Space-Borne Imagery and Geochemical Characters of Post-Orogenic Dyke Swarms, Fatirah-Abu Zawal District, Eastern Desert of Egypt

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 Na 2 O, K 2 O, Ba, Y, Rb, Zr and Th contents increase from basic to acidic dykes and vice versa relative to CaO, MgO, Fe 2 O 3 , 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.