STRUCTURE AND EVOLUTION OF NORTH AFRICAN PASSIVE MARGIN CRUST: AS INFERRED FROM 2-D GRAVITY MODELING OF NILE DELTA AND ITS SURROUNDING AREAS, EGYPT | ||||
| Journal of Egyptian Geophysical Society | ||||
| Volume 2, Issue 1, 2024, Page 17-29 PDF (1.83 MB) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/jegs.2024.374753 | ||||
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| Authors | ||||
| S. R. Salem; S. O. El-Khateeb; M. F. Mousa | ||||
| Faculty of Science, South Valley University, Qena, Egypt | ||||
| Abstract | ||||
| The aim of the present study is to investigate the crust and the upper mantle nature of the Nile Delta and its surroundings; and/or of North African passive margin, in general, using essentially Bouguer gravity data supported by geologic, seismic and other geophysical information. The selected area lies between latitude parallels 29°,31°45'N and longitude parallels 30 ,32°E. To accomplish this study, the Bouguer gravity data has been subjected to evaluation, processing, analysis, modeling and interpretation. From the resulted 2-D crustal geologic models taken along S-N direction, the crust beneath this area comprises two igneous layers: upper and lower crust underlain by the solid upper mantle basaltic layer . A huge sedimentary cover of densities 2.1 g/cc and 2.5 g/cc for the upper (Miocene to Recent) and lower (Pre-Miocene) layer formations, attains athickness that varies nearly between 2 and 12 km; thickens northward, and tops the previous igneous layers. Meanwhile, the thickness of the upper crust (including sediments); or depth to midcrustal discontinuity (Conrad), of density of 2.7 g/cc, ranges between 22 and 13km with visible thinning and stretching northerly. Also, the lower crust, of gabbroic nature, has adensity value of 2.9 3g/cc and thickness ranges, nearly, between 11 and 10 km. Moreover, the depth to the upper mantle-crust boundary (Moho); or the crustal thickness, ranges approximately between 33 and 23 km. The shape and depth of Moho discontinuity reveals clearly the ascending lithosphere material, i.e. the northward thinning and stretching of the crust. From the study, anomaly trends nearly represent all stresses impact responsible for crustal evolution, were inferred. According to the crustal thickness - composition relationship, the crust of North African margin, as depicted from the crust of Nile Delta and its surrounding regions, seemed to be of continental nature, in the southern parts. It has been changed to intermediate that was developed to semi-oceanic type beneath nearly the northern half of the Nile Delta block with more oceanisation northerly offshore. This relation with the obtained anomaly trends and crustal geologic sections reveal clearly the development of Precambrian to Cambrian crust as a result of evolution crustal cycles (crustal framework) prevailed from Early Paleozoic to Present. | ||||
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