BOUNDING THEORY OF ANCIENT MOUNTAIN SYSTEM BETWEEN THE CATHAYSIA FLORISTIC PROVINCE AND THE ANGARA FLORISTIC PROVINCE

摘要

The boundary between the Cathaysia Floristic Province and the Angara Floristic Province refers to the relation between the propagation of the plant kingdom and the environments, and also to the recognition about geotectonics. Therefore, close attention has paid to it by geologists and palaeontologists. Up to now, there are mainly two ideas about the boundary: (1) the bounding theory of geosyncline, and (2) the bounding theory of plate tectonics. The first idea suggests that the Tianshan-Hinggan Geosyncline from Junggar of Xinjiang in the west of China to the northern margin of the Huabei Platform eastwards is a sea basin in late Silurian to early late Permian and a natural barrier between the Cathaysia Flora and the Angara Flora. The geosyncline disappeared on the west probably in early Permian and raised on the earth until early late Permian; and it caused a mutual mingling in some representatives of the two floras in late Permian on the west and in late Permian on the east. The second idea is a current idea about the mechanism of the division of the Cathaysia Flora and the Angara Flora and the " mixture". According to the study of plate tectonics, it is considered that there exists a vast ocean basin between the Sibiria Plate on the north and the China Plate on the south, 35° -40° latitude in width. There developed the temperate Angara Flora on the Sibiria Plate and the tropic-subtropic Cathaysia Flora on the China Plate respectively. At the end of early Permian, the two plates came into collision each other, and the ocean besin between them closed and formed the ancient Asia Land. Then, these yielded the condition of blending mutually between the two floras. The collision zone of the plates situated along the line from southern Tianshan-Suolunshan-Erlian-hote-Xilamulun River, i.e. the boundary line of the two floristic provinces.