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The Ailaoshan Belt in Western Yunnan: Tectonic Framework and Tectonic Evolution

LIU Jun-lai1,TANG Yuan1,2,SONG Zhi-jie1, TRAN My Dung1,3,ZHAI Yun-feng1,4,WU Wen-bin1,CHEN Wen5 1.State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China 2.Chengdu Institute of Geology and Mineral Resources,Chengdu 610081,China 3.Hanoi University of Mining and Geology,Hanoi 100803,Vietnam 4.Exploration & Development Research Institute,Jilin Oil Field Company,PetroChina,Songyuan 138000,Jilin,China 5.Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China  
The Ailaoshan tectonic zone is the most significant lineament in the eastern Tibet(Southeast Asia),which separates the Yangtze-South China and the Indochina blocks.Information on multi-stage complex tectonic evolution is preserved in the rocks in the tectonic zone.Late Archean-Neoproterozoic high grade metamorphic rock series,Cenozoic tectono-magmatic assemblages(shearing deformation structures),Late Permian-Early Triassic Jinping-Song Da rifting rock sequences and Early Carboniferous-Early Triassic Ailaoshan tectonic mélange were well developed from east to west along the Ailaoshan tectonic zone.The various tectonic units of different characteristics are separated by fault structures mainly developed in Cenozoic.Granitic intrusions of various stages which were formed due to allochthonous emplacement or mingmatization are widespread along the tectonic belt.The Ailaoshan tectonic belt has multiple tectonic natures during different geologic history stages.On the whole,it has experienced three important tectonic stages,i.e.Pre-tethys,Tethys,and Cenozoic intracontinental stages.During the Pre-tethys evolution until Early Paleozoic,the major part of the belt(especially along the eastern zone) had affinity to the Yangtze block,and preserved records of Late Archean-Neoproterozoic crustal evolution.Since the Late Paleozoic-Early Mesozoic the tectonic belt became a part of the Tethyan domain with the opening of Paleotethys.The belt was evolved into a tectonic domain with different nature from that of the South China-Yangtze plate.Subsequent closure of the Ailaoshan Ocean in from Early Carboniferous and the Jinping-Song Da Ocean since Early Permian resulted in the formation of the paleo-Ailaoshan orogenic belt.The closure of the Tethyan oceans made Yangtze-South China block and Indochina block to become a unified continent.Interaction between the Indian and the Eurasian plates had a sound influence on the Ailaoshan belt.There are Early Cenozoic(Paleocene to Early Oligocene) orogenic contraction,Late Oligocence-Early Miocene post-orogenic extension and high-potassium alkaline magmatic activity,and Late Oligocence-Early Miocene large-scale southeasternward extrusion of the Indochina block,and large-scale left-lateral strike-slips shearing coeval calc-alkaline magmatic activities.
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