摘要
火山岩的绝对年龄是限定(含)火山岩地层形成时代及进行地层对比的关键依据。内蒙古阴山地区分布有大量的晚中生代白女羊盘组火山岩,而位于卓资县大榆树村附近的白女羊盘组火山岩目前尚缺乏年代学报道。为了厘定该火山岩地层的形成年龄,进而对比阴山—晋北—燕山地区的晚中生代火山—沉积地层,笔者等对分布于卓资县大榆树村附近的白女羊盘组双峰式火山岩进行了锆石U-Pb年龄测试。得到该组火山岩剖面下部流纹岩的LA-ICP-MS锆石U-Pb加权平均年龄为136.9±0.8 Ma,属于早白垩世。结合前人的研究成果,认为分布在阴山不同地区的白女羊盘组火山岩的形成年龄差异较大,分别是不同旋回火山活动的产物。其中分布在武川和固阳盆地的白女羊盘组与燕辽地区的九佛堂组的形成年龄相当;而分布在乌拉特中旗和卓资县的白女羊盘组与燕山地区的张家口组在形成年龄上可对比。
A amount of volcanic rocks named Baintiyangpan Formation have been discovered in the Yinshan Mountains of the Inner Mongolian Plateau in the northern North China Craton. However, their formation age is ambiguous and debated, especially these in Zhuozi county, eastern Yinshan Mountains, have not even been reported before. The age of these volcanic rocks play a key role in establishing the stratigraphie sequence and understanding the stratigraphic correlation in Yinshan Mountains and Yanshan Mountains areas. We did detailed fieldwork on the volcanic rocks of the Baintiyangpan Formation in Zhuozi county, which are charactered by typical bimodal volcanic rocks association. And Zircons from the rhyolitic tuff are dated by LA-ICP-MS U-Pb method, which gave a weighted mean age of 136.9±0.8 Ma, representing the deposition age of the Baintiyangpan Formation. Compared with the previous data form published articles, we found that the age of the Baintiyangpan Formation volcanic rocks have evidently varied in both temporal and spatial, which should be two main period production of volcanic activities (approximately 137Ma and 115Ma, respectively). And those volcanic strata did not show the regularity that their age were older in the west Yinshan Mountains and became younger in the east Yinshan Mountains which previously supposed. Besides, this paper compared the age of the Early Cretaceous volcanic strata distributed in the Yinshan Mountains and Yanshan Mountains regions. The Baintiyangpan Formation in the Zhuozi county and the Wulatezhongqi county correspond closely in age to the Zhangjiakou Formation in Yanshan Mountains, and the Bainuyangpan Formation in the Wuchuan county and the Guyang county was correlated to the Jiufotang Formation in the Yan-Liao area( Yanshan Mountains--Western Liaoning area).
出处
《地质论评》
CAS
CSCD
北大核心
2018年第1期203-212,共10页
Geological Review
基金
内蒙古自治区地质勘查基金资助项目(编号:NMKD2015-27)的成果