褶皱岩层高角度斜交构造裂缝的形成机制

Mechanism of High-angle Fractures in Fold

构造裂缝的发育往往与褶皱、断层等构造密切相关,本文对钱塘坳陷南缘富阳–临安地区褶皱岩层中的同褶皱裂缝进行了研究。在褶皱翼部多发育与层面斜交的构造裂缝,具体表现为与层面高角度斜交构造裂缝较为发育,而与层面低角度相交的构造裂缝发育较少或不发育。其中,与层面高角度斜交的构造裂缝的特征与层间剪切作用下形成的裂缝特征不同。分析认为岩层褶皱初期主应变轴与层面平行或直交,在岩层褶皱变形过程中,主应变轴与层面高斜交。岩层外弧受到与层面不平行的拉伸,而内弧则受到与层面不平行的压缩作用。本文认为褶皱过程中应变轴的变化是导致岩层中形成与层面高角度斜交构造裂缝的主要原因。

Analysis of mechanism of synfolding fracture is the foundation of structure numerical modeling and prediction. Based on the field observation at the Fuyang-Lin’an anticline, Zhejiang, we found that the fractures are apparently high angles to bedding on the fold limbs, and we thus propose that these fractures formed during folding. Characteristics of the fractures show that the high-angle fracture was not resulted from the interlayer-slip. We propose that the high angle fractures were related to the variation of tangential and longitudinal strain during the folding. The direction of strain ellipse axes has a deviation with respect to the directions normal and tangential to the boundaries of the folded layer. In the hinge, strain ellipse axes are perpendicular to the bedding, and on the fold limbs. This mechanism could have led to the formation of high angle fracture.