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Geoscience ›› 2022, Vol. 36 ›› Issue (03): 796-811.DOI: 10.19657/j.geoscience.1000-8527.2022.016

• Petrology • Previous Articles     Next Articles

Dangjiasi Granite Complex and Late Triassic Dykes in Qinghai Nanshan Tectonic Zone, and Its Constraints on the Early Mesozoic Tectonic Environment

YANG Yanwei1(), LU Xinxiang2(), WANG Liwei1, YANG Yi1, YANG Chongke1, HUANG Fan3   

  1. 1. The First Institute of Resources and Environmental Investigation of Henan, Zhengzhou,Henan 450000, China
    2. Scientific Academy of Natural and Resources of Henan, Zhengzhou,Henan 450053, China
    3. Institute of Mineral Resources, CAGS, Beijing 100037, China
  • Received:2021-07-08 Revised:2021-12-18 Online:2022-06-10 Published:2022-07-19
  • Contact: LU Xinxiang

Abstract:

The Dangjiasi granite complex is a larger pluton in the central-eastern part of the Indosinian Nanshan granite belt(Qinghai Province). The complex was emplaced in the Early Triassic (243.5±2.9 Ma,247.2±1.7 Ma)-Middle Triassic (240.1±2.1 Ma,241.0±2.6 Ma). There are many intermediate felsic dykes in the intrusion, comprising mainly diorite porphyry, quartz diorite porphyry, and granite porphyry, LA-MC-ICP-MS zircon U-Pb dating on the diorite porphyry dyke yielded early Late Triassic age (235.6±2.4 Ma), slightly younger than the minimum emplacement age limit of the Dangjiasi granite complex. As a shallow intrusive body, the dykes are similar to the Dangjiasi intrusion in structural setting, and their mineral and geochemical compositions have similar characteristics, indicating that the two rock types have similar genesis and tectonic background, and may have had the same crust-mantle mixed magma source region. Litho-geochemistry shows that the intermediate dykes have low SiO2(54.68%-64.75%), whilst the felsic dykes have high SiO2(66.00%-77.13%), and both have high Al2O3(12.24%-17.11%). The rocks are high-kcalc-alkaline metaluminous-weakly peraluminous (A/CNK=0.85-1.04), with typical island arc granite and collision granite affinities. The rocks are enriched in LREE, Rb, Th and K, but depleted in HREE, Nb, Ta, P, Ti and Ba with (La/Yb)N=5.05-17.61 and medium negative Eu anomaly. Comprehensive analysis suggests that the dykes were formed in the Late Triassic Gonghe rift-closure related collisional orogeny. The tectonic setting changed from compression to intraplate stability-extension, suggesting that the Gonghe Basin(and surroundings) had entered post-collision intracontinental environment in the early Late Triassic.

Key words: intermediate-felsic dyke, zircon U-Pb dating, geochemistry, Dangjiasi complex, Late Triassic, Nanshan, Qinghai Province

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