Earth Science Frontiers ›› 2020, Vol. 27 ›› Issue (3): 168-181.DOI: 10.13745/j.esf.sf.2019.9.24

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Magmatic response to lithospheric thinning of the North China Craton: evidence from porphyritic aegirite-bearing syenite in Wu'an, Hebei, China

ZHANG Bo1(), SU Shangguo1,*(), MO Xuanxue1, FENG Shaochong1,2, WU Yue3, JIANG Xiao4, FENG Yanfang5, LIU Jiangtao5   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
    2. State Radio Monitoring Center Testing Center, Beijing 100041, China
    3. Shenyang Institute of Geology and Mineral Resources, China Geological Survey, Shenyang 110034, China
    4. China Aero Geophysical Survey and Remote-Sensing Center for Land Resources, Beijing 100083, China
    5. Development and Research Center, China Geological Survey, Beijing 100037, China
  • Received:2019-08-16 Revised:2019-10-28 Online:2020-05-20 Published:2020-05-20
  • Contact: SU Shangguo

Abstract:

The Hongshan alkaline complex is located in the southern section of the Taihang Mountains, Hebei Province with an outcrop area of about 53 km2. Its lithology is dominated by syenite and intruded in the Late Paleozoic-Mesozoic strata. Our study showed that the alkaline intrusive complex belongs to alkaline series, formed in an extensional environment at the age of 120.1±4.6 Ma as a product of the peak period of the North China Craton magmatism. The REE patterns showed no Eu anomaly. The complex is enriched in light rare earth and large ion lithophile elements, such as Rb, K, Sr, and depleted in high field strength elements, such as Nb, Ta and Ti, exhibiting continental crustal characteristics. We observed in the field that the rocks are characterized by deep and shallow-ultra shallow formation. We also observed through electron microprobe analysis that the feldspar has a reverse belt that contained no inherited zircon. These observations, combined with the notion that partial melting of Earth's crust is needed to produce syenitic magma without Eu abnormalities, suggested a formation pressure of greater than 20 kbar. That is, the Hongshan syenite formed by partial melting of the thickened crust with some mantle derived magma mixing and mantle fluid injection to produce its mantle Hf and Nd isotopic signatures without altering the major and trace elemental characteristics, and then rose rapidly to the Earth surface under extensional condition.

Key words: Hongshan, syenite, geochemistry, zircon U-Pb age, magma mixing, tensional tectonic background

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