Tectonic Property Research On Zhongba Microterrane,southern Tibet:Evidences From Detrital Zircon U-Pb Geochronology

The Zhongba microterrane located in the southern Tibet,narrowly pinched out between two branches of mélanges within the western part of Yarlung Zangbo suture zone.The Zhongba microterrane confined between two faults: Zhada-Zhongba-Chazang fault in the northeast,Qiongguo-Mentu fault in the southwest,from Beichazang extends to the boundary of China and India.The nautiloids(inoceras sp.,? Discoceras sp.Ancistroceras cf.undulatum,Michelinoceras cf.paraelongatum)and Crinoidea(Pentagonopentagonalis cf.tridens,Cyclocyclicus sp.)fossils in the Ordovician strata,the Brachiopoda(Calliomarginatia-Fusispirifer ? Costiferina-Spiriferella ? Neospirifer-Gypospirifer)and Bryozoa(Fistulipora-Streblotrypa)in the Permian Quga group,which are similar to biota from Tethys-Himalayan,indicating that Zhongba microterrane have Tethys-Himalayan affinity in biogeographic provinciality.In addition,the Muxia subarea was located next to Tethys-Himalayan from Ordovician to Devonian.The difference of sedimentary environments between Zhongba microterrane and Tethys-Himalayan taken place since Permian.Besides,The Zhongba microterrane located in the southern Tibet,narrowly pinched out between two branches of mélanges within the western part of Yarlung Zangbo suture zone.The Zhongba microterrane confined between two faults: Zhada-Zhongba-Chazang fault in the northeast,Qiongguo-Mentu fault in the southwest,from Beichazang extends to the boundary of China and India.Four samples were collected from Ziqudianzhan,Gangzhutang,Zhongba and Tunjuchang formation in the Zhongba microterrane for detrital zircon dating.The age data show two dominated statistical peaks:~510Ma and ~950Ma,two secondary statistical peaks: ~1700Ma and~2450Ma.The age data distributions of Zhongba microterrane are similar to those in western Qiangtang,Tethys-Himalayan and Higg-Himalayan,and they don't have the peak of ~1170Ma which is dominated in Lahsa and Australia.Therefore,the Zhongba microterrane had the same sedimentary source with the Tethys-Himalayan,in early palaeozoic(Ordovician Ziqudianzhan formation),late palaeozoic(Permian Quga formation)and Mesozoic(Triassic Tunjuchang formation),the sediments is mainly from India craton.The lithology,biota and palaeoenvironment and detrital zircon U-Pb age give evidences to that the Zhongba microterrane has Tethys-Himalayan affinity.The Zhongba microterrane might be connected to the northern margin of Indian continent,next to the Panjal Traps and start to separate from India since middle Permian.