الفهرس 
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Abstract
The Precambrian rocks of Egypt cover about 100,000 ~KK? in south Sinai and Eastern Desert. These rocks are generally represented by four principal rock units namely: 1) gneisses and migmatites (oldest), 2) ophiolite suites, 3) arc assemblages and 4) granitoid rocks (youngest). The oldest rocks recogneized (gneisses and migmatites) consist of metaquartzites and quartzitic schists that are locally cross- bedded and predominantly feldspatihic. They are exposed in the composite dome structure e.g. at Hafafit (El-Rarnly et al., 1984) and Beitan (Abdel Khalek, 1967). The primary sedimentary structures of these rocks were largely destroyed by intensive deformation and metamorphism whereas the mylonites and the high-grade gneisses are developed. The migmatization effect is represented by the formation of segregations of light leucosomes in the form of thin lamellae parallel to the main foliation of the host rocks, giving them different structural types. Meanwhile, the second major rock assemblages form dispersed and tectonically dismembered ophiolite that occur in large nappe structures (Shackleton et al., 1980; Ries et al., 1983) or in distinct shear zones that may mark sutures between separate crustal blocks (Kroner, 1985). The major ophiolite occurrences are represented at Wadi Ghadir (El-Bayoumi, 1980) and at Gabal Gerf (Kriher et al., 1987). The metavolcanic rocks and their related volcaniclastic assemblages (formerly known as Shadli metavolcanics, El-Ramly, 1972) exhibit paleotectonic environment similar to arc assemblages of recent orogenic belts (Stern, 1979). They form together with metasediments, the matrix of the ophiolitic suites where the latter are abundant emplaced. All the above rock types are intruded by large masses and bodies of granitic rocks that often constitute composite batholitihs. These igneous suites include Older Granites (El-Ramly and Akaad, 1960) which are later -A followed by a variety. of mostly unfoliated, ioften coarse to medium- grained, red to pinkish granite (Younger Granites of El-Ramly and Akaad, 1960).