Evolving morphology of crustal accumulations in Earth's lowermost mantle
Evolving morphology of crustal accumulations in Earth's lowermost mantle
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DOI：
10.1016/j.epsl.2021.117265
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发表时间：
2021-11-04
影响因子：
5.3
通讯作者：
McNamara, Allen K.
中科院分区：
文献类型：
--
作者：
Li, Mingming;McNamara, Allen K.
俯冲洋壳是地幔成分不均一性的主要来源之一。有人提出，俯冲洋壳可能聚集在地幔底部，导致地震观测到的大的低剪切速度省(LLSVPs)。验证这一假设需要更好地了解最低地幔中地壳堆积的形态。在这里，通过地球动力学模拟实验，我们发现厚厚的俯冲洋壳可以聚集成高度接近核幔边界(CMB)以上1000公里的热化学堆积，并且地壳堆积具有典型的化学模糊的顶部边界和分层的内部。随着地幔冷却，洋壳变薄，CMB上的堆积变得更加困难，以前的地壳堆积逐渐变小，获得了尖锐的顶部边界和相对均匀的内部。我们的结果表明，如果今天的LLSVP主要是由俯冲洋壳的积累引起的，那么它们可能产生于俯冲洋壳较厚的早期地球热区，它们可能从化学上模糊的顶部边界和分层的内部开始，逐渐发展为化学上更尖锐的顶部边界和更均匀的内部。(C)2021年爱思唯尔B.V.保留所有权利。
Subducted oceanic crust is one of the major sources of compositional heterogeneity in Earth's mantle. It has been proposed that subducted oceanic crust may accumulate at the bottom of the Earth's mantle and cause the seismically-observed, Large Low Shear Velocity Provinces (LLSVPs). Testing this hypothesis requires a better understanding of the morphology of the crustal accumulations in the lowermost mantle. Here, through geodynamic modeling experiments, we find that thick subducted oceanic crust could accumulate into thermochemical piles with a height up to similar to 1000 km above the core-mantle boundary (CMB), and the crustal accumulations typically have chemically fuzzy top boundaries and stratified interiors. As the oceanic crust thins with mantle cooling, it becomes more difficult to accumulate on the CMB, and the previous crustal accumulations gradually become smaller in size and gain sharp top boundaries and relatively homogeneous interiors. Our results suggest that if the present-day LLSVPs are mainly caused by the accumulations of subducted oceanic crust, they may be produced in the early hotter Earth when subducted oceanic crust may be thicker, and they may start with chemically fuzzy top boundaries and stratified interiors and gradually develop into chemically sharper top boundaries and more homogenized interiors. (C) 2021 Elsevier B.V. All rights reserved.