Apatite Fission Track Ages And Significance Of The Northern Margin Of The Qaidam Basin

The Tibetan Plateau is the world's highest and youngest plateau.as an important event in Cenozoic,The uplift and formation of this Plateau affects on global and Asian climate and environment.Recent decades,the study on the Tibetan Plateau has made great progresses,yet there are still no uniform agreements on the time,process, intensity as well as the forms of the resource and environment effects causedby the uplift of the Tibetan Plateau.Qaidam basin lies in the northeast margin of Qinghai-Tibet Plateau,and located in the conjoint zone of Asian structural domain and Thetys-Himalayan one in the geotectonic situation,and surrounded by Altyn Mountain,Qilian Mountain and Kunlan Mountain,so its evolution has complicated geodynamic mechanism and reformation characteristic in Mesozoic-Cenozoic.There are very thick Cenozoic stratas deposited in the basin and those sediments came mainly from its surrounding mountains,which preserved very important information on the plateau uplift and basin evolution in Cenozoic.The study of detrial zircon fission track analyses of Cenozoic strata in Qaidam Basin suggests that the sedimentary exhumation-provenance is the peripheric mountains of the basin which had undergone Hercynian-Indochina thermo event.The facts reveal that multiple thermo-tectonic events had taken place in the provenance(～373 Ma,295～335 Ma,280～285 Ma,260～275 Ma,235～260 Ma,220～230和215～225 Ma),which indicate that in the north part of Tibet plateau is characterized by multi-stage and synchronous uplifting before cenozoic.Apatite fission track dating evidences from 16 samples,shows that the samples which fission track ages are older than their respective strata ages reflect the provenance ages of these apatite,the time of tectonothermal episodes is～36Ma,50～58 Ma,86～89 Ma,97～109Ma,和143～183 Ma。The samples which fission track ages are younger than their respective strata ages shows that the maximum burial temperatures for these samples exceeded the total annealing temperatures of the fission tracks,and reflect three tectonothermal episodes which happened in 43.5～47.6Ma,～117Ma.The dating show that there are four uplift phases which corresponding period is Jurassic,early Cretaceous,late Cretaceous,Paleocene,Eocene in the northern margin of the Qaidam basin.which indicate that tectonic activities in Qaidam Basin and its periphery experienced strong-quiescent-strong stages in Cenozoic.