黔东及其邻区早古生代构造变形对华南大陆再造的启示

Sibao orogeny accounted for the collision between Yangtze and Cathaysia into uniform paleo-South China plate from 850 Ma to 800 Ma yr. Paleo-South China plate soon broke up as part of Rodinia supercontinent. These separated blocks reunited into South China orogeny until lower Paleozoic. Remelting granite are massively observed in orogenic belt, while typical collision structure and basic-ultrabasic are absent. East Guizhou and its adjacent regions located in west margin of amalgamative zone between Yangtze and Cathaysia where the two blocks collided in Neoproterozoic and Paleozoic. Abundant Early Paleozoic tectonic deformation, including groups of pre-Devonian superimposed folds, multistage lower-Paleozoic regional conjugate ductile shear zones, fault zones destructing previous pluton and nearby discordant deformation zones, were caused by the Yunan, Duyun( or Chongyu ) and Guangxi movement. Pre-existed deformation is complex and obscure due to late superimposed reworking and compound orogenesis. Megastructure interpretation, microstructure analysis and structural chronological dating will be utilized in this application, combined with regional deposition and magmatism, recognizing early Paleozoic deformation trace, explaining its trigger factor and providing new implication to reworking process in South China and early Paleozoic intracontinental orogeny.

四堡运动（850-800Ma）使得扬子地块与华夏地块对接碰撞形成统一的古华南陆块。之后，作为罗迪尼亚超大陆的组成部分，古华南陆块发生了裂解。至早古生代，裂解的地块重新拼合形成华南早古生代造山带。这个造山带发育大面积重熔型花岗岩，而不发育典型碰撞带构造与基性-超基性岩。黔东及其邻区处于扬子与华夏拼合带的西缘，区内可能包含扬子与华夏在新元古代、早古生代的拼合带。早古生代的郁南运动、都匀（崇余）运动、广西运动在这里形成的丰富的构造变形，包括发育在前泥盆系内的叠加褶皱群、上元古界内多期活动的区域性共轭韧性剪切带、破坏早期岩体的断层带以及研究区周缘的不协调变形带。由于后期叠加变形与复合造山作用，使得早期变形复杂化且不易辨认。本申请拟采用宏观构造解析、显微组构分析、构造年代测定，结合区域沉积与岩浆活动，提炼获得早古生代构造变形形迹，分析其成因机理，为华南大陆再造与早古生代陆内造山过程提供新资料。

黔东及其邻区处于扬子与华夏拼合带的西缘，区内包含扬子与华夏在新元古代、早古生代的拼合带。这里有早古生代郁南运动、都匀（崇余）运动、广西运动形成的丰富构造变形，包括发育在前泥盆系内的复杂褶皱群、上元古界内的区域性共轭韧性剪切带、切过新元古代-早古生代岩体的大型剪切带以及研究区与周缘的不协调构造变形带。区内江南造山带被三个重要的构造不整合界面所分割：其一是冷家溪群与板溪群之间传统上被看做是扬子和华夏地块碰撞造山运动标志的不整合面，即武陵不整合面；其二是板溪群与上覆南华系冰碛岩建造不整合面，即雪峰运动不整合面；而其三为板溪群内部马底驿组与五强溪组之间的不整合面，即“西晃山不整合面”。通过对新元古代-古生代地层的碎屑物源和岩浆岩测试分析以及野外构造解析得以下认识：（1）不整合面上下的冷家溪群与板溪群的物源并未发生明显改变，均主要来自于扬子板块内部物质的再循环，物源的转换发生在板溪群内部；板溪群内部发生了一次重要的物源转变，从接受扬子陆块南缘的物源转变为扬子北缘的物源的输入；（2）雪峰运动界限上下物源的变化以680Ma新物源的加入为典型特征，主要表现为扬子内部的一个物源交流；（3）扬子板块南缘震旦系地层中662-558Ma的峰值指示其在晚新元古代东纲瓦纳超大陆北缘弧火山事件影响范围之内；（4）研究区寒武系至奥陶系碎屑岩年龄谱则转变为以1.1-0.9Ga与600-500Ma为主要特征，其U-Pb与εHf(t)特征与南极Prydz Belt、拉萨地体与马达加斯加地体基本一致。物源在震旦系至寒武系发生了从印度北西缘到北东缘的转变，暗示在这一时期，华南与印度之间发生过与纲瓦纳超大陆最终聚合；（5）研究区志留系地层与下伏地层年龄谱基本一致，显著的460-410 Ma峰值指示其在广西运动时期接受大量的同造山物质；（6）对研究区构造变形研究，认为早古生代晚期华南大陆扬子板块东南缘与华夏板块内的一系列近同时的 NW-SE 向逆冲推覆与 NE 向走滑剪切作用是形成于板块间斜向碰撞背景下的转换挤压构造。