Detrital Fission Track Thermochronology Of Neogene In Lunpola Basin,Central Tibetan Plateau And Its Significance

Since Cenozoic,the compression and collision between Indian plate and Eurasian plate led to the uplift of Qinghai Tibet Plateau,which is mainly composed of Himalayan block,Lhasa block,Qiangtang block,Songpan Ganzi block,Bangong Nujiang suture zone,Jinshajiang suture zone and Yarlung Zangbo Suture Zone.The mutual compression and shear between these blocks and a series of tectonic actions within the blocks resulted in the formation of large-scale thrust faults and strike slip fault zones,the shortening,thickening of the crust,the occurrence of magmatism,sedimentation and metamorphism,which let the Qinghai-Tibet Plateau become a natural laboratory for the study of geodynamics.Lhasa block and Qiangtang block are the main parts of the Qinghai Tibet Plateau.The Bangong-Nujiang suture belt between the two blocks is the sign of ocean closure and the sign of collision and orogeny between plates.The Lunpola basin is located in the middle of Bangong-Nujiang suture zone,which is the key position to study the splicing process of Lhasa-Qiangtang block,and the subsequent collision between India Eurasian plate and the uplift of the Qinghai Tibet Plateau.Based on the apatite fission track thermochronology of the clastic sediments of the Neogene dingqinghu formation in the Lunpola Basin,the paper reveals the cooling and exhumation events in the source area of the clastic rocks.Based on the previous studies on the strata age,sedimentary characteristics,volcanic activities and structural events of the basin,the following conclusions are drawn after comprehensive analysis:(1)The ages of the fission track centers of 11 samples are in the range of 50-151 Ma,mainly in the range of 50-94 Ma.The fitting component ages after single particle age decomposition are concentrated in 50-110 Ma,accounting for more than 70% of the sample particles.The fitting age P3(120-75 Ma)and P2(60-50 Ma)can be regarded as "static peak".(2)The "static peak" age P3(120-75 Ma)indicates that the South Qiangtang terrane in the sediment source area underwent significant rock exhumation in the late Cretaceous,which represents the signal of deformation and exhumation caused by the closure of Ban-Nu Ocean and the collision of Lhasa-Qiangtang block in the late Cretaceous.(3)The "static peak" age P2(60-50 Ma)indicates that the South Qiangtang terrane in the sediment source area underwent rapid rock exhumation in the early Cenozoic,which represents the tectonic deformation response of the central Tibetan Plateau to the collision of India-Eurasia plate in the early Cenozoic.