岩石中的很多褶皱展示了具有尖锐枢纽和平直翼部的尖角状外形。不少作者的研究表明,多层岩层中的这类褶皱形态是由层状或叶理状岩石固有的不均匀性造成的。二维有限元模拟的结果显示,具有尖锐枢纽和平直翼部的褶皱也可以发育在适当流变环境下的孤立的强硬层中。影响褶皱形态的两个基本物质特性是非线性和各向异性。粘塑性流动、幂律流动(应变率软化)和应变软化是3种非线性行为。这些都可导致具有尖锐枢纽和平直翼部的褶皱。各向异性对褶皱的几何形态有相似的影响。随着岩层的非线性程度或各向异性的增加,孤立的强硬层褶皱的尖角度也随之增加。于是有可能建立褶皱尖角度和非线性或各向异性之间的定量关系。实际上,相似的尖角状褶皱形态既可以由岩层的非线性、也可由岩层的各向异性产生。然而,与这些形态相联系的应变分布差别很大。对于非线性行为,应变集中在褶皱枢纽,在翼部最小;对于各向异性行为,情况正好相反,翼部的剪切是主要的。这些特征表明,有可能利用褶皱岩层的形态和应变型式来区分非线性行为和各向异性流变行为。 Many of the folds in the rock show a pointed shape with a sharp hinge and a straight wing. A number of authors have shown that such folds in multilayered rock formations are caused by the inherent inhomogeneities of stratiform or leaf-shaped rocks. The results of the two-dimensional finite element simulation show that folds with sharp hinges and straight wings can also develop in isolated hard layers in an appropriate rheological environment. The two basic material properties that affect the fold morphology are nonlinear and anisotropic. Viscoplastic flow, power law flow (strain rate softening) and strain softening are three kinds of nonlinear behavior. These can all result in folds with sharp hinges and straight wings. Anisotropy has a similar effect on the geometry of folds. With the non-linearity or anisotropy of the rock formation, the sharpness of isolated hard-layer folds also increases. It is then possible to establish a quantitative relationship between the angle of the fold crest and the nonlinearity or anisotropy. In fact, the similar cusp-like folds can be produced either by the non-linearity of the formation or by the anisotropy of the formation. However, the strain distributions associated with these patterns vary greatly. For non-linear behavior, strain is concentrated at the fold hinge with the smallest wing; for anisotropic behavior, the opposite is true and the wing shear is dominant. These features indicate that it is possible to use the morphology and strain patterns of the fold strata to distinguish between non-linear behavior and anisotropic rheological behavior.