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

点击翻译按钮获取中文摘要

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.