豫西双龙剪切带假玄武玻璃的成因及地质意义

Genesis of Pseudotachylites from Shuanglong Ductile Shear Zone and Its Geological Significance

假玄武玻璃是发育在古地震断层带中的一种断层岩,是古地震断层快速滑动的化石记录。目前关于假玄武玻璃的成因还存在争议,有摩擦熔融成因和摩擦碎裂成因2种观点。豫西双龙剪切带是位于秦岭造山带核部的一条韧性剪切带,发育了一系列动力变质岩,后期地质作用在其构造薄弱面上形成了呈简单脉状、平行剪切面发育的假玄武玻璃。假玄武玻璃的出现说明秦岭群曾经历高应变速率的构造运动,即古地震事件。通过对该区假玄武玻璃的镜下观察、粉晶X射线衍射、扫描电镜及石英的EBSD组构等研究,对其成因进行了探讨,结果显示秦岭群核部的假玄武玻璃为摩擦碎裂成因。

Pseudotachylytes are fault rocks that are generally thought to be formed by frictional fusion and comminution during paleoseismic fault movements. It can be considered as an earthquake fossil. However, its formation mechanism has been debated in the past as to whether pseudotachylytes matrix originates from frictional fusion or comminution. Shuanglong ductile shear zone where there is a development of se- ries of dynamic metamorphic rocks such as protomylonite, mylonite and ultramylonite is located in the core of Qinling orogen, a paleo-earthquake later leads to the formation of pseudotachylytes along the weak structure interface in this ductile shear zone. The field characteristics of these pseudotachylytes are simple stockwork and parallel to the shear plane. As a fossil of paleoseismic, the emergence of pseudotachylytes can be accepted as an indicato of high-velocity slip in the core of Qinling Group. According to the results of analysis and test like optical microscope, SEM, powder X-ray diffraction and EBSD fabrics of quartz, we consider the pseudotachylytes in the core of Qinling Group are formed by frictional comminution.