Zircon U-Pb Geochronology And Paleomagnetism Of The Volcanic Rocks Of The Late Permian Nayixi Formation In The Northern Member Of The Qinghai-Tibet Plateau

The northern Qiangtang-Qamdo Block of the Tibetan plateau is a large and stable block with a Precambrian crystalline basement and intact Phanerozoic sedimentary cover.It's very important for researching boundary of Gondwana plate and Eurasia plate,evolution of the paleo-tethys ocean,reconstruction of the paleo continent that reaching paleogeographic location of the northern Qiangtang-Qamdo Block in Phanerozoic.In order to obtain reliable paleomagnetism data with chronology data,a combined petrology,zircon U-Pb chronology,rock magnetism and paleomagnetism was conducted on the Nayixiong Layer' S extrusive rock of later Permian in Zhouqiongmalu,Tanggulashanxiang,Golmud city of Qinghai province.According to the conclusion,we reconstructed the paleogeographic location of the key block and explored the surrounding block on late late Permian paleogeographic location relations.We have observed specimens,identified section,analyzed the main trace elements of the specimens on Nayixiong layer.There are three layers on Nayixiong Layer,dark grey rhyolite of top layer,celadon or grey tuff of middle-level,fuchsia or mahogany basalt and andesite of under layer.A geochronologic study of zircon U-Pb dating on the rhyolite and andesite indicates that the volcanic rocks sampled from the Nayixiong Layer is about 250M,.in other words late Permian.Orientated samples were collected from 39 sites(309 samples)on the Nayixiong Layer.Rock magnetism experiment for 8 samples shows that magnetite-hematite in rhyolite,magnetite in tuff,hematite in basalt and andesite.AMS(anisotropy of magnetic susceptibility)experiment from 309 samples shows that Nayixiong Layer haven't lived through forceful deformation and compaction.After thermal demagnetization for 39 sites(309 samples),analysis and comparison detailedly on the data,the high temperature component for 36 sites(30 sites after combined)253 samples tilt corrected and the paleopole obtained from late Permian Nayixiong Layer sites are Ds=274.8°,Is=23.2°,Ks=27.9,?95=5.1 and-10.6°N,189.4°E,A95=4.0°.The palaeolatitude is-12.1°N.Combined Cheng et al published data and this study data which all passed fold test.The high temperature component is identical KRS shows reversed polarity.The above results show that the ChRM directions are prefolding primary magnetizations.The VGP scatter shows that the volcanic rocks Paleomagnetic data have averaged paleosecular variations.The results support that the northern Qiangtang-Qamdo Block located at-12.1°N atabout 250 Ma.Combined with the paleontologic data,petrology,previous paleomagnetic results,we reconstructed the northern Qiangtang-Qamdo Block and around the block on late Permian paleogeographic location.