Abstract: The MBC (1.7) is a Microsoft® visual basic 6.0 program that enables the user to calculate the model bulk composition of the rocks, the chemical formula of different phases and the volume percent of the phases (modal analysis). The bulk composition plays an important role to identify the rocks, origin of the rocks and its tectonic environments. The X-ray fluorescence spectroscopy (XRF) is the method of choice for analysis of major elements and some trace elements. Erroneous analytical results may arise for a variety of reasons, such as, contamination, calibration and peak overlap. In many petrological problems, the scientists interpret the rocks in scale smaller than a typical XRF sample size. Therefore, the XRF is unsuitable for such studies. The MBC program can calculate the model bulk composition of such small scale samples based on the volume of the phases and the molar amount of each oxide per the formula unit of the phases. The program has the ability to calculate the chemical formula of the phases. The output results can be printed out in the form of A4 papers. The program code and the necessary support files is approximately 1.5 Mb as a self-extracting setup file.
Abstract: Wadi Kareim area is located about 13 Km to the southwest of Quseir, pertain to Neoproterozoic rocks of the Pan-African Nubian shield, central Eastern Desert of Egypt. The exposed rocks of the area cover about 468 square kilometers and include; schists, ophiolites, arc assemblage, intrusive metagabbros (MG), older granites (OG), Dokhan volcanics, Igla Formation, post-Hammamat felsite, younger granites (YG), alkaline volcanics and Phanerozoic sediments. Detailed field mapping revealed that, the study area shows two structural styles. The northern part is characterized mainly by folds and strike-slip faults, while the southern part is characterized mainly by thrust faults and less folding. The folds generally extend in a NW-SE direction, running parallel to the regional strike of the area. The area has been dissected by different faults of different trends. Thrust faults have NW-SE and WNW-ESE directions, normal faults extend in a NNE-SSW and NW-SE directions and strike-slip faults trending in NNW-SSE, NW-SE. Structural analysis suggests three deformation phases. The first phase is NE-SW compressional force, which caused the folding and the thrust relationship between the ophiolite and the arc assemblage together with NNW-SSE, NW-SE strike slip faults which may be related to the Najd Fault System. This phase was accompanied by regional metamorphism, which affected the area. Before the end of this phase, the Hamammat sediments were depositing in foreland basins. Second phase post-dates the deposition of the Igla Formation and proceeded by NE-SW compressional force. This phase led to folding, development of thrusting and small-scale structures. Because of the continuous stress in the NE-SW direction, a extension zone in NW-SE and a normal fault system with NNE-SSW direction were formed. Third phase started during the Red Sea rifting, is responsible for the formation of a NW-SE normal fault system of Tertiary age and the rejuvenation of the pre-existing NNW-SSE, NW-SE strike-slip faults along the same trends. Deformation phases and related magmatic activity are used to elaborate on the tectonic evolution of the study area. kjk
Abstract: The Wadi Kareim area is a part of the Precambrian basement exposed in the central Eastern Desert. The beds exposed in the area are characterized by a general dip direction towards the NE. The major fractures and faults observed in the area are detected, measured and analyzed. Aerial photographs (scale 1:40,000), mosaics (scale 1:50,000) together with field measurements are used for data acquisition. The regional fracture pattern reveals prominent degree of preferred orientation in NW, NE, NNW and EW, and less significant trends are NNE, WNW and ENE. The fracture density in the studied area is characterized by a medium degree of concentration and a homogeneous distribution. On the other hand, the NW, EW and NE trend sets are the most prevalent ones on aerial photographs and in the field. Field measurements of shear planes show a pronounced NW trending set. All the sets control the geomorphic features, particularly the main drainage trends, e.g. Wadi Kareim, Wadi al-Hammariyyah, Wadi Maktali and Wadi Umm Qiradi. A comparison between both fracture and fault patterns indicates that the NW, EW and NE are the major structural trends affecting the area. The main fault trends, arranged according to their relative age, are E-W, NW-SE, and NE-SW. An active compressive stress is necessary to account for the E-W trend, which should be directed from the north. Field study suggests that the E-W oriented faults are mainly thrusts. Field relations revealed that the serpentinite lenses are arranged in a NW direction in the whole area. The association between serpentinite lenses and the NW direction is a good sign indicates that the obducted oceanic crust (serpentinite lenses) is contemporaneous with the NW thrust faults during Pan-African movements. The association between new volcanics and NE-SW trend could indicate that the NE-SW trend is the youngest trend in study area. The NW-SE trend could have been rejuvenated during the Red Sea rifting in Late Tertiary time.
