中文摘要：

位于拉萨地块南缘的桑日群火山岩通常被认为是新特提斯洋沿拉萨地块南缘向北俯冲消减的产物,但其喷发持续时间一直没有得到有效约束。在桑日群火山岩系中识别出一套稍晚于桑日群火山岩的侵入岩脉, 脉岩中的锆石用U-Pb LA-ICPMS 法测得年龄为（93.4±1.1） Ma。据此认为桑日群火山岩的喷发时间应不晚于93.4 Ma。前人的研究表明桑日群的活动时限可以追溯到晚侏罗世-早白垩世, 因此其所代表的新特提斯洋的俯冲消减至少从晚侏罗世延续到了93.4 Ma 左右。另一方面, 这些侵入岩脉的地球化学特征明显不同于俯冲成因的桑日群弧火山岩, 如埃达克岩（麻木下组）和钙碱性的火山岩（比马组）, 而与东部朗县和里龙一带 的侵入岩非常相似, 它们很可能是板片俯冲导致的加厚下地壳部分熔融的产物。这种差异暗示在新特提斯洋 俯冲消减过程中其深部动力学环境发生了较大的改变。

英文摘要：

The Sangri Group volcanic rocks in the south margin of the Lhasa block are generally thought to be typical products of the Neo-Tethys＇ northward subduction along the south margin of the Gangdese arc belt, but it is still argued about their chronology because of lacking reliable data. In this research we recognized a suit of intrusion in Sangri Group, zircons from which were dated by LA-ICPMS, obtaining an age of （93.4±1.1） Ma.Considering previous researches we suggest that the activity time of Sangri Group volcanic rocks last from the Late Jurassic to 93.4 Ma; on another hand, the geochemical characters of these intrusions are different from Sangri Group volcanic rocks （including adakites of Mamuxia Formation and calc-alkaline series of Bima Formation）, but very similar to adakites in Langxian and Lilong area, which hints that they were likely produced by the melting of thickened lower crust. From Sangri Group arc volcanic rocks to later adakitic intrusions, differences between them suggest that the deep kinetic setting have obviously changed during the Neo-Tethys＇ northward subduction.