore, during the Late Triassic, the lithosphere in eastern Tianshan was in an extension-thinning stage.

Key words: magnesian andesite, intraplate extension, lithospheric extension and thinning, Late Triassic, eastern Tianshan

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