Tidal tomography constrains Earth's deep-mantle buoyancy
Tidal tomography constrains Earth's deep-mantle buoyancy
复制标题
DOI：
10.1038/nature24452
复制
发表时间：
2017-11-16
期刊：
影响因子：
64.8
通讯作者：
Al-Attar, David
中科院分区：
文献类型：
--
作者：
Lau, Harriet C. P.;Mitrovica, Jerry X.;Al-Attar, David
地球的体潮-也被称为固体地球潮，由月球和太阳的引力引起的固体地球表面的位移-对非洲和太平洋下面的两个大低剪切速度省（LLSVP）的密度很敏感。这些巨大的区域从地幔底部向上延伸约1 000公里，其浮力在地球物理学界仍有激烈的争论。在这里，我们使用潮汐层析成像来约束地球的深地幔浮力来自全球定位系统（GPS）的半日体潮变形的测量。使用概率的方法，我们表明，在底部的三分之二的两个LLSVP的平均密度是约0.5%，高于平均地幔密度在这个深度范围内（即，其平均浮力为负0.5%），虽然这种异常可能集中在非常底部的地幔。我们的结论是，这些结构的浮力是由高密度的化学成分，可能与俯冲的海洋板块或与地球的形成有关的原始材料的富集。由于地幔的动力学是由密度变化驱动的，我们的结果对LLSVP的稳定性和地球系统的长期演化具有重要的动力学意义。
Earth's body tide-also known as the solid Earth tide, the displacement of the solid Earth's surface caused by gravitational forces from the Moon and the Sun-is sensitive to the density of the two Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific. These massive regions extend approximately 1,000 kilometres upward from the base of the mantle and their buoyancy remains actively debated within the geophysical community. Here we use tidal tomography to constrain Earth's deep-mantle buoyancy derived from Global Positioning System (GPS)-based measurements of semi-diurnal body tide deformation. Using a probabilistic approach, we show that across the bottom two-thirds of the two LLSVPs the mean density is about 0.5 per cent higher than the average mantle density across this depth range (that is, its mean buoyancy is minus 0.5 per cent), although this anomaly may be concentrated towards the very base of the mantle. We conclude that the buoyancy of these structures is dominated by the enrichment of high-density chemical components, probably related to subducted oceanic plates or primordial material associated with Earth's formation. Because the dynamics of the mantle is driven by density variations, our result has important dynamical implications for the stability of the LLSVPs and the long-term evolution of the Earth system.