桂北地区摩天岭韧性剪切带的应变特征及其构造意义

    Strain Characteristics of Motianling Ductile Shear Zone in Northern Guangxi and its Tectonic Significances

    • 摘要: 本文通过对宏-微观构造、岩石有限应变测量和石英EBSD组构分析,讨论摩天岭韧性剪切带的应变特征及其构造意义,深化华南早古生代构造事件的认识。研究表明,摩天岭韧性剪切带具有典型的宏-微观韧性变形组构,包括糜棱面理、旋转碎斑系、S-C组构、书斜构造、不对称眼球体、石英动态重结晶、核幔结构、云母鱼、机械双晶和不对称压力影等。岩石有限应变测量和宏-微观构造表明,摩天岭韧性剪切带呈NNE向延伸超65 km,宽8~12 km。糜棱C面理的倾向220~356°,倾角10~74°,极密点产状285°∠22°。摩天岭韧性剪切带具早期左旋逆冲剪切,晚期右旋正滑剪切的运动学性质。变形岩石呈现既有压扁型应变,也有拉伸型应变的应变特征,以及既有简单剪切,又有纯剪切的剪切性质。石英EBSD组构显示,摩天岭韧性剪切带具有晚期中低温变形(300~450 ℃)叠加早期中高温变形(400~600 ℃)特征。摩天岭韧性剪切带具有相对较低的古差异应力和应变速率,分别介于10.59~36.31 MPa和0.63×10-13~87.18×10-13 s-1。综合上述研究,并结合区域地质资料,认为摩天岭韧性剪切带形成于华夏陆块自SE向扬子陆块挤压受阻后而产生反冲作用的构造背景。早期挤压碰撞阶段,摩天岭韧性剪切带产生中高温左旋逆冲剪切和压扁型应变;造山后伸展阶段,摩天岭韧性剪切带产生中低温右旋正滑剪切和拉伸型应变。上述认识揭示了摩天岭韧性剪切带的产状、应变特征、流变学和动力学背景,为深化认识华南加里东期构造事件提供了新的资料。

       

      Abstract: This is an article in the field of structural geology. In this article, the strain characteristics and tectonic significance of the tile shear zone of Motianling are discussed through macro-microstructure, finite strain measurement of rocks and EBSD structural analysis of quartz. The results show that the Motianling ductile shear zone has typical macro-micro ductile deformation fabrics, including mylonite foliation, rotating porphyry system, S-C fabric, domino structures, asymmetric ocular sphere, quartz dynamic recrystallization, core-mantle structure, mica fish, feldspar mechanical twinning and asymmetric pressure shadow. The finite strain measurement and macro-micro structure shows that the Motianling ductile shear zone extends over 65 km in NNE direction, and its width is 8~12 km. The C-foliation tendency of the mylonite is 220°~356°, the dip angle is 10°~74°, and the extremely dense point occurrence is 285°∠22°. The Motianling ductile shear zone has kinematic characteristics of early sinistral thrust shear and late dextral normal slip shear. The rock strain of Motianling ductile shear zone is mainly flattening strain and tensile strain. At the same time, it shows the shear property of pure shear and simple shear. Quartz EBSD fabric analysis show that the Motianling ductile shear zone is characterized by the late middle-low temperature deformation ( 300~450 ℃ ) superimposed on the early middle-high temperature deformation ( 400~600 ℃ ). The paleo differential stress and strain rate of Motianling ductile shear zone are relatively low, ranging from 10.59~36.31 MPa and 0.63×10-13~87.18×10-13 s-1, respectively. In combination with the above studies and regional geological data, it is considered that the Motianling ductile shear zone was formed in the tectonic setting of recoil after extrusion of the Cathaysia block from SE to the Yangtze block. In the early extrusion and collision stage, the Motianling ductile shear zone has the property of mid-high temperature sinistral thrust shear. After the late orogenic extension, the Motianling ductile shear zone has the property of dextral normal slip shear at mid-low temperature. The above understanding reveals the occurrence, strain characteristics, rheology and dynamics setting of the Motianling ductile shear zone and provides new data for deepening the understand of Caledonian tectonic movement in South China.

       

    /

    返回文章
    返回