Abstract
The Precambrian rocks in Wadi Fatirah-Wadi Abu Zawal area, Eastern Desert of Egypt, are crosscut by numerous post-orogenic dyke swarms. Image processing techniques are applied to the enhanced Thematic Mapper plus (ETM+) data for lithological mapping and spectral characterization of these dyke swarms. Band ratios and principal component analysis (PCA) yield conspicuously effective results. Depending on mineralogical and geochemical data, two petrogenetic groups of dyke swarms have been recognized: the first group (mafic dykes) comprises basalt, basaltic andesite and andesite, while the second group (felsic dykes) corresponds to dacite and rhyolite in composition. The mafic dykes are tholeiitic to calc-alkaline, while the felsic dykes display significant calc-alkaline affinity. The Na2O, K2O, Ba, Y, Rb, Zr and Th contents increase from basic to acidic dykes and vice versa relative to CaO, MgO, Fe2O3, Sr, V, Co and Ni contents. These dyke swarms have been emplaced in post-collisional, destructive plate margin settings during periods of extension. The basic dykes have characteristics of volcanic arc setting, whereas the acidic dykes display geochemical features of within plate rocks. The chemical differences between the mafic and felsic dyke swarms favor that the two groups of dyke swarms cannot be related to the same magma source, but they are formed from two different parental magmas.
Highlights
The Arabian Nubian Shield (ANS) is a compilation of Neoproterozoic juvenile arcs, younger sedimentary and volcanic basins, voluminous granite intrusions, and enclaves of pre-Neoproterozoic crust that crop out in the western Arabian Plate and the northeastern African Plate at the northern end of the East African Orogen [1]-[3]
Visual examination of the generated false color combination (FCC) principal component analysis (PCA) images in this study revealed that the RGB combinations (PC3, PC1, PC4) and (PC4, PC2, PC3) are the most informative images
Ma) in the ANS occurred in an extensional tectonic environment [7] [71] [72] and was accompanied by abundant igneous activity: emplacement of alkaline granitoids, eruption of bimodal volcanics, and intrusion of bimodal dyke swarms [1] [6] [73]-[75]
Summary
The Arabian Nubian Shield (ANS) is a compilation of Neoproterozoic juvenile arcs, younger sedimentary and volcanic basins, voluminous granite intrusions, and enclaves of pre-Neoproterozoic crust that crop out in the western Arabian Plate and the northeastern African Plate at the northern end of the East African Orogen [1]-[3]. Composite dykes that are made up of felsic and mafic rocks are abundant in the ANS, in particular in the Eastern Desert and Sinai of Egypt [14]-[16]. These dykes are incorporated in bimodal basalt-rhyolite dyke suites forming dyke warms up to tens of kilometers long. Band rationing and principal component transformation are the main remote sensing techniques applied to achieve this aim It aims to provide valuable petrological and geochemical data that help in understanding the origin of dyke swarms, their source component(s) and processes involved in magma genesis and evolution
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