Abstract:
We investigated the evolution of the Mekele Sedimentary Basin (MSB) in northern Ethiopia using
geologicfield and gravity data. The depth to Moho and lithospheric structure beneath the basin was
imaged using two-dimensional (2D) radially-averaged power spectral analysis, Lithoflex threedimensional (3D) forward and inverse modeling, and 2D forward modeling of the Bouguer gravity
anomalies. Previous studies proposed that the basin was formed as part of a multi-branched rift system
related to the breakup of Gondwana. Our results show that the MSB: (1) is circular to elliptical in map
view and saucer shaped in cross sectional view, (2) isfilled with terrestrial and shallow marine sedimentary rocks, (3) does not significantly structurally control the sedimentation and the major faults are
post-depositional, (4) is characterized by a concentric gravity minima, (5) is underlain by an unstretched
crust (~40 km thick) and thicker lithosphere (~120 km thick). These features compare positively with a
group of basins known as IntraCONtinental Sags (ICONS), especially those ICONS formed over accretionary orogenic terranes. Since the MSB is located above the Neoproterozoic accretionary orogenic
terranes of the Arabian-Nubian Shield (ANS), we propose that the formation of the MSB to be related to
cooling and thickening of a juvenile sub-continental lithospheric mantle beneath the ANS, which most
probably provided negative buoyancy, and hence subsidence in the MSB, leading to its formation as an
ICONS. The MSB could be used as an outcrop analog for information about the internal facies architecture
of ICONS because it is completely exhumed due to tectonic uplift on the westernflank of the Afar
Depression.
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