Luel Emishaw, Daniel A. Laó Dávila, Mohamed G. Abdelsalam, Estella A. Atekwana, and Steve Gao received news that the manuscript submitted to Tectonophysics was accepted for publication. The article can be accessed following this link: http://www.sciencedirect.com/science/article/pii/S1464343X1630351X
Title: Evolution of the Broadly Rifted Zone in southern Ethiopia through gravitational collapse and extension of dynamic topography
Abstract: The Broadly Rifted Zone (BRZ) is a ~ 315 km wide zone of extension in southern Ethiopia. It is located between the South Main Ethiopian Rift and the Eastern Branch of the East African Rift System (EARS) represented by the Kenya-Turkana Rift. The BRZ is characterized by NE-trending ridges and valleys superimposed on regionally uplifted (~ 2 km average elevation) terrain. Previous studies proposed that the BRZ is an overlap zone resulted from northward propagation of the Kenya-Turkana Rift and southward propagation of the Southern Main Ethiopian Rift. To understand the relationship between the BRZ’s extensional style and its crustal and upper mantle structures, this work first estimated the Moho depth using the two-dimensional (2D) radially-averaged power spectral analysis of the satellite World Gravity Map (WGM 2012) model. Verification of these results was accomplished through lithospheric-scale 2D forward gravity models along E-W profiles. This work found that the Moho topography beneath the BRZ depicts a dome-like shape with a minimum depth of ~ 27 km in the center of this dome. This work proposes that the Moho doming, crustal arching underlying the BRZ and associated topographic uplift are the result of asthenospheric mantle upwelling beneath the BRZ. This upwelling changed to a NE-directed lateral mantle flow at shallower depth. This is supported by seismic tomography imaging which shows slow S-wave velocity anomaly stretching in a NE-SW direction at lithospheric depth of 75 km to 150 km from beneath the BRZ to the Afar Depression. This work proposes that the asthenospheric upwelling created gravitationally unstable dynamic topography that triggered extensional gravitational collapse leading to the formation of the BRZ as a wide rift within the narrow rift segments of the EARS.
