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）是地球上唯一的地方，可以研究跨越4000万火山的大陆镁铁质熔岩的地球化学和同位素组成。 该地球化学信息必须与现代地球物理和地震信息结合使用，以解决有关深地球特征与表面特征之间关系的基本地球动力学问题。我们通过使用有限的地幔深度范围的数值模型来关注地幔温度和成分的演变。耳朵中的地质和地球化学观测对地幔中熔体形成的时间和位置提供了强烈的限制。动态建模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，深度和速率进行定量估计。我们还将对精选的Mgo富含耳朵的玄武岩进行全面的地球化学研究。新的地球化学和同位素（SR-ND-PB-HF-HE）数据，再加上文献中的现有数据，可用于定义化学上不同的储层的分布，以维持岩浆岩浆。痕量元素和同位素地球化学数据可实现上地幔的组成结构的改进，并有助于限制合理的动态模型。我们的主要假设是，一个或多个羽毛从地球内部带到岩石圈以下融化的热物质，因为我们发现在没有如此深厚的运输的情况下，很难理解可以产生多长寿命和大量火山的。一项敏感性研究将使我们能够估算非胶合模型是否可以预测在耳朵中观察到的熔体产生的时间和位置。对于羽流模型，我们将通过合并示踪剂技术来测试观察到的地球化学特征的分布和沿耳朵的岩浆产物的体积是否可以通过单个成分异质的羽流得到满足，以评估各种动态场景。由此产生的动态模型将增强我们对耳朵，非洲超级井以及最终非洲超级胶的理解。地球化学主义者与相互支持的专业领域（Furman Trace Element地球化学，Bryce岩石放射性同位素地球化学，Graham氦同位素地球化学）和地球物理 /数字建模者（Van Keken）之间的合作将提供相互依赖的互动，并提供观察性的努力。 这项工作的结果将纳入参与大学的住宅和电子送货课程中，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，密歇根州和新罕布什尔州的研究生，向这一下一代科学家介绍跨学科研究与合作。