Detrital Zircon U-Pb Age Of The Quaternary Drilling Sediments,Heihe River Basin:Constraints On The Formation And Evolution Of Northern Qilian Orogenic Belt

Dating of eight detrital zircons from the Quaternary drilling sediments in Heihe river basin provides four groups of age(LA-ICP-MS U-Pb,2700 Ma?1700 Ma(32%),1700 Ma?650 Ma(16%),650 Ma?358 Ma(30%),and 358 Ma?230 Ma(22%),including eleven main and secondary peak ages(?2450 Ma,?1850 a,?950 Ma,?520 Ma,505 Ma,?480 Ma,?450 Ma,?430 Ma,?380 Ma,?320 Ma,and?295 Ma).And the late Neoproterozoic and Paleozoic ages accounted for the majority(?50%),when the most intense magmatic activities occurred.Herein,we would like to provide the formation and evolution of northern Qilian Orogenic Belt as follows.On the basis of the evidence from regional geological background,north Qilian mountain experienced weak continental crust consolidation during late Archean,a large amount of base material appeared during early and late ancient Proterozoic(?2450 Ma and?1850 Ma),in addition,the regional dynamo thermal flow metamorphism occurred during late ancient Proterozoic,corresponding,transformation and remelting of continental crust were found during Mesoproterozoic,and the Heihe river basin was controlled by the extension of the Rodinia super continent,which resulted in obvious magmatism and the mature continental crust.In general,early Paleozoic(ca.650 Ma?505 Ma)ocean basin appeared in northern Qilian between late Neoproterozoic and middle-late Cambrian due to continental extension.Owing to the subduction action and active continental margin development during whole Ordovician,the Trench-arc-basin system appeared was developing(480 Ma?450 Ma),and the closing action of ocean basin occurred at-450 Ma.At about 430 Ma,back arc basin appeared due to continent-continent collision.Moreover,the ocean crust in northern Qilian completely disappeared between late Silurian and early Devonian(?395 Ma),subsequently,northern Qilian Orogenic Belt papered as a result of the Collison and closing action between the Qaidam Plate and the North China Craton.The lack of Late Devonian age,together with the Devonian molasse sedimentary development,implying the end of the orogenic process in the study area.The Hercynian magmatic and thermal events(?320 Ma and?295 Ma)occurred in northern Qilian between Carboniferous and Permian,meanwhile,in this study we also obtain some Indosinian ages.The Tethys closed and orogeny happened once again in the study area during Mesozoic,which leaded to the thrust and thrust structures between Carboniferous and Triassic,thus,Hercynian and Indosinian rock mass rarely exposed.Northern Qilian lies between the ancient Asian tectonic system and the Paleo-Tethys tectonic system,the tectonic activities,the tectonic activity in this region is more complicated,and the northern Qilian was controlled by the dynamical system of Paleo-Tethys and the late Paleozoic closure of paleo-Asian Ocean.