关键词: 岩石圈下层, 塑性流动网络, 黏性摩擦生热, 延性弱面, 弱化度

Abstract: Netlike plastic flow in the lower lithosphere,as visco plastic flow involving plastic flow network,controls tectonic deformation and dynamic processes within the continental plate. Plastic-flow network is composed of two conjugate sets of plastic flow belts (PFBs),which are ductile weakness planes (belts) resulted from shear localization,viscous friction heat production,and weakening of intra belt media in the visco-plastic flow field. The study indicates that,similar to brittle weakness planes (e g. faults,joints,etc.),the effect of ductile weakness planes on the yield strength of media is conditional,i.e. when the direction of stress is changed,sliding along the original weakness plane can occur only at the condition that the sliding angle θ is within the range of θ₁ ≤θ≤θ₂,showing the weakening of media; the relative decrease of yield strength of the ductile weakness plane can be expressed by the weakening level R,which is related to the lower limit of the sliding angle,θ₁,as shown by the equation R =sin2θ₁. In terms of the maximum conjugate angle of the "plastic flow/seismic" networks in central eastern Asia,it is estimated that the weakening level of plastic flow belts,R,is approximate to 0.81. Based on the recognition of ductile weakness plane effect,some problems,including the transition of tectonic belts from shear sliding to compressional folding,the inheritance and discarding of PFB,and the permissible change of stress direction,are discussed in this paper.

Key words: lower lithosphere, plastic-flow network, viscous-friction heat production, ductile weakness-plane, weakening level.