The major element chemistry and Sr-Nd isotope composition of three basaltic glasses and two whole rock samples dredged from the Nereus Deep, in the central Red Sea, were used to constrain the nature of the magmatism in the Nereus axial valley. The glass and whole rock compositions show the tholeiitic character of magmas and their affinity with MORE. The chemical composition of the most magnesian glass (mg# = 69.9) would suggest an origin from a melting event in the mantle at a pressure in the range 8-10 kbar. Magma differentiation modelling using the major element chemistry of the more evolved glasses indicates mineral-melt equilibration at moderate pressure, followed by most of the fractionation under low pressure conditions. The observed Ti content and Sr isotope composition suggest the occurrence of additional processes besides fractionation, and could reflect different degrees of partial melting of a slightly heterogeneous mantle source. The Sr-Nd isotope composition reveals the time-integrated depleted nature of the mantle, and overlaps the fields of MORE and basalts from the southern Red Sea axial ridge. The Sr isotope data on glasses resemble more closely the compositional range reported for the Indian Ocean ridges, and suggest a dominant asthenospheric source, with minor enriched components, (C) 1998 Elsevier Science Limited.
A numerical model is presented to assess the probable tsunami impact of future earthquakes occurring along the Eastern Mediterranean Ridge, and their effect on Alexandria, Egypt. On the 8th of August 1303 a major earthquake of magnitude about eight caused a large tsunami that killed many people around Alexandria, where ships were carried over buildings and settled on land.Calculations were done with an initial condition of continuous water flow normal to the shore line. This tsunamigenic event was examined to study the effect of location, direction, travel time and height towards the Egyptian Coast. Computed tsunami features such as travel times and run-up height distribution are given; which are useful in the evaluation of the tsunami hazard.
An eight point Rb/Sr isochron determination on whole rocks yielded an age of 1670 M.a. for the mylonites from the Sassandra couloir of ductile deformation, which extends N-S. A similar age is proposed for the mylonite from a zone of parallel trend stretching NNW-SSE in the Reguibat dome (Mauritania). A correlation is suggested with the Guri fault of the Guayana shield in South America.
Teleseismic Broadband seismograms of P-waves from the May 1990 southern Sudan and the December, 2005 Lake Tanganyika earthquakes; the western branch of the East African Rift System at different azimuths have been investigated on the basis of magnitude spectra. The two earthquakes are the largest shocks in the East African Rift System and its extension in southern Sudan. Focal mechanism solutions along with geological evidences suggest that the first event represents a complex style of the deformation at the intersection of the northern branch of the western branch of the East African Rift and Aswa Shear Zone while the second one represents the current tensional stress on the East African Rift. The maximum average spectral magnitude for the first event is determined to be 6.79 at 4 s period compared to 6.33 at 4 s period for the second event. The other source parameters for the two earthquakes were also estimated. The first event had a seismic moment over fourth that of the second one. The two events are radiated from patches of faults having radii of 13.05 and 7.85 km, respectively. The average displacement and stress drop are estimated to be 0.56 m and 1.65 MPa for the first event and 0.43 m and 2.20 MPa for the second one. The source parameters that describe inhomogeneity of the fault are also determined from the magnitude spectra. These additional parameters are complexity, asperity radius, displacements across the asperity and ambient stress drop. Both events produce moderate rupture complexity. Compared to the second event, the first event is characterized by relatively higher complexity, a low average stress drop and a high ambient stress. A reasonable explanation for the variations in these parameters may suggest variation in the strength of the seismogenic fault which provides the relations between the different source parameters. The values of stress drops and the ambient stresses estimated for both events indicate that these earthquakes are of interplate type.
Two earthquakes occurred in the Congo Basin in March and April 1998. These two events are reported to have comparable size (5.5 mb) and nearly the same epicentral locations, far from the western branch of the East African Rift System (EARS). The P-wave groups of these two earthquakes as recorded at FURI station have nearly identical waveforms, which is indicative of similar rupture process. The epicentral distribution in the area has no apparent trend and the reported seismicity is relatively sporadic. The results of the fault mechanism study show that the two earthquakes have a similar rupture process with slight variation. The duration of the main shock (event 980426) is 3.3 s and its scalar seismic moment, Mo, is 2.6×1017 Nm. The style of the dominant deformation for both events is thrust type, which is not commonly observed in the African Plate. A compressive stress environment may be created by plate-boundary forces of the mid Atlantic Ridge and the EARS.
