The influence of deep mantle compositional heterogeneity on Earth's thermal evolution
The influence of deep mantle compositional heterogeneity on Earth's thermal evolution
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DOI：
10.1016/j.epsl.2018.08.009
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发表时间：
2018-10
影响因子：
5.3
通讯作者：
Mingming Li;A. Mcnamara
中科院分区：
文献类型：
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作者：
Mingming Li;A. Mcnamara
地震观测到的大的低剪切速度省在地球的最低地幔已被假设为造成的热化学堆的成分不同，更原始的材料，这可能是地球的早期分化的残余。然而，一个关键的问题是，地球的热演化是如何影响的长期存在的大规模组成的不均匀性在最低的地幔。在这里，我们进行地球动力学计算，调查的时间演变的大规模组成的不均匀性的形态和它对地球的长期热演化的影响。我们的研究结果表明，全球层的本质致密的材料在最低的地幔显着抑制CMB热通量，这导致更快的冷却的背景地幔相对于一个等化学地幔。随着背景地幔冷却，内在致密的物质逐渐被冷的下行流推入孤立的热化学堆。桩的大小也随着时间的推移，由于夹带到背景地幔桩材料。内禀致密物质堆积的形态变化最终导致CMB热通量的逐渐增加，这显著降低了地幔的冷却速率。
The seismically-observed large low shear velocity provinces in the Earth's lowermost mantle have been hypothesized to be caused by thermochemical piles of compositionally distinct, more-primitive material which may be remnants of Earth's early differentiation. However, one critical question is how the Earth's thermal evolution is affected by the long-term presence of the large-scale compositional heterogeneity in the lowermost mantle. Here, we perform geodynamical calculations to investigate the time evolution of the morphology of large-scale compositional heterogeneity and its influence on the Earth's long-term thermal evolution. Our results show that a global layer of intrinsically dense material in the lowermost mantle significantly suppresses the CMB heat flux, which leads to faster cooling of the background mantle relative to an isochemical mantle. As the background mantle cools, the intrinsically dense material is gradually pushed into isolated thermochemical piles by cold downwellings. The size of the piles also decreases with time due to entraining of pile material into the background mantle. The morphologic change of the accumulations of intrinsic dense material eventually causes a gradual increase of CMB heat flux, which significantly reduces the cooling rate of Earth's mantle.