Numerical models of Alpine-type cover nappes
Numerical models of Alpine-type cover nappes
复制标题
阿尔卑斯型覆盖层的数值模型
DOI：
10.1016/s0040-1951(03)00097-0
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发表时间：
2003
期刊：
影响因子：
2.9
通讯作者：
O. Pfiffner
中科院分区：
文献类型：
--
作者：
S. Wissing;S. Ellis;O. Pfiffner
我们用二维有限元程序研究了继承几何的盆地派生的阿尔卑斯山盖层推覆的动力学。模型研究是以瑞士阿尔卑斯山的Klippen推覆构造为基础的，该推覆构造在基底蒸发岩水平上方从基底分离，并以薄皮构造风格输送到前陆。有限元模型被用来检验特定特征对模型中结构风格发展的影响。关于楔形体几何形状和力学性能影响的实验显示了波长模式和结构的详细修改，但不改变总的趋势。研究了不同层厚、多层岩石以及下伏基底和沉积物内部的横向非均质性对变形方式的控制作用。结果表明，盖层推覆中褶皱冲断构造的发育受控于弱滑脱层的厚度和各层的相对厚度(厚度比n=弱/强层厚度)。如果n>；1形成波长可变且不规则的褶皱，如果0.5<；n<；1，则发育规则间距的滑脱褶皱。当n≤为0.5时，观察到叠瓦状逆冲推覆作用。基底和岩层的横向非均质性导致了应力集中，显著控制了演化褶皱和逆冲的几何形状，并抑制了由粘度对比和厚度比预测的优势波长的增长。
We investigate the dynamics of Alpine cover nappes derived from basins with inherited geometries using a two-dimensional finite element code. Model studies are based on a natural analogue, the Klippen nappe in the Swiss Alps, which detached from the basement over a basal evaporite horizon and was transported onto the foreland in a thin-skinned tectonic style. Finite-element models are used to examine the influence of specific features on the structural style developing in the models. Experiments dealing with the influence of wedge geometry and mechanical properties show modifications in wavelength patterns and structures in detail but do not change the general trends. The control that different layer thicknesses, multilayered rocks and lateral heterogeneities in the underlying basement and within the sediments have on the style of deformation is investigated. Results suggest that the development of fold versus thrust structures in a cover nappe is controlled by the thickness of the weak detachment horizon and the relative thickness of individual layers (thickness ratio n=thickness of weak/thickness of strong layer). If n>1, folds with variable and irregular wavelengths form, if 0.5<n<1, regularly spaced detachment folds develop. Imbricate thrusting is observed for values of n≤0.5. Lateral heterogeneities in both basement and rock formations cause stress concentrations, control the geometry of the evolving folds and thrusts significantly and inhibit the growth of dominant wavelengths predicted by viscosity contrasts and thickness ratios.