Collaborative Research:Multidisciplinary Investigations of Structure and Deformation Beneath Southern Africa

合作研究：南部非洲地下结构和变形的多学科调查

• 批准号: 0125685
• 负责人: Aibing Li
• 金额: $ 7.48万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-01-01 至 2003-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125685&HistoricalAwards=false
• 关键词: Collaborative; Research; Multidisciplinary; Investigations; Structure

This study is providing constraints on the distribution, geometry, and magnitude of structure and deformation within and near the Archean cratons of southern Africa. A combined seismic and numerical modeling approach is used to accomplish these goals. Results from this work are providing key information regarding the accretion and subsequent evolution of stable cratonic regions, the depth distribution of mantle deformation, and the degree of coupling between tectonic plates and sublithospheric mantle. Specifically, the following issues are being addressed: 1) the 3-D seismic structure of the crust and upper mantle in Archean craton regions of southern Africa, with a focus on the depth extent of the lithosphere and on the relationship of crust and upper mantle velocities to geologically-defined tectonic boundaries; and 2) the 3-D distribution of upper mantle anisotropy in this area, and its implications for deformation in the lithosphere and flow in the sublithospheric mantle.A new two plane wave technique that inverts variations in surface wave phase and amplitude across a broadband seismic array constrains three-dimensional (3-D) crust and upper mantle seismic structure. Data for this analysis come from the 82 station Southern Africa Seismic Experiment, part of the larger-scale multidisciplinary Kaapvaal Project. Unlike traditional regional surface wave tomography where planar wavefronts and great circle source-receiver raypaths are assumed, a significant advantage of the current method is that it accounts for wavefield perturbations due to lateral heterogeneity, scattering, or multipathing along ray paths. Both isotropic and anisotropic seismic structure are determined using Rayleigh and Love waves recorded at the SASE stations, and by inverting the surface wave data with existing shear wave splitting results in this area to determine best-fitting 3-D models of seismic velocity and anisotropy beneath southern Africa.The numerical modeling component involves calculating 3-D models of mantle flow and determining the relationship of these models to observations of seismic anisotropy and deformation of the mantle lithosphere. A lithospheric keel morphology appropriate for southern Africa is constructed through integration of the results of the surface wave analyses with previous body wave results. This geometry, is used to examine models of mantle flow around the keel in which flow is driven either by horizontal plate motion or vertical mantle upwelling. Predicted anisotropy for both body and surface waves using the elastic parameters of southern Africa mantle nodules and the results of other deformation studies are calculated to evaluate the potential extent of sublithospheric mantle deformation. The results of predicted seismic anisotropy due to mantle flow will be merged with the observed seismic anisotropy to help constrain the distribution of mantle deformation beneath southern Africa.

这项研究对南部非洲的大将克拉通内外的结构和变形的分布，几何和变形的分布提供了限制。 合并的地震和数值建模方法用于实现这些目标。 这项工作的结果提供了有关稳定克拉通区域的积聚和后续演变的关键信息，地幔变形的深度分布以及构造板和跨石圈地幔之间的耦合程度。 具体而言，正在解决以下问题：1）南部非洲大帝克拉通地区的地壳和上层地壳的3-D地震结构，重点是岩石圈的深度以及地壳和上层地幔速度与地质定义的构造构造边界的关系；和2）上地幔各向异性在该区域的3-D分布及其对岩石层层层层层和流动的变形的影响。一种新的两个平面波技术，它会在宽带地震阵列跨越三维（3-D）构造和上层层层层状结构上跨表面波相和振幅中的变化。 该分析的数据来自南部82个非洲地震实验，这是大型多学科Kaapvaal项目的一部分。 与传统的区域表面波断层扫描不同，假定平面波前和大圆源接收器射线路径，当前方法的一个重要优势是，由于横向异质性，散射或沿射线路径的多态度，它解释了波场扰动。 各向同性和各向异性的地震结构都是使用雷利（Rayleigh）和记录在SASE站记录的爱波（Love Wave）确定的，并通过与现有剪切波分裂的表面波数据相反，从而在该区域中导致表面波数据，以确定最佳的地震速度模型的最佳拟合模型，并在南部非洲下方确定了这些模型的模型。地震和地幔岩石圈的变形。 通过整合表面波分析的结果与先前的身体波结果，构建了适合南部非洲的岩石圈龙骨形态。 该几何形状用于检查围绕龙骨的地幔流量模型，在该龙骨中，该龙骨由水平板运动或垂直地幔上升流动。 使用南部非洲地幔结节的弹性参数预测了身体和表面波的各向异性，并计算了其他变形研究的结果，以评估司座地幔变形的潜在范围。 由于地幔流动引起的预测的地震各向异性的结果将与观察到的地震各向异性合并，以帮助限制南部非洲南部地幔变形的分布。