Detrital Zircon U-Pb Geochronology Of Simao Basin In The Southeastern Tibetan Plateau In The Cenozoic

The uplift of the Tibetan Plateau is one of the most important geological events in the Cenozoic.It had a deep impact on tectonic framework of interior Asia and global climate and environment change.At present,there are many divergences in the study of Tibet Plateau plate collision time,pattern and amplitude as well as deformation in the process of plate collision,uplifting mechanism and so on.It`s in urgent need of using difference methods to study the key areas for testing those previous opinions or coming up with new ideas which solve the problems about uplift time,form and process of the Tibetan Plateau.Under the influence of the Tibet Plateau tectonic activities,Sanjiang region which locate at southeast edge of Tibetan Plateau had taken place large-scale strike-slip shear,compressional fold,thrusting nappe and uplift in the Cenozoic.These history of deformation and uplift of Sanjiang region are the key of studying the formation,evolution and dynamic mechanism of the Tibet Plateau.This paper chooses the Simao basin which belongs to Sanjiang region for research.We do some research of deteital zircon U-Pb age distribution characteristics of the Paleocene-Miocene sediments in Simao basin,and combine the analyses of depositional characteristic,conglomerate composition,paleocurrent and some previous research.Main productions and results are as follows:1.The provenance of Denghei formation that was deposited in Paleocene-Early Eocene came from the recycled material of Yangtze plate and the granite of Ailaoshan and Lincang area.The provenance of Mengla formation mainly came from the Lincang granite and the recycled clastic of Denghei formation and Mengla formation.The provenance of Sanhaogou formation which was deposited in Miocene mianly came from the Lincang granite which located at west side of the basin and Ailaoshan area which located at east side of the basin.2.Tectonic activities of Simao basin were stable during Paleocene-Early Eocene(65-52Ma).Affected by the India-Eurasian plate collision during Early Eocene-Late Eocene(52-37Ma),the thrust nappe happened on the west side of the basin and a thick molasse deposition formed on the front of mountain.It represented a response to the Tibetan Plateau plate collision in a long distance.During Late Eocene-Early Miocene,because of continuous extrusion and collision of India-Eurasian plate,a large-scale left-lateral slip and fold orogeny took place in Lancangjiang orogen and Ailaoshan orogen,which resulted in the uplift of Simao basin and the absence of Oligocene sediment in most area of Simao basin.During Early Miocene-Middle Miocene,tectonic activities of Simao basin became stable and a series of fine grained clastic containing coal versus deposited under a humid monsoon environment.3.the Lanping-Simao block had been suffered the subduction of Proto-Tethys oceanic plate in 380 Ma-440 Ma before the opening of the Ailaoshan ocean.Ailaoshan ocean subducted from Late-Devonian to Early-Carboniferous(300-380 Ma),and during the Late-Permian(270-300Ma),the Simao block sufferd a doubled-sided subduction.In the Triassic(200-250Ma),the collision between Simao block and Baoshan-Sibumasu block happened.Besides,the Simao-Indochina block should be along the India margin as the Qiangtang,Tengchong and Baoshan-Sibumasu blocks in Early Paleozoic.