PLATE-TECTONIC UNITS AND TECTONIC EVOLUTION IN GANSU

In this paper the plate-tectonic units in Gansu Province fall into three orders. The first-or-der units include the Siberian plate, Tarim plate, North China plate and South China plate. Theirboundaries are the Hongshishan fauIt belt, Altun strike-slip fault beIt and Zeku-Wushan faultbelt respectively. Eight second-order and 17 third-order tectonic units are further distinguished. Besides, the basic geological features and evolution of the three orders of tectonic units are dis-cussed brierfly. The basements of the four plates had been consolidated into continental crust inthe Mid-Late Prolerozoic. Then the plates grew with the continental nuclei （or platforms） as thecenters; they were separated by the Paleo-Asiatic Ocean （Beishan Ocean region）, Qilian seatrough and Qinling-Kunlun Ocean. From the Phanerozoic to terminal Paleozoic, the plate config-urations of the whole region were finalized, forming a mosaic framework of fold belts and plat-forms （or blocks）. The authors also suggest that the north belt of Beishan should be assigned tothe Siberian plate, while the central and south belts of Beishan belong to the Tarim plate and thetransitional belt on the northern margin of North Qilian should be the slope of the stable conti-nent on the southwestern margin of the North China platform.