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

3D 球形几何中成分异质羽簇的研究

• 批准号: 0838565
• 负责人: Allen McNamara
• 金额: $ 24.76万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-02-01 至 2013-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838565&HistoricalAwards=false
• 关键词: investigation; into; compositionally; heterogeneous; plume

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.

地震学观测揭示了非洲和太平洋下方地幔下层的两大区域，其地震波速低于平均水平。其他观察结果推断这些异常的原因包括热和成分的异质性。存在一些相互竞争的假设来解释它们，每个假设都对我们理解地幔对流模式、热传输、地球化学演化和地球内部冷却产生重大影响。在这里，我们检验了这样一个假设：非洲和太平洋下方的大型地震异常是由于古代俯冲洋壳与预计在这些地区形成的热上升地幔羽流的相互作用造成的。通过对地幔对流进行 3D 数值模拟研究，并结合以最好地再现地震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，我们将研究与之相关的重要热和化学传输特性，将它们与竞争性想法进行比较和对比。我们将研究这一假设与众多地质、地球化学和地震学约束的吻合程度，最终目标是了解大规模地幔对流的本质。结合其他研究的进展，这项研究将致力于实现了解地幔对流如何导致板块构造的更大目标。该项目的第一部分是进行全面的流体动力学研究，以更好地了解在成分不均匀的情况下与多个羽流相关的基本动力学。使用 3D、球面几何中的数值有限元建模，我们将研究在外部应力（即背景对流）和不同程度的成分异质性主导的环境中地幔羽流簇的形态、随时间变化的动力学、热传输特性和预期的表面表达。其次，我们将研究成分异质的羽流簇是否与地震学和地质学的观测结果一致。利用地球板块的历史来指导热化学数值模型中的俯冲模式，我们将研究俯冲的洋壳如何被分离成上涌的地幔区域。通过对地球动力学模型结果进行层析成像过滤，我们将研究与其他概念性热化学地幔模型相比，地幔柱簇与成分异质性相结合如何更好地拟合地震层析成像观测结果。此外，我们将研究羽流团的预期表面表达，确定它们与地球表面观察到的热点岛特征模式的一致性。