Joint seismic-geodynamic-mineral physical modelling of African geodynamics: A reconciliation of deep-mantle convection with surface geophysical constraints
Joint seismic-geodynamic-mineral physical modelling of African geodynamics: A reconciliation of deep-mantle convection with surface geophysical constraints
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DOI：
10.1016/j.epsl.2010.03.017
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发表时间：
2010-07-01
影响因子：
5.3
通讯作者：
Rowley, David B.
中科院分区：
文献类型：
--
作者：
Forte, Alessandro M.;Quere, Sandrine;Rowley, David B.
地震层析成像技术的最新进展提供了第一张完整的热异常和化学异常组合的 3D 图像，这些图像描绘了非洲大陆下方独特的深部地幔结构的特征。我们提出了一种基于层析成像的地幔对流模型，该模型与内部密度异质性的基本表面地球动力学约束提供了极好的匹配，其中包括成分和热贡献，其中后者受到矿物物理学的约束。将这种热化学对流模型应用于非洲地幔动力学问题，可以在比迄今为止更广泛的波长范围内，对非洲板块下方的深层地幔流进行表面重力和地形异常的协调。根据这些结果，我们预测非洲软流圈的流动特征是晚新生代火山活动主要中心下方的明显集中上升流模式，包括肯尼亚穹顶、霍加尔地块、喀麦隆火山岩、佛得角和加那利群岛。气流预测还揭示了佛得角群岛下方非洲西缘下方存在深层、大规模、活跃的热上升流，该上升流向下延伸至核心-地幔边界。这种“西非超羽流”的规模和动力强度与“南非超羽流”相当，长期以来人们一直认为“南非超羽流”主导着非洲地幔深处的大规模流动动力学。我们通过与非洲剪切波分裂数据独立分析得出的地震方位各向异性进行比较，评估了预测的软流圈流动模式的合理性。 (C) 2010 Elsevier B.V. 保留所有权利。
Recent progress in seismic tomography provides the first complete 3-D images of the combined thermal and chemical anomalies that characterise the unique deep-mantle structure below the African continent. We present a tomography-based model of mantle convection that provides an excellent match to fundamental surface geodynamic constraints on internal density heterogeneity that includes both compositional and thermal contributions, where the latter are constrained by mineral physics. The application of this thermochemical convection model to the problem of African mantle dynamics yields a reconciliation of both surface gravity and topography anomalies to deep-seated mantle flow under the African plate, over a wider range of wavelengths than has been possible to date. On the basis of these results, we predict flow in the African asthenosphere characterised by a clear pattern of focussed upwellings below the major centres of late Cenozoic volcanism, including the Kenya domes, Hoggar massif, Cameroon volcanicline, Cape Verde and Canary Islands. The flow predictions also reveal a deep-seated, large-scale, active hot upwelling below the western margin of Africa under the Cape Verde Islands that extends down to the core-mantle boundary. The scale and dynamical intensity of this 'West African Superplume' is comparable to the 'South African Superplume' that has long been assumed to dominate the large-scale flow dynamics in the deep-mantle under Africa. We evaluate the plausibility of the predicted asthenospheric flow patterns through a comparison with seismic azimuthal anisotropy derived from independent analyses of African shear wave splitting data. (C) 2010 Elsevier B.V. All rights reserved.