Contrasting opacity of bridgmanite and ferropericlase in the lowermost mantle: Implications to radiative and electrical conductivity
Contrasting opacity of bridgmanite and ferropericlase in the lowermost mantle: Implications to radiative and electrical conductivity
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DOI：
10.1016/j.epsl.2021.116871
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发表时间：
2021-05
影响因子：
5.3
通讯作者：
S. Lobanov;F. Soubiran;N. Holtgrewe;J. Badro;Jung‐Fu Lin;A. Goncharov
中科院分区：
文献类型：
--
作者：
S. Lobanov;F. Soubiran;N. Holtgrewe;J. Badro;Jung‐Fu Lin;A. Goncharov
地球最低层的地幔显示出复杂的地质现象，这可能是由于它与地核的非均匀物理相互作用造成的。核幔相互作用的地球物理模型依赖于适当的地质材料的热导率和电导率，然而，从未在代表性的压力和温度（P-T）条件下进行过探测。在这里，我们报告的不透明度的单晶硼镁石和铁方镁石，并将其链接到他们的辐射和电导率。我们的研究结果表明，在可见光谱范围内的光吸收增强加热后，在这两种矿物，但不透明度随温度的变化率是一个因素的六高铁方镁石。因此，最低地幔中的硼镁石是中等透明的，而铁方镁石是高度不透明的。我们的测量结果支持了以前对地幔最低层低（< 1 W/m/K）且主要与温度无关的辐射传导率的间接估计。这意味着在整个地质时期，辐射机制并没有对冷却地球核心做出重大贡献。不透明的铁方镁石是导电的，介导了强烈的核幔电磁耦合，解释了在一天的长度，在中太平洋低长期地磁变化的十年内振荡，和地磁极反转的首选路径。
Earth's lowermost mantle displays complex geological phenomena that likely result from its heterogeneous physical interaction with the core. Geophysical models of core-mantle interaction rely on the thermal and electrical conductivities of appropriate geomaterials which, however, have never been probed at representative pressure and temperature (P-T) conditions. Here we report on the opacity of single crystalline bridgmanite and ferropericlase and link it to their radiative and electrical conductivities. Our results show that light absorption in the visible spectral range is enhanced upon heating in both minerals but the rate of change in opacity with temperature is a factor of six higher in ferropericlase. As a result, bridgmanite in the lowermost mantle is moderately transparent while ferropericlase is highly opaque. Our measurements support previous indirect estimates of low (< 1 W/m/K) and largely temperature-independent radiative conductivity in the lowermost mantle. This implies that the radiative mechanism has not contributed significantly to cooling the Earth's core throughout the geologic time. Opaque ferropericlase is electrically conducting and mediates strong core-mantle electromagnetic coupling, explaining the intradecadal oscillations in the length of day, low secular geomagnetic variations in Central Pacific, and the preferred paths of geomagnetic pole reversals.