Geology and spectral characterization of the basement rocks at Gabal Gerf area, southeastern Egypt

Gabal Gerf area in southeastern Egypt is covered by a sequence of Pan-African basement rocks comprising allochthonous ophiolitic rock assemblages thrusted over calc-alkaline metavolcanics and high grade metasediments. These rocks are intruded by syn-to late-tectonic intrusions including gabbro-diorite and tonalite-granodiorite and late tectonic intrusions of layered gabbro and monzogranite as well as dykes and veins. Sheared metamorphosed ultramafic rocks with the locally pillowed basic metavolcanics are the main components of the Gerf huge ophiolitic nappe complex extending between the N-S Hamisana zone and the Heinai Allaqi ophiolitic belt. The processed digital data of Landsat MSS and ETM ratio images covering the study area have been used. The digital number values (pixel values) and the spectral signature curves have been delineated for the different encountered basement rocks on both raw ETM and false colour composite (FCC) ratio images. This study revealed that the TM image bands 7, 4, 2 improves the lithological discrimination of the schistose rocks and massive intrusions and distinguish the linear features (dyke swarms and faults). On the other hand, the different basement rocks exposed in the investigated area particularly the different varieties of the same lithologic unit can be accurately discriminated using the FCC ratio image (5/7, 5/1, 4) in red, green and blue (RGB).