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Structural Influence on the Evolution of a Pre-eonile Drainage System of Southern Egypt: Insights from Magnetotellurics and Gravity Data

Roden, Jeffrey Dale
Magnetotelluric and gravity surveys were conducted across the Wadi Kobbania in the Western Desert north of Aswan, Egypt. The Wadi Kobbania has been interpreted as the downstream continuation of the Wadi Abu Subeira, comprising an ancient western and northwestern flowing river system, which was sourced from uplifting of the Precambrian Red Sea Hills that occurred during the Oligocene in association with opening of the Red Sea. The purpose of the geophysical surveys was to determine the extent of regional tectonics and local structures on controlling the evolution of the pre-Eonile drainage system predating the modern Nile River. 2D inversion of MT data and gravity models indicate the Wadi Kobbania is filled with loosely-consolidated sedimentary rocks that extend to a depth of ~150-200 m into the Cretaceous sandstone formations which overlie Precambrian crystalline rocks. These results were evaluated by two end member models. One model was an incision model in which the wadi was carved into the bedrock. The second is a structural model in which the wadi is considered to represent a graben that was formed by normal faults that deformed the Cretaceous sandstone formations. Geological considerations as well as gravity, MT, and seismic data favors the interpretation that the Wadi Kobbania is a NW trending graben similar to other graben structures that are found as far northwest as 500 km along strike of Wadi Kobbania. These structures are parallel to the western shorelines of the Red Sea and the Gulf of Suez suggesting a regional tectonic link between these extensional structures. Strain localization on faults within the Precambrian crystalline rocks is suggested by the narrow width of the graben, amount of subsidence observed from cross-sectional models, and lack of other known NW trending grabens in the area.