THE DYNAMIC MECHANISM FOR THE FORMATION AND EVOLUTION OF THE CHUXIONG COMPOSITE BASIN IN YUNNAN

The Chuxiong Basin located in central Yunnan on the southern margin of the Yangtze plate is bounded on the southwest by the Honghe fault,on the northwest by the Chenghai fault,and on the east by the Liizhijiang fault.The basement of the basin consists of the two-storied architecture of crystalline and folded basement,upon which there exist a se-quence of sediments as the sedimentary cover ranging in age from the Middle Triassic to Recent:the marine sediments during the Middle Triassic and early and middle Late Trias-sic 5 the alternating terrestral-marine sediments during the late Late Triassic in the western part of the basin;the terrestrial sediments in the eastern part of the basin,and the thick terrestrial sediments throughout the basin during the Jurassic to Cretaceous. Tectonically,four zones may be distinguished for the Basin.They are the Ailaoshan orogenic zone,fold-thrust zone,central subsidence zone and eastern uplifted zone.The basin has experienced six stages of evolution,i.e.the passive continental margin subsidence phase,extensional thermal uplift margin-rift basin phase,trench-arc-basin system phase, remnant oceanic-peripheral foreland basin phase,strike-slip and extensional basin phase and strike-slip-compression-reworking phase.The formation and evolution have reflected the transformation and combination of the dynamic regimes of the basin.The composite basin was just formed through multiple processes of dynamic systems and polycyclic tec-tonic stages.