At the northwest end of the Lake Turkana Basin (northern Kenya Rift), intensive fieldwork conducted on the Plio-Pleistocene fluvio-lacustrine Nachukui Formation by the National Museums of Kenya and the West Turkana Archaeological Project (WTAP), led to the discovery of more than 50 archaeological sites aged between 2.4 and 0.7 Ma. Among them is the Lokalalei archaeological site complex, which includes the two oldest archaeological sites (2.34 Ma) found in the Kenyan segment of the East African Rift System. The environmental background of the two sites was described as a succession of ephemeral streams with floodplain palaeosols in which the archaeological sites are situated, bordering the western bank of a large axial meandering river flowing southward. The Lokalalei 1 (LA1) and Lokalalei 2C (LA2C) archaeological sites are of extreme importance in terms of knowledge of hominins’ knapping activities. The stratigraphic position of the LA1 and LA2C sites as well as implications on the technical differences between the two sites have been successively discussed by Roche et al., 1999, Brown and Gathogo, 2002 and Delagnes and Roche, 2005. In terms of stratigraphic position, Lokalalei 2C was estimated to be slightly higher in the section (i.e. younger) than Lokalalei 1. An alternative stratigraphic correlation was proposed by Brown and Gathogo (2002), who suggested that LA2C site should have been approximately 100,000 years younger than LA1.
In August 2002, there was high seismic activity in Afar concentrated at the plateau margin of the northern Ethiopian rift east of Mekele, near the western part of the Danakil microplate. The spatial and temporal distributions of this seismic activity over four weeks indicate the NNW propagation of the Gulf of Aden rift across the Afar Depression towards the western Ethiopian plateau. Fault plane solutions for six larger earthquakes from the August 2002 sequence are estimated from moment tensor inversion of local broadband waveform data. The results show only normal faulting on NNW trending and NE dipping faults, which agree with tectonics of the area and distribution of aftershocks. No strike-slip component is observed in any of our fault plane solutions or those of other workers including Harvard CMT solutions in the region. Such motion would be indicative of oblique-slip deformation between the Nubian plate and the Danakil microplate consistent with counter-clockwise rotation of the microplate. Hypocentral depths of well-constrained events are 5–7 km, which is the approximate elastic plate thickness in the Main Ethiopian rift, possibly indicating the depth to the brittle–ductile transition zone in this part of the Afar Depression. The shallowness of the depth estimates agree with the macroseismic reports available from a wide area in northern Ethiopia. Potential future shallow crustal deformation may cause significant loss of human life and damage to property in the densely populated highland region around Mekele unless measures are taken in improving building standards. The b-value for this sequence is estimated to be 0.66 using a least squares fit, while it is 0.67 ± 0.16 from a maximum-likelihood approach. This estimated b-value is low or the frequency of occurrence of relatively larger magnitude events is high indicating that it is a highly stressed region as evidenced by the recent increase of the seismicity in the area.
The 2007 drilling season by the Tanzania drilling project (TDP) reveals a much more expanded Upper Cretaceous sequence than was recognized previously in the Lindi region of southern Tanzania. This TDP expedition targeted recovery of excellently preserved microfossils (foraminifera and calcareous nannofossils) for Late Cretaceous paleoclimatic, paleoceanographic and biostratigraphic studies. A total of 501.17 m of core was drilled at six Upper Cretaceous sites (TDP Sites 21, 22, 23, 24, 24B and 26) and a thin Miocene–Pleistocene section (TDP Site 25). Microfossil preservation at all these sites is good to excellent, with foraminifera often showing glassy shells and consistently good preservation of small and delicate nannofossil taxa. In addition to adding to our knowledge of the subsurface geology, new surface exposures were mapped and the geological map of the region is revised herein.
