西南三江地区洋板块地层特征及构造演化

Oceanic plate stratigraphy and tectonic evolution of the Nujiang-Lancangjiang-Jinshajiang area in southwestern China

关键词:  洋板块地层  蛇绿混杂岩  构造演化  西南三江

Key words:  ocean plate stratigraphy  ophiolitic mélange  tectonic evolution  Nujiang-Lancangjiang-Jinshajiang area in southwestern China

摘要:

以大地构造研究为主导，初步梳理了三江地区洋板块地层系统的分布及其构造演化规律。本文阐述了三江地区经历原-古特提斯大洋连续演化、分阶段拼贴增生至最终俯冲消亡的地质演化历程。甘孜-理塘弧后洋盆于早石炭世打开，二叠纪—中三叠世进入顶峰扩张期，晚三叠世洋盆萎缩引起向西俯冲，最终在晚三叠世末局部地区保留残留海。哀牢山弧后洋盆不晚于早石炭世形成，早石炭世—早二叠世整体扩张发育，早二叠世末或晚二叠世初开始向西俯冲，晚三叠世最终完全关闭。金沙江洋盆早石炭世时已扩张成洋，到早二叠世晚期开始俯冲，石炭纪—早二叠世早期是金沙江洋盆扩张的主体时期，早二叠世晚期至早、中三叠世俯冲消亡。澜沧江弧后洋盆中晚泥盆世开始扩张，在石炭纪—早二叠世发育为成熟洋盆，早二叠世晚期洋内俯冲形成洋内弧，晚二叠世—早、中三叠世双向俯冲消亡。昌宁-孟连洋为特提斯洋主带，具有原-古特提斯洋连续演化的地质记录，晚奥陶世开始向东俯冲消减，二叠纪末、早三叠世发生弧-陆碰撞作用，昌宁-孟连洋盆闭合。

Abstract:

The present paper focuses on the preliminary study of the distribution and tectonic evolution of the oceanic plate stratigraphy,including the successive evolution,stepwise amalgamation and plate-accretion,and final subduction, consumption and closure of the Proto- and Palaeo-Tethys ocean in the Nujiang-Lancangjiang-Jinshajiang area in southwestern China. The Garze-Litang back-arc ocean basin has gone through the initiation during the Early Carboniferous,culmination during the Permian to the Middle Triassic,decline and westward subduction during the Late Triassic,and finally preservation of only a part of the ocean during the latest Late Triassic. The Ailaoshan back-arc ocean basin was formed no later than the Early Carboniferous,fully expanded during the the period from the Early Carboniferous to the Early Permian,subducted westwards at the end of the Early Permian or at the beginning of the Late Permian,and finally terminated during the Late Triassic. The Jinshajiang ocean basin was opened and expanded into an ocean during the Early Carboniferous,began subduction at the end of the Early Permian,culmianted during the period from the Carboniferous to the early Early Permian, and came to the subduction and collapse during the period from the end of the Early Permian to the Early and Middle Triassic. The Lancangjiang back-arc basin began expansion during the Middle to Late Devonian,developed into a mature ocean basin during the period from the Carboniferous to the Early Permian. Then an intra-oceanic arc was created through intra-oceanic subduction,and finally the Lancangjiang back-arc basin was closed as a result of birectional subduction during the period from the Late Permian to the Early and Middle Triassic. The Changning-Menglian ocean as the major part of the Tethys ocean which represents the geological records of Proto- and Palaeo-Tethys oceanic evolution began subduction eastwards and consumption during the Late Ordovician,and finally closed due to the arc-continent collision during the period from the latest Permian to the Early Triassic.