Is There a Neo-Tethys'' Subduction Record Earlier than arc volcanic rocks in the Sangri Group?
存在比桑日群弧火山岩更早的新特提斯洋俯冲记录么

Formation of the Tibetan Plateau is related to evolution of Neo-Tethys.It was thought that volcanic rocks in the Sangri Group were formed in late Jurassic to early Cretaceous,and represented the earliest magmatic record of the Neo-Tethys subduction. However,there is another volcanic suite called Yeba Formation in the east of the Lhasa block.Eruption of Yeba volcanic rocks was thought to be earlier than the Sangri Group,but lack of chronological evidence.Zircons from a sample of Yeba Formation lavas were selected and dated by LAM-ICP-MS,obtaining an age of 174Ma,indicating that Yeba Formation indeed is older than Sangri Group. In addition,lavas of the Yeba Formation show geochemical characteristics similar to volcanic rocks in an arc or active continental margin,such as LILEs' enrichment and HFSEs' depletion.We conclude that northward subduction of the Neo-Tethys resulted in the magmatic eruption of the Yaba Formation in early-middle Jurassic.If it is true,the Neo-tethys subduction probably started in early- middle Jurassic or earlier.