青藏高原北羌塘盆地结扎乡一带二叠系尕笛考组火山岩的特征及构造环境  

Geochemical Characteristics and Tectonic of Volcanic Rocks of the Permian Gadikao Formation in the Jiezha Area,Northern Qiangtang,Qinghai-Tibet Plateau

作　　者：李善平[1] 马海州[1] 沈存祥[2] 魏海成[1] 

机构地区：[1]中国科学院青海盐湖研究所 [2]青海省乐都县国土资源局,青海乐都810700

出　　处：《西北地质》2008年第2期31-40,共10页Northwestern Geology

基　　金：中国地质调查局“1∶25万治多、杂多幅区域地质调查”项目(I46C003004、I46C004004).

摘　　要：对位于北羌塘盆地结扎乡一带二叠系尕笛考组火山岩进行岩石学、岩石化学、微量元素的分析及研究，为恢复二叠纪北羌塘盆地性质与古构造环境提供岩石地球化学约束。主要岩石类型为玄武岩、安山岩、英安岩及少量流纹岩、火山角砾岩等，SiO2=48．49％～74．52％，平均60．87％，Al2O3多数在14．5～18．86之间，K2O含量平均为1．99，显示钙碱性系列特征。LREE／HREE=4．31～14．60，平均8．74，（La／Yb）n=3．72～16．16，平均9．59，具有LREE富集的特征，δEu=0．61～1．11，平均0．80，多数样品δEu〈1．0，表明铕呈弱负异常或不显异常。火山岩La×Nb／Zr×Zr〉0．005，平均0．025．Th×Ta／Hf×Hf〉0．098，平均为0．210，与典型的岛弧火山岩具相似性。由上述特征表明，北羌塘地块在早中二叠世处于岛弧环境的构造背景。This paper deals with the petrological, petrochemical and trace element analyses and studies of the volcanic rocks of Permian Gadikao Formation in Jiezha area northern Qiangtang basin. It provides the geochemical condition to understand the character of the north of Qiangtang basin and tectonic environment. The rock types mainly include basalt, andesite, dacite and little rhyolites, lava breccia etc. The rocks have the following chemical composition： SiO2, 48. 49%-74. 52%, with a mean value of 60.87%, Al2O3 majority between 14.5%-18.86%, K2O mean contents 1.99%. This indicates the volcanic rocks with the character of autunite alkalescence siries, LREE/HREE=4.31-14.60,with a mean value of 8.74, （La/Yb）n=3. 72-16.16, with a mean value of 9.59, enrichment of LREE, δEu=0.61-1.11, with a mean value of 0.80, majority samples δEu〈1.0, indicate Eu pronounced weak negative abnormahy or no pronounced Eu abnormalty. La×Nb/Zr×Zr〉0.005, with a mean value of 0.025, Th×Ta/Hf×Hf〉0. 098, with a mean value of 0. 210. These chemical compositions are similar to typical volcanic rocks of island arc. The above-mentioned characteristics suggest that the plot of north Qiangtang locate in tectonic background of island arc environment in Early Permian.

关 键 词：青藏高原 北羌塘盆地 火山岩 构造环境 岛弧 

分 类 号：P317[天文地球—固体地球物理学]