The Analysis Of Tectonic Stress Field Of Lishu Fault Depression In Northeast China

Lishu Fault Depression constitutes a superimposed one with a break-sinking characteristic developingin the Early Cretaceous Epoch. In the southeast upwelling area of Songliao basin and with Tan-Lu fault zoneto its east, it is located on the juncture part of tectonic domain between pacific ocean and paleoasian oceanfrom a tectonic point of view. Due to its unique tectonic position and richness in petroleum resources, LishuFault Depression has long been concerned by numerous geologists and researchers. However, through yearsof studying, there is still a great divergence on division of its breaking-sinking process and the mechanicalproperties of each phase, which leads to various understandings about the issues and properties of tectonicstress field of Lishu Fault Depression. In order to get in-depth knowledge, this paper, based on the previousresearch findings, further analyses different dynamic environments of breaking-sinking phases of LishuFault Depression by using equilibrium profile technique. Additionally, tectonic stress fields of differentphases also be simulated through the applying ANSYS FEM(Finite Element Modeling) simulation software.The results suggest that:During huoshiling period, the average extensional ratios of Lishu Depression gotten from theequilibrium profile technique are4.98%、2.68%respectively in the directions of NW-SE and NE-SW,corresponding to the stress-field simulation results of4.70%and2.83%. The consistent results show thatLishu Depression developed under a right-lateral strike-slip extensional circumstance, which may be aconsequence of joint extrusions from the closures of Neo-Theys in the southwest and Erkutsk Ocean in thenorth, but a greater force in the southwest;During the shahezi period, the average extensional ratios received by the equilibrium profile techniqueare-0.60%、1.33%in the directions of NW-SE and NE-SW, in accordance with the stress-field simulationresults of-0.60%、1.30%. It can be speculated that at this time the Lishu Fault Depression developed under aleft-lateral strike-slip compressional environment, which may be caused by extrusion from closure ofNeo-Theys and northwestward subduction of the pacific plate in the northwest, but a weaker pressing forcein the northwest;During the yingcheng period, in the directions of NW-SE and NE-SW the average extensional ratiosare2.90%、0.15%by using the equilibrium profile technique, showing no difference with the stress-fieldsimulation results of2.58%、0.10%. These two techniques prove the fact that Lishu Depression developedunder a right-lateral strike-slip extensional environment at this time, which may be a result of cooperative extrusion from closures of Erkutsk Ocean in the north and Neo-Theys in the southwest, but a bigger force inthe southwest;In the period of denglouku, the average extensional ratios reached from the equilibrium profile are-0.23%、1.40%respectively in the directions of NW-SE and NE-SW, consistent with the stress-fieldsimulation results of-0.33%、1.15%. The results of these two techniques show that Lishu Depression at thistime developed in a left-lateral strike-slip geological background, which may be the consequence of jointextrusions from northwestward subduction of pacific plate and closures of neo-thys in the southwest andErkutsk Ocean in the north, but a bigger subduction force in the northwest.Meanwhile, this research also provides certain reference significance for further understanding ofdynamic environments of formation and evolution of the contemporaneous depressions in its surroundingarea.