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Characteristics of Magnetic Fabrics of Feixianguan Fault-Propagation Fold in the Front of Longmenshan Fold-Thrust Belt and Its Structural Significance

HU Qian-wei, JIA Dong, CHEN Zhu-xin, LUO Liang, JIA Qiu-peng   

  1. Department of Earth Sciences, Nanjing University, Nanjing 210093, China
  • Received:2005-12-20 Revised:2005-12-20 Online:2005-12-20 Published:2005-12-20

Abstract: Along Feixiangnan fault-propagation fold cross-section in the southern Longmenshan front, 270 oriented specimens were drilled to conduct the analysis of magnetic minerals and anisotropy of magnetic susceptibility (AMS). We find that hematite is the main magnetic carrier mineral according to isothermal remanent magnetization acquisition and demagnetization of three orthogonal isothermal remanent magnetization. The AMS results show two types of magnetic fabrics: intermediate magnetic fabric and tectonic magnetic fabric. Based on the kinematic model of fauh-propagation fold and distribution features of magnetic fabrics, we deduce the evolution of magnetic fabrics through the development of fault-propagation fold: primary sedimentary fabrics were transformed into intermediate fabrics by the pre-folding layer parallel shortening; during the propagation of fault, simple shear caused by limbs' rotation and lift affects the AMS at limbs, which make Pj rise locally within limbs, and structural fabric appears in strong deformation area.