Abstract: In1999,XU Xi-wei et al.made an expedition to the Jinshajiang suture zone,northern Xizang.During the expedition,several rock samples were collected,among which some are granite samples.The granite samples belong separately to Amdo and Baingoin rock masses of the Nyanqentanglha granite zone that have been studied previously by other investigators.Petrographical observation,whole-rock chemical analysis,REE and trace elements analysis and isotopic age dating of these samples have been carried out.The results show that the sample collected from Amdo rock mass differs from the granitic rocks in this area reported in previous works.It is more acid and enriched in Na,and has a younger K-Ar age(157Ma)than previously reported.The REE pattern of this sample is characterized by negative Eu anomaly,having remarkable inclination to the right with lower gradient.The basic characteristics of the other samples collected from Baingoin rock mass are similar to those of the granitic rocks previously reported in this area.Their K-Ar ages are also within the range of the previously obtained results.The ⁴⁰Ar/³⁹Ar incremental heating experiments of biotite and K-feldspar from one of the sample have yielded ages of129.5?1.9Ma and131.3?1.9Ma,respectively,indicating relatively rapid cooling or shallow emplacement depth of the rock mass.All the obtained results provide important supplement to the previous work and may be useful for further study in this region.

Key words: granite, petrology, petrochemistry, REE pattern, isotopic age dating, Jinshajiang suture zone, northern Xizang

摘要： 对采自西藏金沙江缝合带的花岗岩样品进行了岩石学、岩石化学、稀土和微量元素分析以及年龄测定等。研究结果表明,这些花岗岩样品属于前人所划分的念青唐古拉岩带中的安多和班戈岩体,为花岗二长岩,属于钙系-钙碱性系列。其中属于安多岩体的样品与前人在该地区所描述的稍有不同,主要表现在更为酸性和富钠;其稀土配分的右倾斜率较小,所测得的K-Ar年龄(15 7Ma)也较前人的结果年轻。属于班戈岩体的其他样品均与前人的研究结果基本一致,所获K-Ar年龄数据(12.1Ma)也在前人测定的结果范围内。此外,对其中1件样品的黑云母和钾长石的⁴⁰Ar/³⁹Ar分段加热测定,获得了(12.9±1.9)Ma和(131±1.9)Ma的坪年龄,并揭示出岩体冷却速度较快、侵位较浅的特征。

关键词: 花岗岩, 岩石学, 岩石化学, 稀土元素配分, 年代学测定, 金沙江缝合带, 西藏