The Cretaceous deposits in central Tunisia blocks were studied by sequence stratigraphy, 2D seismic interpretation calibrated to the well and associated outcrop data. The constructing and comparing histories of the northern and southern blocks of the Gafsa master fault was the establishment of platform to basin stratigraphic configuration based on the major unconformity surfaces.Three important basin zones mark subsurface structures: Gafsa to the south, Souinia-Majoura to the northeast and Sidi Aïch-Mèjel Bel Abbès to the northwest. Basin depocenters and upthrown blocks are bounded by the N120° Gafsa and Majoura and N180° Sidi Ali Ben Aoun wrench fault salt-intruded tectonic corridors and subdivided by the associated N60° and N90° trending second-order fault corridors. The Mèjel Bel Abbès block is characterized by brittle structures associated with a deep asymmetric geometry that is organized into depressions and uplifts. Halokinesis of Triassic salt began in the Jurassic and continued during the Cretaceous periods. During extensional deformations, salt movement controlled sedimentation distribution and location of pre-compressional structures. During compressional deformations, salt remobilization accentuated the folded uplifts. The Triassic salt facies constitutes a level of decollement at the base of the Mesozoic deposits during the later displacements.The coeval dextral strike-slip motion along the three northwest–southeast bounding master faults (Gafsa, Sehib-Alima and Majoura-Mech) suggests a pull-apart opening of the Gafsa basin. Synchronous movements of the Gafsa first-order dextral strike-slip fault with the Sidi Ali Ben Aoun sinistral wrench fault caused formation of tectonic obstacles that are shown first by the sealed structures, then by development of the local compressive stress that caused formation of the south overturned folds and the syncline depressions. The transcurrent fault systems caused formation of Turonian and Senonian unconformities and hiatuses on the Sidi Aïch and Souinia-Majoura uplifts that corresponded to the Kasserine Islets. Sedimentary distribution and structural features indicate two events of regional deformation. The Albian–Cenomanian and Turonian transtensional displacements are demonstrated by depressions and grabens, with divergent reflectors striking against dipping growth fault. The Coniacian–Maastrichtian transpressional movements are marked by reverse faults and folds associated with pinch out structures and stratigraphic unconformities.
The Nsuze Group (∼3000 Ma) in South Africa is comprised of volcanics and sediments that rest unconformably on older continental crust. Nsuze volcanics, which range in composition from basalt to rhyolite and include a significant proportion of andesites, have tholelitic to calc-alkaline geochemical affinities. Incompatible element distributions in Nsuze volcanics are similar to those in volcanics associated with continental-margin arcs and exhibit a typical subduction zone component (SZC) (enrichment in LILE and relative to Nb-Ta). The volcanics can be related to each other by shallow fractional crystallization of average Nsuze basalt, together with up to 10% assimilation of granite with a composition similar to that of the underlying Mpuluzi granite.Geological data are consistent with an origin for the Nsuze Group in an intracratonic rift. The SZC in Nsuze volcanics may have been inherited from an older subcontinental lithospheric source.
The mafic to ultramafic rocks of the Barberton greenstone belt, South Africa, form a pseudostratigraphy comparable to that of Phanerozoic ophiolites. This Archaean complex, referred to here as the Jamestown Ophiolite Complex, consists of a high temperature tectono-metamorphic peridotite overlain by an intrusive extrusive igneous section, which in turn is capped by a chert-shale sequence. There is a complete range from komatiitic to tholeiitic compositions within single intrusive units. Crustal contamination and magma mixing is evident from field and geochemical data.Pillow structures, 40Ar/39Ar ages and oxygen isotope analysis suggest that hydrothermal interaction with the Archaean ocean severely hydrated and chemically altered the entire simatic section during its formation. As a consequence, only a ‘ghost’ igneous geochemistry is preserved. This regional open-system alteration may have increased the MgO content of the igneous rocks by as much as 13%, and the most primitive liquids, from which the extrusive sequence evolved, were ‘picritic’ in character. Rocks with a komatiitic chemistry were derived during crystal accumulation from picritic-crystal mushes (predominantly olivine-clinopyroxene) and/or by metasomatism during one or more subsequent episodes of hydration-dehydration.In contrast to Phanerozoic ophiolites, the Jamestown complex is relatively thin (≦3 km), which implies that locally at least the ca 3.5 Ga oceanic crust was also thin. This is consistent with the regionally extensive metasomatic alteration, and is compatible with theoretical and experimental models predicting higher Archaean heat transfer from the mantle concentrated within Archaean oceans.
