东昆仑那陵格勒河南上三叠统鄂拉山组火山岩地球化学特征及构造环境

东昆仑那陵格勒河南地区发育上三叠统鄂拉山组(T_3e)火山岩,岩石类型主要以英安质玻屑晶屑凝灰岩和英安质熔结凝灰岩为主,具有高碱、高钾、高铝的特征;岩石的二氧化硅含量w(SiO_2)=69.12%~74.52%,全碱含量w(Na_2O+K_2O)=6.42%~7.33%,里特曼指数σ=1.39~2.01,岩石的铝过饱和指数ASI介于1.02~1.17之间,属典型的过铝质高钾钙碱性系列。岩石的稀土元素w(LREE)/w(HREE)=11.02~15.99,δEu=0.54~0.67,铕具中等亏损,属轻稀土富集型;微量元素K、Rb、Ba和Th较强的富集,Sr、Ti、Sc、Cr明显亏损,具有后碰撞下地壳重熔产物的特征。在鄂拉山组玄武质晶屑凝灰熔岩中获U-Pb同位素年龄值为231 Ma±1 Ma,形成时代为晚三叠世。通过综合分析认为,鄂拉山组火山岩可能形成于以侧向挤压为主的陆—陆后碰撞过程中加厚地壳物质部分熔融的产物,属于印支期后碰撞火山盆地岩石建造。

Geochemistry and Tectonic Setting of Late Triassic Volcanics In Elashan formation in South of Nalingelehe river, East Kunlun

Volcanics of Late Triassic Elashan formation (T3e) in south Nalinggele river,East Kunlun are mainly dacitic glassy,crystal fragmental tuff and dacitic ignimbrite with high alkaline,high potassium and high aluminum.ω(SiO2)=69.12～74.52％,ω(Na2O+K2O)=6.42％～7.33％,Rittmann coefficient δEu=0.54～0.67,aluminum saturation index ASI 1.02～1.17 belonging to paraluminal high-K calc-alkaline rock series.Analysis of ω(LREE)/ω(HREE)=11.02～15.99 and δEu=0.54～0.67 are of LREE enrichment and medium Eu depletion.Trace element analysis shows stronger enrichment of K,Rb,Ba and Th and evident depletion of Sr,Ti,Sc,Cr.The data mentioned above are characteristic of post collision crust remelting products.Sample from basaltic crystal fragmental tuff of Elashan formation dated at U-Pb age of 246.8 Ma±1.7 Ma thus the formation is formed in Late Triassic Epoch.According to com prehensive analysis volcanics of Elashan formation may be the product of the partially remelted thickening crust during the post lateral compression dominant continent-continent collision thus is a post Indosinian period rock formation in collisional volcanic basin.