额纳旗及其邻区闪长岩—花岗岩类地球化学特征及意义

摘要

Geochemistry of granitoid rocks in Eji'naqi and four neighboring areas was analyzed and discussed so as to better understand its lithology and rock geochemistery characteristics , as well as its tectonic significance. Their rock types are mainly dioritoid and granitoid rocks. Content of SiOz ranges from 47. 88% to 75.29% and A12O3 from 13. 09% to 17. 49%. The CIPW report shows that most samples belong to series saturated with aluminium and excessive SiO2,and are rich in aluminium,natrium and kalium. All these characteristics suggest that it belongs to series of peraluminous rocks. The REE original mantel standard cobweb diagram shows that these four areas are slightly different in modalities, with Yagan showing negative Sr abnormity, while other three areas shows obvious negative Ta,Nb abnormity. The REE diagram shows slow rightward incline and relatively rich in light REE and poor in heavy REE, and some samples in Yagan 、 Peng-boshan and Yabulai areas show negative Eu abnormity. In the research area ,the neutral and acidic intrusive rocks are mainly type I, according to Chapppell et al.., and diagenetic material is probably partially melt newly formed crust owing to dynamics of collisional orogeny. The types of strongly peraluminous rocks are probably resulted in rising and emplacement of partially melt magama, which is crust source compressional environment genesis. In the Rl -R2 tectonic setting distinguish diagram .samples in Yingen area are within the bounds of synchronized collisional deep melted granite, those in the Yagan area are within the bounds of rising deep formed rockbody after collision, while those in the Pengboshan area are all on the verge of destroyed plate before they collide, which shows that these three areas have obvious different genesis.%对额济纳旗及其邻区四个地区的花岗岩类作了系统的地球化学研究,重点讨论了几个地区的岩石学特征,岩石地球化学特征及其构造意义.其岩石类型主要以闪长岩类和花岗岩类为主；四个地区SiO,和Al2O3含量变化范围较大,从w(SiO2)为47.88％～75.29％；w(Al2O3)为13.09％～17.49％；CIPW报告显示样品大多属于铝饱和-SiO2过饱和系列,并且都有富铝、富钠、富钾的特点,属于过铝质岩石系列.在微量元素原始地幔标准化蜘蛛网图上,四个地区的型式稍有不同,在雅干地区表现出Sr的负异常,而其他三个地区则明显是Ta、Nb负异常；银根地区样品还表现出岩浆源区以陆壳组分为主.在稀土元素配分曲线上,总体呈平缓右倾,轻稀土相对富集,而重稀土相对亏损,雅干、蓬勃山、雅布赖地区部分祥品表现出Eu的负异常.研究区中酸性侵入岩以Chappell等划分的Ⅰ型为主,成岩物质可能是由碰撞造山作用形成的新生地壳经部分熔融而形成；强过铝质岩石类型可能是部分熔融导致岩浆上升侵位形成,是一种壳源挤压环境成因.在R1-R2构造环境判别图上,三个地区成因类型明显不同,银根地区样品落入同碰撞的深融花岗岩区；雅干地区样品落入碰撞后上升的深成岩体；蓬勃山地区样品全部分布在板块碰撞前破坏性板块边缘.