北秦岭瓦穴子—乔端断裂带的构造特征及形成温度—压力条件探讨

Study on Structural Features and P—T Conditions of the Waxuezi—Qiaoduan Fault Zone in Northern Qinling Mountains

瓦乔(瓦穴子—乔端)断裂带是北秦岭尤为重要的断裂带之一,该带经历了长期的变质变形作用,记录了二郎坪弧后盆地向华北板块南缘俯冲消亡的信息。本文运用多种方法,对瓦乔断裂带几何学、运动学及形成温压条件进行研究和探讨,得出以下几点认识:①瓦乔断裂带产状基本倾向NNE,带内线理发育,表现为由N向S逆冲的运动学特征,且存在左旋剪切的分量;②瓦乔断裂带变形岩石显微构造特征明显,反映了挤压应力下塑性流变的特征;③运用角闪石全铝压力计,得到瓦乔断裂带形成压力为0.64GPa。越靠近瓦乔断裂带中心,压力逐渐变大,位于断裂带中心压力达到0.68GPa,已达到中压相系环境;④运用角闪石—斜长石地质温压计算得瓦乔断裂带形成温度范围500～550℃,属中温环境。

The Waxuezi—Qiaoduan fault zone is one of the most important fault zones in North Qinling Mountains, it had a long history of metamorphism and deformation, and recorded the information of the subduction and demise of the Erlangping arc basin northward to the south edge of the North China plate. This paper used several methods to do a study on geometry,kinematics,and the formation P—T conditions of the Waxuezi—Qiaoduan fault zone,and obtained the following understandings： ① the trend of the Waxuezi—Qiaoduan fault zone is NNE. Lineations developed in the fault zone indicate the kinematics characteristics of thrusting from north to south,and contained sinistral shearing component; ② the deformed rocks in fault zone had abvious characteristics of microstructures,which reflect the plastic flow under compressive stress. ③ Al-in-hornblende barometer is employed in this paper to analyze the formation pressure of the Waxuezi—Qiaoduan fault zone,and the result is about 0.64 GPa.The pressure becomes larger while closer to the fault zone center.The maximum pressure which comes from the center of the fault zone is 0.68GPa,and indicates the environment of medium-pressure phase; ④ We used hornblende—plagioclase T—P meter to limit the formation temperature of the Waxuezi—Qiaoduan fault zone,and got the range of 500~550℃, which shows a medium temperature environment.