A Geological and Geophysical Study of the Area South-East of Qerri Station, Eastern Sabaloka, North Khartoum Province, Sudan

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Ahmed Suleiman, Dawoud
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The area investigated lies 80km north of Khartoum and forms a portion of the eastern part of the Sabaloka Basement inlier. The dominant rock types are metamorphic gneisses and schists with later granitic and gabbroic intrusions all of which are pre-Nubian Sandstone Formation in age. Meta-sediments interbanded with acid and basic gneisses, have been isoclinaly folded on N-S axes by an early folding, coeval with an early period of metamorphism which caused the formation of foliation and structural concordancy between the various rock units. A period of progressive metamorphism occurred and the rocks were folded by a second period of tight similar folding with dominant N-S axes. Metamorphism in some places reached a sillimanite grade and was accompanied by migatisation, elsewhere there was wide-spread formation of granet. The process of feldspathisation ended with the formation of the Ban Gadeed granite. Localised thermal metamorphism, best seen in the basic gneisses, is considered to be due to the intrusion of a basic body which in turn has been affected by the latest stages of feldspathisation and regional metamorphism. A third period of E-W axial open folding affected all the rocks. The metagabbro and Ban Gadeed granite are considered to be pre-third folding though not themselves showing folding due to their massive characters. A group of granites, Characterised by a particular mineralogical composition and post organic emplacement are recognized as belonging to a younger granite suite. The most widespread of these intrusions are felsite dyke swarms which are genetically correlated to the Sabaloka Igneous Complex and which form a prominent feature in the Sabaloka inlier. Undeformed sediments of the Nubian Sandstone Formation lie unconformably upon all the basement Complex rocks. Normal faulting trending north-south affects both Basement Complex and the Nubian Sandstone Formation rocks. Some of the GEOLOGY faults are considered to be a rejuvenation of pre-Nubian fractures. An important north-south fault affecting both Nubian Sandstone and Basement rocks extends across the area and is considered to explain the regional steep gravity gradient recorded by Sadig (1969). A Detailed gravity and Magnetic survey across a basic gneiss outcrop revealed concordancy between gravity and magnetic anomalies and supported the explanations of the regional anomalies as being due to dense, magnetic basic bodies within the acid gneisses
A Geological and Geophysical Study of the Area South-East of Qerri Station, Eastern Sabaloka, North Khartoum Province, Sudan.