Study On Structural Features And Formation Environment Of Waxuezi-Qiaoduan Fault Zone In North Qinling

Waxuezi-Qiaoduan fault zone is one of the most important fault zones in North Qinling,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 fine study on geometry,kinematics,and the formation environmental of Wa-Qiao fault zone, and obtained the following understandings:(1)The trend of WaQiao fault zone is NNE.The lineations developed in the fault zone indicates the kinematics characteristics of thrusting from north to south, and contained sinistral shearing component.(2) Characteristics of microtectonics and finite strain measurement of deformed rocks in WaQiao fault zone indicate that the fault zone was in a compressive stress background.The strain ellipsoid is flat-ellipsoidal (flattening), and the strain becomes stronger and the stress greater while comes to the center of WaQiao fault zone;(3) Quartz C-axis fabrics of deformed rocks in the fault zone are mainly rhombohedral{1101}<a> slip system, when comes to the center of the fault zone, the quartz C-axis fabrics will change from rhombohedral <a> slip systems into cylinder<a> slip systems and deformation temperature will be gradually increased;(4)Al-in-hornblende barometer is employed in this paper to analyze the formation pressure of WaQiao fault, and the reault is about0.64GPa.The pressure becomes larger while closer to the fault zone center.The maximum pressure which comes from the center of the fault zone is0.68GPa, and indicates the environment of medium-pressure phase;(5)We used hornblende-plagioclase T-P meter to limit the formation temperature of WaQiao fault zone, and got the range500～550℃,which shows a low temperature environment.