内蒙古贝力克玄武岩台地火山地质及成因探讨

GEOLOGICAL CHARACTERISTICS AND GENESIS OF BASALT PLATFORM IN BEILIKE,INNER MONGOLIA

根据火山地质特征,内蒙古锡林郭勒地区的新生代玄武岩可以划分为阿巴嘎玄武岩、贝力克玄武岩和达里诺尔玄武岩,呈NW-SE向展布。贝力克玄武岩以面积小、没有火山锥体、岩性较为单一(绝大多数为拉斑玄武岩)及不含慢源包体的熔岩台地而显著区别于另两种玄武岩。贝力克玄武岩以发育4级高低错落有致、大小不一的熔岩台地为特征,各级熔岩台地标高变化依次为:1034～1057m、1070～1120m、1150～1200m和1280m以上。结合前人年代学研究结果,贝力克玄武岩台地的年代为上新世中期至更新世中期,并形成一种台地标高越高其年龄越老,即上老下新的格局,这种格局的形成是新构造运动使得地壳发生差异性抬升的结果。

Cenozoic basalts distribute along NW-SE direction in Xilinguole,Inner Mongolia.According to volcanic geology,they are divided into three volcanic fields,namely,Abaga basalt,Beilike basalt and Dalinuoer basalt.The Beilike basalt is distinctive to the other two basaltic areas,for its characteristics of simple petrology of tholeiite,no volcanic cones or vents surviving from aging,and mantle derived xenoliths free.Geographically,Beilike basalt forms four steps of lava platforms at different heights：1034～1057m,1070～1120m,1150～1200m and 1280m,respectively.Isotopic dating reveals the ages of the Beilike basalt varying from middle Pliocene to middle Pleistocene,and the upper lavas are older than the lower ones.According to this fact,we can tell the scenario of the Beilike basalt as that the Cenozoic volcanic eruptions form the lava shield,then it is elevated by episodic uplift of the Neotectonic movement.