The significance of gneissic rocks and synmagmatic extensional ductile shear zones of the Barud area for the tectonics of the North Eastern Desert, Egypt
Abstract The mainly tonalitic gneissic rocks, amphibolites, schists and rarer migmatites of the Barud area, at the southern margin of the Egyptian North Eastern Desert (NED) have previously been viewed as products of ultrametamorphism or granitization of pre-PanAfrican basement. The Qena–Safaga Line of approximately NW-striking steeply dipping faults was also regarded as marking the boundary between these NED rocks and the low grade metavolcanics and ophiolitic melange of the Central Eastern Desert (CED). Detailed investigation of the Barud area indicates that the amphibolites, schists and migmatites formed by shearing and medium grade metamorphism of similar arc metavolcanics to those of the CED in normal shear sense extensional ductile shear zones heated by numerous syn-kinematic dolerite, gabbro, diorite, granodiorite, tonalite and granite dykes. They are thus hot sheared equivalents of the CED metavolcanics and basic arc plutonites, accompanied by sheared mafic and felsic intrusive rocks, and are not deep-seated crystalline basement rocks. The shear zones are interpreted as having formed by arc-rifting, not necessarily reaching the stage of marginal basin formation. Arc-accretion structures and those produced by later orogen squeezing are also described. The somewhat gneissic Barud Tonalitic is found to be entirely magmatic. Following intrusion of the Barud Tonalite, and before or during Hammamat and Dokhan deposition, the NED experienced a rapid uplift relative to the CED (∼620–600 Ma) that was not achieved by thrusting along the Qena–Safaga Line.
An integrated approach for mapping mineral resources in the Eastern Desert of Egypt
Abstract Observations of the Earth from space either by satellites or aircrafts are significant approaches for mineral exploration, because of their capability of revealing hydrothermal alteration minerals and sensing the surface/subsurface fracture/fault zones. A study area that is situated in the Pan-African belt of Egypt is tested for targeting potential area of mineral resources involved the hydrothermal system using satellite imagery combined with aeromagnetic, geochemical and field data. Extracted alteration layers using ASTER data and major structures (fault/fracture zones) from DEM, ALOS/PALSAR and aeromagnetic data were prepared and integrated using Knowledge-driven technique in multicriteria-decision making tools for producing mineral prospect map. The results revealed five predictive areas of expected mineral occurrences ranging from excellent to very low. Spectral analysis using ASTER data allowed defining the key-hydrothermal minerals which revealed three successive zones of alterations e.g., argillic, phyllic and propylitic. Plausible areas of minerals fitting to the ore body representing the center of the extensive alterations. Field, geochemical, and ore microscopic investigations validated the results of integrated data. Field data revealed that the mineralization zones extend along NNE-SSW thrust trend that later modified by NW-SE, N-S and NE-SW strike slip faults. Hydrothermal processes related to later magmatic stages probably were responsible for destruction and remobilization of the primary minerals of the host metavolcanics. Microscopic examination revealed that Fe-Cu-Zn-Pb sulfide minerals are associated with auriferous quartz veins. Plausible areas of prospective interest for possible mineralization also were characterized using geochemical analysis. This study successfully displays the key role of integration approach for exploring mineral resources in arid regions.
Detection of Fractures Based on Directional Filtering in Image Logging
According to the feature of the direction of fractures in image logging, a method of fracture detection in image logging based on directional filtering is presented in this paper. The fracture image is filtered by the corresponding filter based on the local direction of fractures, which enhances the fracture traces in the direction of fractures in image logging. The final fracture traces are extracted by the combination of the results of both directional filtering and the threshold segmentation. Experimental results show this method effectively detect the fractures in image logging.