银额盆地苏红图坳陷北部埋汗哈达组碎屑锆石U-Pb测年及其地质意义

巴北凹陷是银根-额济纳旗盆地(简称银额盆地)苏红图坳陷北部的一个次级构造单元,通过埋汗哈达组的孢粉组合特征研究及碎屑锆石U-Pb同位素测试,探讨了地层年代及物源方向。从孢粉组合特征可以看出,除晚古生代和中生代都存在的类型外,仅在白垩纪出现的类型没有见到,且见到的绝大多数类型都出现在晚古生代和三叠纪;银额盆地苏红图坳陷北部埋汗哈达组碎屑岩锆石阴极发光图像和Th/U值(0.4),表明大部分属于岩浆成因锆石。锆石年龄分布在246～1010Ma之间,集中分布在246～390Ma、400～560Ma,最年轻的峰值为260Ma。综合分析后将埋汗哈达组归入二叠系,与切刀古隆起和巴彦诺尔公—狼山—阴山一带岩浆岩的年龄分布相似,由此认为,切刀古隆起和巴彦诺尔公—狼山—阴山一带的岩浆岩可能为埋汗哈达组的沉积物质来源。

Detrital zircon U-Pb dating of Maihanhada Formation in Yin'E Basin of northern Suhongtu depression and its geological significance

The Babei Sag is a secondary tectonic unit in the north of Suhongtu Depression in Yingen-Ejinaqi Basin(or Yin''E Basin). Based on the sporopollen assemblages and U-Pb isotope tests of clastic zircons of the Maihanhada Formation, the stratigraphic age and provenance direction are studied. The characteristics of sporopollen assemblages show that except for the types existing in the Late Paleozoic and Mesozoic, the types appearing only in the Cretaceous are not found, and most of the types appearing in the Late Paleozoic and Triassic. The CL image and Th/U(>0.4)of zircons in the clastic rocks of the Maihanhada Formation in the Northern Suhongtu depression, Yin-E basin, indicate that most of them belong to the zircons of magma, and the age distribution of zircons is between 246Ma and 1010Ma,the concentrated distribution is the 246~390Ma, 400~560Ma. The youngest peak is 260Ma. The geological age of the Maihanhada Formation should be Permian. And the age distributions of the magmatic rocks in the area of the dagger and the Bayannuoer-Langshan-Yinshan are similar, so the two are the possible sedimentary material sources of the Maihanhada Formation.