北秦岭二郎坪岩群两侧韧性剪切带的构造变形及其意义

北秦岭二郎坪岩群南、北两侧分别被朱夏韧性剪切带和瓦乔韧性剪切带与秦岭岩群和宽坪岩群分开，这两条韧性剪切带对二郎坪弧后盆地的演化起着十分重要的作用。本文对这两条剪切带进行了详细的几何学、运动学和⁴⁰Ar-³⁹Ar年代学研究。几何学和运动学分析结果指示瓦乔剪切带具有由北向南逆冲剪切的运动学特征，而朱夏剪切带早期具有由南向北逆冲的运动学特征，而后期又发生右行走滑活动。对瓦乔剪切带和朱夏剪切带内的糜棱岩中白云母进行了⁴⁰Ar-³⁹Ar法定年，结果指示瓦乔剪切带逆冲活动发生在387±1.7 Ma，朱夏韧性剪切早期逆冲发生在晚古生代，后期右行走滑的年龄为146±2.8 Ma。综合两条剪切带的构造变形特征和年代学数据，结合前人的地质资料，本文认为二郎坪弧后盆地曾沿着瓦乔剪切带和朱夏剪切带发生双向式俯冲。

Structural deformation of ductile shear zone on both sides of the Erlangping Group in North Qinling and its tectonic significance

The Erlangping Group is bounded by the Waqiao ductile shear zone on the north and Zhuxia ductile shear zone on the south in the North Qinling tectonic belt. These two shear zones play very important role in the evolution of the Erlangping back-arc basin. This paper presents a detailed study on the two shear zones by geometric analysis,kinematic analysis and ⁴⁰Ar-³⁹Ar dating. The geometry and kinematics suggests that the Waqiao shear zone thrust from north to south,while the kinematic characteristic of the Zhuxia shear zone is thrusting from south to north in early stage,then dextral strike-slip in the Late stage. ⁴⁰Ar-³⁹Ar chronological study was undertaken on muscovite in the mylonite from the Waqiao shear zone and Zhuxia shear zone in this work. A plateau age of 387±1.7 Ma obtained from mylonite is interpreted as the deformation age related to the thrusting movement of the Waqiao shear zone. The geologic age of early thrusting activity of the Zhuxia shear zone was occurred in the late Paleozoic,and the later dextral strike-slip movement yield a ⁴⁰Ar-³⁹Ar plateau age of 146±2.8 Ma. Based on deformation characteristics and chronological data of the two shear zones,combined with previous geological data,the Erlangping back-arc basin is considered to be characterized by bidirectional subduction along the Waqiao shear zone and Zhuxia shear zone,respectively.