The Discussion On Record Of Neopaleozoic Cuomai Basin,tibety

The research area is located at the center of the Tibetan Plateau,within the area of the Angren city of Shigatse.We studied the lithology,chronostratigraphy,and biostratigraphy of the Neopaleozoic strata within the Cuomai basin based on the regional geology background,measured section,and field investigation.The sedimentary characteristics and basin evolutionary history of this region are investigated.The LA-ICP-MS U-Pb dating technique of zircons is employed to date the detrital zircons sampled from the Yongzhu Formation.The age is then compared with those from the adjacent Qiangtang and Lasha blocks to study the implications for regional tectonic evolution and Potential provenance.The main finding of this work is summarized as the following:?1?Building the depositional sequence?sedimentary cycle of the upper Carboniferous Yongzhu Formation;the upper Carboniferous-lower Permian Laga Formation;lower Permian Angjie Formation;and the middle Permian Xiala Formation,and definiting their ages??2?Making a regional stratigraphic comparison among with each Neopaleozoic stratum,defining evolution characteristics of the sedimentary facies,whice is shoreside facies to clastic shelf facies to mixed product shelf facies to carbonate platform facies.?3?Zircons from Yongzhu Formation rocks have three age spectrums with peaks at about 1175 Ma?1562Ma and 1783Ma,by comparing among the detrital zircons sampled from the upper Carboniferous strata and those from the Anduo micro continental,western Qiangtang block,Lasha block,Tethys Himalaya,Himalaya,the result suggests that the detrital zircon age 1175Ma of Yongzhu Formation has similar zircon ages with the whole Lasha block,while is difficult from the 950Ma of the other blocks.By comparing among the detrital zircons sampled from western and northern Australia,Zircons from Yongzhu Formation rocks have the similar age spectrums with a peak at about 1170Ma,it shows that Lasha block was from northern Australia.Albany-Fraser orogens provide clastic source for Neopaleozoic Cuomai basin.After that,we rebuild the late proterozoic-Early Paleozoic paleogeographic map.?4?The ages of Granite boulders from Laga Formation are about 2450Ma,the Granites are geared to A₂ type Granites,they belong to VAG,stretching environment before subduction,Glenloth Granite from Sleaford complex,southern Gawler Craton,Australia,have the similar ages and geochemical characteristics,all of those point that Granites at about 2450Ma from Gawler Craton are sources for Cuomai Granite boulders,the Granites moved with ice in late proterozoic-Early Paleozoic and hosted in clastic rocks as boulders.?5?the sedimentary geochemistry of quartz sandstones from Yongzhu-Laga Formation shows that,in late proterozoic-Early Paleozoic,Lasha block is in a structural environment include continental island arc and active continental margin.in this time,the source of clastic rocks is from Albany-Fraser orogen,source rocks are acid rocks and basic rocks.we rebuild the end of middle Permian paleogeographic map.