摘要
内蒙古中南段白云鄂博群和渣尔泰群长期以来一直被人们认为属于中一新元古代地层,但是,笔者最近在此处发现了大量的小壳化石,因此认为白云鄂博群、渣尔泰群等应归属于晚震旦—早古生代。人们都知道,渣尔泰群与什那干群从不发生任何地质接触关系,与渣尔泰群、白云鄂博群共存的加里东、海西期花岗岩基不出现在固阳—小佘太断裂以南的地区,现在又发现小壳化石只沿固阳—小佘太断裂以北分布。同时,二道凹群被认为是古元古代后期地层,年龄小于2.0Ma,而魏家窑子群属于古元古代地层。分布在大青山和乌拉山地区的200m厚的大理岩,过去分属太古宙的三个岩群:魏家窑子群,乌拉山群和集宁群,现在把三套厚层大理岩恢复成为可以对比的古元古代沉积层,承上启下,可以把内蒙古前寒武系地层柱理清。大青山拗拉谷西起土默特—蘑菇窑子,向NNE方向延伸,经呼和浩特—哈乐向东至卓资—察右中旗,宽40km,长150km,元古宙沉积物近10km厚,南北两侧构造边界为两大断裂所控制。这个拗拉谷是作者在1987～1990年构造研究过程中发现的。
Bayanobo and Chaertai Group in Middle-Southern part of Inner Mongolia have been considered belonging to Middle-Late Proterozoic strata for a long time, but recently the auther and others has just discovered a gigantic Early Cambrian fossil zone in the arca of Inner mongolia Earth Axis including the distribution area of Bayanobo and Chaertai Groups. So those fossils would change the prior consideration about the geology and tectonics. In this way, the great differences of geology along the wuchun-Guyang-Xiaoshertal fault were obviously showed that Bayanobo and Chaertai Groups mentiond above associate with calidonian and variscian granitoid together and without Archaean and Proterozoic basement in the north of the fault, but Proterozoic Shinagan and Majiadian Groups appear with Archaean strata and Trilobite fossil-bear- ing Cambrian-Ordovician strata together in the south side of the great fault. So these two sides of wuchun-Guyang-Xiaoshetai fault attribute to different terranes respectively. Simultaneously Erdowa Group belongs to Proterozoic strata during tyhe age from 2.0 Ga to 1.6 Ga (based on the age of U-Pb 1667 Ma) and weijiayaozi Group shouid attribute to Early Proterozoic (2.5-2.0 Ga according to the age of U-Pb 1965, 2230 Ma). thus the mar- ble of 2000m thick distributing in the area of Daqinshan and wulashan montains and pre- viously attributing to three Archaean Groups (weijiayaozi, wulashan and Jining Groups) respectively, now would change its attribution in to Proterozoic strata, and they become the main member of Daqingshan aulacogen. The Proterozoic activiting zone dis- tribute along NEE orintation from Tumete at the west, through Huhehaute-Hale going up to Zhuozi-Chayou at the east, 40 km wide and 150km long. In the aulacogen the Ptoterozoic sediments were cummulated up to 10km in thickness. The volcanic rocks oc- curred in the bottom and muddy and carbonate metamorphosed strata appear in the mid- dle-upper part. All of them were controlled by two huge faults along north and south side of the aulacogen and undergone metamorphism. The aulacogen was founded by author during the study of structure project in 1987--1990.
