North Eastern Desert Research Articles

Geochemistry, mineral chemistry and petrogenesis of a Neoproterozoic dyke swarm in the north Eastern Desert, Egypt

Dyke swarms traverse Neoproterozoic rocks in the Hawashiya region in the extreme northern part of the Eastern Desert of Egypt. They are a suite of basaltic andesite and andesite mafic dykes, and dacitic and rhyolitic felsic dykes. The mafic dyke suite is more abundant in the younger granites (577 ± 6 Ma) than in the older granitoids (614 Ma), in which the felsic dykes are the most common. The dyke swarms trend predominantly NE–SW, and the felsic dyke suite is older than the mafic dyke suite. Both dyke suites are calc-alkaline (alkaline dykes are rare) and are relatively poor in TiO2 and Nb but enriched in the incompatible elements and HFSE. The felsic dyke suite is enriched in REE and is strongly LREE fractionated relative to the mafic dyke suite. Although the Hawashiya dykes were emplaced at the end of the Neoproterozoic era in an extensional tectonic setting, they have geochemical characteristics that are consistent with a subduction-related regime. These chemical signatures were inherited from the lithospheric rocks that produced their host Hawashiya granitoids. The felsic dyke suite magma may be derived from crustal rocks (essential source component) by partial melting. The mafic dyke suite magma was generated from a lithospheric mantle and has undergone fractional crystallization of plagioclase, amphibole, clinopyroxene and magnetite, as documented by major and trace elements fractionation modelling.

Petrological and geochemical constraints on the tectonomagmatic evolution of the late Neoproterozoic granitoid suites in the Gattar area, North Eastern Desert, Egypt

Late Neoproterozoic granitoid rocks from the Gattar area, north Eastern Desert of Egypt, belong to three distinctive magmatic suites, namely: (1) calc-alkaline older granitoids, (2) mildly alkaline subsolvus younger granitoids, and (3) alkaline hypersolvus younger granitoids. These suites are genetically unrelated. The older granitoids consist of three main varieties: quartz-monzodiorite, quartz-monzonite and granodiorite. They show enrichment of LIL elements, high LREE/HREE ratio, with little or no Eu anomalies, and HFS elements are generally low, and further, exhibit metaluminous (ASI < 1) affinity with I-type features. The parental magma for this suite is most probably of mantle derivation. The most mafic quartz monzodiorite represents 25 % batch melting of garnet lherzolite lower crustal source followed by fractional crystallization producing quartz-monzonite and granodiorite emplaced in a volcanic arc environment. The Gattar younger granitoids have metaluminous to slightly peraluminous and alkaline affinities. They can be classified as mildly alkaline subsolvus and alkaline hypersolvus granites. The younger granitoids cannot be related to the older granitoids by simple fractionation from one parental magma. Hypersolvus granites have higher contents of Rb, Y, and Nb and lower contents of TiO 2 , Sr, Ba and REE and have more pronounced negative Eu anomalies than the subsolvus granites. Subsolvus granites have post-orogenic (A2-subtype) features, while hypersolvus granites have anorogenic (Al-subtype) characters. Mildly alkaline subsolvus granites have been generated by fractional crystallization of mainly K-feldspar, plagioclase, biotite, hornblende and accessory phases such as allanite, titanite and zircon from a mafic magma in order to generate their chemical variations. The alkaline hypersolvus granites, on the other hand, could be generated by about 10 % batch melting of amphibolite in the lower crust. The presence of leached biotite-hematite-fluoride clots in the hypersolvus granites suggests that fluid fractionation and fluorine complexing have played some role during the evolution of the hypersolvus granites.

A re-evaluation of the origin and setting of the Late Precambrian Hammamat Group based on SHRIMP U–Pb dating of detrital zircons from Gebel Umm Tawat, North Eastern Desert, Egypt

