西藏冈底斯带东段石炭纪构造环境讨论

摘要

冈底斯带东段石炭纪构造环境存有争议.本文通过岩石地球化学分析,发现石炭纪诺错组和来姑组火山岩具有碱性系列向拉斑系列过渡的特征,具有双峰火山岩特点；石炭纪玄武岩样品的平均化学成分与大陆拉斑玄武岩的平均值较为接近；微量元素除Ti、Yb、Y之外,其他元素都富集,其中Rb、Th、Ce富集程度相对较高；稀土元素特征表现为轻稀土富集,铕、铈异常不明显.显示出石炭纪玄武岩的地球化学特征均与大陆拉斑玄武岩相似.构造环境判别图解显示,石炭纪玄武岩样品主要落入板内环境的大陆拉张带(或初始裂谷)玄武岩区.因而认为冈底斯东段在石炭纪属于陆内裂谷或被动陆缘裂谷环境.%There has been controversial in eastern sector of the Gangdise belt. Through the analysis on geochemistry of rock, this paper found out the Nuocuo Fm. And Laigu Fm. Possess transitional characteristics from the alkalis series and own bimodal igneous tectonic features. The average chemical composition of the basalt in the Gangdise belt is closer to continent tholeiite; all the microelements are enriched except Ti, Yb and Y; of them Rb, Th, Ce are more obviously high; rare earth elements showed LREE enrichment, Eu, Ce anomaly not observable. These data showed that the characteristics of Carboniferous tholeiite are similar to continental tholeiite. On the tectonic discrimination diagrams, the tholeiite samples of the basalt from the eastern sector of the Ganddise are focused on the intraplate continental stretching belt or beginning rift. So it is considered that the eastern sector of the Gangdise belt in Carboniferous belongs to an intracontinental rift or a rift on passive continental margin.