Recent seismic studies suggested an anisotropic Mantle Transition Zone (MTZ) in areas adjacent to subducted slabs. Wadsleyite is the main anisotropy contributor in the upper MTZ, therefore the interpretation of these seismic observations requires the knowledge of single-crystal elastic moduli ($C_{ij}s$) and the deformation-induced lattice preferred orientation (LPO) of wadsleyite. Wadsleyite can host up to 3 wt% water in its crystal structure as point defects in the form of hydroxyl groups, however, the combined effect of water content, Fe content, and pressure on the $C_{ij}s$ of wadsleyite remains unclear. In this study, we measured the high-pressure single-crystal elasticity of a synthetic hydrous Fe-bearing wadsleyite (0.14 (4) wt% water, Fe#=9.4, Fe³⁺/ΣFe=0.3) up to 18.2 (2) GPa. In combination with previous experimental data, we separated the effects of pressure, water, and Fe contents on the $C_{ij}s$ and intrinsic elastic anisotropy of wadsleyite. Our results suggest that the intrinsic elastic anisotropy of wadsleyite decreases with pressure, water, and Fe contents. At 15 GPa, increasing the water content by 0.1 wt% or Fe# by 1 decreases the $V_{\mathrm{P}}$ and $V_{\mathrm{S}}$ anisotropy of wadsleyite by ∼1.1-1.3%, and ∼0.8-1.3% in average, respectively. Combining the LPO determined in previous deformation experiments, we modeled the seismic anisotropy in the upper MTZ generated by a sub-vertical mantle flow near cold subducted slabs and a sub-horizontal mantle flow in the ambient mantle. In both scenarios, the LPO of wadsleyite leads to V_SV (vertically polarized shear wave velocity) > V_SH (horizontally polarized shear wave velocity). Our results suggest that wadsleyite may account for a weak anisotropic MTZ (<1%) on the global scale. Considering the fact that water decreases the elastic anisotropy but promotes LPO of wadsleyite, seismic anisotropy may not be a good water sensor in the upper MTZ.

最近的地震研究表明，在俯冲板块附近存在各向异性的地幔过渡带（MTZ）。沃兹利岩是上层MTZ的主要各向异性贡献者，因此对这些地震观测的解释需要了解单晶弹性模量（$C_{\mathrm{一世}Ĵ}s$）和变形诱导的硅钙石晶格优先取向（LPO）。硅灰石在其晶体结构中最多可容纳3 wt％的水，以羟基的形式作为点缺陷，但是，水含量，铁含量和压力对硅酸盐的综合影响$C_{\mathrm{一世}Ĵ}s$沃兹利石的含量仍不清楚。在这项研究中，我们测量了合成含水含Fe的辉石矿（水含量为0.14（4）wt％，Fe＃= 9.4，Fe ^3+/ ΣFe = 0.3）至18.2（2）的高压单晶弹性。GPa。结合以前的实验数据，我们分离了压力，水和铁含量对合金的影响。$C_{\mathrm{一世}Ĵ}s$硅钙石的内在和弹性各向异性。我们的研究结果表明，硅镁石的固有弹性各向异性随压力，水和铁含量的降低而降低。在15 GPa时，将水含量增加0.1 wt％或将Fe＃增加1会降低${\mathrm{伏特}}_{\mathrm{P}}$ 和 ${\mathrm{伏特}}_{\mathrm{小号}}$硅灰石的平均各向异性分别为约1.1-1.3％和约0.8-1.3％。结合先前变形实验中确定的LPO，我们对冷俯冲板附近的亚垂直地幔流和周围地幔中的亚水平地幔流生成的上部MTZ的地震各向异性进行了建模。在这两种情况下，钠钙铝石的LPO均会导致V _SV（垂直极化剪切波速度）> V _SH（水平极化剪切波速度）。我们的结果表明，辉石岩可能是全球范围内弱的各向异性MTZ（<1％）。考虑到水降低了弹性各向异性，但增加了辉绿岩的LPO的事实，地震各向异性可能不是MTZ上部的良好水传感器。