Provenance Analysis And Tectonic Significance Of Lower Cretaceous Chu Mulong Formation In Linzhou Basin,Tibet

At present,the tectonic evolution of the Mesozoic strata in the southern part of the gangdise block is not sufficiently understood.By studying the properties of the cretaceous basin in the southern part of the gangdise block,the tectonic structure and crustal growth mechanism of the Mesozoic strata can be better understood.There are many views on this issue.Whether the foreland basin formed by the Gangdis-Qiangtang collision,the continental marginal intra-arc basin formed on the Yeba volcanic platform in the early northern subduction of the new tethys ocean,or the back-arc basin formed by the new tethys ocean subduction is a matter of debate.Based on this background,this article selects the early cretaceous in the south of the mountain,land Chu Mu Long group stratum,the sedimentary environment,substance sources and the development history and structural evolution and so on to conduct a comprehensive analysis,to determine the structural properties,of the neo-tethys ocean basin opening and subduction to reduce such problems as the starting time is of great significance.In this paper,on the basis of detailed field geological investigation,combined with regional geological data and the background of tectonic evolution,make use of the petrography,geochemistry,methods of detrital zircon chronology,and stipulate Chu Mu Long group basin deposition time,sedimentary environments,tectonic property as well as the main material source,etc.,and managed to prove that the mountain massif crustal growth "back-arc hyperplasia model",as constraint,the mountain massif in the Mesozoic tectonic evolution to provide important support.According to the study,both the chumulong formation(K1c),the overlying Ta Ke Na formation(K1t)and the underlying Lin Bu Zong formation(J3K1l)are in integrated contact,and the sedimentary environment is a Marine and continental transitional facies deposition dominated by coastal facies and intracontinental fluvial-lacustrine facies.The clastic tectonic environment identification map shows that the Chu Mulong formation is the environmental product of the transition between the continental island arc and the active continental margin,and the source rock is the upper crustal recirculating feldspathic rock.The age of detrital zircons in the Chu Mulong formation is characterized by a large data span and a large number of peaks,indicating that the sediments in the Chu Mulong formation have multiple material sources,or that its original rocks have gone through multiple sedimentary cycles.The youngest age of detrital zircon u-pb test in the Chu Mulong group was ? 137 Ma,representing the lower limit of deposition in the Chu Mulong group.By comparing the morphological characteristics of detrital zircon in the Chu Mulong group with the age spectrum of detrital zircon at the peak,it was found that most of the main provenance may come from the recycling of materials in the north of Gangdis and a few from the magmatic arc in the south of Gangdis.The sediments of the Chu Mulong formation were formed in the back-arc basin with active continental margin type,which was subducted northward by the neotethys ocean.The sediment sources were mostly deposits from distant sediments.The young materials mainly came from Sang Ria volcanic rocks produced in extensional environment or bimodal volcanic rocks south of Gangdise.Most of the provenance comes from the north-central part of Gangdise.