摘要
在龙木错-双湖-澜沧江缝合带北侧,沿青海省囊谦县尕羊及其以西,新发现呈北西向带状分布的晚二叠世正长花岗岩侵入体。其岩性为中细粒含白云母正长花岗岩,岩石以酸性程度高、富硅、富碱、富铝及非常高的稀土含量为特点,岩石的铝过饱和指数ASI平均值达1.166,CIPW标准矿物中刚玉分子平均为5.08,为典型的高钾钙碱性系列的过铝质花岗岩。其岩石类型相当MPG含白云母过铝质花岗岩类;岩石ΣREE高达466.55×10-6~682.80×10-6,具有强的Eu负异常,δEu平均值为0.06,微量元素含量富不相容元素(LILE),贫高场强元素(HFSE),具有典型的S型花岗岩的特征,与冈底斯碰撞花岗岩特征近一致,构造分析相当于Maniar花岗岩分类中的CCG花岗岩(大陆碰撞花岗岩)。在尕羊正长花岗岩中获得了251.4±0.6Ma的TIMS法锆石U-Pb同位素年龄,其形成时代为晚二叠世,与在乌兰乌拉湖-澜沧江结合带内获得的251.5±2.6Ma和249±49Ma热年代信息一致,反映晚二叠世—早三叠世构造热事件的存在,可能属于晚二叠世—早三叠世乌兰乌拉湖-澜沧江结合带陆-陆碰撞的产物。
In northern Qiangtang-Changdu plate of Longmucuo-Shuanghu-Lancangjiang suture zone , the syenitegranite mass of late Permian Epoch is disjointed from the granites of Yanshannia Age. The component of the rocks is characterized by Al2O3〉CaO +Na2O A-K2O, with the average value of ASI reaching 1. 166, showing the character of typical peraluminous granite; in addition, the EREE value of the rock is as high as 466.55×10^-6~682.80×10^-6, with the average value of of δEu being 0. 06, showing the character of typical S-type granites. The rock type is equivalent MPG-granite and is interpreted as the syncollisional granite. The zircon U-Pb isotope age is 251. 43-0. 6Ma, indicating that the implacement age is in late Permian Epoch. All these reflect a tectonic-thermal event during late Permian Epoch to Triassic Epoch, which might be the tectonic outcome of continent-continent collision in Wulanlua lake-Lancangjiang suture zone .
出处
《西北地质》
CAS
CSCD
2009年第3期26-35,共10页
Northwestern Geology
基金
中国地质调查局《1:25万治多(I46C003004)、杂多幅(I46C004004)区域地质调查》项目(编号:200313000007)