鄂尔多斯盆地西缘北段逆冲推覆带缩短量分形研究

鄂尔多斯盆地西缘发育南北向展布的逆冲推覆构造带,通过求其地层的缩短量和正确估计应变的分布,可以定量地揭示岩层的变形特征,从而对逆冲推覆构造形成的动力学机制做出客观的判断。由于小尺度褶皱和断层的发育,采用传统的平衡地质剖面方法计算其缩短量往往存在较大的误差,因此,采用非线性的方法———分形几何学求取逆冲推覆构造的缩短量,将剖面中某一地层界线作为二维平面中的一条复杂曲线,求其分维数D,进而计算构造变形的总缩短量。以鄂尔多斯盆地西缘北段桌子山地区AB地质剖面为例进行了应用研究。计算结果表明,桌子山AB地质剖面的缩短量为8 km,应变为22.2%,其中由小尺度褶皱和断层引起的的缩短量为1 km。

Fractal Theory Applied to the Study of Cross-section Shortening Amount in Northern Thrust-nappe Belt of the Western Ordos Basin

A NS-striking thrust-nappe belt is developed in the western Ordos Basin,through the cross-section shortening amount calculated and the strain distribution of the strata exactly estimated,the deformation(chara-)(cteristics) of the strata have been quantitatively revealed,therefore the dynamic mechanism of the thrust-nappe was recognized.Due to the development of small-scale folds and faults,a bigger error of the shortening amount may appear using traditional cross-section balancing.In this study,a nonlinear method called fractal theory has been adopted to calculate the cross-section shortening amount.Through this method,a bedded plane can be(regarded) as a complex curve in the two-dimension plane,and the fractal dimension D can be calculated,furthermore,the total amount of cross-section shortening can be obtained.A case study of geological profile AB across Zhuozishan which is located in the north of the western Ordos Basin indicates that the shortening amount and strain are 8 km and 22.2% respectively,and the shortening amount caused by the small-scale folds and faults is 1 km.