الفهرس 
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Abstract
Summary and Conclusions
The present work is mainly devoted to:
1- the study of the surface structural pattern of the area located between latitudes 28o 23/ and 28o 55/ and longitudes 29 o 50َ/ N and 30o 57َ/ E in west Beni Mazar – Maghagha cities, western desert Egypt.
2- Geoelectrical studies around El Bahnasa basaltic ridge.
The classic and modern techniques in structural studies such as description and paleostress were applied.
Lineaments were determined from the mosaics and TM landsat images, while folds, faults and joints are measured in the field.
Physiographically, the study area exhibits morphotectonic high lands and depressions. It ranges in elevation from 0 to 200 m.
The surface sedimentary sequence in the area under investigation includes:-
1- Lower Eocene (El-Nashfa Formation).
2-Middle Eocene(El Minia, Samalut, Midawara, Sath El Hadid Formations .
3- Oligocene (Basaltic intrusion).
4- Quaternary (Sand Dunes, Sand and Gravels).
The morphometric analysis of seven wadies trending NW-SE indicates that they have a complex geomorphologic history probably due to tectonic effects. Bifurcation morphometeric diagram reflects that the major part of the area has been drained mainly by Wadi number 1 relative to other Wadies.
The drainage density values of the Wadies range from to1-7, indicating their structurally controlled origin. Large number of the water wells in the study area are located along these Wadies, which indicate that the ground water in the study area is controlled by structural Wadies.
The structural interpretation of the mosaics and Landsat images as well as field measurements indicate that the main trends of the lineaments are N 15o W, N 35 o W, N25 o E, and N 55 o E.
The structural analysis of the NW joint set indicates that these joints are right stepping and overlapping. The right stepping in these joints was probably developed as a result of a right handed rotation of the maximum principal stress at that time. In the light of the theoretical results after Olson and Pollard (1988, 1989), the overlapped joints are interpreted as a decrease in the stability of propagation direction of the joints and the normal stress parallel to the main joint has a greater tension than that normal to the main joint.
The description analysis of the folds in the area indicates two NE-SW plunging anticline folds (El Nashfa and Dur El Abyad). These folds are probably related to ENE deep seated right-lateral shear zones like the shear zones in Abu Roash and El Baharyia Oasis. These shear zones are probably related to the NW-SE compression as result of the convergence between the Afro-Arabian plate and Eurasian plate since Upper Cretaceous and till the present time.
The field measurements of the faults indicate three main trends (NE-SW, NW-SE and WNW-ESE). The WNW-ESE trends is associated by volcanic eruptions. These faults are probably inherited from old Precambrian tectonic events. They were rejuvenated during the NE-SW divergence movement between Arabian and African plates in Oligocene- Early Miocene.
The fault planes and slickenlines are measured along the NW-SE and NE-SW fault trend.
About thirteen fault planes and their striations were measured in the study area. The paleostress analysis of these data indicates that the maximum principal stress axis σ1 is nearly vertical, while the orientation of the minimum principal stress axis σ3 has NE-SW trend.
The geophysical studies indicate that the area around El Bahnasa basaltic ridge is structurally complicated. It was occupied by large semi-basin like structure. The basin depocenter is located at the eastern side of the basaltic ridge in which sub-sea depth equal – 60m was reached. The periphery of this basin is located in the eastern and southern edges in which up-sea depths of about 30m and 50m were recorded.
The basin indicates subsurface features as; lateral variation in rock succession, up and down displacement, thinning and thickening, abrupt and conspicuous thickening of layers on the downthrown blocks.
This basin is dissected by three faults (F1, F2 and F3). The fault (F1) and The fault (F3) is normal fault trending in NW-SE direction (Suez trend) and has throw equal 40m toward NE direction are major normal faults with maximum throw of 80m toward northeast direction and is aligned in WNW-ESE direction. This fault appears to be played an important role in the formation of the El Bahnasa basaltic eruption . The fault (F2) is strike-slip one with lateral displacement equal 400m. It trends in NE-SW direction.
The basaltic magma was extended along the zone of the major normal fault (F1) within the shale basin. lateral shift of the basalt body and also the major fault (F1) are dislocated by the strike-slip fault (F2).