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Geoscience ›› 2021, Vol. 35 ›› Issue (06): 1677-1690.DOI: 10.19657/j.geoscience.1000-8527.2021.125

• Gold-polymetallic Mineralization in Qinling Orogens • Previous Articles     Next Articles

Middle-Late Triassic Tectonic Attribute in West Qinling: Evidence from Geochronology and Geochemistry of the Jiangqinaliang Intrusive Complex

YAN Jing1(), LIU Jingxian1, PU Wanfeng1, WEI Xueping2, LI Zhibin1   

  1. 1. The Third Institute of Geology and Mineral Exploration of Gansu Bureau of Geology and Mineral Resources, Lanzhou, Gansu 730050, China
    2. Central Laboratory of Gansu Province, Lanzhou, Gansu 730050, China
  • Received:2021-09-11 Revised:2021-10-11 Online:2021-12-10 Published:2022-02-14

Abstract:

There are still many controversies about the early Indosinian tectonic setting of the West Qinling orogenic belt. To deepen our understanding on this issue, a study of the petrology, geochronology, and geochemistry on the Jiangqinaliang intrusive complex in West Qinling were reported. The Jiangqinaliang intrusive complex is composed of quartz diorite and granite porphyry. LA-ICP-MS zircon U-Pb age of the quartz diorite is (240.0±1.5)Ma, representing the formation age is Middle Triassic, which belongs to the early Indosinian. The Jiang-qinaliang intrusion complex is characterized by high potassium (K2O=3.09%-3.54%), rich alkali (K2O+Na2O=6.44%-7.20%) and peraluminous (A/CNK=1.05-1.56), as well as high Mg# values (54-67), belonging to the high-potassium calcium-alkaline peraluminous rocks. Quartz diorite and granite porphyry have similar trace element and rare earth element composition and show that light and heavy rare earth elements clearly fractionated (LREE/HREE=8.19-14.63), with right-leaning characteristics. In addition, they exhibit no or weak negative Eu anomaly (δEu=0.87-1.03), depleted in the high-field elements, such as Nb, Ta, and Zr, and enriched in the large ion lithophile elements, such as Ba, Rb, and Sr. These characteristics indicate that the Jiangqinaliang intrusion complex is mainly derived from partial melting of high-potassium metabasic rocks in lower crust, and involved mantle materials. Combined with regional geological background, it is suggested that the Jiangqinaliang intrusion complex was formed in a volcanic arc tectonic setting and may be related to the northward subduction of the Animaqin-Mianlue ocean during the Middle-Late Triassic, showing that the West Qinling area has the attribute of an active continental margin in the Middle-Late Triassic.

Key words: Middle Triassic, geochemical characteristic, tectonic setting, West Qinling, Jiangqinaliang intrusion complex

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