الفهرس 
Geomorphic featuresOnly 14 pages are availabe for public view
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Abstract
The present study is mady concerned with geology, geochemistry, radioactivity and tectonic setting of granitoid rocks and their envelops west Gulf of Aqaba, Sinai, Egypt. The investigated area lies between Dahab and Nuweiba cities and covers about 584 ~rofn Pa~n-h can rocks. It is hted by latitudes 28 29 44 -28 55 33 N and longitudes 34” 24’ 51”-34” 39’ 00 E. The investigated area is mostly covered by granitoid rocks forming moderate to hgh mountainous terrain reachmg up to 985 m a.s.1.. Volcanic and gabbroid rocks constitute minor exposures in the studied area. The most rock units are invaded by pegmatites and dykes of different types running in harmony with the structural trends. Structurallyi faults and joints are the most evident fractures in the study area. It is dissected by 35 major faults trending mady NS, NE, NW, NNW, NNE; WNW, ENE and EW. Joints are the most common minor structure developed in the studied rocks. They are mostly straight and rarely curved. Their trends are generally consistent with the major trends of faults detected. The volcanic rocks cover about 20 ~rannd ~crop out in the southwestern part of the map area. They show mady thrust contacts with their adjacent granitoid rocks. However, small xenoliths of these volcanics are encountered wih the granitoid rocks. Petrographically, three main rock types of volcanics including; rhyolite porphyry,dacite porphyry and trachyandesites are distmgushed. Geochemically, the studied volcanics are characterized by increasing Si02, K20, Zr, Ba and La contents fiom trachyandesites, dacite porphyry to rhyolite porphyry and decrease in N2o3, Ti02, Fe203, FeO, MgO, CaO, P205, Ni, CO and Zn contents in the same trend. They are generally similar to Dokhan Volcanics of Gabal Dokhan, Eastern Desert and have great resemblance with Kid volcanics, southern Sinai (Moghazi, 1994). The studied volcanics have been derived fi-om a magma of calc-alkaline affhty and developed in island arc setting. Radiometrically, the studied rhyolite porphyries are relatively more enriched in U and Th than the other types of the studied volcanics. Ths confirms the fact of increasing the contents of the ralo-elements with increasing the acidity of rocks. The gabbroid rocks (- 4 ISm2) crop out in two isolated localities; El Hibeigyia and Dahab. Petrographically, the gabbroid rocks of El Hzbeigyia locality are represented mainly by pyroxene-hornblende gabbronorite and pyroxene-hornblende gabbro whereas gabbroid rocks of Dahab locality are represented by gabbronorite, norite and uralitized gabbro. The opaque mineralogy showed that magnetite is the main constituent in El Hibeigyia gabbro whereas titanomagnetite and henite are the main opaques for such rocks in Dahab local. Geochemically, Dahab gabbros are relatively more enriched in Ti02, FeO and V contents as well as Mg# than those at El Heibigyia. Both types are classified geochernically as syenogabbror. They were derived fi-om transitional calcalkaline tholeiitic magrna.Tectonically, the studied gabbroid rocks are mostly generated in continental environment passing through an active continental margin and intraplate settings in early and later stages of magma crystallization respectively. Radiometrically, the studied gabbroid rocks show low contents of the radio-elements; U, Th, eU(Ra) and K. Their average contents of U and Th fall wih the average of the similar basic rocks given by many authors. The granitoid rocks represent the main target of the present study. They cover about 560 of the study area. The field aspects and petrographic studies indicated that these rocks are represented mady by four fractionated granitic masses of intrusive nature; granodiorites / MMZ granodiorites, monzogranites and syenogranites. GranodioritesIMMZ granodiorites cover about 144 K.rd of the study area and constitute the central part of the area. They are usually exfoliated and enriched in mafic inclusions especially along Wadi hssasa. Monzogranites cover about 304 &I? of the study area. They are exposed in the northeastern, central and southern parts of the area. These rocks are mostly jointed and fractured especially at Wad Farsh where tectonized monzogranites are recognizable. Syenogranites cover about 112 Km2 of the study area and are mainly exposed in the central eastern and western parts of the area. They are h@ly fractured and jointed.