A sample from near the base of the sedimentary Hammamat Group at Gebel Umm Tawat, North Eastern Desert, Egypt, contains detrital zircons with sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages as young as 585 ± 13 Ma. This age is within error of recent SHRIMP dates from the adjacent Dokhan Volcanic Series and establishes that they contributed material to the sediments. It is also c . 45 Ma younger than any zircon analysed from the upper part of the sedimentary sequence, suggesting that the volcanic source was either totally eroded or lay buried beneath the evolving Hammamat Group. Zircon populations in both samples show age peaks at 640 and 680 Ma; the former not previously identified as the time of major igneous activity in the North Eastern Desert. Both samples also contain zircons with ages ranging between c . 750 and c . 2630 Ma, indicating contributions from Proterozoic and Archaean sources unknown in the North Eastern Desert. The source of these zircons may lie to the SE in the Central and South Eastern Desert, to the SW in the Nile Craton, where sparse zircons of this age have previously been recorded, or they may be derived from further afield in the Arabian–Nubian Shield, from earlier continental nuclei incorporated during crustal accretion. Alternatively, as sedimentary clasts in the Hammamat samples indicate erosion of earlier sedimentary rocks, also unknown in the area, these may have been the direct source of the older zircons. However, whichever interpretation is correct, it appears likely that the Hammamat Group was deposited in a major fluvial system of continental proportions and not in isolated basins as previously believed.

Dinoflagellate cyst biostratigraphy of Jurassic-Lower Cretaceous formations of the North Eastern Desert, Egypt

Dinoflagellate cyst biostratigraphy of Jurassic-Lower Cretaceous formations of the North Eastern Desert, Egypt

Construction of a hydrologic model for estimating Wadi runoff and groundwater recharge in the Eastern Desert, Egypt

We constructed a hydrologic model to estimate the groundwater recharge rate for alluvial aquifers of the Eastern Desert from sporadic precipitation over the Red Sea hills. To estimate initial losses over sub-basins, transmission losses through channel routing, and downstream runoff, we developed an integrated model combining spatial rainfall distribution, an appropriate basin unit hydrograph, and appropriate infiltration parameters. Watersheds and stream networks identified from digital terrain elevation data were verified by comparison with co-registered Landsat thematic mapper scenes and geologic maps. Records of a November 1994 storm event acquired from rain gauges along the Nile River and the Red Sea shore were used to generate a spatial precipitation distribution for the study area. A 2 hour design hyetograph was adopted from rain gauge data for the 1994 flood event. The model was tested against records from the November 1994 flood event at the outlets of the Tarfa and Hammamat watersheds.Groundwater recharge rates were estimated for the alluvial aquifers within the major watersheds of the north Eastern Desert. We estimated that during the 1994 flood event, the ground water recharge through transmission losses ranged from 21 to 31% (Tarfa: 15.8×106m3; Asyuti: 20×106m3, Qena: 49×106m3, Hammamat: 59×106m3) of the precipitated volume. The initial losses ranged from 65 to 77%. Only 3–7% of the precipitation reached the watershed outlets. Archival data show that rainfall events of the size of the November 1994 storm or larger occur every 40 months; thus, the annual recharge rates for the Tarfa, Asyuti, Qena, and Hammamat alluvial aquifers are estimated at 4.7×106m3, 6×106m3, 14.7×106m3, and 17.7×106m3, respectively. Implications for the use of these renewable ground waters and similar water resources in other arid areas of Egypt and in neighboring countries are clear.

Application of thorium-normalized airborne radio-spectrometric survey data of Wadi Araba area, North-eastern Desert, Egypt, as a guide to the recognition of probable subsurface petroleum accumulations

A new exploration method has been developed by Saunders et al. (Geophysics 58(10) (1993) 1417) using surface and aerial gamma-ray spectral measurements in prospecting for petroleum in stratigraphic and structural traps. Wadi Araba area, North-eastern Desert, Egypt, was selected to apply this method on its recorded aerial gamma-ray spectrometric survey data, due to its distinct stratigraphic and structural setting as well as its situation in close connection with the Gulf of Suez, which represents one of the important sites of oil production in Egypt. The three variables (eU, eTh, and K) registered for the whole study area, in the form of three contour maps, were digitized along the flight paths every 1.0 km. The DRAD arithmetic means plus three standard deviations for the data set were computed. Any single profile value greater than this quantity should have a probability of 99.87% that it represents a valid anomaly and is not caused by random variations in the background values. The use of these criteria has identified one flight line which has a valid anomaly that is not caused by random variations in the background values. This might indicate a prospective possibility for petroleum accumulation in the Wadi Araba area, North-eastern Desert, Egypt.

