Lateral variations in CMB heat flux and deep mantle seismic velocity caused by a thermal–chemical-phase boundary layer in 3D spherical convection

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• 作者：Takashi Nakagawa ; Paul J. Tackley
• 关键词：thermo-chemical mantle convection ; 3D spherical shell ; CMB heat flow ; seismic anomalies ; lateral heterogeneities
• 刊名：Earth and Planetary Science Letters
• 出版年：2008
• 期刊代码：18_0012821x
• 类别：ph
• 出版时间：15 July 2008
• 卷：271
• 期：1-4
• 页码：348-358
• 文件大小：1654 K

摘要

Numerical simulations of thermo-chemical, multi-phase, compressible mantle convection in a three-dimensional spherical shell are used to investigate the relationship between lateral variations in seismic shear-wave velocity V_s above the core–mantle boundary (CMB) and lateral variations in heat flux across the CMB (q_CMB), when compositional variations and the post-perovskite phase transition are included. For simple thermal convection, the V_s–q_CMB relationship is reasonably but not perfectly linear. The post-perovskite transition introduces a non-linearity that amplifies fast V_s anomalies in cold regions, but there is still a unique mapping between δV_s and q_CMB. Lateral variations in composition such as piles of dense material introduce another non-linearity that affects hot upwelling regions, and introduces a non-uniqueness in δV_s–q_CMB if the dense material (e.g., MORB) is seismically fast compared to the surrounding material. In this case, dense piles are ringed by sharp, low-V_s anomalies. If the CMB is covered by a global dense layer than variations in δV_s and q_CMB are reduced but so is the mean value of q_CMB. In all cases, the peak-to-peak lateral variation in q_CMB is similar to or larger than twice the mean value, which might create problems for generating a dynamo according to existing numerical dynamo simulations. Analytical scalings are developed to explain the observed trends.