内蒙古前进场花岗岩体的地质特征及其构造环境

GEOLOGICAL CHARACTERS AND TECTONIC SETTING OF QIANJINCHANG GRANITE IN INNER MONGOLIA

内蒙古前进场花岗岩体的岩石类型主要为黑云母花岗岩,SiO2 含量 67 17% ~ 70 27%,Al2O3 含量 14 85% ~15 61%,A/CNK(分子比 ) >1 1,K2O/Na2O为 1 25 ~1 35, 里特曼指数 (δ)为1 88~ 2 44,分异指数(DI)为 86,ΣREE为 181 9×10-6 ~247 8×10-6之间,ΣLREE/ΣHREE为 2 98,δEu为 0 42~0 56,Rb-Sr同位素年龄为 196±5Ma,表明属于富钾、过铝、钙碱性花岗岩,有利于钨和铜的矿化。岩相学和岩石地球化学研究表明岩体具有S型花岗岩特征,形成的构造环境为大陆弧花岗岩类(CAG),是华北板块与西伯利亚板块碰撞造山后伸展作用下的产物。

The Qianjinchang granite in Inner Mongolia is mainly Indo-Sinian S-type biotite granite. Chemical composition of the granite is SiO_2=67.17%~70.27%, Al_2O_3=14.85%~15.61%, A/CNK (molecule ratio)>1.1, K_2O/Na_2O=1.25~1.35, δ =1.88~2.44, DI=86, ΣREE=181.9×10^(-6)~2478×10^(-6), ΣLREE/ΣHREE=2.98, δ Eu=0.42～0.56. Rb-Sr ages of the granite is 196±5Ma. The characteristics showed it is calc-alkaline granite with abundant potassium and peraluminous, and beneficial to W and Cu mineralization. As lithofacies and geochemical characteristics of the granite are similar to those of S-type granites, the granite belongs to continental arc granite (CAG) formed within an extensional regime in a post-collision setting between North China and Siberia Plates.