内蒙古乌拉特中旗新忽热地区二叠纪花岗岩地球化学特征及其地质意义

Geochemical characteristics and geological significance of Permian granites in Xinhure area of Urad Zhongqi,Inner Mongolia

为进一步认识古亚洲洋闭合时限问题,选择位于华北克拉通北缘,索伦山缝合带以南的内蒙古乌拉特中旗作为研究区。对乌拉特中旗新忽热地区出露的二叠纪黑云母花岗岩和二长花岗岩进行岩石地球化学研究,结果显示:二叠纪花岗岩属弱过铝质碱钙性系列岩石,富硅、富钾,低磷;轻重稀土分馏明显,轻稀土富集,重稀土亏损,微量元素K、Rb、Ba富集,Nb、Ta、P、Ti相对亏损,弱铕负异常,具高分异Ⅰ型花岗岩特征。根据研究区所处大地构造位置、时代及岩石地球化学特征分析,花岗岩形成于中二叠世古亚洲洋俯冲消减向碰撞转化的阶段。

In order to further understand the closure time limit of the Paleo-Asian Ocean,the Urad Zhongqi region in Inner Mongolia,located in the northern margin of the North China Craton and south of the Suolun Mountain suture zone,was selected as the research area. The study of the whole-rock geochemistry of Permian biotite granite and monzogranite exposed in the Xinhure area of the Urad Zhongqi region was carried out. The results show that the Permian granite is a series of weak peraluminous alkaline-calcium rocks,which is rich in silicon,potassium and low in phosphorus. LREE and trace elements K,Rb,Ba are enriched,HREE and Nb,Ta,P,Ti are depleted,with weak negative europium anomaly. It belongs to high-differentiation Ⅰ type granites. According to the geotectonic location of the study area,age and geochemical characteristics of the rocks,it is suggested that the formation of the granite occurred during the subduction of the Paleo-Asian Ocean and transition to collision in the Middle Permian.