辽宁营口虎皮峪地区古元古代岩浆事件及地质意义

摘要

Three episodes of intrusive magmatic activities occurred at the Hupiyu area of Yingkou in Liaoning province during the Paleoproterozoic.The early Hupiyu Liaoji granite emplacing in 2123±17 Ma is characterized by rich Si and alkali,low Ca,and negative Eu anomaly,suggesting its geochemical features similar to that of A-type granite.Extremely low Sr and high Yb indicate that the granite formed in a low-pressure crust thinning setting.The second-episode Housongshugou granodiorite forming in 1892±16 Ma is high in SiO2,Na2O,Al2O3,with the value of Na2O/K2O greater than 1.3,no or positive Eu anomaly,indicating that it is similar to adakitic rocks.Low-high Sr and low Yb suggest that the granidiorite formed in a high pressure setting with great depth,probably related to the partial melting of underplating basaltic magma in the post-collisional thickening crust setting.The Nantaizi quartz monzonite at the late stage formed in 1851±11 Ma,and has high alkali (Na2O+K2O=11.32％～11.93％) and Rittmann index of 6.62～ 7.05,indicating that the magma was the product of the intra-continental extension after the orogeny.Low Sr and Yb also indicate the middle pressure and a depth of 40 ～ 50 km.Three magmatic events mentioned above have a significant indication for tectonic evolution of Liaoji Paleoproterozoic active belt:the early Liaoji granite possibly formed in the back arc extentional setting of Liaoji Paleoproterozoic active bethe Housongshugou granodiorites were the product of thickened crust after later Paleoproterozoic collision;and the Nantaizi quartz monzonite belongs to the post-orogenic granite which marks completion of cratonization in the Liaodong area and beginning of the post-orogenic extension evolution.%辽宁营口虎皮峪地区存在3期古元古代侵入岩浆活动:早期虎皮峪辽吉花岗岩成岩时代为2119±16Ma,富硅、富碱、低铝、低钙及负Eu异常显示其具有类似A型花岗岩的地球化学特征,非常低Sr高Yb的特点指示其形成压力很低,与减薄的地壳有关;第二期后松树沟奥长花岗岩成岩时代为1892±16Ma,富硅、富钠、高铝,Na2O/K2O＞ 1.35及无Eu异常或正Eu异常显示其具有埃达克质岩石的特征,中—高Sr低Yb的特点指示其形成压力较高、深度较大,与碰撞后加厚地壳底侵玄武岩的部分熔融有关;晚期南台子石英二长岩成岩时代为1850±11Ma,富碱(Na2O+K2O=11.32％～11.93％),里特曼指数δ=4.78～7.20,属碱性岩,低Sr低Yb的特点指示其形成压力中等,深度大概40～50km,是造山作用完成后板内伸展背景下的产物.上述3期岩浆事件对整个辽吉古元古代活动带的构造演化具有重要指示意义:早期辽吉花岗岩可能形成于辽吉古元古代活动带早期弧后伸展阶段;后松树沟奥长花岗岩则代表古元古代晚期碰撞后地壳加厚阶段的产物;南台子石英二长岩属后造山花岗岩,标志着辽东地区克拉通化的完成,开始进入后造山伸展演化阶段.