Abstract: Numerical viscoelastic modeling for porphyroclast rotation in ductile shear zones is done by a viscoelastic finite element program based on detailed investigation to three ductile shear zones, the Taihangshan Mountains, North China. In this model porphyroclast (garnet) is assumed as isotropic elastic material with small elastic deformation, while the matrix (quartz, feldspar) as viscous fluid (Maxwell material) which has increasing deformation with time. The viscosity of matrix is supposed to be 10²⁰Pa·s, which is varied in alternating models to discuss the effect of visvosity on deformation because it is hard to estimate the true value of the crust. Some results acquired by computer calculation show that the rigid garnet porphyroclasts can rotate as the matrix flows, and the rotational degree depends on the shear stress, shear strain, ratio of porphroclasts to matrix and the locations of porphyroclasts in the zone.

Key words: shear zones, porphyroclast, Maxwell body, numerical modeling, Taihangshan Mountains

摘要： 采用粘弹性力学分析程序对太行山阜平地区剪切带中斑晶旋转问题进行了有限元数值模拟。在计算模型中假定：石榴石斑晶为弹性材料，在应力作用下只产生很小的弹性变形；石英、长石质的基质部分为粘弹性材料，它具有随时间变形不断增大的特性。计算结果显示：沿剪切力方向的最大位移能达到模型宽度的3～4倍，相当于简单剪切的角度达到70°以上，斑晶的最大旋转角度能达到60°左右。这样的变形量级已经十分接近野外实际情况。由于目前地壳物质的粘度值基本上是通过间接推测得到的，其可信度较低，因此文中还讨论了基质的粘度变化对变形和应力的影响，分别取了7个不同量级的粘度值(10¹⁷～10²³ Pa·s)进行计算。

关键词: 剪切带, 斑晶, Maxwell体, 有限元数值模拟, 太行山