Seismic anisotropy has been widely observed in the lower mantle transition zone and the uppermost lower mantle near several subducting slabs, which is typically attributed to the crystallographic preferred orientation (CPO) of constituent minerals. In this study, well-controlled uniaxial and simple shear deformation experiments were conducted on Mg-endmember phase D and Al-bearing phase D aggregates at 20 GPa and 500–1,000°C. Strong (0001) fabrics were observed in the uniaxially compressed samples. The CPO from all experiments, including extension and simple shear, indicated that the most active slip systems in phase D were <11$\bar{2}$0>(0001) and <10$\bar{1}$0>(0001), with a dominance of <11$\bar{2}$0>(0001). The calculated seismic velocity suggests that the deformed phase D generates positive radial seismic anisotropy (V_SH > V_SV) in both subhorizontal shearing and subvertical compression, causing significant shear-wave splitting time. Our results suggest that the observed seismic anisotropy in the mid-mantle in several cold subduction zones can be well explained by the presence of deformed phase D.

中文翻译：

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高压高温下 D 相的晶体学择优取向：对中地幔地震各向异性的影响


在下地幔过渡带和靠近几个俯冲板块的最上部下地幔中广泛观察到地震各向异性，这通常归因于组成矿物的晶体学择优取向 （CPO）。在本研究中，在 20 GPa 和 500–1,000°C 下，对 Mg 端元相 D 和含铝相 D 聚集体进行了控制良好的单轴和简单剪切变形实验。 在单轴压缩样品中观察到坚固的 （0001） 织物。所有实验（包括拉伸和简单剪切）的 CPO 表明，D 阶段最活跃的滑移系统是 <11$\bar{2}$0>（0001） 和 <10$\bar{1}$0>（0001），其中 <11$\bar{2}占主导地位$0>（0001） 的计算的地震速度表明，变形相 D 在亚水平剪切和亚垂直压缩中都产生了正的径向地震各向异性 （V_SH > V_SV），导致显著的剪切波分裂时间。我们的结果表明，在几个冷俯冲带中地幔中观察到的地震各向异性可以用变形相 D 的存在很好地解释。