关键词: 兴安地块, 埃达克质, 花岗岩, 蒙古鄂霍茨克洋, 碰撞造山

Abstract: Although intense Mesozoic magmatism widely occurred in the Great Hinggan Range and is a hot topic in tectonic research, reports on the Late Jurassic granites is scarce. In this paper, we present three new LA-ICP-MS zircon U-Pb ages 158.5±1.6 Ma, 156.1±0.59 Ma and 154.1±1.1 Ma for granite outcrop in northeastern Xingan block to confirm that the granite emplacement occurred in the late Jurassic, not the early Mesozoic. These Late Jurassic granites are composed of medium coarse-grained granodiorite and monzonitic granite. Petrochemically they belong to peraluminous and high-K calc-alkaline series with high Si, K, Na and Al contents and low Fe, Mg and Ti contents. They are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE, e.g. Rb, Ba, Th, U, Sr), depleted in heavy rare earth elements (HREE), Y and high field strength elements (HFSE, e.g. Nb, Ta, Zr, Hf), with high La/Yb, Sr/Y ratios and possibly belong to “C-type” adakites. Genetics of the granite is closely related to the continental collision orogeny caused by the closure of the Mongol-Okhotsk ocean. The magma originated from the partial melting of basic rocks of the thickened lower crust under the orogenic belt with the addition of rich Al crustal material during magmatic evolution. The difference between the Late Jurrasic adakitic and adjacent Early-Middle Jurassic TTG granites reflects the tectonic evolution of the Mongol-Okhotsk ocean from subduction to continental collision during the Jurassic.

Key words: Xingan block, adakitic, granite, Mongol-Okhotsk ocean, continental collision