鄂尔多斯盆地西缘汝箕沟大岭－鼓鼓台玄武岩锆石U-Pb定年及其构造意义

利用显微镜、地球化学、ELA-ICPMS定年等技术, 对鄂尔多斯盆地西缘汝箕沟大岭－鼓鼓台玄武岩及其样品中的锆石进行了内部结构、元素组成分析和原位定年。汝箕沟大岭－鼓鼓台玄武岩为典型的大陆拉斑玄武岩, 所获得的锆石年龄分别为1966±15 Ma、344±22 Ma和241±7 Ma, 其中1966±15 Ma为继承锆石年龄, 344±22 Ma为岩浆第一次分离结晶年龄, 而241±7 Ma代表了玄武质岩浆最后喷出时的锆石结晶年龄。可见, 中晚三叠世盆地西缘北部贺兰山地区处于区域挤压背景下的局部伸展环境, 可能为一小型裂谷盆地。

U-Pb Zircon Dating of the Daling-Gugutai Basalt in Rujigou on the Western Margin of Ordos Basin

Based on an analysis of data obtained by such means as microscope observation, geochemistry and ELA-ICPMS, the authors studied the Daling-Gugutai basalt in such aspects as the internal structure, element composition and original location dating of its zircons. It is shown that the Daling-Gugutai basalt is a typical tholeiitic basalt, with its zircon ages being 1966±15Ma, 344±22 Ma and 241±7Ma, respectively. Of these data, 1966±15Ma is the age of inherited zircon, 344±22Ma is the first fractional crystallization age of magma, and 241±7Ma is the age of zircon crystallization during the last eruption of basaltic magma. It is thus suggested that the Helan Mountain area was probably a rift under an extending condition in Middle-Late Triassic period.