对辉铜山、帐房山蛇绿岩中的辉长岩进行LA-ICP-MS锆石U-Pb同位素定年,获得辉铜山蛇绿岩中的辉长岩形成年龄为446.1Ma±3.0Ma,相当于晚奥陶世；帐房山蛇绿岩中辉长岩形成于362.6Ma±4.0Ma,相当于晚泥盆世.显然辉铜山蛇绿岩和帐房山蛇绿岩并不是同一条蛇绿岩带.结合前人研究成果,认为北山地区的蛇绿岩带至少有5条,其中红柳河-牛圈子-白云山-洗肠井蛇绿岩带可能是北山古生代洋盆俯冲消减环境下的产物,辉铜山蛇绿岩是古生代洋盆陆缘裂谷环境的产物;而红石山-百合山-蓬勃山、芨芨台子-小黄山和帐房山3条蛇绿岩带可能是晚古生代红海型洋盆环境的产物.该工作进一步完善甘蒙北山地区构造单元划分及其大地构造属性的研究提供了依据.%The lack of precise ophiolite ages has seriously restricted the research on the tectonic properties of Beishan area. LA—ICP— MS zircon U—Pb dating shows that gabbro in Huitongshan ophiolite was formed at 446.1Ma+3.0Ma, suggesting late Silurian, whereas gabbro in Zhangfangfhan ophiolite was formed at 362.6Ma+4.0Ma, implying Late Devonian. Obviously they do not belong to the same ophiolite. Combined with previous researches, it is held that there are at least five ophiolite belts in Beishan area. Hongliuhe—Ni-ujuanzi—Baiyunshan—Xichangjing ophiolite belt might have resulted from the Beishan ocean basin subduction—reduction environment in Paleozoic, whereas Huitongshan ophiolite belt might have been formed in the Beishan ocean basin continental margin rift environment in Paleozoic. Hongshishan—Baiheshan—Pengboshan, Jijitaizi—Xiaohuangshan and Zhangfangshan ophiolite belts might have been produced in the Late Paleozoic intraplate embryonic ocean basin environment. The result obtained by the authors has provided some foundations for improving the division of tectonic units and the study of tectonic properties of Beishan area in Gansu.
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