构造变形流变场分配多尺度数值模拟研究

流变场分配(flow field partitioning)现象在自然界高应变岩石中十分常见。传统的基于固体连续变形机制理论的变形分析中,流变场分配问题往往被忽略,致使应变带中流变场如何分配一直都缺乏深入认识。Eshelby阐述了嵌入均匀介质中的椭球体内流变场的数学方法,为探讨流变场的分配奠定了理论基础。本文从固体连续变形机制入手,重点介绍基于Eshelby理论的多尺度数值模拟思路和方法,探讨流变场分配问题。模拟结果表明:嵌入基质中的椭球体内分布的流变场主要取决于椭球体与基质间的相对流变强度,椭球体的相对流变强度越低,其变形越接近于简单剪切,且有限应变积累越快。模拟还揭示,不同流变强度的椭球体内模拟拉伸线理和面理产状的总体格局反映基质流变场特征。由此得到以下结论:(1)在流变场分配现象显著的区域,局部小尺度上应变、涡度测量分析结果无法直接揭示区域流变场运动学边界条件,对这些区域的构造变形分析必须是多尺度的;(2)基于Eshelby理论的以实质变形组构为约束的多尺度数值模拟分析,能更为合理地揭示高应变岩石中流变场的分配。

Multi-scale Numerically Modeling Flow Field Partitioning During Structural Deformation

Flow field partitioning is common in inhomogeneous rocks in high strain area. However, the classic structural analysis based on the continuum mechanics usually ignores the ways of flow field partition. Eshelby’s formulation deals with the flow field in an ellipsoid embedded in a homogeneous matrix, which established the foundation for the study of flow field partitioning. In this paper, we begin with the continuum mechanism and focus on the multi-scales structural analysis concept and method by numerical modeling based on the Eshelby’s formulation. Numerical modeling results show that the flow field in embedding ellipsoids depends on the relative rheology between the ellipsoid and matrix. Under an imposed matrix flow field, the weaker the ellipsoid is, the more noncoaxial the partitioned flow field is and the more dramatic finite strain increase. Modeling results also show that the imposed flow field can be characterized by the whole pattern composed of fabrics in all embeddings with different rheology. Thereafter, we got two conclusions: (1) in a flow field partitioning area, the traditional structural analysis by the finite and vorticity number measurements can not be directly used to explain the regional kinematical boundary conditions; (2) the traditional single-scale method is not enough to explain flow field partitioning and a multi-scale modeling limited by natural fabrics should be a feasible way to understand the kinematic boundary conditions of a regional deformation.