Gravity analysis of the main Ethiopian rift

An analysis of gravity data collected during the 2003 Ethiopia-Afar Geoscientific Lithospheric Experiment (EAGLE) and previously available data is used in conjunction with EAGLE seismic results to determine a preliminary crustal structure model of the main Ethiopian rift (MER). The Bouguer gravity anomaly is dominated by a regional gravity anomaly that increases in amplitude from the central MER to the southern Afar region, while the residual gravity anomaly indicates gravity maxima occur over magmatic segments that occur within the MER. Gravity modeling using the EAGLE controlled-source axial seismic model as a constraint indicates that the crust thins from similar to 40 km over the central MER to similar to 30 km over the southern Afar region. However, to model the large amplitude gravity gradient in the Nazreth region, a denser lower crust and less dense upper mantle were needed over the southern Afar region. The denser lower crust is interpreted to be caused by mafic material formed during extensional tectonics, while the less dense upper mantle is indicative of a hotter thermal regime. The presence of a thinned crust and higher density lower crust is characteristic of volcanic rifted margins and implies that the southern Afar region may be developing into a continental margin. The gravity maxima occurring over the magmatic segments were modeled as dense, matic bodies caused by intrusion into the lower and upper crust with tops between 7 and 10 km. These bodies add constraints to recently obtained three-dimensional seismic tomographic models suggest that the lower to lower-upper crust is in a ductile regime and the upper 7 km of the upper crust is in a brittle regime. (c) 2007 Elsevier Ltd. All rights reserved.