STRUCTURAL LINEAMENTS IN THE BASEMENT ROCKS OF THE CENTRAL EASTERN DESERT, EGYPT

The Egyptian basementrocks outcrop in Eastern Desert, southern Sinai and southwestern Desert. The rocks belong to Precambrian and consist of igneous and metamorphic rocks which are characterized by crystalline character. Not much work has been done on the tectonics and structure of the basement rocks in Eastern Desert. The present work is a photogeological interpretation of the structural lineaments representing dykes, faults and joints in central Eastern Desert to differentiate between igneous and metamorphic rocks. The photogeological interpretation was carried out using normal aerial photographs scale 1:40 000 and photomosaics scale 1:50 000. The main trends of lineaments in the studied area are: E-W, ENE-WSW and WNW-ESE, constituting 58.4% of the total length and 54.5% of the total number. Correlating the structural lineaments in igneous rocks of Gebel El Bakriya locality with those in the metamorphic rocks of Gebel Abu Mireiwa shows that there is a marked difference between the two types. Lineaments in igneous rocks are elongated and widely spaced while those in metamorphic rocks are short and closely spaced. The different trends of joints in igneous rocks can be arranged as follows: WNW > E-W > NW > NNW > ENE > NE > N-S > NNE while the different trends of lineaments in metamorphic rocks can be arranged as follows: E-W > ENE > WNW > NW > NNW > NE > N-S > NNE. Comparison between the structural contour maps constructed for the total length of all lineaments and those representing joints in igneous and metamorphic rocks indicates that igneous rocks have lower density of lineaments than metamorphic rocks. The total length of all lineaments in Gebel El Bakriya amounts to 375 km, while lineaments representing joints have a total length of 150 km. In the metamorphic rocks of Gebel Abu Mireiwa, the total length of all lineaments is 425 km and those representing joints have a total length of 175 km. It was found that there is a relationship between the structural lineaments and radioactivity of the igneous rocks in Gebel El Bakriya. The centers of high density of lineaments in the structural contour maps coincide with the center of high intensity in the radiometric map.