石英C轴组构指示北大别造山后伸展期中-下地壳流变形式

造山带中-下地壳韧性流变形式反映深部岩石圈构造活动形式,是造山带深部岩石圈运动学及动力学研究的重要内容。前人对板块俯冲阶段造山带中-下地壳流动开展了较为深入的研究,但对造山后伸展期中-下地壳流变形式及其深部动力学认识不足。本次工作对北大别造山后伸展期中-下地壳岩石开展了详尽的构造观察和石英C轴组构分析,研究造山后伸展期中-下地壳流变形式。本次研究表明,中-下地壳流变带内岩石变形从边界区域的简单剪切变形为主导逐渐转变为在核部区域以纯剪切变形为主。流变带内部岩石变形特征表明北大别中-下地壳流变带的流变形式是介于活动边界条件下的透入性剪切流动和固定边界条件下韧性垮塌流动的过渡形式。这一流变形式可能是深俯冲太平洋板块的绕屈回撤和加厚造山带地壳活化韧性垮塌叠加的结果。

Quartz C-axis as an Indicator of the Middle-Lower Crust Flowing during the Post-orogenic Extension in the North Dabie

The flowing type of the middle-lower crust in the orogenic belt resulted from activation of the deep lithosphere is the key subject of the kinematics and dynamics study for the deep lithosphere.Previous studies focused on the flowing model of the middle-lower crust in the subduction stage of the plate,but rarely on the flowing during post-orogenic extension.In this study,detailed tectonic observation and quartz C-axis structure analysis were carried out to study the middle-lower crustal rocks during the post-orogenic extension.The results show that the deformation of the rocks in the middle-lower crust gradually changes from the simple shear dominated deformation in the boundary region to the mainly pure shear deformation in the core region.The deformation characteristics of the internal rocks in the North Dabie indicates a transition flow model between the penetrative simple shear model with active boundaries and the ductile collapsing model with fixing boundaries.This flow model of the North Dabie middle-lower crust may result from the roll back of the deeply subducted Pacific plate and the ductile collapse in the thickened orogenic crust.