THE BASIC FEATURES OF THE ACCORDION-STYLE OPENING-CLOSING EVOLUTION OF STRUCTURES IN XINJIANG

There are definite criteria for determining the accordion-style opening and closing of structures in Xinjiang. The opening and closing history may involve three major stages: pre-Sinian, Paleozoic and Meso-Cenozoic. The opening-closing forms and features of the three stages are notably different. The Paleozoic stage （from Sinian to Early Permian） involves six cycles of opening-closing. Generally the opening-closing progressed from north to south. The opening-closing is characterized by polycyclicity, unequilibrium, orientation, migration, duality and limitation. The opening-closing evolution is described as follows: the continental crustal basement was opened to form a regenerated geosyncline; the rift further developed into a restricted ocanic basin, which later converged to form new continental crust. The general process of development was paleo-crust （paleo-craton）→rift→restricted oceanic basin→ new contiental crust （new platform）→extensional nappe→basin-and-mountain.