CHARACTERISTICS AND TECTONIC SIGNIFICANCE OF THE LATE DEVONIAN INTRUSIVE ROCKS IN JIRIGALANGTU, INNER MONGOLIA

The Late Devonian intrusive rocks in Jirigalangtu, Inner Mongolia are distributed on the northern side of the Erlian-Hegenshan connect zone, with rock association of quartz diorite, tonalite and granodiorite. Lithochemically, the rocks are assigned to calk-alkaline series, with contents of SiO₂ for 64.23%-74.47%, Al₂O₃ for 13.59%-16.26%, TiO₂ for 0.19%-0.76% and Na₂O+K₂O for 6.28%-8.15%, with A/CNK ratio of 1.06-1.21, belonging to peraluminous granites. The An-Ab-Or diagram shows the T₂G₁G₂QM assemblage, which belongs to TTG type. The trace elements display the characteristics of volcanic arc granite. The rare earth elements are characterized by high fractionation and deficient HREE. The characteristics of the intrusive rocks reflect typical TTG resulted from the subduction of oceanic plate towards continental plate. The single zircon U-Pb isotopic age of the granodiorite is 361.1±1.0 Ma (Late Devonian). Therefore, the matching time of Sino-Korean plate and North China plate should not be earlier than Late Devonian.