Al-Azhar Bull. Sci. Vol. 21, No. 2 (Dec.): PP. 19-43, 2010 TECTONIC FRAMEWORK OF EAST GABAL NUQRA AREA, SOUTH EASTERN DESERT, EGYPT MOSTAFA, M.S., IBRAHIM, I. H. AND HASSAAN, A. H. Nuclear Material Authority, Cairo, Egypt. Abstract A singular complex-shaped, circular structure of crescent-shape (centered on 24 o 22 ’ N and 33 o 45 ’ 30 ’’ E), about 10 km in diameter, are located to the east of Gabal Nuqra at the extreme western part of Natash volcanic in the south of Eastern Desert, Egypt. This structure is a clear incomplete ring dyke complex that produced by volcano-plutonic systems comprising a suite of alkaline granite intrusions and volcanic ring dykes (dacite porphery, alkaline rhyolite and granophyre) extruded by a recent trachy-basltic flow. These rocks cut into the local geology of the Nubian Sandstone, which defines the rim of the structure that emplaced through out three magmatic events, the 1 st (granites) associated with development of the Nubian sandstone basin, the 2 nd (volcanic ring dykes) is post to its formation (Natash volcanics) whereas the 3 rd (trachy-basltic flow) is related to the Red Sea rifting. The detailed field studies show that east Gabal Nuqra area has been affect by at least three tectonic events where the reactivation interaction of the preexisting NW- SE with the E-W to ENE-WSW basement fabrics as normal configure the Nubian sandstone basin while the granitic intrusions are mainly controlled by the NW-SE structural trend whereas their reactivation localize the emplacement of the ring dykes and their interaction with NE-SW ones configure the trachy-basltic flow. Hydrothermal activities enriched in REEs, Zr, Nb, Ba, U and Th that could be late to post 2 nd magmatic event have been clearly recorded at the ring dykes complex at east Gabal Nuqra area that confirmed by the presence of hydrothermal zircon, REE-silicate, cerrusite (Pb-carbonate), kasolite and barite among the whole ring structure. These rocks show eU-contents ranging from 2 ppm to 45 ppm and eTh- contents ranging between 5 ppm and 98 ppm. The all area is affected by highly ferrugination and silicification. Key words: Gabal Nuqra, ring dykes, fault systems, tectonic setting & Nubian sandstone basin. Introduction Over, 50 discrete ring complexes (mostly per-alkaline granites) had been emplaced throughout the Arabian Shield (Stoesser and Elliott 1980) and more than 130 ring complexes in Egypt, Sudan and Ethiopia with their greatest concentration between Lat. 18˚ to 25˚ N in the Eastern Desert and Nile Valley. Razvalyayev and