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: 0338430
• 负责人: Aibing Li
• 金额: $ 5.56万
• 依托单位: University of Houston
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-01-01 至 2004-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0338430&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.

这项研究为南部非洲太古宙克拉通内部和附近的结构和变形的分布、几何形状以及大小提供了限制。 地震和数值模拟相结合的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增生和后续演化、地幔变形的深度分布以及构造板块与岩石圈下地幔之间的耦合程度的关键信息。 具体来说，正在解决以下问题：1）南部非洲太古代克拉通地区地壳和上地幔的三维地震结构，重点关注岩石圈的深度范围以及地壳和上地幔的关系达到地质定义的构造边界的速度； 2) 该区域上地幔各向异性的 3-D 分布，及其对岩石圈变形和岩石圈下地幔流动的影响。一种新的双平面波技术，可反演宽带地震中表面波相位和振幅的变化阵列约束三维（3-D）地壳和上地幔地震结构。 此分析的数据来自 82 个站点的南部非洲地震实验，该实验是更大规模的多学科 Kaapvaal 项目的一部分。 与假设平面波前和大圆源接收器射线路径的传统区域表面波层析成像不同，当前方法的一个显着优点是它考虑了由于横向异质性、散射或多路径沿射线路径引起的波场扰动。 各向同性和各向异性地震结构都是使用 SASE 台站记录的瑞利波和洛夫波确定的，并通过将该区域现有的剪切波分裂结果反演表面波数据，以确定最适合的地震速度和下方各向异性的 3-D 模型南部非洲。数值模拟部分涉及计算地幔流的 3D 模型并确定这些模型与地震各向异性和地幔岩石圈变形观测的关系。 通过将表面波分析结果与先前的体波结果相结合，构建了适合南部非洲的岩石圈龙骨形态。 这种几何形状用于检查龙骨周围的地幔流模型，其中流动是由水平板块运动或垂直地幔上涌驱动的。 利用南部非洲地幔结核的弹性参数和其他变形研究的结果计算预测的体波和面波各向异性，以评估岩石圈下地幔变形的潜在程度。 地幔流引起的地震各向异性预测结果将与观测到的地震各向异性合并，以帮助约束南部非洲下方地幔变形的分布。