桐柏山L构造岩的构造特征与形成环境探讨

桐柏山太白顶、殷店和天河口一带，发育有大量的L构造岩，拉伸线理极其发育，面理较弱，线理产状向南东东倾伏，倾伏角为1°～20°。桐柏山L构造岩具有以下主要特征：在三维空间上，L构造岩强烈发育杆状构造，这种“杆”状构造是由大量沿X轴方向定向排列连在一起的椭球体矿物构成的，其变形机制主要为石英的颗粒边界迁移和长石的位错蠕变，形成的平均压力为0.59GPa，平均温度为550 ℃～600 ℃，形成于中-高温-中压环境，变质相为高绿片岩相到低角闪岩相，形成深度大致在15～20 km，属于中地壳的产物。L构造岩在桐柏山的发现可能反映了桐柏山造山带中桐柏杂岩岩块相对两侧榴辉岩岩片具有近东西向挤出构造的特征。

Study on structural features and P-T conditions of the L tectonites in Tongbai Mountains

In the wild,find that a lot of L tectonics develop in Taibaiding and Tianhekou. Lineation plunging to the SEE or NWW. Plunge angle is 1°～20°. In order to clarify the formation mechanism and forming temperature-pressure conditions of L tectonics in Tongbai, we used several methods like field survey and microstructural analysis and finite strain measurement and electron probe experiments,finally obtained that: In three-dimensional space,L tectonics develop rob-shaped structure strongly,and the rob-shaped structure composed by a large number of orientation constituted mineral ellipsoid in the X-axis direction, Its main deformation mechanism are high-temperature grain boundary migration recrystallization of quartz and bulging recrystallization of feldspar, Its forming average pressure is 0.59 GPa,and its forming average temperature is 550 ℃～600 ℃,which indicates the environment of medium-high temperature and medium pressure,metamorphic phase is high greenschist facies-lower amphibolite facies,the forming depth is substantially in the 10～15 km which in middle and lower crust. L rocks found in the Tongbai Mountain may reflect that Tongbai metamorphic terrane comparing to the sliver of eclogite has characteristics of extrusion tectonics in the east-west direction.