CSEDI: Dynamics and Melting of a Heterogeneous Mantle: Importance to the Geochemical Variability of Hotspot and Mid-Ocean Ridge Magmas

CSEDI：异质地幔的动力学和熔化：对热点和大洋中脊岩浆地球化学变化的重要性

• 批准号: 0440365
• 负责人: Garrett Apuzen-Ito
• 金额: $ 20.81万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-04-15 至 2009-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0440365&HistoricalAwards=false
• 关键词: CSEDI; Dynamics; Melting; Heterogeneous; Mantle

The proposed study will address two problems in solid Earth dynamics: (I) How to reconcile the geochemical distinctions between mid-ocean ridge basalts (MORBs) and hotspot ocean island basalts (OIBs) which are widely interpreted in terms of a chemically layered mantle, with geophysical evidence for whole mantle (i.e., single layer) convection. (II) Determining the origin of the geographic variations in lava geochemistry observed at hotspots. The hypothesis is that variations in melting and ductile flow of a compositionally heterogeneous mantle cause many of the key geochemical characteristics of OIBs and MORBs. This hypothesis will be tested using numerical models that simulate the three-dimensional viscous flow, heat transport, and melting in the upper mantle. Models will be constructed based on the assumption that hotspots are formed by buoyant upwellings, or mantle plumes, interacting with the base of the lithosphere. The melting calculations will incorporate laboratory experimental data on the pressure-temperature conditions for melting of materials with different compositions. Computational results will quantify the relationships between specific physical conditions and predicted geographic variability of trace-element and Sr, Nd, Pb, and He isotope geochemistry in erupted magmas at three tectonic scenarios where adequate data sets exist for comparisons: an intraplate hotspot (Hawaii), a hotspot centered on a mid-ocean ridge (Iceland), and a hotspot off of, but near a mid-ocean ridge (Galapagos). Problem (I) will be addressed by determining whether models do or do not require mantle plumes--which could come from the lower mantle--to be compositionally distinct from the upper mantle. Problem (II) will be addressed by determining the physical conditions needed to explain the nature of spatial geochemical variability observed at the above types of hotspots. The origin of hotspot islands and the question of whole- versus two-layer mantle convection are of broad scientific interest, as evidenced by their treatment in high school and college textbooks. The investigators have given, and will continue giving, lectures and extracurricular seminars on these topics to local high school and undergraduate students. Most of the requested budget will support a Ph. D. student, providing funds needed for a comprehensive, cross-disciplinary dissertation.

拟议的研究将解决固体地球动力学中的两个问题：（I）如何协调洋中脊玄武岩（MORB）和热点洋岛玄武岩（OIB）之间的地球化学差异，这些玄武岩被广泛解释为化学分层地幔，具有全地幔的地球物理证据（即，单层）对流。 (II)确定在热点观测到的熔岩地球化学地理变化的起源。 这一假说认为，在熔融和韧性流动的组成不均匀的地幔的变化造成的OIB和MORB的许多关键的地球化学特征。这一假设将使用模拟上地幔三维粘性流动、热传输和熔融的数值模型进行检验。模型将建立在这样一种假设的基础上，即热点是由浮力上升或地幔柱与岩石圈底部相互作用形成的。熔化计算将结合实验室实验数据的压力-温度条件熔化的材料与不同的组成。计算结果将量化特定的物理条件和预测的地质变化的微量元素和Sr，Nd，Pb和He同位素地球化学在喷发的岩浆在三个构造的情况下，有足够的数据集进行比较：板内热点（夏威夷），热点集中在洋中脊（冰岛），热点关闭，但靠近洋中脊（加拉帕戈斯）之间的关系。问题（I）将通过确定模型是否需要地幔柱（可能来自下地幔）在成分上不同于上地幔来解决。 问题（II）将通过确定解释在上述类型的热点观察到的空间地球化学变异性的性质所需的物理条件来解决。 热点岛屿的起源和全地幔对流与双层地幔对流的问题具有广泛的科学意义，高中和大学教科书中的处理证明了这一点。 调查人员已经并将继续为当地高中和本科生举办有关这些主题的讲座和课外研讨会。申请的预算大部分将用于资助一个博士学位。学生，提供资金需要一个全面的，跨学科的论文。