Naturally deformed dunite cores with a preexisting crystallographic preferred orientation (CPO), collected from a shear zone in the Josephine peridotite (southwest Oregon, USA), were deformed experimentally in triaxial compression. The compression axis was varied relative to the CPO geometry to measure the anisotropy in viscosity of these rocks. Deformation experiments were performed in a gas-medium apparatus at three constant displacement-rate steps, at a temperature of 1250 °C and a confining pressure of 300 MPa. Cores were dehydrated at 1200 °C in a controlled CO/CO₂ atmosphere prior to deformation to achieve nominally dry conditions. Data from individual experiments were fit by a power-law, yielding a stress exponent of n ≈ 3.6, indicative of deformation by dislocation creep. The maximum difference in viscosity was a factor of 2.6 at constant stress. The CPO of the olivine grains was measured after deformation by electron backscatter diffraction (EBSD). The flow stress correlated with the mean Schmid factor (or resolved shear stress) on the easiest dislocation slip systems, calculated from grain orientations determined from EBSD analyses. Analysis of our data with a simplified effective-medium model, which incorporated constraints from published single-crystal flow laws, demonstrated the link between CPO and anisotropy in viscosity. Predictions from viscoplastic self-consistent (VPSC) models support our simplified analysis of the measured anisotropy.

从约瑟芬橄榄岩（美国俄勒冈州西南部）的剪切带中收集的具有预先存在的晶体择优取向 (CPO) 的自然变形的单晶岩核在三轴压缩下进行了实验变形。压缩轴相对于 CPO 几何形状发生变化，以测量这些岩石的粘度各向异性。变形实验在气体介质装置中以三个恒定位移速率步骤进行，温度为 1250 °C，围压为 300 MPa。岩心在变形前在受控的 CO/CO ₂气氛中在 1200 °C 下脱水，以达到名义上的干燥条件。来自单个实验的数据通过幂律拟合，产生n的应力指数 ≈ 3.6，表示位错蠕变引起的变形。在恒定应力下，粘度的最大差异为 2.6 倍。橄榄石晶粒的 CPO 在变形后通过电子背散射衍射 (EBSD) 测量。流动应力与最简单的位错滑移系统上的平均施密德因子（或解析剪切应力）相关，根据 EBSD 分析确定的晶粒取向计算。使用简化的有效介质模型分析我们的数据，该模型结合了已发表的单晶流动定律的约束，证明了 CPO 与粘度各向异性之间的联系。粘塑性自洽 (VPSC) 模型的预测支持我们对测量的各向异性的简化分析。