桐柏山L构造岩形成机制构造解析及其对造山带演化的制约

桐柏杂岩中发育一套典型的L构造岩,其构造位置位于桐柏造山带核部,被两条近似对称的韧性剪切带所夹持,北侧剪切带左旋,南侧剪切带右旋。由于L构造岩构造位置特殊,其位于剪切带、桐柏背形、桐柏穹窿等多种构造体的交叉部位,L构造岩的构造成因解析可以为桐柏造山带的形成演化提供重要制约。通过对桐柏造山带L构造岩的构造成因机理解析和其变形温压条件的研究,同时结合前人对桐柏山其它主要构造单元的研究,我们提出,桐柏山L构造岩的形成主要受其南北两侧两条韧性剪切带控制,传统意义的桐柏杂岩体白垩纪之前与南北一体的韧性剪切带沿近似东西方向发生管状韧性剪切,剪切作用形成了一套典型的L构造岩。L构造岩的形成指示了桐柏山单元可能经历了一期中下地壳物质的管状的韧性的向东剪切流动,后期白垩纪桐柏山核部的L构造岩经历了大规模的岩浆上升与浮力增加,该L构造岩同剪切带一起发生隆升但管状剪切构造特征并未被改造,随着不均匀隆升桐柏山出现了现今的几何学特征。L构造岩反映出管状剪切形成了现今桐柏造山带近东西向线状构造样式的主体。

The Structural Formation Mechanism of L Tectonites in Tongbai Mountain and its Constraints on the Orogenic Evolution

There is a typical rock unit called L tectonites that developed in Tongbai complex. Its tectonic position is located in the core of Tongbai orogenic belt. It develops between two approximate symmetrical ductile shear zones. Because of the special tectonic position of L tectonites, which located in the intersection parts of shear zones, Tongbai antiformal, Tongbai doom and so on. Structural analysis of the formation mechanism of the L tectonites can be important for better understanding the evolution of Tongbai orogenic belt. By the study of characteristics and rock deformation conditions and formation mechanism analysis of L tectonites, it suggests that the formation process of L tectonites in Tongbai is mainly controlled by the two ductile shear zones in north and south sides of the Tongbai complex. Tongbai complex rock unit developed a characteristic of pipy ductile shearing along the north and south ductile shear zones which are one in the West-East direction before Cretaceous. It forms a set of typical L tectonites in the process of pipy ductile shear. The formation of L tectonite indicates the Tongbai orogenic belt went throngh a period that the middle and lower crust material came to a pipy ductile shearing to the east. In late Cretaceous Tongbai has experienced massive magma rising and increasing buoyancy, the L tectonites occurs uplift with shear zones but the main feature has not been transformed, and with uneven uplifting Tongbai orogenic appeared today''s geometry characteristics. L tectonites reflects pipy shearing formed the main structural characteristics of Tongbai orogenic belt with a nearly east-west linear structure style.