Lower Miocene stratigraphy of the Gebel Shabrawet area, north Eastern desert Egypt

The Lower Miocene carbonate/siliciclastic sequence of the Shabrawet area, comprises a complex alternation of autochthonous and allogenic sediments. The sequence can be subdivided into two lithostratigraphic units. The lower unit (unit I) is equivalent to the Gharra Formation. It is mainly clastic and composed of sandstones, siltstones and shales with minor limestone intercalations. These sediments are rich in Clypeaster spp., Scutella spp., Miogypsina intermedia, Operculina complanata, and smaller foraminifera. The upper unit (unit II) was considered by previous workers as being equivalent to the Marmarica Formation. It consists mainly of non-clastic rocks, dominated by sandy and chalky limestones rich in larger foraminifera (miogypsinids and nummulitids). This unit is topped by a highly fossiliferous ( Heterostegina, Operculina and Planostegina) sandy limestone. The present study places both units in the Gharra Formation and reports for the first time M. intermedia from the Miocene sequence of the Shabrawet area.

Study of radioactivity levels in granite of Gable Gattar II in the north eastern desert of Egypt

The present work deals with the radioactivity of granites in Gable Gattar II, which is located in the north eastern desert of Egypt. Fifty samples from the area of Gable Gattar II were investigated. The radionuclides of the samples, in Bq/kg, have been measured using a hyper-pure germanium spectrometer. The dose obtained for 238U and 232Th ranged from 165±5 to 27851±836 and 71±2 to 274±8 Bq/kg, respectively. The dose of 40K only changes slightly. To assess the radiological hazard of the natural radioactivity in the samples, the radium equivalent activity, the absorbed dose rate and the external hazard index were calculated. This study provides a baseline map of radioactivity background levels in the Egyptian environment and will be used as reference information to assess any changes in the radioactive background level due to geological processes. The Gable Gattar granite, from uranium mineralization, has high economic potential.

SHRIMP U-Pb Dating of Detrital Zircons from the Hammamat Group at Gebel Umm Tawat, North-Eastern Desert, Egypt

SHRIMP U-Pb Dating of Detrital Zircons from the Hammamat Group at Gebel Umm Tawat, North-Eastern Desert, Egypt

Significance of SHRIMP U-Pb dating of the Imperial Porphyry and associated Dokhan Volcanics, Gebel Dokhan, north Eastern Desert, Egypt

SHRIMP U-Pb zircon dating was undertaken on two samples of Dokhan Volcanics from the type area at Gebel Dokhan, north Eastern Desert, Egypt. A quartz andesite from the Imperial Porphyry unit has a weighted 206Pb/238U age of 593 ± 13 Ma (2σ). A sample of grey andesite, from ~450 m lower in the succession, has a weighted 206Pb/238U age of 602 ± 9 Ma (2σ). These ages are interpreted to record the time of eruption of the Dokhan Volcanics. Two concordant zircon cores in the upper sample define a weighted 206Pb/238U age of 685 ± 16 Ma (2σ), indicating inheritance from an older source. These cores have oscillatory zoning and may be derived from the ‘older’ granite basement or even an earlier volcanic sequence in the area. Care should, therefore, be taken in correlating all volcanic rocks in the Eastern Desert of Egypt with the Dokhan Volcanic Formation, as defined at the type locality.

00/00681 Study of structure analysis of oil shale and fuel manufacturing technology. 9

Lower Paleozoic rocks are exposed in various regions of Egypt (south central Sinai, north Eastern Desert and southwest Western Desert), in addition to occurring in the subsurface such as north Western Desert and the Gulf of Suez. The Lower Paleozoic rocks in Egypt include surface and subsurface rock units of formational status. The surface rock units are the Taba, Araba and Naqus formations. The subsurface rock units include the Shifa, Kohla and Basur formations.The Infracambrian Taba Formation has been discovered recently in the outcrops of the southeast central Sinai in the Taba-Ras El-Naqab area. It is missing and/or not recognized in the subsurface. The Taba Formation consists mainly of reddish brown, unfossiliferous gravelly fine- to medium-grained kaolinitic sandstones and subordinate horizons of paleosols. The Cambrian Araba Formation and its subsurface equivalent (the Shifa Formation) are essentially composed of reddish brown, fine-grained laminated sandstone and siltstone with abundant Skolithos and Cruziana sp. In contrast, the Ordovician–Silurian Naqus Formation and its subsurface equivalents (the Kohla Formation and Basur Formation) are mainly composed of white, unfossiliferous, cross-bedded, medium- to coarse-grained sandstones with haphazardly distributed pebbles and cobbles. Sedimentological analysis indicates that the Araba Formation and its subsurface equivalent were deposited in a marginal-marine environment, whereas the Naqus Formation and its subsurface equivalents were laid down in a fluvio-glacial environment.Integrated stratigraphic and sedimentological studies of the Lower Paleozoic rocks permit reconstruction of the paleogeography of Egypt at that time. Egypt has been largely controlled since the Cambrian by the pre-existing structural framework of the pre-Phanerozoic basement rocks inherited from the Late Proterozoic Pan-African event. Additionally, sedimentation processes were controlled during Cambro-Ordovician times by tectonic movements, whereas glacio-eustatic control predominated during the Late Ordovician–Silurian Period. These studies suggest that most areas of Egypt were exposed lands with episodically transgression by epi-continental seas related to the paleo-Tethys. These lands formed a part of a stable subsiding shelf at the northern Gondwana margin.

