GEOLOGY, PETROGRAPHY, GEOCHEMISTRY AND RADIOACTIVITY STUDIES ON THE DYKE SWARMS OF GABAL AL AGLAB AREA, NORTH EASTERN DESERT, EGYPT

Gabal Al Aglab area is located in the North Eastern Desert of Egypt bounded by lat. 27° 14'–27° 19' N
and long. 33° 00'–33° 05' E. It is covered by pan African basement rocks. The present study concern with
the geology, petrography, geochemistry and radioactivity of various types of the dyke swarms in Gabal Al
Aglab area. The field studies revealed that the area comprises the following litho-tectonic units ; Dokhan
volcanic (oldest) and Hamammat sedimentary rocks and younger granites are represented by both Gabal
Um Twier and Gabal Al Aglab syenogranites (youngest). Many dykes of acidic, intermediate and basic
composition have a large extension and dissect all the mentioned rock units.
The dyke swarms intruding Gabal Al Aglab area include the acidic (felsite and granite porphyry)
dykes, while the intermediate comprise andesite and andesite porphyry and the basic dykes show basalt
and dolerites. The chronologic relations of these dykes indicate the following sequence of emplacement
beginning with the oldest acidic, followed by intermediate and then basic ones.
The geochemical studies indicate that the acidic dykes were derived from a highly differentiated calcalkaline
magma, while the basic and intermediate dykes were developed from magma of subalkaline
nature. The dykes were derived from separate magmas and not by magmatic differentiation of single
mother magma.
The radioactivity of the studied dyke rocks revealed that the high levels of radioactivity mainly linked
to the acidity, differentiation and alkalinity characters. Radioactive granitic spot was observed along the
contact with some basic dykes due to their thermal effect during its emplacement on the granite, at the
northern part of the studied area. This radioactive spot display anomalies with higher values in U and Th
contents, than the normal background value of the younger granite.