甘肃北山牛圈子地区基性岩墙群年代学、地球化学特征及构造意义

Geochronology,Geochemistry and Tectonic Significance of Diabase Dike Swarms in Beishan,Gansu

通过LA-ICP-MS锆石U-Pb定年法,获得甘肃北山牛圈子地区辉绿岩中锆石加权平均年龄为(313.6±3.3)Ma(MSWD=0.61),为晚石炭世,代表岩墙侵位年龄。岩石地球化学特征具高Mg、贫K,P和Ti,富集不相容元素,亏损相容元素,Nb,Ta明显亏损等特点,具亚碱性拉斑玄武岩特征。构造环境判别图解显示其形成于陆内裂谷环境。结合前人研究成果认为,晚石炭世牛圈子地区处于伸展拉张的构造背景。通过对比天山和本地区岩体的主微量和稀土元素认为,其可能是晚石炭世天山大火成岩省的组成部分,为晚石炭世塔里木地幔柱作用的产物。

In Beishan,Niuquanzi area develops a lot of diabase dikes which provide good materials for the study of dike swarms.The age of diabase is concentrated,so diabase dike swarms formed in(313.6 ± 3.3) Ma(MSWD=0.61),the Late Carboniferous.The geochemistry analysis of diabase dikes show which belong to sub-alkaline tholeiitic,with high Mg,poor K,P,Ti,relatively enriched in incompatible elements,losses compatible elements.Significant loss in Nb,Ta.Diabase dike swarms tectonic discrimination diagrams show that they formed in continental-rift environment.Combined previous research,it is considered that Qiuquanzi area was under a extensional environment.The comparison of major and trace elements as well as REE geochemistry,confirmed they are an integral part of Tianshan Late Carboniferous-Early Permian large igneous province which probably the result of the role of the Tarim mantle plume in the Late Carboniferous.