Year of Award
2024
Document Type
Thesis
Degree Type
Master of Science (MS)
Degree Name
Geosciences
Other Degree Name/Area of Focus
Geophysics
Department or School/College
Geoscience
Committee Chair
Rebecca Bendick
Commitee Members
Hilary Martens, Doug Brinkerhoff
Keywords
East African Rift Zone, Lithosphere Mechanics, Mantle Plume, Active Rifting
Publisher
University of Montana
Abstract
Active rifting, elastic failure in the lithosphere from rising density anomalies in the mantle, is fundamental to the Wilson Cycle which describes the cycle of tectonic plates. Active rift zones are common in the oceanic lithosphere but are less common in the thicker continental lithosphere. The current largest active continental rift zone is the East African Rift Zone (EARZ). Although active rifting is fundamental to plate tectonic theory, the mechanics and parameters needed for a density anomaly to initiate a rift have not been undertaken. This model aims to solve the problem of a density anomaly initiating a continental rift zone by looking at the parameters involved and comparing it to a portion of EARZ called the Main Ethiopian Rift (MER).
The model found that a spherical density anomaly alone can cause tensile stresses high enough to initiate rifting in the lithosphere even in the absence of any far-field forces. Therefore, we show that a spherical density anomaly is a viable mechanical source for creating a rift in the lithosphere. For topography similar to that observed in the Ethiopian Plateau, a density anomaly needs to be a substantial size with a radius of 60km (~37mi), about 190km (~118mi) from the bottom of the lithosphere, and the lithosphere needs to be previously thinned from its elastic thickness of about 100km (~62mi) to 45km (~28mi). The topographical match has stresses in the same order of magnitude as the yield stress of the lithosphere implying that the flexure could cause a top-down rift. Combined this shows that the Ethiopian Plateau and MER could have been formed by a rising density anomaly.
The mechanical in-depth look at active rifting found that a rising density anomaly alone can cause a rift in the continental lithosphere. Moreover, the parameters needed to initiate a top-down rift are at an impressive scale that is not common. This matches the lack of current active rift zones and may help explain the existence of many failed rift zones. The generality of the model creates solutions that are not specific to EARS so the findings could be applied to different projects.
Recommended Citation
Boucher, Chloe, "Density Anomaly Leads to Rift Initiation: Quantifying Active Rifting and Comparison to the East African Rift Zone" (2024). Graduate Student Theses, Dissertations, & Professional Papers. 12263.
https://scholarworks.umt.edu/etd/12263
© Copyright 2024 Chloe Boucher