化德群的重新厘定及其大地构造意义

Redefinition of the Huade Group and its tectonic significance

区域填图研究表明,化德群上、下亚群并不是上下关系,而是层位相当的一套地层,而且商都一带的白云鄂博群也属化德群的一部分。依据详细的构造解析和地层剖面研究,重新建立了化德群的地层层序,从老到新划分为毛忽庆组、戈家营组和三夏天组。侵入化德群的杂岩体分别获得1854Ma、1808Ma和2091Ma、2154Ma锆石U-Pb年龄,表明化德群形成时代为古元古代,而不是过去所认为的中新元古代。化德群经历了两期构造变形,早期为北东东走向的复式向斜,晚期又遭受了构造叠加,形成了北北西向褶皱构造,其主期变形可能发生在2.0Ga左右,它的褶皱造山是华北克拉通在古元古代向北增生的体现,这对研究华北克拉通的增生、裂解具有重要意义。

Regional mapping and isotope dating indicate that the upper and lower subgroups of the Huade Group are located in stratigraphically equivalent horizons rather than have an overlying and underlying contact relationships, and that the Bayan Obo Group in the Shangdu area is also a part of the Huade Group. According to a detailed structural analysis and stratigraphic sections,the stratal sequences of the Huade Group have been reconstructed;the group may be subdivided in ascending order into the Maohuqing Formation,Gejiaying Formation and Sanxiatian Formation. Zircons from the complex intruded into the Huade Group yielded U-Pb ages of 1808 Ma, 1853 Ma, 2091 Ma and 2154Ma suggesting that Huade Group formed in the Paleoproterozoic rather than Meso- and Neoproterozoic as thought previously. The Huade Group underwent at least two phases of deformation ：the early phase of deformation gave rise to ENE-trending synclinorium and the late phase was marked by tectonic superimposition ,forming NNW-trending folds. The main phase of deformation likely occurred in -2.0 Ga B.P.The deformation of the Huade Group is related to a Paleoproterozoic orogenic event along the northern margin of the North China Craton, which has great significance for the study of accretion and breakup of the North China Craton.