MgSiO₃ majorite is the most significant endmember of the Al-deficient majorite garnets that form at depths higher than ∼400 km, in the mantle transition zone (MTZ). Here, we report elastic wave velocity measurements on polycrystalline MgSiO₃ majorite samples, up to 18.4 GPa and 2000 K by ultrasonic interferometry techniques combined with in situ X-ray diffraction measurements in a multianvil apparatus. Our data show MgSiO₃ majorite has the lowest elastic moduli among silicate garnet endmembers, under the pressure and temperature conditions of the MTZ. These new data combined with those of other garnet endmembers allowed to estimate V_P and V_S of majorite with compositions relevant to the MTZ. The results suggest that variation of MgSiO₃ component in garnet may play a role for interpreting seismic gradients atop the 410-km discontinuity while below ∼520 km, the velocity contrasts hold too low values to explain the discrepancy between mineral physics data and seismological observations.

中文翻译：

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MgSiO3 主要石榴石的声速高达 18 GPa 和 2000 K

MgSiO ₃榴是所述Al-缺陷榴石榴石的最显著端元，在深度形式大于〜400公里以上，在地幔过渡带（MTZ）。在这里，我们通过超声干涉技术结合多砧装置中的原位 X 射线衍射测量报告了对多晶MgSiO ₃主要样品的弹性波速度测量，高达 18.4 GPa 和 2000 K。我们的数据表明，在 MTZ 的压力和温度条件下，MgSiO _{3 大}长石在硅酸盐石榴石端元中具有最低的弹性模量。这些新数据与其他石榴石端元的数据相结合，可以估计V _P和V _S大多数与 MTZ 相关的成分。结果表明，石榴石中 MgSiO ₃组分的变化可能对解释 410 公里不连续性顶部的地震梯度起作用，而在 520 公里以下，速度对比值太低，无法解释矿物物理数据与地震观测之间的差异。