An investigation into compositionally heterogeneous plume clusters in 3D spherical geometry

地震学的观测显示，非洲和太平洋下方地幔最低的两大区域的地震波速低于平均水平。更多的观察推断，这些异常的原因包括热和成分的不均一性。存在一些相互竞争的假说来解释它们，每一种假说都对我们理解地幔对流模式、热输运、地球化学演化和地球内部的冷却都有重要的影响--S。在这里，我们检验了一种假设，即非洲和太平洋下面的大型地震异常是由于古老的俯冲洋壳与预计将在这些地区形成的高温上涌地幔的相互作用造成的。通过对地幔对流进行3D数值模拟研究，结合以最好地再现地震学技术固有的失真的方式处理我们的结果，我们将检验这一假设在动态上是否可行。如果是这样的话，我们将研究与之相关的重要的热和化学传输性质，将它们与竞争的想法进行比较和对比。我们将调查这一假说与许多地质、地球化学和地震学约束的吻合程度，最终目的是了解大规模地幔对流的本质。结合其他研究的进展，这项研究将朝着更大的目标努力，了解地幔对流如何导致板块构造。该项目的第一部分是进行全面的流体动力学研究，以更好地了解在存在成分不均质性的情况下与多个羽流相关的基本动力学。利用三维球面几何中的有限元数值模拟，我们将研究在外应力(即背景对流)和不同程度的成分非均质性主导的环境中，地幔热柱团的形态、随时间变化的动力学、热传输特性和预期的表面表达。其次，我们将调查成分不均匀的烟羽星团是否与地震学和地质学的观测结果一致。利用地球-S板块历史来指导热化学数值模式中的俯冲模式，我们将研究俯冲洋壳是如何分离成上升地幔区域的。通过对地球动力学模型结果的层析滤波，我们将调查与其他概念性热化学地幔模型相比，烟柱群与成分非均质性相结合的地震层析成像观测结果的拟合程度。此外，我们将研究羽状团的预期表面表达，确定它们与地球上观测到的热点岛的特征图案--S表面--的一致性。

Observations from seismology reveal two large regions of the lowermost mantle, beneath Africa and the Pacific, that exhibit slower-than-average seismic wavespeeds. Additional observations infer the cause of these anomalies to include both thermal and compositional heterogeneity. A few, competing hypotheses exist to explain them, each of which have significant consequencestoward our understanding of mantle convection patterns, thermal transport, geochemical evolution, and cooling of the Earth?s interior. Here, we test the hypothesis that the large seismic anomalies beneath Africa and the Pacific are due to the interaction of ancient, subducted oceanic crust with plumes of hot, upwelling mantle that are expected to form in these regions. By performing 3D numerical modeling studies of mantle convection, combined with processing our results in a manner that best reproduces the distortion inherent to seismological techniques, we will examine whether this hypothesis is dynamically feasible. If so, we will investigate the important thermal and chemical transport properties associated with it, comparing and contrasting them to those of competing ideas. We will investigate how well this hypothesis fits numerous geological, geochemical, and seismological constraints, with the ultimate goal of understanding the nature of large-scale mantle convection. Combined with advances from other research, this research will work toward the larger goal of understanding how mantle convection causes plate tectonics. The first part of this project is to perform a comprehensive fluid dynamical study to better understand the fundamental dynamics associated with multiple plumes in the presence of compositional heterogeneity. Using numerical finite-element modeling in 3D, spherical geometry, we will investigate the morphology, time-dependent dynamics, heat transport properties, and expected surface expression of mantle plume clusters in an environment dominated by external stress forces (i.e., background convection) and various degrees of compositional heterogeneity. Secondly, we will investigate whether compositionally-heterogeneous plume clusters are consistent with observations from seismology and geology. Employing Earth?s plate history to guide subduction patterns in thermochemical numerical models, we will investigate how subducted oceanic crust is segregated into upwelling mantle regions. Through tomographic filtering of geodynamical model results, we will investigate how well plume clusters, combined with compositional heterogeneity, fit observations of seismic tomography, compared to other conceptual thermochemical mantle models. Furthermore, we will investigate the expected surface expression of plume clusters, determining their consistency with characteristic patterns of hotspot islands observed on Earth?s surface.