FINITE STRAIN ANALYSIS OF THE LINGYUAN-BEIPIAO FAULT ZONE IN WEST LIAONING PROVINCE AND ITS GEOLOGICAL SIGNIFICANCE

Lingyuan-Beipiao fault zone is an important structural zone, which makes up the boundary of Inner Mongolia geological axis and Yanshan platform folding zone.The fault controls not only geotectonic framework but also Mesozoic-Cenozoic fault basins in West Liaoning.This paper reconstructs strain history of the Lingyuan-Beipiao fault zone by means of three-dimensional finite strain analysis, and estimates its differential paleostress.The study shows that the stress of the fault zone is an intermediate type of stretching strain and plane strain.The longest principal axis of strain had two azimuths of NW-SE and NE-SW, which showed that the fault had two obvious different types of strain states.The longest principal axis of strain, which was formed in the second phase of Yanshanian movement and earlier, is in NW-SE azimuth.The longest principal axis of strain, formed in the period of Mesozoic fault basins, is in NE SW azimuth.The differential paleostress of the fault is 32.7 MPa, which is estimated by the density of dislocation.The fault was formed in Proterozoic, and superimposed and transformed by Liaohe, Yanliao and Indosinian movements, with a complicated history of deformation.The second phase of Yanshanian movement established the geotectonic framework of West Liaoning with the final pattern.