Consideration and practice of the construction of litho stratigraphic systems in high-grade metamorphic terrains -Acase study in the Daqingshan-Wulashan area
YANG Zhen-sheng, XU Zhong-yuan, LIU Zheng-hong, Peng Xiang-dong(College of Earth Sciences, Jilin University, Changchun 130061, Jilin,China )
The early Precambrian stratigraphic system in the Daqingshan-Wulashan area is reconstructed based on recent regional geological survey. A Meidaizhao Group-complex is eslatlished and classified as the Paleoproterozoic. The high-grade metamorphic rocks in the area are regrouped, i.e. the granulite sequence is subdivided into two formation complexes, which are merged into the Sanggan Group-complex, and the Wulashan Group-complex is subdivided into two subgroup-complex, a lower subgroup complex. and an upper subgroup complex.The former is known as the gneiss sequence and the latter is equivalent to the Jining Group, a khondalite sequence. The major structural patterns of the high-grade terrain in the area are characterized by dome structures and fold groups between the domes (simply called `dome-fold' structures). It is suggested that the large-scale ledding detachment system is a key factor for determining the spatial distrilution,composition and interrelations of high-grade metamorphic rocks.The new ways and methods of estallishing lithostatigraphic systems in high-grade metamorphic terrains are proposed in the paper.