U-Pb ages of the zircons from primary rocks in middle-northern Daxinganling and its implications to geotectonic evolution
大兴安岭中北段原岩锆石U-Pb测年及其与区域构造演化关系

The age of single zircon is thought to be the recording of single tectonic, magmatic or metamorphism activity, the ages of a large amount of zircons got from different types of primary rocks should be able to indicate the geotectonic evolution history. The authors of the paper collected 2636 zircon ages determined by U-Pb dating from 123 samples in middle-northern Daxinganling, dated by authors or gatherd from published data, the statistics on these data has shown that the zircon ages have several peak value ages of 840~780Ma, 530~440Ma, 330~280Ma, 240~190Ma, 180~160Ma and 150~120Ma, and three blank time space of >840Ma, 770~540Ma, 440~400Ma. The ages of different types zircons generated by magmatism, metamorphism, or that inherited from former rocks have similar statistics features. The peak value of zircon ages has a good accordance with the time that important tectonic event took place in middle-northern Daxinganling Mountains, such as, the formation of basement, mircoplate subduction and collision. The blank period of zircon ages is corresponded to that of ocean spread or passive continental margin event. It is concluded that a large amount of zircon ages determined by U-Pb dating method for primary rocks also can be applied to study the geotectonic evolution history, just like the zircon ages from rivers detrita. Study on the statistics on zircon ages, granite association and tetonics indicates a very complicated tectonic evolution history has been taken place in middle-northern Daxinganling Mountain, that is, the formation of basement in Plaeoprotozoic, growth of continental crust in Neoprotozoic, breakdown of plate in the end of Neoprotozoic, subdution, spreading, accretion and collision between miroplates in Paleozoic, continental collision in Early Mesozoic, postorogenic extension and collapse in Late Mesozoic related to the Mongolia-Okhotsk orogeny and continental marginal tectonic-magmatic event related to the subdution of West Pacific Ocean in Mesozoic. The study has also shown that the Mongol-Okhostsk Ocecn has been closed in Late Triassic Period in Transbakal area. There is a large amount of granites, migmatites related to continental collision, and metaomorphic complex, basin-range, continental bimodal volcanic rocks related to postorogenic collapse, occurred in middle-northern Daxinganling. It is suggesting that the geodynamic background for the polymetal mineralizaton in the area need to be reconsidered.