关键词: 高角逆断层, 菱形构造, 鳄鱼嘴构造, 拆离褶皱, 最大有效力矩准则, 褶劈理, 低角正断层

Abstract: Conjugate fractures have an acute angle to σ₁, while conjugate deformation zones with an obtuse angle to it. The acute angle can be explained with the Mohr-Coulomb criterion, whereas the obtuse one can be elucidated with the Maximum Effective Moment Criterion (MEMC), which is recently proposed. The MEMC is mathematically expressed as M_eff=0.5(σ₁-σ₃)Lsin2αsinα, where α₁-α₃ represents the yield strength of the related rock, L is a unit length and α is the angle between α₁ and deformation bands. This criterion demonstrates that the maximum value appears at angles of ±54.7° to α₁ and there is little difference in the moment in the range of 55°±10°. The range covers all the observations available from nature and experiments. In practice, it can be used for elucidate many geological structures such as kink-bands and extensional crenulation cleavages, yield zones in evaporates, low-angle normal faults and high-angle reverse faults, lozenge ductile shear zones in basement terranes, some crocodile structures in seismic profiles and detachment folds in foreland basins. It may be used to determine the stress state when the related deformation features formed and provides a new approach to determine the W_k of the related ductile shear zone. It can also be extended to explain the relationship between orogenic and late-orogenic extension events, and uplift and exhumation of ultrahigh pressure rocks that experienced deep subduction.

Key words: low-angle normal fault, high-angle reverse fault, crocodile structure, lozenge structure, detachment fold, maximum effective moment criterion, crenulation cleavage