Folding in power-law viscous multi-layers
Folding in power-law viscous multi-layers
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幂律粘性多层折叠
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发表时间：
2012
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影响因子：
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通讯作者：
D. Schmid
中科院分区：
文献类型：
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作者：
S. Schmalholz;D. Schmid
用二维数值模拟方法研究了层状岩石的高振幅褶皱。本文采用有限元方法模拟了具有幂律粘性流变的不可压缩多层材料的缩短过程。对拉格朗日数值网格进行变形和重新网格划分，以精确地跟踪层界面。考虑了三种情况：(i)受约束多层的纯剪切，（ii）剥离以上多层的简单剪切，以及（iii）由于重力滑动引起的滑塌褶皱。在我们的纯剪切模拟中，尽管有约束和薄的弱夹层，有限振幅的褶皱仍然会发展。褶皱形状可能是明显不规则的，这是由于初始几何非均质性造成的，这些非均质性是层界面的扰动和层厚度的差异。随着折叠的进行，多层材料的体粘度显著降低。这种结构软化使体正常粘度降低2-20倍。在单纯剪切作用下，多层不形成明显的不对称褶皱形态。多层中的折轴面大多是弯曲的，并不平行。对于滑塌褶皱，褶皱形态具有明显的不对称性，表现为强烈弯曲的褶皱轴面和倒转的褶皱分支。在重力驱动的多层褶皱中，主管层的流变性对褶皱形态有重要影响。
We study high-amplitude folding in layered rocks with two-dimensional numerical simulations. We employ the finite-element method to model shortening of an incompressible multi-layer with power-law viscous rheology. The Lagrangian numerical mesh is deformed and re-meshed to accurately follow the layer interfaces. Three settings are considered: (i) pure shearing of a confined multi-layer, (ii) simple shearing of a multi-layer above a detachment, and (iii) slump folding owing to gravity sliding. In our pure shear simulations, finite-amplitude folds always develop despite confinement and thin weak interlayers. The fold shapes can be significantly irregular, resulting from initial geometrical heterogeneities that are perturbations of the layer interfaces and differences in layer thickness. The bulk normal viscosity of the multi-layer decreases significantly with progressive folding. This structural softening decreases the bulk normal viscosities by a factor of 2–20. For simple shear, the multi-layer does not develop asymmetric fold shapes significantly. Fold axial planes in the multi-layer are mostly curved and not parallel. For slump folding, fold shapes can be significantly asymmetric exhibiting strongly curved fold axial planes and overturned fold limbs. The rheology of the competent layers has a major impact on the fold shapes for gravity-driven multi-layer folding.