Department of Mathematics, Colorado State University, Fort Collins, CO 80523-1874;
Department of Mathematics, Texas A&M University, College Station, TX 77843-3368.
Proc Natl Acad Sci U S A. 2018 Apr 24;115(17):4351-4356. doi: 10.1073/pnas.1714125115. Epub 2018 Apr 9.
Earth's surface shows many features, of which the genesis can be understood only through their connection with processes in Earth's deep interior. Recent studies indicate that spatial geochemical patterns at oceanic islands correspond to structures in the lowermost mantle inferred from seismic tomographic models. This suggests that hot, buoyant upwellings can carry chemical heterogeneities from the deep lower mantle toward the surface, providing a window to the composition of the lowermost mantle. The exact nature of this link between surface and deep Earth remains debated and poorly understood. Using computational models, we show that subducted slabs interacting with dense thermochemical piles can trigger the ascent of hot plumes that inherit chemical gradients present in the lowermost mantle. We identify two key factors controlling this process: () If slabs induce strong lower-mantle flow toward the edges of these piles where plumes rise, the pile-facing side of the plume preferentially samples material originating from the pile, and bilaterally asymmetric chemical zoning develops. () The composition of the melt produced reflects this bilateral zoning if the overlying plate moves roughly perpendicular to the chemical gradient in the plume conduit. Our results explain some of the observed geochemical trends of oceanic islands and provide insights into how these trends may originate.
地球表面呈现出许多特征，这些特征的成因只有通过它们与地球深部内部过程的联系才能理解。最近的研究表明，大洋岛屿的空间地球化学模式与地震层析成像模型推断的下地幔最底层结构相对应。这表明，热的、上升的地幔柱可以将化学不均匀性从深部下地幔带到地表，为了解下地幔的组成提供了一个窗口。这种地表与深部地球之间的联系的确切性质仍存在争议，人们对此了解甚少。我们使用计算模型表明，与密集的热化学堆相互作用的俯冲板块可以引发热地幔柱的上升，这些地幔柱继承了存在于下地幔中的化学梯度。我们确定了控制这一过程的两个关键因素：（1）如果板块导致强烈的下地幔流流向地幔柱上升的这些堆的边缘，地幔柱面向堆的一侧优先采样来自堆的物质，并且会出现双侧不对称的化学分带。（2）如果上覆板块大致垂直于地幔柱管道中的化学梯度移动，则产生的熔体的成分反映了这种双侧分带。我们的结果解释了一些大洋岛屿的观测到的地球化学趋势，并提供了关于这些趋势如何起源的见解。
