广东正果韧性剪切带变形特征及其年代学研究

Deformation Characteristics and Chronology of Zhengguo Ductile Shear Zone in Guangdong Province

岭南地区韧性剪切带广泛出露于华南板块的扬子地块和华夏地块的过渡区域,其构造演化受到太平洋板块俯冲的影响,对于认识板块活动背景下的陆内大型变形带地壳深部特征及过程具有重要意义.通过野外宏观、室内微观特征的调查与研究,在广东增城地区首次识别出正果韧性剪切带,近东西向展布约16km,最宽处达6.7km.正果剪切带几何学及运动学的特征研究表明,该韧性剪切带为逆冲兼具左行走滑性质;韧性剪切带内白云母40Ar/39Ar法同位素测年为(160.80±0.65)Ma和(160.17±0.65)Ma,表明其形成于晚侏罗世早期,在晚侏罗世早期太平洋板块与华夏地块之间强烈俯冲-汇聚作用下,华南沿海地区表现为水平收缩和斜向汇聚.本研究对深化理解燕山运动在华南地区的响应提供了数据支持.

The ductile shear zone is widely exposed in the transitional area between the Yangtze Block and the Cathaysia Block of the South China plate.The Mesozoic tectonic movement and magmatic activity of the ductile shear zone were deeply influenced by the subduction of the adjacent oceanic plate since the Jurassic,which is of great significance for understanding the characteristics and processes of the deep crust of the large intra-continent deformation zone under the background of plate activity.Based on the systematic investigation of in-situ macroscopic and indoor microscopic characteristics,a prominent ductile shear zone has for the first time been determined in Zengcheng area,Guangdong Province.Moreover,the 40Ar/°Ar chronology data of single mica grains in the shear zone are used to constrain the deformation age of the zone.In this paper,the geometrical and kinematic characteristics of the shear zone show that the ductile shear zone that has the character of both thrust and sinistral strike-slip.The 40Ar/39Ar dating on single mica grains and plateau ages obtained are(160.80±0.65)Ma and(160.17±0.65)Ma,respectively,from the Zhengguo ductile shear zone.It is inferred that the Zhenggou ductile shear zone was probably formed in the early Late Jurassic.Combined with the regional geological data and the zircon U-Pb age(161.9±2.6)Ma in this study,the formation features of granites on the western side of Zhengguo ductile shear zone may indicate a strong collision between the Pacific plate and the Cathaysia Block in the early periods of Late Jurassic,characterized by the horizontal contraction and oblique convergence,Thus,this study provides new data for further understanding the Yanshan movement in South China.