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。这个项目的重点是大陆裂谷边缘最重要的特征之一，即在裂谷边缘内喷发的岩浆的起源。虽然在裂谷旋回晚期海洋地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旋回早期也起着关键作用。在裂谷起裂过程中，岩浆渗入构造板块，通过弱化和聚焦应变，促进裂谷过程。然而，裂谷过程中熔体产生的过程却没有得到很好的约束。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。该项目利用喷发熔岩的地球化学技术，试图确定岩浆是如何在大陆裂谷期间产生的，以提高我们对各种机制产生融化的贡献范围的理解。研究结果将对认识裂陷起始和演化过程中的岩浆生成，以及岩石圈、上地幔和深部地幔源的贡献具有重要意义。考虑到世界上大部分人口和油气资源都位于裂谷大陆边缘，研究控制裂谷边缘构造和特征的机制具有广泛的社会和经济效益。该提案概述了一项计划，以获得新的地球化学和地质年代学数据，以便更好地了解裂谷熔岩的来源。将评价地幔柱和岩石圈易熔化部分在熔体产生过程中作用的时间变化。研究区域位于东非裂谷的东部分支，是地球地质系统项目的重点地点。要验证的假设是，研究地区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)裂谷熔岩不同来源的地球化学特征是什么；(2)这些来源的贡献是如何随时间变化的？这些问题将通过对熔岩的地质年代学、地球化学和古地磁研究来解决，目的是建立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。对沿东非裂谷长期伸展过程的大陆裂谷熔岩的研究有可能提高对各种熔体产生机制的贡献范围的理解。虽然许多研究集中在孤立的熔体产生时期，但这里提出的工作将研究熔体储层的时间发育以及这些储层的贡献如何随着裂谷作用的成熟而随时间演变。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变”是地球地质系统科学计划草案中确定的四个关键裂谷发生和演化问题之一，因此，这个项目的结果将与地球地质系统跨学科的其他工作相结合，以研究裂谷的发展。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。

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
• 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. Alex;Girard, Guillaume;Karson, Jeffery A.
• 通讯作者: Karson, Jeffery A.