The source location of mantle plumes from 3D spherical models of mantle convection
The source location of mantle plumes from 3D spherical models of mantle convection
复制标题
地幔对流三维球状模型中地幔柱的源区位置
DOI：
10.1016/j.epsl.2017.08.033
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发表时间：
2017-11-15
影响因子：
5.3
通讯作者：
Zhong, Shijie
中科院分区：
文献类型：
--
作者：
Li, Mingming;Zhong, Shijie
地幔柱被认为起源于热边界层，如地球的核幔边界（CMB），并可能导致板内火山活动，如地球表面的大火成岩省（LIP）。以往的研究表明，过去2亿年来深源LIP的原始喷发地点主要发生在最低地幔中地震观测到的大型低剪切速度区（LLSVP）的边缘上方。然而，导致LIPs分布的机制尚不清楚。LIPs的位置很大程度上取决于地幔柱的来源位置，但问题是在什么条件下地幔柱形成外部，在边缘，或以上的LLSVPs的中间。在这里，我们进行了三维地球动力学计算和理论分析，以研究地幔柱源的位置在最低地幔。我们发现，从表面到CMB的热膨胀率降低五倍，热扩散率增加两倍，这与矿物物理学研究一致，显着减少了在热化学堆之外形成的地幔柱的数量（即，LLSVP）。地幔底部地幔粘度的增加也减少了远离地幔柱的地幔柱数量。此外，我们发现，强大的羽流优先形成在/附近的边缘的桩，一般比形成在桩的顶部，这可以解释的意见，大多数LIPs发生在LLSVP边缘以上。然而，由于羽流和桩的横向运动以及桩的形态变化，一些起源于桩边缘的羽流可以稍后出现在桩的中部上方。在我们的模型中，65-70%的强羽流在离堆边缘10度以内。尽管板块运动对下地幔的大规模地幔对流具有重要的控制作用，但CMB地幔柱的形成仍主要受热边界层不稳定性的控制，这使得很难预测大多数地幔柱的地理位置。然而，我们所有的模型都显示出来自冰岛最低地幔的强烈地幔柱，支持冰岛火山作用的深地幔柱起源。(C)2017爱思唯尔B. V.保留所有权利。
Mantle plumes are thought to originate from thermal boundary layers such as Earth's core-mantle boundary (CMB), and may cause intraplate volcanism such as large igneous provinces (LIPs) on the Earth's surface. Previous studies showed that the original eruption sites of deep-sourced LIPs for the last 200 Myrs occur mostly above the margins of the seismically-observed large low shear velocity provinces (LLSVPs) in the lowermost mantle. However, the mechanism that leads to the distribution of the LIPs is not clear. The location of the LIPs is largely determined by the source location of mantle plumes, but the question is under what conditions mantle plumes form outside, at the edges, or above the middle of LLSVPs. Here, we perform 3D geodynamic calculations and theoretical analyses to study the plume source location in the lowermost mantle. We find that a factor of five decrease of thermal expansivity and a factor of two increase of thermal diffusivity from the surface to the CMB, which are consistent with mineral physics studies, significantly reduce the number of mantle plumes forming far outside of thermochemical piles (i.e., LLSVPs). An increase of mantle viscosity in the lowermost mantle also reduces number of plumes far outside of piles. In addition, we find that strong plumes preferentially form at/near the edges of piles and are generally hotter than that forming on top of piles, which may explain the observations that most LIPs occur above LLSVP margins. However, some plumes originated at pile edges can later appear above the middle of piles due to lateral movement of the plumes and piles and morphologic changes of the piles. 65-70% strong plumes are found within 10 degrees from pile edges in our models. Although plate motion exerts significant controls over the large-scale mantle convection in the lower mantle, mantle plume formation at the CMB remains largely controlled by thermal boundary layer instability which makes it difficult to predict geographic locations of most mantle plumes. However, all our models show consistently strong plumes originating from the lowermost mantle beneath Iceland, supporting a deep mantle plume origin of the Iceland volcanism. (C) 2017 Elsevier B.V. All rights reserved.