西南三江金沙江弧盆系时空结构及构造演化

The temporal and spatial framework and its tectonic evolution of the Jinsha River arc-basin system,Southwest China

金沙江(-哀牢山)弧盆系是西南三江多岛弧盆系的重要组成部分,恢复其时空格架及其形成演化过程对理解古特提斯多岛弧盆系的时空格局具有重要意义。根据新的地质调查资料、研究成果并结合分析数据,系统总结了金沙江弧盆系不同构造单元的物质组成及其构造属性,讨论了其构造演化过程及其对VMS型矿床的控制作用。金沙江洋壳发育时限主要为晚志留世-二叠纪,古洋壳地幔受到了早期俯冲带物质富集组分的影响,主体形成于弧后盆地的构造环境。江达-德钦-维西岩浆弧为一复杂的陆缘弧,经历了俯冲消减(300~260 Ma)、早碰撞聚合(255~250 Ma)、同碰撞伸展(249~237 Ma)和晚碰撞造山(236~212 Ma)等构造事件叠加改造,形成了不同类型、不同环境的岩浆活动及其盆地。金沙江带新发现的贡觉榴辉岩、维西退变榴辉岩等高压变质带,为恢复金沙江古特提斯洋的俯冲-碰撞造山的复杂演化过程提供了重要证据。在此基础上,结合区域地质资料,构建了金沙江弧盆系的演化历史,认为经历了晚志留世-早二叠世金沙江(-哀牢山)弧后洋盆扩张、早二叠世晚期-晚二叠世洋壳俯冲消减、早三叠世-晚三叠世弧-陆碰撞造山与盆-山转换、晚三叠世末期后碰撞陆内造山至陆内汇聚-走滑转换等阶段的演化过程,每个阶段控制着不同类型的VMS型矿床。

As the important part of the Sanjiang archipelagic arc-basin systems in southwest China,the tectonic evolution of the Jinsha River arc-basin system is of great significance to understanding the spatial-temporal pattern of Paleo-Tethys archipelagic arc-basin systems.In the light of the new geological survey data,research results and analysis data,this paper systematically summarizes the material composition and tectonic characteristics of different tectonic units of Jinsha River arc-basin system,and discuss the tectonic evolution process and its effect on controlling volcanogenic massive sulfide(VMS)deposits.Jinsha River Ocean mainly developed during the Late Silurian to Permian,and the ancient oceanic mantle was affected by the early subduction zone which is enriched in material formed in back-arc basin environment.As a complex epicontinental arc,Jomda-Deqen-Weixi continental margin arc has experienced four evolutionary stages,including subduction stage(300-260 Ma),the early collision convergence stage(255-250Ma),syn-collision extension stage(249-237Ma)and late collision orogenesis stage(236-212Ma),resulting in the formation of various types of magmatic activities and basins.High-pressure metamorphic belts such as Gonjo eclogite and Weixi retrograde eclogite have been recently recognized in Jinsha River suture zone,and provided key evidence for restoring the complex evolution of subduction-collision orogeny of Jinsha River Tethys.The new findings combined with the regional geological data,the evolutionary processes of the Jinsha River arc-basin system are constructed,mainly including the Late Silurian to Early Permian back-arc ocean basin expansion stage,the Late Early Permian to the Late Permian oceanic crust subduction stage,the Early Triassic to the Late Triassic arc-continental collision orogeny and basin-mountain conversion stage and the late Late Triassic post-collision intra-continental orogeny to intra-continental convergence-strike-slip transition stage.Each stage has controlled different types of VMS deposits.