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Seismological constraints on a possible plume root at the core-mantle boundary

机译：地幔边界可能羽状根的地震学约束

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Recent seismological discoveries have indicated that the Earth's core - mantle boundary is far more complex than a simple boundary between the molten outer core and the silicate mantle. Instead, its structural complexities probably rival those of the Earth's crust(1). Some regions of the lowermost mantle have been observed to have seismic wave speed reductions of at least 10 per cent(2-7), which appear not to be global in extent(7-9). Here we present robust evidence for an 8.5-km- thick and similar to 50-km-wide pocket of dense, partially molten material at the core - mantle boundary east of Australia. Array analyses of an anomalous precursor to the reflected seismic wave ScP reveal compressional and shear-wave velocity reductions of 8 and 25 per cent, respectively, and a 10 per cent increase in density of the partially molten aggregate. Seismological data are incompatible with a basal layer composed of pure melt, and thus require a mechanism to prevent downward percolation of dense melt within the layer. This may be possible by trapping of melt by cumulus crystal growth following melt drainage from an anomalously hot overlying region of the lowermost mantle. This magmatic evolution and the resulting cumulate structure seem to be associated with overlying thermal instabilities, and thus may mark a root zone of an upwelling plume.
机译：最近的地震发现表明，地心-地幔边界要比熔融外核和硅酸盐地幔之间的简单边界复杂得多。取而代之的是，它的结构复杂性可能会与地壳相媲美（1）。观察到最低地幔的某些区域地震波速度降低了至少10％（2-7），在范围上似乎不是全球性的（7-9）。在这里，我们为澳大利亚东部以东的地幔边界的核心部分约8.5公里厚，约50公里宽的稠密，部分熔融的物质袋提供了有力的证据。对反射的地震波ScP的异常前兆进行的阵列分析表明，压缩波和剪切波速度分别降低了8％和25％，部分熔融的骨料的密度增加了10％。地震数据与由纯熔体组成的基底层不兼容，因此需要一种机制来防止该层中的浓熔体向下渗透。这可能是由于熔体从最低地幔的异常热的上覆区域排出后，由于积云状晶体的生长而捕获熔体而实现的。这种岩浆演化和由此形成的累积结构似乎与上覆的热不稳定性有关，因此可能标志着上升流羽的根部区域。

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