Travel times from earthquakes recorded at two seismic networks were used to derive an average P wavespeed model for the crust and upper mantle to depths of 320 km below southern Africa. The simplest model (BPI1) has a Moho depth of 34 km, and an uppermost mantle wavespeed of 8.04 km/s, below which the seismic wavespeeds have low positive gradients. Wavespeed gradients decrease slightly around 150 km depth to give a ‘knee’ in the wavespeed-depth model, and the wavespeed reaches 8.72 km/s at a depth of 320 km. Between the Moho and depths of 270 km, the seismic wavespeeds lie above those of reference model IASP91 of Kennett [Research School of Earth Sciences, Australian National University, Canberra, Australia (1991)] and below the southern African model of Zhao et al. [Journal of Geophysical Research 104 (1999) 4783]. At depths near 300 km all three models have similar wavespeeds. The mantle P wavespeeds for southern Africa of Qiu et al. [Geophysical Journal International 127 (1996) 563] lie close to BPI1 at depths between 40 and 140 km, but become lower at greater depths. The seismic wavespeeds in the upper mantle of model BPI1 agree satisfactorily with those estimated from peridotite xenoliths in kimberlites from within the Kaapvaal craton.The crustal thickness of 34 km of model BPI1 is systematically lower than the average thickness of 41 km computed over the same region from receiver functions. This discrepancy can be partly explained by an alternative model (BPI2) in which there is a crust–mantle transition zone between depths of 35 and 47 km, below which seismic wavespeed increases to 8.23 km/s. A low-wavespeed layer is then required at depths between 65 and 125 km.
The coal deposits of southern Africa (Botswana, Malawi, Mozambique, Namibia, South Africa, Swaziland, Tanzania, Zambia and Zimbabwe) are reviewed. The coal seams formed during two periods, the Early Permian (Artinskian–Kungurian) and the Late Permian (Ufimian–Kazanian). The coals are associated with non-marine terrestrial clastic sedimentary sequences, most commonly mudrock and sandstones, assigned to the Karoo Supergroup. The Early Permian coals are most commonly sandstone-hosted while the younger coals typically occur interbedded with mudstones. The sediments were deposited in varying tectono-sedimentary basins such as foreland, intracratonic rifts and intercratonic grabens and half-grabens. The depositional environments that produced the coal-bearing successions were primarily deltaic and fluvial, with some minor shoreline and lacustrine settings. Coals vary in rank from high-volatile bituminous to anthracite and characteristically have a relatively high inertinite component, and medium- to high-ash content. In countries where coal is mined, it is used for power generation, coking coal, synfuel generation, gasification and for (local) domestic household consumption.
Existing tectonic models for the evolution of the Usagaran Orogen place much significance on Palaeoproterozoic K–Ar and Rb–Sr ages. Laser 40Ar/39Ar data from single mica grains from the Isimani Suite near the western margin of the orogen indicate that excess 40Ar is common in micas and this casts considerable doubt on tectonic models that are based on previously published K–Ar ages. Biotites lying within a well-developed S2 foliation (previously constrained at 1999–1991 Ma) yield ages up to 3.3 Ga and contain a significant excess 40Ar component that is variable at an intra- and inter-sample scale. Textural evidence indicates that muscovite grew or recrystallized after the synkinematic biotites and they also record younger 40Ar/39Ar ages with individual steps from 524 to 1055 Ma. It is shown that the mica age variation does not reflect different periods of growth but the preferential partitioning of excess 40Ar into the biotite. The muscovite data also have a component of excess 40Ar and the youngest muscovite 40Ar/39Ar date (535.4 ± 2.3 Ma) indicates a maximum age for greenschist facies metamorphism. This date corresponds to thermal activity associated with the East African Orogen. Greenschist facies deformation (D4 and D5) is interpreted to have been coincident with this thermal event and indicates localized tectonic activity associated with Gondwanan amalgamation. The data are also consistent with greenschist facies deformation, metamorphism and deposition of the Usagaran Konse Group being of Neoproterozoic–Early Palaeozoic age. These new data therefore preclude a solely Palaeoproterozoic tectonic history for the Usagaran Orogen and indicate a complex thermal-tectonic reworking in the Neoproterozoic–Early Palaeozoic.
