粤北下庄铀矿田岩体地球化学特征及其构造环境

下庄铀矿田出露的中生代鲁溪岩体、下庄岩体和帽峰岩体、分水坳岩体是南岭地区贵东复式岩体的重要组成部分。矿区岩体主量元素显示出富硅、富碱、过铝质-强过铝质等特征,w（K2O）/w（Na2O）〉1,在w（K2O）-w（SiO2）图解中大部分样品落在高钾钙碱性岩石系列,少部分样品落在钾玄岩系列,表明岩体富碱。铝饱和指数ASI=1.02~1.30,为过铝质-强过铝质岩石系列。w（CaO）/w（Na2O）值为0.07~0.74,表明岩体原岩为变泥质岩和变砂岩,是重熔作用的产物。根据主量、微量元素构造环境判别图分析,粤北下庄铀矿田处于后碰撞的构造环境,岩体为后造山花岗岩。在lgCaO/（Na2O＋K2O）]-SiO2图解中样品全部落在伸展区域,也表明岩体形成时粤北地区处于伸展拉张的后碰撞构造环境。

The characteristics of pluton and its tectonic environment in Xiazhuang ore-field, North Guangdong

The Luxi,Xiazhuang and Maofeng-Fen Shui＇ao plutons,located in the Xiazhuang ore-field,are the main parts of Guidong complex granitic pluton lying in Nanling area.The pluton here is characterized with high content of silicon,alkaline and especially enrichment of aluminum,w（K2O）/w（Na2O）1,the alumina saturation index（ASI） is about 1.02—1.30,while the w（CaO）/ w（Na2O） ratio varies from 0.07 to 0.74,all of which indicate that the rocks belong to peraluminous-strongly peraluminous granite,the ratios of w（CaO）/w（Na2O） range from-0.3 to-0.74,standing for the anatexis products of pelite-derived and psammite-derived rocks.According to the analysis of tectonic discrimination diagrams of major and trace elements,the post-collisional tectonic environment and post-collisional granite in Xiazhuang ore-field has been established.In addition,in lgCaO/（Na2O＋K2O）]-SiO2diagram all the samples fall in the extensional area,indicating that the continental crust in North Guangdong area was under a post-collisional geodynamic background of a loose and extensional tectonic environment when the granitic rocks in Xiazhuang ore-field was emplaced.