The combination of field surveys with analysis of microstructure of tectonite and Electron Backscatter Diffraction(EBSD) on quartz fabric indicated that three periods of ductile shear events developed in the Paishanlou gold deposits and the E-W and NE-striking ductile shear zones were formed during each event.The E-W-striking ductile shear zone,accompanied by compressional and dextral shear slip,was shear-cut by the NE-striking shear zones,accompanied by compressional-sinistral shear slip and sinistral-normal shear slip,successively.An E-W-striking ductile shear zone developed at a deeper tectonic level and at middle- to high-temperatures,accompanied by abundant microstructures,including microlayering between a polycrystal quartz belt and mica,and quartz deformation was depended on cylinder(10-10) or glide.The development of an E-W-striking shear zone can be seen as a tectonic pattern in the region of the Paishanlou gold deposits of the collision between the Mongolian tectonic belt and the North Archean Craton from Suolun to the Linxi suture zone during the Indosinian.The NE-striking ductile shear zone developed approximately 160 Ma during the early Yianshanian at middle to shallow tectonic levels and at middle- to low-temperatures,accompanied by typical microstructures,including polycrystal quartz aggregation and quartz subgrain rotation recrystallization,etc.,and quartz deformation was depended on prismatic(1011) glide.The last ductile shear event around the NE-striking shear zone developed at low temperatures and shallow tectonic levels,yielding to a pre-existing NE-striking shear zone,accompanied by abundant microstructures,including low-temperature quartz grain boundary migration and bulging recrystallization.The last ductile shear movement may be related to lithosphere thinning and the destruction of the North China Craton from approximately 130-120 Ma,and this shear event resulted directly in the mineralization in the Paishanlou region.
NI JinLongLIU JunLaiTANG XiaoLingZHAO ChunQiangZENG QingDong
As one of the vital tectonic units of the Wulian Metamorphic Core Complex(MCC), the Wulian detachment fault zone(WDFZ), which developed in the Jiaodong peninsula, separates the lower plate of the ultrahigh pressure(UHP) metamorphic rocks in the Sulu orogenic belt from the upper plate of the early Cretaceous Zhucheng basin and the basin basement. The fault zone generally strikes NNE with a dip in the west along the southern portion of the MCC and strikes NE with a dip in the WNWalong the northern portion. The fault zone displays a wavy-tile-shaped extension on the plane, principally composed of the fault breccias and mylonite and transits downward to the mylonitic gneiss. As a whole, the detachment fault zone shows a top-towest or a WNW extension. By calculating the harmonic mean, we obtain a Flynn index K of 0.98–2.0, and the mean value is approximately 1.35 in the fault zone. According to the polar Mohr construction, the extensional crenulation cleavage, the RS/θ,and the quartz C-axial fabric methods, we acquire mean kinematic vorticity values of 0.64–0.97, 0.76–0.93, 0.6–0.92, and 0.63–0.98 with mean values of 0.83, 0.80, 0.78 and 0.86, respectively, for mylonite and promylonite. The strain measurement results and the kinematic vorticity values indicate that the WDFZ is a normal ductile shear zone developed in the extensional setting.The kinematic track shows that the kinematic vorticity value decreases gradually from the NW to the SE as a whole. A simple shear dominates in the middle and upper parts of the shear zone, which is reflected by a higher vorticity value(>0.75, up to 0.98),a low thinning rate and a lower K value. In contrast, toward the footwall, the pure shear is increased significantly, showing a lower vorticity value(<0.70, low to 0.64), a relatively high thinning rate and a higher K value. Combined with the geotectonic background, the development and evolution of the WDFZ should respond to lithospheric thinning and the destruction of the North China Craton(NCC). As a result, the WDFZ c
