晓天—磨子潭断裂的运动学涡度、应变速率及其大地构造意义

The kinematic vorticity and strain rate of Xiaotian-Mozitan fault and their tectonic significance.

晓天-磨子潭断裂作为北大别带与北淮阳带的地表分界线，是大别造山带内重要的折返边界之一。本次工作在详细的野外观察、糜棱岩化过程中温-压条件的计算、糜棱岩中石英C轴组构分析等一系列工作的基础上，计算晓天-磨子潭断裂内同造山糜棱岩化过程的运动学涡度和应变速率。变形温-压条件指示糜棱岩形成于30-40km的深部，明显大于早白垩世以来的剥蚀深度，指示断裂带糜棱岩化过程发生于同造山折返过程中。涡度分析表明，断裂带的涡度值大于0．9，指示其变形以简单剪切变形为主，并说明大别造山带同造山晚期折返的驱动力表现为浮力。显微构造与石英C轴组构分析均指示了一致的上盘向NW的运动方式。断裂带同造山糜棱岩化过程的应变速率为10^-10 s^-1左右，表明造山带峰期变质之后的折返过程是非常快速的。

As the boundary between the north Huaiyang unit and the North Dabie complex unit, the Xiaotian-Mozitan fault is a very important exhumation channel. Based on the detailed field survey, the estimation of temperature and pressure during the mylonitization, and the measurement of quartz C-axis fabrics, we calculate the kinematic vortieity numbers and strain rate during the syn-orogen mylonitization of the Xiaotian-Mozitan fault. The mylonites formed in the depth of 30-40 km as indicated by the temperature and pressure of the deformation, which is more than the amount of denudation since the Cretaceous and suggests that the mylonitization was formed in the exhumation of the Dabie orogenic belts. The kinematic vorticities are all more than 0.9, which indicates that the deformation was mainly the simple shear. The Xiaotian-Mozitan fault is a fault with shear sense of top-to-the-NW as shown by microstructures and quartz Caxis fabrics. The strain rate of the syn-orogen mylonitization is about 10^-10 s^-1 peak metamorphism in the Dabie orogenic , which suggests that the exhumation rate is very high after the belts.