新疆巴楚地区共轭膝折带的物理模拟研究

Physical Modeling for Kink Bands in the Bachu Uplift Belt in Tarim Basin,China

本文以塔里木地区巴楚隆起地层及构造为原型,设计了3层结构模型:底部为黄油层,作为滑脱层;中间为黏土层,模拟该地区膝折发育的地层;上部为细砂层,模拟上部松散沉积。研究了挤压速率、黄油层厚度、砂层厚度等因素对共轭膝折带形成的影响,对共轭膝折带的形成和演化阶段进行分析。结果表明:形成膝折带的有利条件是较厚的基底滑脱单元、上覆压力,中等挤压速率;在基底滑脱单元较厚的条件下,首先在能干单元的边部发育逆冲断裂体系,随后在能干单元的中央位置发育膝折型褶皱;膝折构造产生之后,随着挤压变形的持续进行,将产生调节断裂;在持续的挤压应变环境中,膝折型褶皱的演变基本经历了宽缓褶皱→紧闭褶皱→突起构造变形或断层调节变形。

Kink-bands are tabular fold-zones that commonly occur as conjugate sets. The Bachu uplift belt in the western segment of the Tazhong is interpreted to be constituted by series of kink-style detachment folds. A 3-layer structure model was designed based on the segment and deformation of the Bachu uplift：a butter layer as a slip layer at the bottom part; 8 or 10 layers of clay in the middle part to simulate the kink-bands; a fine sand layer in the upper part to simulate the deformation of the loose sediments. The influence of compression rate,the thickness of butter layer and sand layer are investigated. The results show that 1） the advantages to form a kink band include a thicker layer of detachment segment,overburden pressure and a moderate compression rate; 2）with the presence of thicker layered detachment segment,thrust faults will first produce in the competent layer edges,then the conjugate kink-band in the middle of the competent layer; 3）three distinct stages of kinking are identified,i.e.,relief folds,closed fold and box-shaped lift-off fold or a little thrust fault to accommodate further deformation.