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)2011 – 2010( الفصل الدراسي الثاني Basement rocks صخور قاع:المادة "كيمياء- ثالثة علوم "جيولوجيا:الفرقة جامعة بنها كلية العلوم قسم الجيولوجيا "كيمياء-االجابة النموذجية المتحان مادة القاعية للفرقة الثالثة "جيولوجيا )(ورقة امتحانية كاملة 2011-6-25 :تاريخ االمتحان عبدالعظيم أحمد رشوان/. د:اسم الممتحن استاذ الجيولوجيا المساعد بقسم الجيولوجيا – كلية العلوم – جامعة بنها 1- a. the magmatism in Egypt during the Phanerozoic include the following rock group: 1- Basalts. 2- Wadi Natash volcanic 3- Post-granitic dykes 4- Ring complexes. b. The characters of the Egyptian ring complexes are: 1- They intruded within the Pan-African rocks. 2- They consist mainly of different varieties of granites and syenites, nephline syenites, gabbros and equivalent volcanic, all arranged in concentric fashion. 3- They are circular or elliptical in plan, few kilometers diameter. 4- All occurring in the ED south Lat. 25o N, with the exception of Wadi Dip ring complex in the NED. 5- They include complete ring complex, incomplete or crecent-shape. 6- Their compositions ranging basic, intermediate and acidic alkaline. 2- The characters of G2 granites are: 1- All are calc-alkaline in nature. 2- They were formed under environment of compression. 3- They are usually formed small plutons. 4- biotite is always dominant over Hornblende, muscovite is present. 5- Ilmenite is the iron oxide. 6- SiO2 content is more than 65 %, Na2O content is less than 3.2 %. 7- Nb content is from 40 – 50 ppm. 8- The radioactive minerals are high. 9- Low REE. 3- a. A complete ophioltic sections is composed of the following units: Top V- Pelagic sediments IV- Pillow basalt. III- Sheeted dykes complex. II- Cumulate gabbros, massive gabbros. I- Peridotite. Bottom. b. Wadi Gadir ophiolite. The ophiolitic sequence of Wadi Gadir consists from below to upwards of: 1234- The serpentinized peridotites. The gabbro complex. The sheeted dykes. The Pillow basalts 4- The features of the Essexite gabbros are characterized by: 1- These gabbros pertaining to ring complexes. 2- They form small bodies of alkaline gabbros. 3- These rocks show ophitic textures and composed essentially of plagioclase, titanoaugite, biotite, alkali amphibole and little orthoclase. 4- The age recorded for these rocks that were formed from Upper Paleozoic to Upper Cretaceous. 5- The following age succession of units of the Migif-Hafafit with the youngest on the top: - Gneissic tonalite. Intrusive calc-alkaline metagabbros. Psammitic gneisses Biotite shists Foliated metagabbros. Ultramafic rocks.