Collaborative Research: Constraining the temporal evolution of mantle plume contributions to magmatism in the Turkana Depression

地球大陆块分裂形成新海洋的过程是板块构造范式的核心原则。该项目的重点是大陆裂谷边缘最重要的特征之一-即在其中喷发的岩浆的起源。虽然裂谷循环后期洋壳的建造需要大量的岩浆活动，但人们越来越认识到岩浆在裂谷过程的早期也发挥着关键作用。在裂谷形成过程中，岩浆向构造板块的渗透通过弱化和集中应变而促进了裂谷作用。然而，在裂谷过程中的熔体生成的过程是不受约束的。东非是本研究项目的地理重点区域，是大陆裂谷的典型例子，在这里获得的见解具有全球应用价值。利用喷发熔岩的地球化学技术，该项目旨在确定大陆裂谷期间岩浆是如何产生的，以提高我们对各种机制产生熔体的贡献范围的理解。这一结果对于理解裂谷作用的起源和演化过程中岩浆的生成，以及岩石圈、上地幔和深地幔源区的贡献具有重要意义。鉴于世界人口和碳氢化合物资源众多，而且沿着断裂大陆边缘分布，限制控制断裂边缘结构和特征的机制具有广泛的社会和经济效益，这项建议概述了一项计划，以获得新的地球化学和年代学数据，从而更好地了解断裂熔岩的来源。将评估地幔柱和岩石圈易熔融部分在熔体生成过程中的作用随时间的变化。研究区域位于东非大裂谷的东部分支，是GeoPRISMS方案的一个重点地点。有待检验的假设是，研究区域的火山活动自始新世以来一直受到羽流的影响。这一假设将通过研究以下问题来解决：（1）裂谷熔岩的不同来源的地球化学特征是什么？（2）这些来源的贡献如何随时间而变化？这些问题将通过地质年代学，地球化学和古地磁研究的熔岩与目标，以建立一个详细的地球化学特征的裂谷内熔岩的来源，并确定其空间分布和时间变化来解决。对东非裂谷沿着长期伸展过程中大陆裂谷熔岩的研究有可能提高对各种熔体生成机制的贡献范围的认识。虽然许多研究集中在孤立时期的熔体生产，这里提出的工作将研究熔体水库的时间发展，以及如何从这些水库的贡献随着时间的推移裂谷成熟。确定“基本裂谷过程及其之间的反馈如何在时间和空间上演变”是GeoPRISMS科学计划草案中确定的四个关键裂谷启动和演变问题之一，因此，该项目的结果将与GeoPRISMS跨学科的其他努力相结合，以研究裂谷的发展。该项目得到了NSF国际科学与工程办公室的部分支持。

The process by which the Earth's continental masses split apart to form new oceans is a central tenet of the plate tectonic paradigm. This project focuses on one of the most important features of continental rifted margins - that is the origin of magmas that are erupted within them. While the construction of oceanic crust late in the rifting cycle requires voluminous magmatic activity, there is a growing understanding that magmas also play a pivotal role earlier in the rifting process. Infiltration of magma into the tectonic plate during rift initiation contributes to the rifting process by weakening and focusing strain. However, the process of melt generation during rifting is poorly constrained. East Africa, the geographic focus area of this research project, is the classic example of a continental rift, and insights gained here have global application. Using geochemical techniques on erupted lavas, this project seeks to determine how magma is produced during continental rifting to improve our understanding of the range of contributions from various mechanisms to generate melt. The results will have important implications for understanding magma generation during the initiation and evolution of rifting, and for our understanding of the contribution of lithospheric, upper mantle, and deep mantle sources. Constraining the mechanisms which control the structure and characteristics of rifted margins has broad societal and economic benefits given much of the world's population and hydrocarbon resources and located along rifted continental margins.This proposal outlines a plan to obtain new geochemical and geochronological data in order to better understand the sources of rift lavas. The temporal variation in the role of a mantle plume and easily melted portions of the lithosphere in melt generation processes will be evaluated. The study region, in the eastern branch of the East African Rift, is a focus site of the GeoPRISMS program. The hypothesis to be tested is that volcanism in the study region has been plume influenced since the Eocene. This hypothesis will be addressed by examining the following questions: (1) What are the geochemical characteristics of the different sources of rift lavas; and (2) how have contributions from these source(s) changed over time? These questions will be addressed through a geochronological, geochemical, and paleomagnetic study of lavas with a goal to construct a detailed geochemical characterization of the sources of within-rift lavas and determine their spatial distribution and temporal variation. The study of continental rift lavas throughout the long-lived extensional process along the East African Rift has the potential to improve understanding of the range of contributions from various melt generation mechanisms. While many studies focus on isolated periods of melt production, the work proposed here would examine the temporal development of melt reservoirs and how contributions from these reservoirs evolve over time as rifting matures. Establishing how "fundamental rifting processes, and feedbacks between them, evolve in time and space" is one of the four key Rift Initiation and Evolution questions identified in the GeoPRISMS draft science plan, thus the result of this project will interface with other GeoPRISMS efforts across disciplines to examine rift development. This project has been supported in part by the Office of International Science and Engineering at NSF.