Utilization of ETM+ Landsat data in geologic mapping of wadi Ghadir-Gabal Zabara area, Central Eastern Desert, Egypt

Abstract

The Wadi Ghadir area, Central Eastern Desert, Egypt is covered by a sequence of Pan-African basement rocks comprising allochthonous ophiolitic rock assemblage thrust over Gabal Zabara gneiss. The ophiolite sequence comprises layered gabbro, pillowed basalts, island arc metavolcanics and low grade metasediments. These rocks are intruded by syn-to late tectonic intrusions followed by basic and acidic dyke swarms. The processed digital data of Landsat 7 ETM+ covering the study area have been used. Several products of Landsat-7 ETM+ digital data such as true color image (3, 2 and 1 in RGB), false color composite images (7, 4, 2 and 7, 5, 1 in RGB), principal component (PC2, PC1, PC4), band rationing images (5/1, 3/2, 7/2), (5/3, 4/2, 3/1) and (3/1, 4/2, 5/7) are generated. Products of image processing improve lithological discrimination specially of serpentinites talc carbonate rocks and different varieties of intrusive rocks. Supervised and unsupervised classifications have been used to recognize and discriminate between the different rock units.The obvious color contrast of ratio images enabled easier delineation of major structural features characterizing the mapped area. NNW-SSE striking, easterly dipping, thrust faults are located in the western part within the study area. They are associated with asymmetrical folds whose axial planes are parallel to these thrusts. Other NW folds affecting gabbro masses and mélange rocks could easily be delineated and verified during field observations. Two sets of shear zones of NW and NE trends affect the mapped area. Lineament analysis revealed the prevalence of two main structural trends NW-SE and NE-SW.