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

地球大陆块体分裂形成新海洋的过程是板块构造范式的核心原则。这个项目的重点是大陆裂谷边缘最重要的特征之一--即它们内部喷发的岩浆的起源。虽然在裂谷周期后期建造洋壳需要大量的岩浆活动，但人们越来越多地认识到，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，岩浆渗入构造板块，通过削弱和集中应变，促进了裂谷过程。然而，裂谷过程中熔体的产生过程受到的约束很少。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，这里获得的见解具有全球应用价值。这个项目利用对喷发的熔岩的地球化学技术，试图确定大陆裂谷过程中岩浆是如何产生的，以提高我们对产生熔体的各种机制的贡献范围的理解。这一结果对于理解裂谷作用形成和演化过程中的岩浆生成，以及理解岩石圈、上地幔和深部地幔源区的贡献具有重要意义。限制控制裂谷边缘结构和特征的机制具有广泛的社会和经济效益，因为世界上大部分人口和油气资源位于裂谷大陆边缘。这项提议概述了一项获取新的地球化学和地质年代学数据的计划，以更好地了解裂谷熔岩的来源。将评估地幔热柱和岩石圈易熔融部分在熔体形成过程中作用的时间变化。该研究区域位于东非裂谷的东部分支，是GeoPRISMS计划的重点地点。需要检验的假设是，自始新世以来，研究区的火山活动受到了羽流的影响。这一假说将通过检验以下问题来解决：(1)不同来源的裂谷熔岩的地球化学特征是什么；以及(2)这些来源(S)的贡献随着时间的推移有何变化？这些问题将通过熔岩的地质年代学、地球化学和古地磁研究来解决，目的是构建裂谷内熔岩来源的详细地球化学特征，并确定它们的空间分布和时间变化。对东非裂谷沿线长期伸展过程中大陆裂谷熔岩的研究，有可能增进对各种熔体形成机制的贡献范围的理解。虽然许多研究集中在熔体生产的孤立时期，但这里提出的工作将研究熔体储集层的时间发展，以及随着裂谷作用的成熟，这些储集层的贡献如何随着时间的推移而演变。确定“基本的裂谷过程及其之间的反馈如何在时间和空间上演化”是GeoPRISMS科学计划草案中确定的四个关键的裂谷启动和演化问题之一，因此，该项目的结果将与GeoPRISMS的其他跨学科努力相结合，以审查裂谷的发展。该项目得到了美国国家科学基金会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.