Provenance Characteristics And Structural Evolution Of The Linbuzong Formation In The Cretaceous Basin,South Gangdese,Tibet

The Gangdese sub-terrane records a lot of key information about the Qinghai-Tibet Plateau uplift and the Indian-Asian slab collision,which has important scientific research value.Most scholars use volcanic rocks and Gangdese rock bases in the south Gangdese sub-terrane as research objects to determine the Indian-Asian slab collision time.However,little research has been done on the evolution of Mesozoic sedimentary basins in south Gangdese sub-terrane and the tectonic evolution and dynamics of earth the Tibetan Plateau before the collision of the Indian-Asian slab collision.Against this background,this article studies the detrital zircon and volcanic rocks of the Linbuzong Formation in the Early Cretaceous sedimentary basin in the middle-east of south Gangdese sub-terrane.The study area is mainly located in the Lhasa-Mozhugongka-Linzhou zone.Based on the study of the sedimentary era,sedimentary environment and provenance characteristics of the Linbuzong Formation,it provides important basic data for the tectonic evolution of the Early Cretaceous sedimentary basin in the middle-east of south Gangdese sub-terrane,and provides insight into the formation and evolution of the Qinghai-Tibet Plateau.It has important scientific significance.Based on regional geological data and tectonic background,we analyzed and studied the petrographic and geochemical characteristics of the clastic sedimentary rocks and the Andesitic tuff of the Late Jurassic-Early Cretaceous Linbuzong Formation.The sedimentary rocks of the Linbuzong Formation are rich in large ion lithophilic elements?LILEs?such as Rb,Pb,and U,and deficient in high field strength elements?HFSEs?such as Nb and Ta.Light and heavy rare earth fractionation is obvious.All samples have moderately Eu negative anomalies??Eu of0.66 to 0.72?,showing a very consistent distribution pattern with the upper crust.The rock may be formed in the continental island arc tectonic environment,and some passive continental marginal tectonic environments exist.It is speculated that it has the characteristics of island arc volcanic rocks;The sedimentary tuff of the Linbuzong Formation is rich in large ionite elements?LILEs?,deficient in high field strength elements?HFSEs?,and weakly Eu negative anomalies??Eu of 0.87 to 0.92?.The rock tectonic setting is continental island arc environment.According to the characteristics of detrital zircon U-Pb geochronology and Hf isotope,it is revealed that the youngest zircon deposition age in the detrital sedimentary rocks of the Linbuzong Formation is137±2Ma,which represents the lower sedimentary limit of the Linbuzong Formation.The zircon U-Pb age of the Andesitic sedimentary tuff is 158±1.2Ma?MSWD=1.07?,probably represents contemporaneous volcanic activity;The?_Hf?t?value of some clastic sedimentary rocks of the Linbuzong Formation is-18.4?4.51,of which only one zircon has an?_Hf?t?value>0.At the same time,combined with the detrital zircon age distribution curve,it can be known that most of the provenances of the Linbuzong Formation come from the circulation of the central Gangdese sub-terrane,and a small amount from the south Gangdese sub-terrane;In this paper,the main age range of the sedimentary detrital zircons in the Linbuzong Formation is 470 Ma to700 Ma,and the peak age is 560 Ma.We propose that the Carboniferous-Permian strata from central Gangdese sub-terrane serve as the main source of sediments for the Linbuzong Formation.Based on the petrographic and geochemical characteristics of the Linbuzong Formation and the previous research results of other Cretaceous formations,We believe that the Cretaceous back-arc basin form the southern Gangdese sub-terrane has undergone multiple stages of compression,stretching,and compression.In the late Jurassic-Early Cretaceous,the mainly affected by the collision between the Gangdese sub-terrane and the Qiangtang sub-terrane,which caused the crust to thicken of the central and northern Gangdese sub-terrane.At the same time,it is affected by the increase of the northward subduction angle of the Neo-Tethys slab.During the Late Cretaceous,the southern Gangdese sub-terrane may slow down due to the northward subduction angle of the Neo-Tethys slab,causing magmatic activity to erupt and the asthenosphere to surge.The direction of the water flow is from south to north.Therefore,provenance conversion occurred in the basin.