Décollement folding as a mechanism for thrust‐ramp spacing
Décollement folding as a mechanism for thrust‐ramp spacing
复制标题
脱扣折叠作为推力坡道间距的机制
DOI：
10.1029/96jb00172
复制
发表时间：
1996
影响因子：
--
通讯作者：
R. C. Fletcher
中科院分区：
文献类型：
--
作者：
D. Goff;D. Wiltschko;R. C. Fletcher
探讨了早期形成的滑脱褶皱局部化冲断坡道的假说，解释了在许多山带中观测到的主要冲断坡道的规则间距。褶皱失稳模型由刚性基底、弱滑脱带和刚性逆冲层组成。该模型考虑了地形应力、同构造侵蚀和再沉积的影响，并对冲断片采用线性化幂律流变学。这种近似对于小的褶皱边缘倾角（<15°）是有效的，并且适合于分析变形开始时褶皱的波长选择。利用塞维尔褶皱冲断带怀俄明部分主要冲断坡道的间距、滑脱带和冲断片的地层厚度对模型进行了验证。褶皱主导波长与逆冲层厚度之比Ld/h2随刚性层黏度与滑脱区黏度之比R而增大，随幂律应力指数n2而减小。随着地形衰减比D的增大，在固定的n2和r下，Ld/h2增大，Absaroka和Darby逆冲片岩的可接受模型n2≥3。只有当R < 1000且冲断片的折叠过程中伴有明显的侵蚀和沉积物再沉积（D≥103）时，所需的R才会低于合理限度。因此，滑脱褶皱伴随同构造侵蚀，再沉积先于逆冲的模式与现有的观测条件是一致的。
The hypothesis that early formed decollement folds localize thrust ramps, explaining the regular spacing of major thrust ramps observed in many mountain belts, is examined. The model for folding instability consists of a rigid basement, a weak decollement zone, and a stiff thrust sheet. The model incorporates the effects of topographic stresses, and syntectonic erosion and redeposition and uses a linearized power law rheology for the thrust sheet. This approximation is valid for small angles of fold limb dip (<15°) and is appropriate for analysis of the wave-length selection of folds at the onset of deformation. The spacing of major thrust ramps and the stratigraphic thicknesses of the decollement zone and thrust sheet from the Wyoming portion of the Sevier fold-and-thrust belt are used to test the model. The ratio of the fold dominant wavelength to thrust sheet thickness, Ld/h2, increases with the ratio, R, of the viscosity of the stiff layer to that of the decollement zone and decreases with the power law stress exponent, n2. The fold amplification factor increases with both n2 and R. As the topographic decay ratio, D, increases, Ld/h2 increases at fixed n2 and R. Acceptable models for the Absaroka and Darby thrust sheets have n2 ≥ 3. Only when R < 1000 and significant erosion and redeposition of sediments accompany the folding of the thrust sheet (D ≥ 103) does the required R fall below a reasonable limit. Thus a model in which decollement folding is accompanied by syntectonic erosion and redeposition precedes thrusting is consistent with the available observational constraints.