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

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