哀牢山带大皮甲岩体的地质地球化学特征及形成构造环境

哀牢山深变质岩带大皮甲小岩体的岩石类型主要为二云二长花岗岩。w(SiO2)的平均值为72.42%,A/CNK>1.1(平均值1.17),K2O/Na2O的平均值为2.18,里特曼指数(σ)为1.76～4.19(平均值3.02),分异指数(DI)为90～92,∑w(REE)为103.34×10-6～247.39×10-6,∑w(LREE)/∑w(HREE)为1.16～7.45,具弱Eu正异常,在原始地幔标准化蛛网图上显示出Nb、P和Ti负异常及K、Rb、Ba、Th和U正异常,具明显的分异结晶作用特征。岩体的地球化学特征属于高硅、过铝、钙碱性花岗岩,具有壳幔混源型花岗岩的特征。经多种相关图解判别,大皮甲岩体为碰撞造山花岗岩类,形成于同碰撞及后造山的构造环境。

Geological, geochemical characteristics and tectonic setting of Dapijia rockbody in Ailaoshan zone

The Dapijia rockbody in the Ailaoshan zone is composed mainly of two-mica adamellite.The average mass fraction of the rockbody is w(SiO2)=72.42%,A/CNK>1.1(1.17 on average),K2O/Na2O=2.18(on average),with Rittmann index σ=1.76-4.19(2.88 on average),DI=90-92,∑w(REE)=103.34×10-6-247.39×10-6,∑w(LREE)/ ∑w(HREE)=1.16-7.45 and δ(Eu)=0.67-1.34.The rockbody shows remarkable negative Nb,P and Ti anomalies as well as positive K,Rb,Ba,Th and U anomalies as shown in the primitive mantle-normalized trace element spider diagrams,suggesting evident fractional crystallization.According to its lithofacies,petrological and geochemical characteristics,the Dapijia rockbody is silica-high and potassium-rich,belonging to peraluminous calc-alkaline crust-mantle mix derived type granites.Various oxide and trace element diagrams for discrimination of tectonic settings reveal that the Dapijia rockbody is orogenic granite formed in an orogenic extensional structural environment.