Asthenospheric shear causes some minerals, particularly olivine, to develop anisotropic textures that can be detected seismically. In laboratory experiments, these textures are also associated with anisotropic viscous behavior, which should be important for geodynamic processes. To examine the role of anisotropic viscosity for asthenospheric deformation, we developed a numerical model of coupled anisotropic texture development and anisotropic viscosity, both calibrated with laboratory measurements of olivine aggregates. This model characterizes the time‐dependent coupling between large‐scale formation of lattice‐preferred orientation (i.e., texture) and changes in asthenospheric viscosity for a series of simple deformation paths that represent upper mantle geodynamic processes. We find that texture development beneath a moving surface plate tends to align the a axes of olivine into the plate motion direction, which weakens the effective viscosity in this direction and increases plate velocity for a given driving force. Our models indicate that the effective viscosity increases for shear in the horizontal direction perpendicular to the a axes. This increase should slow plate motions and new texture development in this perpendicular direction and could impede changes to the plate motion direction for tens of millions of years. However, the same well‐developed asthenospheric texture may foster subduction initiation perpendicular to the plate motion and deformations related to transform faults, as shearing on vertical planes seems to be favored across a sublithospheric olivine texture. These end‐member cases examining shear deformation in the presence of a well‐formed asthenospheric texture illustrate the importance of the mean olivine orientation, and its associated viscous anisotropy, for a variety of geodynamic processes.

中文翻译：

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上地幔演化中的各向异性各向异性及其地球动力学意义

流变层的剪切力导致某些矿物，特别是橄榄石，形成各向异性的纹理，可以通过地震检测到。在实验室实验中，这些纹理还与各向异性的粘性行为有关，这对于地球动力学过程应该很重要。为了检查各向异性粘度对软流圈变形的作用，我们开发了耦合的各向异性织构发展和各向异性粘度的数值模型，二者均通过实验室测量橄榄石骨料进行校准。该模型描述了代表上地幔地球动力学过程的一系列简单变形路径的​​大尺寸晶格优先取向（即纹理）的形成与软流层粘度变化之间的时间依赖性。一个轴橄榄石到板运动方向，这削弱了有效粘度在对于给定的驱动力这个方向并增加板速度。我们的模型表明，在垂直于a的水平方向上剪切的有效粘度增加轴。这种增加将减缓印版运动和沿该垂直方向的新纹理的发展，并可能在数千万年内阻止印版运动方向的变化。但是，同样发达的软流圈结构可能会促进垂直于板块运动的俯冲起始以及与变形断层有关的变形，因为似乎在岩石圈下的橄榄石纹理上倾向于在垂直平面上剪切。这些最终成员在存在良好形成的软流圈结构的情况下检查剪切变形的案例说明了平均橄榄石取向及其相关的粘性各向异性对于各种地球动力学过程的重要性。