Abstract: The banded iron formation (BIF) of Wadi Kareim is one of the important Precambrian iron deposits of the Central Eastern Desert of Egypt. It occurs in the form of successive bands and lenses intercalating with the volcanogenic metasediments and metavolcanics. The bands extend for about 2.5 kilometers along NW strike direction and parallel to the regional structure of the study area. The BIF bands vary in thickness from a few centimeters up to 80 meters.
The Wadi Kareim iron-ores and associated rocks exhibit a complicated structural pattern and regionally metamorphosed into greenschist facies. Two compressional phases caused by NE-SW compressional forces have been recognized in the study area. The first phase, developed in BIF and associated volcanogenic rocks, was responsible for the formation of Kareim anticline, trending NW-SE. This phase was synchronous with the regional metamorphism. A second compressional phase causes the development of NW thrusting and small-scale folds. By the continuous of stress in the NE-SW, a tension zone in NW-SE was found and a normal fault system with NE-SW direction was formed. These faults may be rejuvenated as strike-slip faults of the same direction during the Red sea rifting and dissected the banded iron formation, associated metavolcanics and running perpendicular to the Kareim fold axis. The fault population and the iron ore bands are concentrated in the overturned limb and the fold hinge zone.
Mineralogically, the BIF of Wadi Kareim classified into three main types; magnetite, magnetite-hematite and hematite ore. The present ore consist essentially of magnetite and hematite with subordinate amounts of goethite. The gangue minerals include: quartz, calcite and chlorite.
The geochemical study indicates that the ores of Wadi Kareim have the characteristics of the Algoma â type BIF. Field observation indicates that several episodes of volcanic activity occurred. The repetition between the volcanic activity and the relaxation periods is responsible for the interfingering and repetition between banded iron ores and volcanic rocks. The iron ores were precipitated during the relaxation of volcanism, apparently in an intraoceanic island-arc environment.
Abstract:
A group of intrusive and extrusive igneous rocks is located south of Wadi Abu Ziran, Central Eastern Desert. These rocks have diversed petrographic compositions ranging from gabbros to granites with their volcanic equivalents. They belong to four distinct Neoproterozoic units of the Eastern Desert, namely; âMetagabbros (MG), Older Granites (OG), Metavolcanics (MV) and Younger Granites (YG)â. Both major and trace elements are compiled to deduce their genetic relationships. 1/Sr vs. Rb/Sr and Rb/Ba vs. Rb plots suggests that these rock units exhibit comparative magmatic relationships. The trace elements data and the numerical modeling are treated according to the general equation of partial melting (Shaw 1970) and Rayleigh equation of fractional crystallization. These rock types favor complex petrogenetic processes during their generation. The magmatic model is based on âin-sequenceâ genesis between partial melting and fractional crystallization as well as assimilation and / or magma mixing processes in the late stage. It is evident that these rocks resulted from five essential stages during magmatic evolution of the area; 1) Meta-andesite (MV) was generated throughout partial melting (5 %) of oceanic crust followed by fractional crystallization (25-50 %); 2) Gabbroic rocks (MG) were derived by partial melting (46 %) of oceanic crust followed by fractional crystallization (20-40 %); 3) Granodiorite (OG) were derived throughout partial melting (6-6.5 %) of gabbroic parent followed by (5-20 %) fractional crystallization; 4) Alkali-feldspar granite (YG) was derived throughout (45-60 %) fractional crystallization of granodiorite (OG), finally; 5) The recorded hybrid granodiorite rocks (HG) were generated by partial melting of granodiorite (OG) (24.5 %), assimilation and / or partial melting of metagabbros (MG) (11.7 %), followed by magma mixing and (35-55 %) fractional crystallization.
