中生代川东褶皱带的数值模拟:滑脱带深度对地台盖层褶皱型式的影响

Numerical Modeling of the Mesozoic East Sichuan Fold Belt: Influence of Detachment Depth on the Fold Pattern in the Platform Cover

纵弯褶皱作用是中生代川东褶皱带的主导宏观变形机制，造成了区内各褶皱近等间距相间排列，褶皱轴延伸稳定，区域性逆冲断层不发育。本文利用FLAC6．0软件模拟了在不同变形基底厚度的情形下该褶皱带的形成过程。无论变形基底厚度如何变化，盖层浅处（三叠系顶部褶皱面）始终出现隔槽式褶皱，意味着影响褶皱发育的滑脱带在隔档式和隔槽式褶皱区是不一样的，分别处于盖层内和基底内。随着变形基底厚度加大，盖层深处（志留系顶部褶皱面）由隔档式褶皱逐渐转变成隔槽式褶皱，尤其是在变形基底厚度为3-4km的情形下，盖层深部出现的褶皱型式与真实的隔槽式褶皱非常相似。在志留系为滑脱带的情形下，盖层浅部呈现出与真实的隔档式褶皱相似的形态特征。这些认识得到了该区地震反射剖面解释成果的证实。

Buckling is the major mesoscopic deformation mechanism of the Mesozoic East Sichuan fold belt, which responsible for the approximately spaced pattern of folds, the long, stable extent of folds, and underdevelopment of regional thrusts in the fold belt. This paper uses FLAC6.0 software to simulate the formation of the fold belt for a variable detached basement thickness （DBT）. No matter how the DBT is set, only trough-like folds form in the shallow cover, or the fold surface of the top layers of the Triassic strata. This suggests that the difference in depth of the detachment zone （DZ） throughout the belt： the DZ seems to occur in the cover in the area of ridge-like folds and in the basement in the area of trough-like folds. With the increase of the DBT, ridge-like folds are gradually replaced by trough-like folds in the deep cover, or the fold surface of the bottom layers of the Silurian strata. For a DBT value of 3-4 km, the simulated folds in the deep cover resemble those observed in the area of trough-like folds. When the DZ occurs in the Silurian strata, the simulated folds in the shallow cover have a similar geometry to those in the area of ridge-like folds. These inferences are confirmed in the interpreted seismic reflection profiles across the fold belt.