Geochemistry And Zircon U-Pb Chronology Of Linzizong Group Volcanic Rocks In Western Gangdese, Tibet

The Paleogene volcanic rocks in Linzizong Group is widely developed in the southern Gangdese belt of Tibet plateau, it is deemed to represent the result of Neo-tethys from its subduction to the India-Asia collision as it contains the information from syn-collisioal to post-collisioal affinities in the whole group. The study area saturated in the west of Gangdese belt, it belongs to the southern Gangdese magmatic arc tectonic unit. Herein a systematic, including zircon U-Pb ages, major and trace elements and Pb isotopic geochemistry, has been done to volcanic of Dianzhong Formation from Linzizong Group of western Gangdese belt. The petrogenesis source region evolution of the rocks has been discussed. Based on the previous studies, the results of this thesis were also compared to the Linzizong Group in the Linzhou basin of the east of Gangdese belt, and to distributed in other different regions of southern Gangdese belt,in order to find the spatial and temporal change among these volcanic rocks.In the research, we find that most volcanic rocks of Linzizong Group belong to peraluminous and high-potassim, calc-alkaline and high-K calc-alkaline volcanic. They show LREE enrichment with a significant Eu negative anamaly (the average is 0.6453). The rocks are depleted in Nd,Ta,Ti and other HFSE and enriched in Rb,Th and other LILE, both of which showing the typical arc-related magmatism affinities. The rocks are enriched in Pb ( 208Pb/204Pb=36.9801~39.003,207Pb/204Pb=15.328~15.645,206Pb/204Pb=16.664~18.563), which revealed a mixture source region controlled by the continental basement materials in Gangdese belt. The LA-ICP-MS zircon U-Pb data of the 3th group of Dianzhong Formation volcanic rocks which we obtain showing the following ages: 64.25±0.91Ma and 64.52±0.48Ma. Reviewing the data of different area of southern Gangdese belt, which indicate that the India-Asia collision along Gangdese belt may be diachronous.