Structural geology, tectonic geomorphology, and neotectonics of the central Afar Rift, Ethiopia and Djibouti

Abstract

The central Afar depression offers an opportunity for quantitative analysis of the final stages of continental breakup at a divergent triple junction. Here, Quaternary faulting dissects Plio-Pleistocene flood basalts, providing a regionally pervasive datum to quantify the regional finite strain and fault scaling laws. To this end, I mapped and measured more than 8500 normal faults using remote sensing products. Fault length generally follows a power law distribution, but exponential distributions are found in areas of magmatic extension. Fault throw and fault length scale following a power law relationship where T = 0.031L[subscript 0.96], similar to previous studies in Afar and elsewhere in the world. Combining the power law distribution with this throw scaling enables a comprehensive assessment of Quaternary finite strain throughout the region. The presence of moderate to high strain in the amagmatic portions of the central Afar rift suggests that those areas accommodate a significant proportion of plate motion. This may provide a future path for propagation between the Gulf of Aden Rift and the Red Sea Rift . ... In order to examine the kinematic evolution of the central Afar, I conducted a morphotectonic analysis on fault scarps in unlithified alluvial material to determine uplift rates on major faults across the region. I have analyzed fault scarps in Hanle, Dobe, Guma, and Immino grabens, and document a northwest decreasing trend in uplift rates. Along a transect parallel to the mean extension direction, the cumulative extension from these faults is 1.09 mm/yr. The decreasing trend in slip rates is incompatible with the “Bookshelf Faulting” model commonly applied to explain deformation in the central Afar. Instead, the more likely model involves distributed extension across the region, possibly resulting from the rotation of the Danakil block away from stable Nubia.