Constraining Thermo-Chemical Mantle Convection from Observations of Mantle Plumes and Upper Mantle Temperature

从地幔柱和上地幔温度的观测来约束地幔热化学对流

• 批准号: 0538255
• 负责人: Shijie Zhong
• 金额: $ 12.5万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-01-01 至 2007-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0538255&HistoricalAwards=false
• 关键词: Constraining; Thermo; Chemical; Mantle; Convection

Recent seismic observations indicate that the bottom part of the lower mantle is compositionally distinct from the overlying mantle, suggesting a layered mantle model that may be consistent with geochemical observations. However, the composition and volume of each layer of the layered mantle and consequences of the layering to surface observations remain poorly understood. This study seeks to constrain the thermochemical convection of the mantle by using observations of plume heat flux, plume excess temperature, and the upper mantle temperature. 3-D regional spherical models of isochemical (i.e., whole mantle convection) and thermochemical (i.e., layered mantle convection) convection are formulated to examine controls on plume heat flux, plume excess temperature, and the upper mantle temperature. It is hypothesized that the controlling parameter on these observables is internal heating rate for the layer (i.e., the top layer of a layered mantle) overlying the thermal boundary layer from which mantle plumes are derived, while other parameters including Rayleigh number play secondary roles. This hypothesis is supported by the investigator's preliminary modeling calculations. Model calculations over a large model parameter space are to be performed to test this hypothesis. These model calculations determine the internal heating rate that is required to reproduce all these three observations for isochemical models and thermochemical models with different layering depths. This study explores the implications of the required internal heating rate for the top layer for a range of geophysical and geochemical problems including mantle secular cooling, distribution of radioactive elements, mantle composition, core heat flux and cooling, and mantle layering.

最近的地震观测表明，下地幔的底部在成分上与上覆地幔不同，这表明层状地幔模型可能与地球化学观测结果一致。然而，人们对层状地幔各层的组成和体积以及分层对地表观测的影响仍然知之甚少。本研究旨在通过对羽流热通量、羽流超温和上地幔温度的观测来限制地幔的热化学对流。制定了等化学（即全地幔对流）和热化学（即层状地幔对流）对流的 3-D 区域球形模型，以检查对羽流热通量、羽流过剩温度和上地幔温度的控制。据推测，这些可观测值的控制参数是地幔柱产生的热边界层上方的层（即层状地幔的顶层）的内部加热速率，而包括瑞利数在内的其他参数起次要作用。这一假设得到了研究者初步建模计算的支持。将在大模型参数空间上进行模型计算来检验这一假设。这些模型计算确定了为具有不同分层深度的等化学模型和热化学模型重现所有这三个观察结果所需的内部加热速率。这项研究探讨了顶层所需的内部加热速率对一系列地球物理和地球化学问题的影响，包括地幔长期冷却、放射性元素的分布、地幔成分、地核热通量和冷却以及地幔分层。