Constraining the timing of graben initiation in the central Afar using fluvial knickpoint erosion and terrestrial cosmogenic nuclides
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The Afar region constitutes the diffuse ridge-ridge-ridge triple junction adjoining the Red Sea, Gulf of Aden, and Main Ethiopian Rifts. Extension in the Afar is distributed between on-axis, magmatic crustal stretching spreading, and off-axis, amagmatic extension, such as the Dobe Graben. The timing of initiation and development of these amagmatic grabens is important to understanding the final stages of continental extension in the Afar region. All major graben-bounding faults cut through the Afar Stratoid Basalt series, constraining the ages of initiation to younger than 1 million years. The Afar Stratoid lavas make up the bedrock of the region, forming a uniform pre-graben, paleo surface which includes low-relief drainage systems. The initiation of a particular fault (or location along a graben-bounding fault) is expressed as a knickpoint that incises the paleo drainage in the footwalls of the grabens, connecting it to the basin floor with a deep canyon. The rate at which knickpoints retreat upstream permits a space-for-time approach to assessing initiation. This study develops and applies a landscape evolution model to estimate relative maturity of drainage basins by measuring the long profile response to tectonic forcings over intermediate timescales in the Afar region. The model is calibrated by analysis of stream longitudinal profiles and terrestrial cosmogenic nuclide (TCN) analysis of samples collected in the field. Stream profiles are mapped through remote sensing and photogrammetry, and TCN concentrations are assessed to calculate the uplift rate along the graben-bounding faults.
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