Composition-Volume Changes during Metasomatic Alteration of Pan African Andesitic Volcanic Rocks at Gabal El Dokhan Area, Northeastern Desert, Egypt.

Metasomatic alterations of the Late Proterozoic andesites at Gabal El Dokhan area display obvious change in mineralogical and chemical composition, if compared with the least altered andesitic rock types (assumed protoliths). These altered andesitic rocks have been metamorphosed to lower-middle greenschist facies typified by biotite-actinolite-chlorite-albite-epidote-quartz-opaque minerals/sphene assemblages. Five alteration facies have been recognized: 1) Bio- titization-silicification, 2) Sericitization-silicification, 3) Albitization- silicification, 4) Epidotization-silicification, and 5) Chloritization. The biotitized-silicified rock types are enriched in K-Rb-Ba-FTSM and depleted in LREE relative to the least altered rock. The se- ricitized-silicified rock types are significantly enriched in K-Rb-Ba and depleted in FTSM and LREE. The albitized-silicified rock types are strongly enriched in Na and depleted in LILE and LREE relative to the least altered rock types. The epidotized-silicified rock types are enriched in Ca-Cu-Pb and depleted in LILE and LREE. The chlo- ritized rock types exhibit relative enrichment in Mg, FTSM, Zn-As-Pb and depletion in LILE and LREE. The behavior of the Ti, Al, Fet, P, and most HFS elements during biotitization, sericitization, albitization, epidotization and chlorit- ization suggests that they were inert during metasomatic modification of the andesites. Mass balance calculations suggest that volume change was restricted between zero and up to + 20% for the altered upper andesites and -25 and up to +25% for the altered lower an- desites during the different types of metasomatic facies. Elemental mobilities are interpreted in terms of the controlling mineral phases and the possible nature of the various metasomatising fluids.

Wadi vegetation of the North-Eastern desert of Egypt

Wadi vegetation of the North-Eastern desert of Egypt

Barite mineralisation in the south Um Monqul area, north Eastern Desert, Egypt

The barite mineralisation in the north Eastern Desert of Egypt is hosted by Pan-African dacite, dacite porphyry and granite. The host rocks are variably altered by potassic, phyllic, phyllic-argillic, propylitic and advanced argillic alteration. The barite mineralisation is in veins trending east-northeast — west-southwest and dipping 65°–80° to the southeast. The veins are mainly of barite with subordinate quartz, accessory magnetite and specularite with minor sulphides (chalcopyrite, pyrite, covellite, enargite, bornite and pyrrhotite) and traces of Au. The barite mineralisation is associated with advanced argillic alteration, which resulted from interaction of the host rocks with acid sulphate fluids. It is envisaged that these fluids were released from high level intrusives similar to Cu bearing porphyry rocks.

Multiple episodes of aridity in southern Africa since the last interglacial period

There is generally a dearth of evidence of the nature of Quaternary climate change within desert systems, which has limited previous interpretations of past environmental change at low latitudes. The Last Glacial Maximum has previously been identified as the peak of Late Quaternary aridity, when desert systems expanded to five times their present extent1,2,3, and low-latitude aridity has been described for previous glaciations4. But little evidence has been derived directly for large desert basins, particularly southern Africa. Here we report new chronological (optical dating) evidence of arid episodes recorded in aeolian sediments from the Mega Kalahari sand sea. Episodic aeolian activity is recorded at the northeastern desert margin, whereas more sustained activity is evident from the southwestern desert core. Several significant arid events are apparent since the last interglacial period, with dune-building (arid) phases at ∼95–115, 41–46, 20–26 and 9–16 kyr before present. Existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast–southwest summer rainfall gradient, which are in turn related to sea surface temperatures in the southeastern Atlantic Ocean.

