Mineralogical and Dynamic Origin of the South African Superplume

南非超羽流的矿物学和动态起源

• 批准号: 79644183
• 负责人: Professor Dr. Hans-Peter Bunge, Ph.D.
• 金额: --
• 依托单位: Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2008
• 资助国家: 德国
• 起止时间: 2007-12-31 至 2013-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/79644183?language=en
• 关键词: Mineralogical; Dynamic; Origin; South; African

Global models from seismic tomography show an extensive low shear wave velocity (vS) feature beneath southern African that extents from the core-mantle boundary for ~1000 km upwards. This feature is also characterized by anticorrelation of vS and the bulk sound velocity vΦ, relative to 1-dimensional reference profiles, with a high bulk and low shear modulus. Detailed studies using travel time anomalies were able to further demonstrate that this feature has very sharp, near vertical boundaries. While seismoloigcal constraints on this South-African superplume have been robust over the past couple of years, the physical or chemical origin of this anomaly has not adequately been investigated. For example, it is not clear to date if this is a dynamic or stagnant feature in the mantle. Attempts have been made to ascribe its origin to thermal upwellings, stabilized by the insulating effect of the stagnant overriding African plate, kept neutrally buoyant by enrichment of the lowermost mantle in terms of iron content and/or subducted material. However, the mineralogical models used in such dynamic studies are compiled on an ad-hoc basis, and competing effects are not investigated in a systematic way. Here, we propose to use a thermodynamic model of mantle mineralogy embedded in a 3-dimensional convection model to test the competing thermal and chemical influences on buoyancy of a broad upwelling feature in the lower most mantle. We will estimate under what boundary conditions of composition, size and shape the African superplume could stay neutrally buoyant and be indeed one of the ‘oldest geological features existing on our planet’.

来自地震层析成像的全球模型显示，在非洲南部，从核心-地幔边界向上延伸约1000公里，存在广泛的低横波速度（vS）特征。相对于一维参考剖面，该特征还表现为vS与体声速vΦ的反相关，具有高体模量和低剪切模量。使用旅行时间异常的详细研究能够进一步证明该特征具有非常明显的接近垂直的边界。虽然在过去的几年里，对南非超级羽流的地震限制一直很强大，但这种异常的物理或化学起源尚未得到充分的研究。例如，到目前为止还不清楚这是地幔中的动态特征还是停滞特征。有人试图把它的起源归结为热上升流，由于停滞的压倒非洲板块的绝缘作用而稳定下来，由于最下层地幔的铁含量和/或俯冲物质的富集而保持中性浮力。然而，在这种动态研究中使用的矿物学模型是在特别的基础上编制的，并且没有以系统的方式调查竞争效应。在这里，我们建议使用嵌入在三维对流模型中的地幔矿物学热力学模型来测试最下部地幔中广泛上升流特征对浮力的竞争热化学影响。我们将估计在构成、大小和形状的边界条件下，非洲超级羽流可以保持中性浮力，并且确实是“我们星球上存在的最古老的地质特征”之一。