Chronology Of Detrital Zircon From Upper Carboniferous And Its Geological Significance In The Middle Part Of Xing'an-Mongolian Orogenic Belt

The final collision position and geologic age between Siberia Plate and North China Plate has always been the focus in geologists,which leads to the discussions that the Xing'an Mongolian Orogenic Belt(XMOB)is the product of one or two tectonic cycles.The difference of sedimentary development and sedimentary facies between the Late Carboniferous strata in the XMOB contains the key information of tectonic evolution and plate merging in the XMOB.Therefore,based on the detrital zircon age characteristics and the provenance analysis of the Late Carboniferous sedimentary strata,this thesis discussed the tectonic evolution of the orogenic belt since the Late Paleozoic.Through the study of zircon age characteristics and the provenance analysis from the Upper-Carboniferous Baoligaomiao Formation and Gegenaobao Formation combined with previous research data,this study argues that the Paleo-Asian Ocean(PAO)was divided into Hegenshan and Xar Moron Oceans by Xilinhot Block.Xar Moron Ocean was closed in the Late Silurian but Hegenshan Ocean in the Late Devonian,which means that the PAO was completely closed in the Late Devonian.Considering the Solonker-Xar Moron suture zone in the south is already closed,So the Upper-Carboniferous Benbatu and Amushan formations in West-Ujimqin area contains the ~1.8 Ga and ~2.5 Ga ages in the basement of the North China Plate.Because of the uplift of the Earth's crust caused by orogeny in Hegenshan area,the source of the North China Plate cannot reach Baoligaomiao and Gegenaobao formations in Eest-Ujimqin area.The Solonker-Xar Moron suture zone was reopened in the Early Permian,and the terminated last to Late Permian-early Triassic.To sum up,the PAO has been completely closed in the Late Devonian,while the new oceanic crust appeared in the Early Permian,and the two belong to different tectonic cycles.