Discovery and Geological Significance of Late Triassic A–Type Granite in Jalaid Banner, Middle of Great Xing’an Range

The middle of Great Xing’an Range superimposed the influence of the Paleo–Asian ocean and the Mongol–Okhotsk ocean in the Triassic, and its tectonic setting remains controversial. Taking the medium-coarse grained texture syenogranite in Jalaid Banner, middle of Great Xing’an Range as research object, the study on petrology, geochemistry, zircon LA–ICP–MS U–Pb age and Lu–Hf isotope compositions have been carried out. The results show that the weighted average zircon U–Pb age of the granite is (228.5±2.0) Ma (MSWD=2.8); The rocks are high in Si, Fe and K, depleted in Sr and EU, relatively rich in Nb and Zr, and high in 10000×Ga/Al (3.0～3.1); The average of zircon saturation temperature is 805 ℃; It is comprehensively determined that the granite is considered to be the aluminous A–type granite. The granite ε_Hf(t) values range from + 5.28 to + 8.00, and the T_DM2 range from 683 Ma to 832 Ma, indicating that the granite may have been formed by partial melting of neoaccretionary crustal materials. Based on the regional research results, this paper holds that the residual ocean basin of the Paleo–Asian ocean in the Jalaid Banner closed and entered the collision orogeny stage in the Permian, and the appearance of A–type granite in the Late Triassic indicates that the area entered the post-orogenic extension stage.