Paleomagnetism of Late Neoproterozoic African Dike Swarms from the South Eastern Desert and the Paleo-Neoproterozoic Dat
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Pure and Applied Geophysics
Paleomagnetism of Late Neoproterozoic African Dike Swarms from the South Eastern Desert and the Paleo-Neoproterozoic Dataset from Egypt AHMED SALEH1 Abstract—Paleomagnetic analysis has been carried out on Late Neoproterozoic dike swarms from two areas along the Red Sea coast: 13 dikes (87 samples) close to the Um Rus gold mine and eight dikes (59 samples) at Sadi Salem. Rock magnetic experiments indicate that the main carrier of magnetization of these dikes is titanomagnetite and/or magnetite. Most samples display a component of magnetization (CA) that is in agreement with previously published Paleo-Late Neoproterozoic poles from other dikes and from one ore complex. But they cluster around the Cenozoic (0–60 Ma) portion of Torsvik’s Gondwana apparent polar wander path (APWP) when plotted in southern African coordinates. We suggest two causes of this behavior (remagnetization related to the opening of the Red Sea or later emplacement of the dikes along pre-existing Paleo-Late Neoproterozoic fractures) will have to be tested with new reliable paleomagnetic data on carefully dated rocks. A second component (CB) seen in many of our samples but which is difficult to estimate is in agreement with Late Neoproterozoic granite poles and a dike supposed to be Triassic in age. However, all these poles plot on the Jurassic-Cretaceous portion (80–200 Ma) of Torsvik’s path. These results, as well as the Cambro-Carboniferous sediments from Sinai and the Late Neoproterozoic Dokhan volcanic formation that cluster around the Late Paleozoic portion (280–300 Ma) of Torsvik’s APWP, are tentatively interpreted as global viscous remagnetizations acquired, respectively, during the Cretaceous Normal and the Kiaman Reverse superchrons. Keywords: Paleomagnetism, Africa, remagnetization, Egypt, Late Neoproterozoic, dike swarms.
1. Introduction and Geological Background The basement complex of the Eastern Desert of Egypt is part of the Arabian-Nubian shield that extends from Saudi Arabia and Egypt to the north, and from Sudan, Ethiopia and Uganda-Kenya to the
1 National Research Institute for Astronomy and Geophysics (NRIAG), Helwan, Cairo 11421, Egypt. E-mail: [email protected]
south. The occurrence of ophiolites and their association with calc-alkaline rocks of island-arc affinity has led to the conclusion that the continental crust in this area formed by microplate accretion related to subduction processes and collision tectonics during the Pan-African orogenic event (Farahat et al. 2004). Large masses of volcanic rocks (Dokhan volcanics) and alkaline granites were emplaced during the postorogenic stage. The abundance of east-to-northeasttrending dikes, clastic sedimentary basins and volcanic fields with axes of similar orientation indicates that the crust was actively extending during at least the period 600–575 Ma using Rb/Sr and U/Pb ages (Stern et al. 1984). K/Ar ages in the range 530–480 Ma were obtained from dike swarms located north of the Qena-Safaga road in the Central Eastern Desert (Nairn et al.
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