关键词: 大兴安岭中段, 侏罗纪, 花岗岩, 锆石U-Pb测年, 地球化学, 岩石成因, 构造背景

Abstract: Great Xing’an Range is located in the eastern part of the Central Asian orogenic belt. It is a composite part of the Paleo Asian Ocean, circum Pacific Ocean and Mongolia Okhotsk Ocean. Having strong tectonic magmatic activity, it is the best window to study the Mesozoic tectonic magmatic evolution in Northeast China. The authors studied the Jurassic granitoids in the Jinjianggou of Central Great Xing’an Range, and performed systematic analyses of zircon U-Pb chronology and whole-rock elemental geochemistry. The zircon U-Pb age data indicate that petrogenic ages of medium-fine grained granodiorite is (165±1)Ma, the diagenetic ages belong to Middle Jurassic, the petrogenic ages of medium-fine grained syenogranite and medium-coarse grained monzogranite are (152±1)Ma, (147±1)Ma and (148±1)Ma, with their diagenetic ages belong to Late Jurassic. Geochemical data show that the granodiorite and monzogranite samples have low silicon, and are poor in magnesium, iron and titanium, TFeO/MgO ratio and Zr/Hf ratio; They are enriched in Th, Rb, U, Ce, La, Hf and poor in Sr、Nb、Ba、Ti、P, and have geochemical characteristics of type I granite. The magma was originated from the source area of partial melting of igneous material in the lower crust. The syenogranite samples are enriched in silicon, high in potassium, poor in magnesium, iron and titanium, low in TFeO/MgO ratio and Zr/Hf ratio, relatively high in differentiation index, strong europium negative anomaly, relatively rich in Th, Rb, U, Hf, Ce, La, Nd elements, and deficient in Sr, Nb, Ba, Ti, P and other elements, and has geochemical characteristics belonging to highly differentiated type I granite. The magma was originated from the source area of partial melting of igneous material in the lower crust. Combined with the chronology and geochemical characteristics, the medium-fine grained granodiorite was formed in the syn-collision tectonic setting, and medium-fine grained syenogranite and medium-coarse grained monzogranite were formed in post-orogenic extensional tectonic environment, which were related to the scissor closure of the Mongol-Okhotsk Ocean from west to east. We believe that the final closing time of the western section of the Mongol-Okhotz suture zone is the Late Middle Jurassic.

Key words: Central Great Xing’an Range, Jurassic, granite, zircon U-Pb dating, geochemistry, petrogenesis, tectonic setting