CSEDI Collaborative Research: Geochemical Structure and Dynamics of the Mantle Below the East African Rift System

CSEDI合作研究：东非裂谷系下方地幔的地球化学结构和动力学

• 批准号: 0551960
• 负责人: Julia Bryce
• 金额: $ 7.22万
• 依托单位: University of New Hampshire
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-06-01 至 2009-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0551960&HistoricalAwards=false
• 关键词: CSEDI; Collaborative; Research; Geochemical; Structure

The East African Rift System (EARS) is the only place on the planet where the geochemical and isotopic compositions of continental mafic lavas spanning 40 million years of volcanism can be studied. This geochemical information must be used in conjunction with modern geophysical and seismic information to address fundamental geodynamic questions about the relationship between features of the deep Earth and those at the surface. We focus on the evolution of upper mantle temperature and composition by using numerical models of limited mantle depth extent. Geological and geochemical observations in the EARS provide strong constraints on the timing and location of melt formation in the mantle. The dynamical modeling provides the ability to predict the formation of melt in a self-consistent manner and make quantitative estimates of the temperature, depth and rate of melting. We will also pursue a comprehensive geochemical study of select MgO-rich EARS basalts. New geochemical and isotopic (Sr-Nd-Pb-Hf-He) data, coupled with existing data from the literature, will be used to define the distribution of chemically distinct reservoirs that sustain EARS magmatism. Trace element and isotope geochemical data enable refinement of the compositional structure of the upper mantle and will help constrain reasonable dynamical models. Our main hypothesis is that one or more plumes bring hot material from the Earths interior to melt below the EARS lithosphere, since we find it difficult to understand how long-lived and voluminous volcanism can be generated without such deep transport. A sensitivity study will allow us to estimate whether and how non-plume models can predict the timing and location of melt generation observed in the EARS. For plume models, we will assess a variety of dynamical scenarios by incorporating tracer techniques to test whether the observed distribution of geochemical signatures and volumes of magmatic products along the EARS can be satisfied with a single compositionally heterogeneous plume. The resulting dynamical models will enhance our understanding of the origin of the EARS, the African superswell and eventually the African superplume. The collaboration between geochemists with mutually supporting areas of expertise (Furman trace element geochemistry, Bryce lithophile radiogenic isotope geochemistry, Graham helium isotope geochemistry) and a geophysicist / numerical modeler (van Keken) will provide a much-needed interaction between observational and theoretical efforts. The results of the work will be incorporated into residential and electronic delivery courses at the participating universities, including several Historically Black Colleges and Universities. We will support graduate students at Penn State, Michigan and New Hampshire, introducing this next generation of scientists to interdisciplinary research and collaboration.

东非裂谷系统(EARS)是地球上唯一可以研究跨越4000万年火山活动的大陆镁铁质熔岩的地球化学和同位素组成的地方。这些地球化学信息必须与现代地球物理和地震信息结合使用，以解决有关地球深部特征与地表特征之间关系的基本地球动力学问题。利用有限地幔深度范围的数值模式，重点研究了上地幔温度和成分的演化。耳朵中的地质和地球化学观察为地幔中熔体形成的时间和位置提供了强有力的约束。动态模拟提供了以自洽的方式预测熔体形成的能力，并对熔化的温度、深度和速率进行了定量估计。我们还将对精选的富含镁的EARS玄武岩进行全面的地球化学研究。新的地球化学和同位素(锶-钕-铅-氢氟化氢-氦)数据，结合现有的文献数据，将被用来确定维持EAR岩浆作用的化学上不同的储集层的分布。微量元素和同位素地球化学数据有助于精炼上地幔的成分结构，并有助于约束合理的动力学模型。我们的主要假设是，一个或多个羽流将热物质从地球内部带到EARS岩石圈下方融化，因为我们发现很难理解如果没有如此深的传输，如何才能产生长寿和巨大的火山活动。敏感度研究将使我们能够估计非羽流模型是否以及如何预测在耳朵中观察到的熔融产生的时间和位置。对于羽流模型，我们将通过采用示踪技术来评估各种动力学情景，以测试观察到的地球化学特征和岩浆产物沿耳朵的体积分布是否可以满足单个成分不均匀的羽流的要求。由此产生的动力学模型将加强我们对耳朵、非洲超强喷发以及最终非洲超强喷流起源的理解。拥有相互支持的专门知识领域(福尔曼微量元素地球化学、布莱斯亲岩石放射性同位素地球化学、格雷厄姆氦同位素地球化学)的地球化学家与地球物理学家/数值模型师(Van Keken)之间的合作将在观测工作和理论工作之间提供亟需的互动。这项工作的成果将被纳入参与的大学的住宅和电子交付课程，包括几所历史悠久的黑人学院和大学。我们将支持宾夕法尼亚州立大学、密歇根州和新罕布夏州的研究生，向这些下一代科学家介绍跨学科的研究和合作。