Oligocene Basin Record And Its Response To The Early Uplift Of The Tibetan Plateau In Xurucuo,Tibet

There is only one set of sedimentary strata(Rigongla formation)in the Paleogene basin of Xurucuo area.It is mainly composed of rudaceous rock with fine clastic rock,a small amount of volcanic rocks in the bottom.Within the Linzizong volcanic rocks,it recorded the rich information of the collision and post collision between India and Asia.The study area is located in the middle of Gangdise metallogenic belt,The study area is located in the Gangdise metallogenic belt,the tectonic location runs through three tectonic units.Through field survey,measured profiles,thin section identification,rock geochemical analysis,zircon geochronology and indoor comprehensive study,described the basin records of Oligocene Rigongla Formation.In order to further explore the early uplift of the Tibetan Plateau and the collision time of the India-Asia plate.Study results showed that it can be divided into three lithologic segments.At the bottom is a set of medium-thick purple red dark purple conglomerate,pebbly sandstone to the transition of coarse sandstone,it can see volcanic rocks in some areas.The middle part is a set of mudstone,silty mudstone and argillaceous siltstone,Gypsum layer in local area.The top is also a set of purple red coarse clastic rocks.According to the lithologic assemblage and tectonic position,the sedimentary environment is Fan Delta-River-Lake.Geochemistry of volcanic rocks show that Rigongla formation volcanic rocks belongs to calc-alkaline series and shoshonite series.The emergence of shoshonite suggests that the end of the oceanic lithosphere's subduction and the start of intracontinental convergence.In the process of diagenesis,there is obvious mixing.Distribution curves of REE chondrite standardized the whole change law is consistent,light rare earth fractionation characteristic is obvious,Eu negative anomaly.The heavy rare earth shows a concave pattern,which indicates that the separation and crystallization of plagioclase and garnet occur.And it's forming environment is the Island arc environment.Based on the Zircon analysis of clastic rocks,it is concluded that the source of the formation is from the early Cretaceous granites in the north-north west side of Central Lhasa.Based on the analysis of the volcanic rocks and provenance,the sediments are located in the first two stages of the uplift of the Tibitan Plateau,the uplift stage of subduction collision and the stage of intracontinental convergent compression uplift.