Affinity Analysis Of The Metamorphic Basement Of Zhongba Microterrane:Evidence From Detrital Zircon U-Pb Geochronology,Tibet

Yarlung Zangbo suture zone is the collision suture of Indian plate and Eurasian plate,which is a hot spot in recent decades of the Tibetan plateau research,attracting the attention of many domestic and foreign geologists.In the western part of the Yarlung Zangbo suture zone,from Saga to China and India border region is characterized by two north and south Mélanges branches.Sandwiched between two north and south mélange branches is Zhongba Microterrane mainly assembled by Paleozoic and Triassic.In the western area of Zhongba Microterrane distributes a set of greenschist facies metamorphic rocks,that is considered metamorphic basement of Zhongba Microterrane.The layer was called Qiwugongba Group in the early study and the stratigraphic age is Sinian-Cambrian.However,different scholars had different points to the division of the greenschist facies metamorphic rocks in the late studies.The article researches U-Pb geochronology of quartzite and Muscovite-quartz schist of the greenschist facies metamorphic rocks at Mayoumu region in the western part of Zhongba Microterrane.By the study we hope use the youngest detrital zircon ages toconstrain the deposition age of the stratum.At the same time,the article analysises the source area and the construction affinity of Zhongba Microterrane by comparing detrital zircon ages.The youngest magmatic detrital zircon age is 421 Ma of quartzite and there are also have 457 Ma,473Ma,476 Ma age distribution.The four youngest detrital zircon ages of Muscovite-quartz schist is 402 Ma,403Ma,407 Ma and 409 Ma.Thus the deposition age of the strata would not earlier than 402 Ma.Combined with the fossils discovered in previous 1:250000 regional geological survey and lithological characteristics,the paper considers the deposition age of stratum is Early Devonian.The peak of detrital zircon ages of quartzite sample is 980 Ma in this work,that is similar to the peak age of ~950Ma of West Qiangtang,Tethys Himalaya and High Himalaya.Obvious different from western Australia and Lhasa Terrane characterized with peak age of 1170 Ma.The detrital zircon age of muscovite-quartz schist concentrated between 402Ma-711 Ma,the peak age is 491 Ma,that has a huge difference with quartzite's.Meanwhile,from the morphology of detrital zircon we could know that the source of muscovite-quartz schist maybe came from nearby region.It suggestes that the source area may change at study area at that time.The source of 980 Ma detritus of quartzite may be derived from the high Himalayas,Eastern Ghats in India or even Rayner area of Antarctica.The source of~ 500 Ma detritus of quartzite and quartz muscovite schist may be derived from the palaeozoic orogenic areas in the Indian plate of the edge of Gondwana.By contrast detrital zircon ages of Zhongba microterrane,the paper considers that the Zhongba microterrane belongs to Great India-Tethys Himalaya-West Qiangtang structural system and has no plate affinity with Lhasa Terrane.