Geochemical Characteristics And Tectonic Significance Of Late Carboniferous Basalt In Bailang,Southern Tibet

The Yarlung Zangbo suture zone records the evolution information of the Neo-Tethys.From the perspective of the evolution model of the Neo-Tethys,the degree of research on the early evolution of the Neo-Tethys is relatively low,and the opening of the Neo-Tethys even more controversial.Late Carboniferous basalts are exposed in the Yarlung Zangbo suture zone in southern Tibet,which is in fault contact with the Triassic strata.This paper discusses the formation environment and geological significance of the Late Carboniferous Basalt in the Yarlung Zangbo suture zone in southern Tibet by chronological and geochemical studies,and defines the evolution model of the Neo-Tethys.Late Carboniferous Basalt is alkaline basalt with stomatal almond characteristics.And the measurement result of the zircon U-Pb dating experiment is300.48±1.16Ma(MSWD=0.57),its LOI is 2.80%-10.08%,depleted in Heavy Rare Earth Elements(HREE),showing OIB characteristics,and its trace element distribution and Sr-Nd isotopic characteristics show that Panjal Traps are related and also show the origin of asthenospheric mantle.La/Ta values of 8.54-13.43 and La/Sm values of 3.14-4.63 indicate that Late Carboniferous Basalt is not significantly contaminated by the lithospheric mantle and crust,and(Th/Ta)_PM-(La/Nb)_PMdiscriminant chart shows the same result.Combining Panjal Traps and Late Carboniferous Basalt data for analysis,The breakup of the East Gondwana continent(the opening of the Neo-Tethys)may be controlled by the dual dynamic mechanism of asthenospheric mantle upwelling and back-arc stretching caused by the subduction of the Paleo-Tethys.And it may have started before the end of the Late Carboniferous.Late Carboniferous Basalt show inter-plate characteristics.Combining the background of the times and the characteristics of contemporary volcanic rocks,it refers to the formation environment of the continental rift.Judging from the characteristics of basalt,at that time,the East Gondwana was in a state of continuous stretching,thinning the crust,resulting in decompression melting,and at the same time,the increase of mantle material caused an asthenospheric upwelling.The formation of Late Carboniferous Basalt may represent the time when the lithosphere in the eastern part of the Indian plate completely fractured.Therefore,it is likely to limit the upper limit of the breakup of the East Gondwana or the lower limit of the opening of the Neo-Tethys.