THE THIRD INTERNATIONAL CONFERENCE ON THE GEOLOGY OF AFRICA Vol. (2), P-P. 201-231 (DEC. 2003) ASSIUT-EGYPT PETROLOGY, MINERAL CHEMISTRY AND TECTONIC EVOLUTION OF THE NORTHERN PART OF WADI HAFAFIT AREA, EASTERN DESERT, EGYPT. G.A. El Bahariya* and M.A. Abd El-Wahed** Geology Department, Faculty of Science, Tanta University, Tanta, Egypt ABSTRACT The studied area is located between the central and southern parts of the Eastern Desert of Egypt and occupies the northern part of Wadi Hafafit. Field geology, structural criteria, petrography and mineral chemistry have been used to construct the origin and tectonic evolution of this area. The rocks are mapped and classified lithologically into foliated metagabbro, foliated tonalite, mylonitic unit and deformed granite, together with slices of metamorphosed ultramafics along tectonic faults. An outline of the kinematics is presented in order to show the interaction of the major magmatic, structural and metamorphic events. Four deformational events have been recognized in the studied rocks (D 1 -D 4 ). D 1 event is manifested by a major F 1 oval-shaped closed fold in foliated tonalite and metagabbro with the axes plunging 19 o / N32 o W and 10 o /S30 o E. During D 2 , minor folds were formed with the axes plunging 30 o /S40 o W. D 1 and D 2 represent two successive but continuous phases of deformation and appear to be responsible for the domal structure in the studied area. D 3 resulted in a major thrusting and mylonitic foliation. The axes of minor F 3 folds with the axes plunge 12 o /S6 o E and 16 o /N5 o W. D 4 is a consequence of later thrusting, major and local strike slip faults and shearing. Three metamorphic phases synchronous with the four deformational events have been recognized. Syn-D 1 and D 2 regional metamorphism (M 1 ) and migmatization occurred under upper amphibolite and granulite facies conditions. Local dynamo-thermal metamorphism (M 2 ) synchronous with D 3 , which overlapped or ended by the intrusion of the deformed granite. Late retrograde metamorphism (M 3 ) occurred during D 4 later shearing. The P-T conditions of magmatic and metamorphic processes have been estimated using mineral chemistry and geothermobarometry of plagioclase, pyroxene and amphibole, muscovite, biotite, garnet and chlorite. The first metamorphic event (M 1 ) of the foliated metagabbro records a peak metamorphism at about 800 o C and 7.5 kbar, corresponding to upper amphibolite to lower granulite facies metamorphism, under which the tonalite is suggested to have been formed by partial melting of lower crustal gabbroic rocks. This melt has ascended and was syntectonically emplaced into middle crustal levels where it crystallized at relatively low T (550 o C) and P (6.2 kbar). The mylonitic unit has undergone dynamo-thermal metamorphism (M 2 ) under greenschist to lower amphibolite facies conditions (T 550 o C and P 3-4 kbar). The deformed granite was most probably formed by partial melting of lower to middle crustal protoliths under P-T conditions of 770 o C and 4-8 kbar, which was later emplaced and crystallize at relatively low T (550 o C). M 3 retrograde metamorphism occurred during D 4 under temperature range of 170 o -227 o C. The studied rocks are the consequence of tectono-magmatic and tectono-metamorphic processes. They were formed during the orogenic compressional phase of the Pan-African orogeny in an active continental margin tectonic setting. Later tectonics and uplift were followed by deep-erosion which led to the exhumation and exposure of the deep-seated rocks. INTRODUCTION The continental crust of the NE Africa was formed during the late Precambrian to early Palaeozoic Pan-African event (950-450 o C; Kröner, 1984). One of the most spectacular Precambrian rocks in the Eastern Desert of Egypt is exposed in the Migif-Hafafit area. Gneisses and associated migmatites, by and large, have long been thought to constitute the