中文摘要：

方解石机械e-双晶是低温、低围压和低有限应变下主要的晶体塑性变形机制。假设方解石双晶面为剪切面，双晶形成方向平行于最大有效剪应力方向，最大主应力（σ1）和最小主应力（σ3）与主晶c-轴和e-双晶法线四者共平面，与c-轴夹角分别为71°和19°，与e-双晶面夹角为45°，确定方解石主晶和双晶的晶体学方位即可确定主应力方向。电子背散射衍射（electron backscatter diffraction，简称EBSD）技术可以精确测定方解石主晶和双晶的晶体学参数。从样品野外采集、室内薄片切制、EBSD数据获取、数据处理等方面详细介绍了利用方解石双晶恢复古应力方向的方法。

英文摘要：

Mechanical e twinning of calcite is the dominant crystal-plastic deformation at low temperature, low confining pressure and low finite strain. The twin plane was assumed as a shear plane and the twin di- rection was parallel to the maximum resolved shear stress （RSS）. Orientation of calcite twins can be corre- lated to stress orientation. The electron backscatter diffraction （EBSD） technique is used to check precise crystal orientations of calcite and its twins in calcite vein, which was collected from Lower Triassic lime- stone of Weiyuan uplift, Sichuan Basin. Crystallographic data, including c-axis of host calcite, e （011（--） 2） of host crystal and twinning plane, were tested through automatic SEM-based EBSD after thin oriented sections were carefully polished. The paleostress orientations, resulted in e-twinning, were determined on the basis of orientation relationships among twin planes, c-axes and shear direction.