青藏高原羌塘北部托和平错一带二叠系展金组火山岩的特征及构造环境  

Characteristics and tectonic setting of volcanic rocks of the Permian Zhanjin Formation in the Tuoheping Co area, northern Qiangtang, Qinghai-Tibet Plateau.

作　　者：王权[1] 续世朝[1] 魏荣珠[1] 杨月生[1] 田志勇[1] 董挨管 杨五宝 魏云峰[1] 

机构地区：[1]山西省地质调查院

出　　处：《地质通报》2006年第1期146-155,共10页Geological Bulletin of China

基　　金：中国地质调查局<1:25万土则岗日幅(I44C002003);托和平错幅(I44C002004)区域地质调查>项目(200313000011)成果。

摘　　要：西藏改则县托和平错地区展金组中发育一套早—中二叠世以玄武岩类为主、玄武安山岩次之、安山岩少量的海相火山岩组合。该火山岩中玄武岩、玄武安山岩的SiO2含量为44.43%～54.87%,TiO2含量多在4%以上,K2O+Na2O平均为4.57%,玄武岩类富K,玄武安山岩富Na。区内火山岩富集K、Ba、Th、Ta、Ce、P、Zr、Sm、Ti、Cr,亏损Rb、Nb、Hf、Sc,Y/Nb在0.322～0.499之间。综合常量元素和微量元素特征,可将该火山岩归入碱性玄武岩系列。区内火山岩从基性到中性稀土元素总量基本没有变化,REE平均为402.31×10-6,LREE/HREE为8.17～12.69,为轻稀土强烈富集型,δEu为0.93～1.04,平均为0.99,无Eu异常,玄武岩的Th/Ta值多数大于1.6。火山岩的地质特征和地球化学特征表明,本区火山岩产出的大地构造环境为冈瓦纳大陆北缘裂谷环境。A marine volcanic rock association consisting predominantly of Early-Mid Permian basalts with subordinate basaltic andesite and minor andesite is developed in the Zhanjin Formation in the Tuoheping Co area, Gerze County, Tibet. Basalts and basaltic andesite have the following chemical composition： SiO2, 44.43-54.87%, TiO2〉4% and K2O＋Na2O=4.57% on the average. Basalts are rich in K2O, while basaltic andesite is rich in Na2O. The volcanic rocks in the Zhanjin Formation are enriched in K, Ba, Th, Ta, ce, P, Zr, Sm, Ti and Cr and depleted in R.b, Nb, Hf and Sc with Y/Nb ranging between 0.322 and 0.499. According to the characteristics of the major and trace elements, the volcanic rocks may be assigned to the alkali basalt suite. The total REE content from basic to intermediate volcanic rocks in the main remains unchanged. The volcanic rocks have an average REE content of 402.31×10^-6 with LREE/HREE=8.17-12.69, so they are of strongly LREE-enriched type. 8Eu ranges from 0.93 to 1.04 with an average of 0.99, exhibiting no Eu abnormity. The Th/Ta values of basalts are mostly 〉1.6. The geological and geochemical characteristics of the volcanic rocks suggest that the volcanic rocks in the area formed in a rift environment on the northern margin of Gondwana.

关 键 词：青藏高原羌塘北部 托和平错 早——中二叠世 火山岩 大地构造环境 冈瓦纳大陆北缘 裂谷 

分 类 号：P534.46[天文地球—古生物学与地层学] P588.14[天文地球—地质学]