Structural interpretation of aeromagnetic data, Gabal Zubeir area, North Eastern Desert, Egypt

Abstract A structural interpretation of aeromagnetic data of the Gabal Zubeir area, North Eastern Desert, Egypt, is presented. The average depth to the causative magnetic bodies within the basement complex (intrabasement) is determined in the form of aggregated bodies at two disturbing interfaces l.0km and 2.1 km depth through the application of two-dimensional power spectrum. Filtering, combined with analytical downward continuation on the two assigned interface has been carried out—this can assist in discriminating between shallow and deep anomalies. The structural elements affecting the basement complex at the two assigned interfaces with faults and folds (down-faulted and uplifted blocks) are delineated. The fault system is analysed in the form of azimuth-length frequency relations.

Rock unit mapping using statistical analysis applied to aeroradioactivity data and trend analysis for BIR Araiyida and surrounding area, north eastern desert, Egypt

The airborne radiometric survey data recorded in the study area was used to delineate boundaries of rock units and aims at the establishment of the natural background radioactivity levels of the surficial rock types and soils through the application of the statistical methods of analysis. Aeroradiometric trend analysis applying Linsser's technique [Linsser H. (1967) Geophys. Pros. V57, 480–515] and also, the tectonic trends expressing the surface faults taken from the landsat map (1980) were analysed.

Natural radioactivity of basement younger granite rocks from the eastern desert

The present work deals with a study of natural radioactivity of various samples of granite rocks from the Umm Gidri area located in North Eastern Desert. In this area, about 300 km apart from El-Minia, some geological investigations were carried out. Several samples of the basement rocks (of the Precambrian Age) 5 m subsurface were obtained from different locations. Suitable samples were prepared for natural gamma ray measurements using a 5 × 5 in. NaI(Tl) scintillation spectrometer. Qualitative analysis of natural gamma radiations from the present samples have revealed the presence of the radioisotopes: 40K, 214Bi, 208Tl and 228Ac in meaningful concentrations. These results are thought to correlate with the findings of a recent trace element geological assay done at the same area, and it would be of help in monitoring and assessing the national background radiation levels.

Rejuvenation of the eastern Mediterranean passive continental margin in northern and central Sinai: new data from the Themed Fault

AbstractThe Themed Fault marks the southernmost border of the Early Mesozoic passive continental margin of north Sinai. This 200-km long fault transects the northern part of the Tih Plateau that supposedly occupies a tectonically stable area. Post-Middle Eocene–pre-Early Miocene rejuvenation of this fault proceeded by right-lateral wrenching and represents a newly recognized phase of deformation in the history of north and central Sinai. The minimum estimate for the strike-slip movement on this fault is about 300–750 m. To the north of the Themed Fault is a narrow fault belt (Sinai hinge belt) that marks the boundary between a tectonically unstable crustal block to the north (the north Sinai fold belt area) and a tectonically stable crustal block to the south, the main part of the Tih plateau area.Four phases of dextral wrenching rejuvenated the faults of the Early Mesozoic passive continental margin in northern Egypt; one of them affected the Themed Fault. The oldest (Dl) deformation is early Late Senonian and is related to the closure of Neotethys and the Eastern Mediterranean basin. The D1 deformation proceeded by pure wrenching in the north Western Desert of Egypt. In contrast, it proceeded by transpression in north Sinai due to the irregular plate boundary and the relationship of this boundary to the slip vectors. D2 deformation (post-Middle Eocene–pre-Early Miocene) is clear in the Themed Fault area although reported herein for the first time; it is related to continued closure of the Eastern Mediterranean basin and proceeded by pure wrenching. D3 deformation (Late Oligocene–Early Miocene) proceeded by divergent wrenching in the north Eastern Desert and is kinematically related to the transfer of slip from the nearby faults of the Suez rift. D4 deformation (post-Early Miocene to Recent) affected the Sinai hinge belt by pure wrenching and is probably related to the left-lateral slip on the Dead Sea Transform and the related drag of the eastern edges of the fault blocks of this hinge belt. Recent seismic activity in the Sinai hinge belt perhaps indicates that the D4 deformation has continued to the present time, although morphological expression of recent tectonic movement is lacking. In contrast, the Themed Fault is seismically quiet at present.

Upper Cretaceous ammonites from the El Sheikh Fadl - Ras Gharib Road, Northeastern Desert, Egypt

Upper Cretaceous ammonites from the El Sheikh Fadl - Ras Gharib Road, Northeastern Desert, Egypt