大陆岩石圈塑性流动网络的延性弱面效应

DUCTILE WEAKNESS-PLANE EFFECT OF PLASTIC-FLOW NETWORKS IN THE CONTINENTAL LITHOSPHERE

岩石圈下层的网状塑性流动 ,作为包含塑性流动网络的黏塑性流动 ,控制着大陆板块内部的构造变形和动力学过程。塑性流动网络由两组网带共轭相交而成 ,而塑性流动网带是黏塑性流动过程中因剪切局部化、黏性摩擦生热和网带介质的弱化而形成的延性弱面 (弱带 )。研究表明 ,类似于断裂和节理等脆性弱面 ,延性弱面对介质强度的影响也具有条件性 ,即当应力方向改变时 ,只有在滑移角θ不超出一定限值的条件 (θ1≤θ≤θ2 )下才可能沿原有弱面滑移 ,显示其弱化效应 ;延性弱面可以用弱化度R表示其屈服限的相对降低程度 ,弱化度与滑移角下限值之间的关系为R =sin2θ1;根据亚洲中东部地区“塑性流动 -地震”网络的最大共轭角推算 ,网带的弱化度R近似于 0 81。基于延性弱面效应的认识 ,文中就网带由剪切滑移向压性褶皱的转化。

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 θ 1 ≤θ≤θ 2 , 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, θ 1 , as shown by the equation R =sin2θ 1 . 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.