甘肃北山地区牛圈子蛇绿岩的形成时代及地质意义

摘要

为了厘定甘肃北山地区洗肠井-牛圈子-红柳河蛇绿岩带的形成时代,对该地区牛圈子蛇绿岩中的辉长岩进行了LA-ICP-MS(激光剥蚀等离子体质谱)单颗粒锆石U-Pb定年,其形成时代为446.5Ma±4Ma,属晚奥陶世.结合前人研究,认为牛圈子蛇绿岩与红柳河蛇绿岩共同代表了区域早古生代大洋演化的产物,对于研究北山早古生代的构造演化有着重要的意义.%In order to study the age of Xichangjing-Niujuanzi-Hongliuhe ophiolite belt in Beishan area of Gansu Province, the authors conducted zircon LA—ICP—MS U—Pb dating of gabbro from this ophiolite belt. The result shows that the weighted average 206Pb/238U age of this ophiolite is 446.5 Ma±4Ma, suggesting late Ordovician. In combination with previous researches, the authors hold that Niujuanzi ophiolite and Hongliuhe ophiolite should be the products of early Paleozoic Ocean evolution. This study is of important significance for the study of tectonic evolution in Beishan area during early Paleozoic period.