Geology, structure, geochemistry and ASTER-based mapping of Neoproterozoic Gebel El-Delihimmi granites, Central Eastern Desert of Egypt

Abstract

The Gebel El-Delihimmi granite intrusion, located in the Central Eastern Desert of Egypt, cuts the core of a major anticlinal structure of calc-alkaline metavolcanics and ophiolitic mélange rocks. The intrusion is microscopically differentiated into granodiorite, monzogranite, syenogranite and alkali-feldspar granite. Decorrelation stretch and band-ratio techniques were applied to Advanced Spaceborne Thermal Emission and Reflection Radiometer data. Processing of ASTER-SWIR bands enabled discrimination of El-Delihimmi granite phases and generation of a detailed lithologic map of the study area. The structural and microfabric data suggest that the El-Delihimmi granite underwent at least two phases of deformations. The first was related to the Najd fault system during which the older granodiorite phase of the intrusion was affected by sinistral ductile shearing. During the second phase, monzogranite and syenogranite in the intrusion were affected by brittle E–W compressional deformation. Geochemical data reported here reveal that the granodiorite phase has K2O/Na2O ratio <1 and represents an evolved calc-alkaline granite. The monzogranite, syenogranite and alkali-feldspar granite phases have K2O/Na2O ratio >1. The granite phases are generally I-type, metaluminous to slightly peraluminous and are interpreted as formed above subducted slabs of oceanic lithosphere rather than in continental collision zones.