滇西哀牢山构造带:结构与演化

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

哀牢山构造带是藏东(东南亚)地区的一条重要线性构造,它分隔了扬子—华南地块与印支地块,并保存了多阶段复杂大地构造演化的记录。哀牢山构造带内由东向西依次发育了晚太古代—新元古代深变质岩系、新生代构造-岩浆活动带(剪切带)、金平—沱江晚二叠—早三叠世裂谷带残余和哀牢山早石炭世—早三叠世混杂岩带。具有不同特点的地质单元间被以新生代为主发育的断裂构造所间隔;而不同时期异地就位或混合岩化成因的花岗质岩石在构造带中普遍存在。哀牢山构造带在不同地质历史阶段具有多重大地构造属性,总体上经历了3个重要大地构造演化阶段:前特提斯演化、特提斯演化和新生代陆内演化阶段。前特提斯演化时期,主体部分(尤其是其东部带)具有亲扬子地块的属性,保留了自晚太古代到新元古代地壳演化的记录。一直到早古生代时期,哀牢山构造带的大地构造属性与扬子—华南地区依然具有密切的亲缘关系。自晚古生代—早中生代时期古特提斯洋打开之后,该带与华南-扬子板块之间分化成2个属性不同的构造域,始于早石炭世打开的哀牢山洋与始于早二叠世打开的金平—沱江洋依次消亡。特提斯洋的闭合,一方面形成了古哀牢山造山带,同时使得扬子—华南地块与印支地块回复到一个统一的陆内环境中;印度—欧亚板块之间的交互作用,对这一地区有着深刻的影响,相继形成了早新生代哀牢山造山带、晚渐新世—早中新世造山后区域性伸展与高钾碱性岩浆活动性和晚渐新世—早中新世印支地块的大规模南东向逃逸、哀牢山大型左行走滑剪切作用及伴生的钙碱性岩浆活动性。

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.