中文摘要：

野外地质调查和SHRIMP锆石U／Pb地质年代学研究表明，拉萨地块中带措勤地区发育一套形成于晚白垩世中期的英安岩（88．5±1．2Ma）。该套火山岩具有岛弧火山岩的地球化学特征，为地壳深部岩浆岩部分熔融形成的I型岩浆岩，经历了明显的斜长石分离结晶作用。与同时代的侵入岩相比，该套火山岩为高度演化的岩浆，Rb／Sr比值较高，但Sr／Y比值较低。在拉萨地块内部，广泛发育的90～85Ma的岩浆作用与新特提斯洋的北向俯冲作用相关。

英文摘要：

Field investigations and zircon SHRIMP U-Pb dating show that a suite of dacite formed at Late Cretaceous （ 88.5± 1.2 Ma） occurred in the southeast of Coqen, western Gangdese Batholith,Tibet. This suite of volcanic rocks is characterized by trace element geochemistry similar to those formed in the arc environment. Geochmical and isotopic data indicate that they are I-type igneous rocks and have experienced high degrees of plagioclase fractional crystallization. As compared to those intrusive rocks of similar ages, this suite of rocks represents highly evolved magmas drieved from partial melting of deep crustal mafic rocks and is characterized by elevated Rb/Sr but lower Sr/Y ratios. Our new data as well as those from the literature further indicate that the Lhasa terrane had experinecd extensive magmatism at 90-85 Ma due to northward subduction the Lhasa terrane Neo-Tethyan oceanic lithosphere beneath the