الفهرس 
Physiography
Geological SettingOnly 14 pages are availabe for public view
 |  | from | 313 |  |  |
| | | from | 313 | | |
Abstract
Um Gheig area is delimited by the latitudes (25◦ 39’ N and 25◦ 45’ N), longitudes (34◦ 20’ E and 34◦ 29’ E) and located at the eastern part of the Eastern Desert of Egypt. The study area dissected by several wadis (e.g. W. Um Gheig, W. Umm Luseifa, W. Wizar, W. Kab Ahmed and W. Umm shaddad) which drain into the Red Sea to the east. The granitic units represent the highest relief in the area. According to the Field studies, the study area can divided into four main rock units, they are from the oldest to the youngest: ophiolitic associations, foliated metavolcanics, granitoids and hammamat sediments as well as some unmapple units of metagabbros and metavolcanics. Ophiolitic associations considered the oldest rock unit and form the largest part of the study area. Based on the field and petrographic investigation, the ophiolitic association subdivided into serpentinites, metagabbros, volcanoclastic metasediments and hornblende schist. Microscopically, the different rock units show several varieties through the petrographic description. Serpentinites comprised antigorite serpentinite with pyroxene relics, antigorite serpentinite and talc carbonate serpentinite. Metagabbros subdivided into hornblende metagabbro and metagabbro with slightly high amount of quartz. Volcanoclastic metasediments includes biotite schist, biotite hornblende schist, garnet biotite hornblende schist, highly mylonitic schist and actionolite schist. Foliated metavolcanics include schistose metatuffs and mylonitic schist. Metavolcanics subdivided according to microscopic investigation into metaandesite and fine metatuff. Granitoids represented by El Deilihimmi granite that includes cataclastic monzogranite and granodiorite as well as syenogranite and alkali feldspar granite of Gabal Umm Shaddad. Hammamat sediments consist mainly conglomerate and greywacke. The pebbles and boulders in conglomerate consist mainly of acid volcanic, felsites, basalt and tuffs as well as subordinate metamudstone. Landsat 8 (OLI) satellite imagery data are successfully used for detailed lithological mapping of Um Gheig area. Different remote sensing techniques such as false compination color (FCC), band ratio, principle component analysis (PCA) and supervised classification were applied on satellite imagery to facilitate the discrimination of the widely exposed lithological units in the study area. The best color composite 432 FCC, 126FCC, 146 FCC and 762 FCC in RGB, band ratio 6/2, 4/3, 7/3 - 7/6, 6/5, 4/2- 7/5, 2/3, 5/6 and 1/4, 3/6, 5/7in RGB, were selected and successfully used for detailed mapping of the different lithological units exposed in the study area. PCA 213, 314, 236 and 321 in RGB used for the accurate delineation of the boundaries between these rock units and Supervised image classification that used to improve the geologic map of Um Gheig area and produce new modified geololgical map of the study area as well as mineral detection. A total of 307 representative spot microprobe analyses of some selected minerals including amphibole, plagioclase, chlorite, epidote, muscovite, biotite, magnetite, hematite, titanite and ilminite were carried out. The raw data were recalculated to obtain the structural formulae and the probable classification diagrams using Minepet software. All the amphiboles from metagabbro rocks range in composition between actinolite hornblende to magnesio hornblende, while all the amphiboles from volcanoclastic metasediments, foliated metavolcanics and hornblende schist are vary in composition from magnesio hornblende, ferrohornblende, tschermakite hornblende to ferro-teschermakite hornblende. Plagioclase composition of metagabbro range in composition from albite to anorthoclase, while plagioclases of hornblende schist, actinolite hornblende schist and biotite-hornblende schist are of oligoclase composition and the plagioclase from mylonitic schist are of albite composition. The analyzed Chlorite from metagabbro are mainly pycnochlorite while those from schist are of brunsvigite, pycnochlorite and diabanite in composition. The analysed epidote from metagabbros and schist fall in the transitional area between epidote and zoisite. selected microprobe analyses of plagioclase, amphibole and chlorite from the different rock units are used to estimate the P-T condition. The calculation of P-T conditions during metamorphism was depended on plagioclase-amphibole pairs and by plotting the microprobe data for the analyzed minerals on appropriate diagrams (e.g. Na + K vs. AlIV diagram of Jamieson, 1981 and Plyusnina ,1982 diagram) and using some spreadsheets (e.g. thermometer of Holland and Blundy, 1994 and equation of Zang and Fyfe, 1995). The available mineral assemblages and the P–T conditions obtained from the different geothermobarometers indicate that the hornblende schist, volcanoclastic metasediments and metagabbros were subjected to prograde low-medium grade regional metamorphism in the range of greenschist to lower amphibolites facies (350–621°C at 2–6 kb). This greenschist to lower amphibolites facies overprint was syn-tectonic with development of foliation associated with thrusting. Structurally, Um Gheig shear belt (UGSB) divided into three main structural domains characterized by distinctive lithology, metamorphic grade, and structural style orientations of foliation and trending of major and minor folds. from east to west these are; Abu Lassaf shear belt, Umm Luseifa shear belt and Kab Ahmed shear belt. Abu Lassaf Shear Belt constitutes the eastern part of the UGSB. It comprised S1 and L1 which transposed by S2, L2 and striking NW to NNW and NE and dips moderately to SW in general and to NE. A number of major asymmetrical folds (Wizr folds and Um Gheig folds) whit fold axis gently plunging to NW and axial plane striking NW-SE as well as a number of major thrusts and normal fault. Major folds and thrusts are sinisterly displaced for up to 1 km by an undulated oblique strike-slip fault mainly between Abu Lassaf serpentinites and foliated metavolcanics. Local shearing along this fault produces S3 schistosity striking mainly NE and E-W and dipping steeply toward SE to S.