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本文选取秦岭商丹断裂带以南,南秦岭刘岭群以北的弧前沉积体为研究对象,研究扬子板块向北秦岭俯冲的运动学特征。这套弧前沉积体产状北倾,矿物拉伸线理为倾向线理,岩片强烈褶皱,断裂发育,表现出由北向南逆冲的运动学特征。利用糜棱岩与云母石英片岩中矿物变形温度计,结合石英C轴组构估算岩石变形温度集中在400℃~550℃之间。结合其所处的构造位置,本文认为这套强烈变形的岩石构造组合体形成于秦岭古岛弧弧前沉积背景,在扬子板块向北秦岭俯冲过程中,北秦岭沿着商丹带由北向南逆冲形成。后期又遭受商丹韧性剪切带左行走滑活动的改造。
In this paper, we choose the forearc sedimentary bodies to the north of Shangling Dan fault belt in the Qinling Mountains and the north of Liuling Group in the South Qinling Mountains as research objects, and study the kinematics characteristics of the subduction of the Yangtze Plate to the North Qinling. The pre-arcuate sediments are prone to be north-dipping. The mineral stratification line is dip-line, with intense folds and faults. The kinematics of north-south thrusting are shown. Based on the mineral deformation thermometer of mylonite and mica quartz schist, the deformation temperature of rock is estimated to be between 400 ℃ and 550 ℃ based on the quartz C-axis structure. Combined with its tectonic position, this paper argues that the strongly deformed rock structure assemblage was formed on the forearc arc-arc sedimentary background of the ancient island in the Qinling Mountains. During the subduction of the Yangtze Plate to the North Qinling, the North Qinling Mountains developed along the Shangdan belt from north to south Thrust formation. In the later period, it was also subjected to the alteration of the left-slippage activity of Shangdan ductile shear zone.