桐柏杂岩南北边界剪切带的对比以及对桐柏造山带构造格局的制约

桐柏杂岩的南北边界的剪切带分别是殷店-马垅韧性剪切带和晓天-磨子潭韧性剪切带,这两条韧性剪切带内都发育杆状构造,且杆状构造具有层状结构,层与层之间通过一种特殊的滑脱面结合。由于晓天-磨子潭韧性剪切带相对于殷店-马垅剪切带位置明显更靠近商丹断裂带,早期商丹断裂带的活动在岩石中留下的变形痕迹导致了后期晓天-磨子潭韧性剪切带的变形程度要略强于殷店-马垅剪切带。这两条剪切带都是以简单剪切为主的剪切带,变质条件也相似,都属于角闪岩相变质,处于中-下地壳流变层位置。U-Pb同位素测年结果显示,晓天-磨子潭韧性剪切带的活动年龄为171~142Ma,殷店-马垅韧性剪切带的活动年龄为164~137Ma,两条剪切带的主活动期都在中-晚侏罗世,在早白垩世随着岩浆活动的峰期到来慢慢减弱停止。桐柏造山带在印支晚期碰撞挤压背景下的向东挤出不是一个整体的挤出,而是有层次的差异挤出,挤出的同时层与层之间会发生滑动,滑脱面类似滑动的润滑剂,酷似"管状流动"的构造。在晓天-磨子潭韧性剪切带和殷店-马垅韧性剪切带的牵引作用下,整个桐柏造山带由西向东发生管状流动。

The comparison about the shear zones in the northern and the southern boundary of the Tongbai Complex and constraints on the tectonic framework of the Tongbai orogenic belt

The northern and southern shear zones of Tongbai Complex are Yindian-Malong ductile shear zone and Xiaotian-Mozitan ductile shear zone. They both develop rodding structure with layer structure, and the layers are linked by a special detachment surface. Because of the Xiaotian-Mozitan ductile shear zone closer to Shangdan fault than Yindian-Malong shear zone, the deformation traces in the rock of early Shangdan fault caused the deformation degree of Xiaotian-Mozitan ductile shear zone just a little stronger than Yindian-Malong shear zone. Xiaotian-Mozitan shear zone and Yindian-Malong shear zone are mianly simple sheared, and the metamorphic conditions are also similar, both belong to the amphibolite facies metamorphism, which may exist in the earth''s rheological layer position of middle and lower crust. U-Pb isotopic dating results show that, Xiaotian-Mozitan shear zone''s active age is from 171Ma to 142Ma,and the active age of Yindian-Malong shear zone is from 164Ma to 137Ma. Two shear zones'' active periods are both from the Middle Jurassic to the Late Jurassic, and they both subsided when the peak period of magmatic activity comes in the Early Cretaceous. Under the background of collision in Indosinian, the extrusion of Tongbai mountain towards the east is not a monolithic extrusion but the differential levels of extrusion. At the same time of extrusion, layer and layer will slide, and the detachment surface is similar to the sliding of the lubricant, which is similar to the tubular flow structure. With the tractive effort of Xiaotian-Mozitan ductile shear zone and Yindian-Malong ductile shear zone, the Tongbai mountain occurs tubular flow from west to east.