Geochemistry, zircon U-Pb age and implications of the Linzizong Group volcanic rocks in Shiquan River area, western Gangdise belt, Tibet

Located in the southern part of Gangdise belt, the Linzizong Group volcanic rocks are regarded as the magmatic response to the continental collision between India and Asia, which is essentially important in understanding the evolutionary history of the Gangdise belt. The present research is only focused on central-western part of Gangdese belt, while the research on the western part is very insufficient. The authors conducted for the first time a systematic study of geochronology and major and trace element geochemistry of the Linzizong Group volcanic rocks in Shiquan River area in western Gangdise belt. The results indicate that the Nianbo Formation is of the calc-alkalic and high-potassic calc-alkalic series and is composed mostly of basaltic andesite, andesite and rhyolite, whereas the Pana Formation is of the high-potassic calc-alkalic to Shoshonite series with rhyolite. The Linzizong Group volcanic rocks in Shiquan River area are enriched in Rb, Th and U and depleted in Nb, Ta, Ti, Sr and Ba, which is similar to characteristics of central-eastern Gangdise belt, indicating the arc-related volcanics. The LA-ICP-MS zircon U-Pb age of Pana Formation in Shiquan River area is 53.9±0.5Ma, which is older than that of central-eastern Gangdise belt. The results combined with previous researches show that the initial collision between India and Asia continent took place earlier in western Gangdise belt but late in central-eastern Gangdise belt.