Major progress in Early Precambrian research in the Daqing Shan-Wula Shan region, central Inner Mongolia, China, and some suggestions for stratigraphic work in high-grade metamorphic areas

Some progress has been made in the study of Early Precambrian strata, especially high-grade metamorphic strata, in the Daqing Shan-Wula Shan region, Inner Mongolia, through 1:50000 and 1:250000 regional geological surveys from 1996 to 2003. The progress may be summarized as follows: an Early Precambrian stratigraphic system composed of 4 group-complexes and 12 formation-complexes has been re-established; the Zao'ergou unconformity has been found and the Paleoproterozoic Meidaizhao Group-complex newly established; and a work idea and method of the "tectono-lithostratigraphic-event" suitable for the stratigraphic work in areas of high-grade metamorphic strata have been proposed. Under the guidance of the work idea and method, the authors ascertain the relationship between the evolution of the tectonic styles and reconstruction of the stratigraphic system in high-grade areas and propose the ideas that the tectonics in the main phase controlled the present distribution characteristics of the lithostratigraphic units, that the early-phase tectonics formed the present composition, structural characters, spatial superimposition and contact relationships of the lithostratigraphic units and that the late-phase tectonics locally complicated and reconstructed the high-grade metamorphic strata in the region. At last, four suggestions about how to carry out the lithostratigraphic research in high-grade areas are put forward.