The majority of Earth's surface is covered in oceans, below which lie rocks that constitute the oceanic crust. Unlike Earth's continents, which may persist for billions of years, the oceanic crust is continually destroyed and created. These dynamic processes lead to the opening and closure of ocean basins, and even the breaking apart of continents. Continental rifts, which manifest as a series of interconnected linear to arcuate valleys on continents, are the manifestation of the process by which continents may split and new oceans form. Insights into the creation of new oceans thus depends on the processes active within continental rifts. This project focuses on the generation of large volumes of lavas within continental rifts. These lavas form the basis of later oceanic crust, but the mechanism of magma generation is currently unclear. The project focuses on the East African rift - the premier example of a modern continental rift, and examines how magmas are generated in the mantle, evolve in the crust, and eventually erupt in this rift. One of the eventual aims of this project is to develop an understanding as to why large-volumes of lavas flood onto the surface of the rift during certain periods, while during other periods the lavas are restricted to linear belts. This work can feed into evolving models that seek to constrain the architecture of the crust within rifts and nascent ocean basins. Insights gained from East Africa have broad implications in understanding rifted margins globally, and how the crust and offshore basins along these margins develop. By examining rocks that are exposed in East Africa, we may generate better conceptual models of regions where these rocks may be buried by kilometers of sediments (e.g., Eastern U.S. seaboard). Broader Impacts include undergraduate research experience.
In this proposal new geochemical and petrographic constraints on lavas from the East African rift will be obtained. The focus will be on lava fields that represent end members in eruption style - large lava flows, isolated shields, and smaller lava cones. The proposed study regions in East Africa are the following: (i) Afar, a region where researchers vigorously debate if ocean crust is already being formed, and (ii) Turkana, a region where an earlier rifting event has made the crust thinner than would be anticipated. The work being undertaken in this proposal will be arranged around four interlinked questions: (A) What is the mechanism of magma generation for the different lavas fields? (B) What mantle sources contribute to magma creation within these lavas fields? (C) How does magma generation/ source contribution change over time? (D) Is there a difference in the conditions of magma evolution within the crust between the different lava fields? The region this project focuses on spans two of the targets elucidated by the GeoPRISMS Implementation Plan. Turkana lies within the "Primary area for focused investigations", while Afar lies within the "collaborative target" region. Thus, the results of this study can be collated with other NSF-sponsored science being undertaken in the same region to address GeoPRISMS science goals. When combined, these data will be used to address the science question: "How is strain accommodated and partitioned throughout the lithosphere, and what are the controls on strain localization and migration?" The results of this work will have further impact upon other science questions related to the distribution of deep mantle material in the East African upper mantle. These questions are currently being addressed through other interdisciplinary studies and the proposed work would add a critical component to the the constraints on the rifting process that is recorded in the recent lavas. When considered in aggregate, these studies aim to push the boundaries of current knowledge as to how rifting initiates, evolves, and transitions to oceanic spreading.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
