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

合作研究：限制图尔卡纳凹陷地幔柱对岩浆作用的时间演化

• 批准号: 1551872
• 负责人: Tyrone Rooney
• 金额: $ 21.01万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1551872&HistoricalAwards=false
• 关键词: Collaborative; Research; Constraining; temporal; evolution

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.

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。虽然裂谷周期后期洋壳的形成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。在裂谷萌生过程中，岩浆渗透到构造板块中，通过削弱和集中应变而促进裂谷过程。然而，裂谷过程中熔体生成过程受到的限制很少。东非是该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。该项目利用喷发熔岩的地球化学技术，试图确定大陆裂谷期间岩浆是如何产生的，以提高我们对各种产生熔岩的机制的贡献范围的理解。这些结果对于了解裂谷起始和演化过程中岩浆的生成，以及我们了解岩石圈、上地幔和深部地幔来源的贡献具有重要意义。考虑到世界上大部分人口和碳氢化合物资源都位于裂谷边缘，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。该提案概述了一项获取新地球化学和地质年代数据的计划，以便更好地了解裂谷熔岩的来源。将评估地幔柱和岩石圈易熔化部分在熔体生成过程中的作用的时间变化。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。要检验的假设是，自始新世以来，研究区域的火山活动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）不同来源的裂谷熔岩的地球化学特征是什么； (2) 这些来源的贡献随时间发生了怎样的变化？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，并确定其空间分布和时间变化。对东非裂谷整个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理解。虽然许多研究都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层的时间发展以及随着裂谷的成熟，这些储层的贡献如何随着时间的推移而演变。确定“基本裂谷过程以及它们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裂谷起始和演化问题之一，因此该项目的结果将与其他 GeoPRISMS 工作相结合检查裂谷发育的学科。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。

项目成果

Transition to magma-driven rifting in the South Turkana Basin, Kenya: Part 2

肯尼亚南图尔卡纳盆地向岩浆驱动裂谷的转变：第 2 部分

• DOI: 10.1144/jgs2021-160
• 发表时间: 2022-08
• 期刊: Journal of the Geological Society
• 影响因子: 2.7
• 作者: Rooney, Tyrone O.;Wallace, Paul J.;Muirhead, James D.;Chiasera, Brandon;Steiner, R. Ale;Girard, Guillaume;Karson, Jeffery A.
• 通讯作者: Karson, Jeffery A.