Numerical investigation of deformation mechanics in fold‐and‐thrust belts: Influence of rheology of single and multiple décollements
Numerical investigation of deformation mechanics in fold‐and‐thrust belts: Influence of rheology of single and multiple décollements
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DOI：
10.1029/2011tc003047
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发表时间：
2012-06
期刊：
影响因子：
4.2
通讯作者：
J. Ruh;B. Kaus;J. Burg
中科院分区：
文献类型：
--
作者：
J. Ruh;B. Kaus;J. Burg
与辐合构造相关的薄皮褶皱和逆冲带，是通过沿着较弱的基底地层（通常由含水饱和的页岩层或低粘度盐层形成）刮掉岩石层序而形成的。本文采用粘弹塑性流变的二维有限元模型，研究了覆在不同类型杂岩上的褶皱带和逆冲带的构造演化。此外，还研究了地层柱中多个弱层的影响。模型页岩油层为摩擦层，摩擦角较小，为覆盖层。模型盐层表现为线性粘性，由于较低的粘度作为覆盖序列，或具有幂律流变。将单粘性介质模拟与关于断裂与褶皱的解析解进行了比较。研究结果表明，具有单一摩擦基底的褶皱和冲断带产生了从基底向地表延伸的冲断系统。推力坡道之间的间距取决于盖层的厚度。具有附加低摩擦层的模拟结构的演化取决于基层和互序层之间的强度关系。如果层序内沉积较弱，则会发生构造底沉积和反形式堆积。在模型的正面部分，变形仅限于上部，并发生瓦叠，其波长取决于中间弱层的深度。黏度为1018 Pa⋅s的“盐”质结导致孤立的盒状褶皱（脱离褶皱）。多个盐层（1018 Pa⋅s）导致长波长折叠。我们对摩擦和粘性介质的研究结果与Mohr - Coulomb型临界楔形理论基本一致。
Thin‐skinned fold‐and‐thrust belts related to convergence tectonics develop by scraping off a rock sequence along a weaker basal décollement often formed by water‐saturated shale layers or low‐viscosity salt horizons. A two‐dimensional finite element model with a viscoelastoplastic rheology is used to investigate the structural evolution of fold‐and‐thrust belts overlying different types of décollements. In addition, the influence of multiple weak layers in the stratigraphic column is studied. Model shale décollements are frictional, with lower friction angles as the cover sequence. Model salt layers behave linear viscous, due to a lower viscosity as the cover sequence, or with a power law rheology. Single viscous décollement simulations have been compared to an analytical solution concerning faulting versus folding. Results show that fold‐and‐thrust belts with a single frictional basal décollement generate thrust systems ramping from the décollement to the surface. Spacing between thrust ramps depends on the thickness of the cover sequence. The structural evolution of simulations with an additional low‐frictional layer depends on the strength relationship between the basal and the intersequential décollement. Tectonic underplating and antiformal stacking occur if the within‐sequence décollement is weaker. In the frontal part of models, deformation is restricted to the upper part and imbrication occurs with a wavelength depending on the depth of the intermediate weak layer. “Salt” décollement with a viscosity of 1018 Pa⋅s leads to isolated box folds (detachment folds). Multiple salt layers (1018 Pa⋅s) result in long‐wavelength folding. Our results for both frictional and viscous décollements are in bulk agreement with the Mohr‐Coulomb type, critical wedge theory.