Karoo-equivalent rocks in the Tuli Basin of Zimbabwe are described, with a focus on the dinosaur-bearing Mpandi Formation, which correlates with the Elliot Formation (Late Triassic–Early Jurassic) in the main Karoo Basin. Isolated exposures of the Mpandi Formation along the banks of the Limpopo River consist of red silty claystones and siltstones that preserve root traces, small carbonate nodules, and hematite-coated prosauropod bones. These fine-grained facies accumulated on an ancient semi-arid floodplain. Widespread exposures of quartz-rich sandstone and siltstone representing the upper Mpandi Formation crop out on Sentinel Ranch. These strata preserve carbonate concretions and silicified root casts, and exhibit cross-bedding indicative of deposition via traction currents, presumably in stream channels. Prosauropod fossils are also preserved in the Sentinel Ranch exposures, with one particularly noteworthy site characterized by a nearly complete and articulated Massospondylus individual.An unconformity caps the Mpandi Formation in the study area, and this stratigraphically significant surface rests on a laterally-continuous zone of pervasive silicification interpreted as a silcrete. Morphologic, petrographic, and geochemical data indicate that the Mpandi silcrete formed by intensive leaching near the ground surface during prolonged hiatus. Chert clasts eroded from the silcrete are intercalated at the base of the overlying Samkoto Formation (equivalent to the Clarens Formation in the main Karoo Basin), which in turn is overlain by the Tuli basalts. These basalts, which are part of the Karoo Igneous Province, yield a new 40Ar/39Ar plateau age of 186.3 ± 1.2 Ma.
Deformed conglomeratic clasts exposed along the Neoproterozoic Nakasib Suture and the Oko Shear Zone are used to calculate three-dimensional (3D) tectonic strain associated with the latter to quantify strain associated with post-accretionary deformational belts in the Arabian–Nubian Shield. The Nakasib Suture is a NE-trending fold and thrust belt that is sinistrally offset (∼10 km) by the cross-cutting NNW- to NW-trending strike-slip faults of the Oko Shear Zone. The Nakasib Suture was formed as a result of collision between the Haya terrane and the Gebeit terrane at ∼750 Ma ago. The Oko Shear Zone was subsequently formed as a result of an E–W directed shortening of the Arabian–Nubian Shield due to collision between East and West Gondwana at ∼670–610 Ma ago. This analysis indicates the following: (1) The Nakasib Suture is dominated by flattening strain with the flattening plane of the associated strain ellipsoid oriented at 21°/77°SE. This flattening deformation is interpreted to be associated with nappe emplacement from north to south. (2) Some regions along the Nakasib Suture are characterized by constriction strain that might be due to refolding of the early nappes about NE-trending axes. (3) The Oko Shear Zone is characterized by constriction strain, with the XY plane of the strain ellipsoid oriented at 171°/68°E. The strain ellipsoid associated with the Oko Shear Zone manifests superimposition of E–W shortening on the NE-trending fold and thrust belt associated with the Nakasib Suture. (4) The tectonic strain of the Oko Shear Zone, superimposed over the structures of the Nakasib Suture, is characterized by a strain ellipsoid whose flattening plane is oriented at 21°/49°W. The strain ellipsoid of the tectonic strain has a major axis with a quadratic elongation of 3.6 and an orientation of 357°/25°, an intermediate axis with a quadratic elongation of 1.2 and an orientation of 231°/30°, and a minor axis with a quadratic elongation of 0.25 and an orientation of 115°/18°. This suggests that the post-accretionary deformation of the Arabian–Nubian Shield was superimposed as a NW–SE directed shortening that created early N–S shortening zones and late NW-trending sinistral strike-slip faults.
The legendary wealth in gold of ancient Egypt seems to correspond with an unexpected high number of gold production sites in the Eastern Desert of Egypt and Nubia. This contribution introduces briefly the general geology of these vast regions and discusses the geology of the different varieties of the primary gold occurrences (always related to auriferous quartz mineralization in veins or shear zones) as well as the variable physico-chemical genesis of the gold concentrations. The development of gold mining over time, from Predynastic (ca. 3000 BC) until the end of Arab gold production times (about 1350 AD), including the spectacular Pharaonic periods is outlined, with examples of its remaining artefacts, settlements and mining sites in remote regions of the Eastern Desert of Egypt and Nubia. Finally, some estimates on the scale of gold production are presented.
The Mission Paléoanthropologique Franco-Tchadienne (MPFT) found a new species of Orycteropodidae (Mammalia, Tubulidentata) in the Kollé fossiliferous sector, northern Chad. After Orycteropus abundulafus [Journal of Vertebrate Paleontology 20 (1) (2000) 205–209; Lehmann, T., Vignaud, P., Likius A., Brunet M., in press. A new Orycteropodidae (Mammalia, Tubulidentata) in the Mio-Pliocene of Northern Chad. Zool. J. Linnean Soc.], this specimen is the second complete skeleton of fossil aardvark found in the Djurab desert. It is the first complete representative of an Orycteropus species found in the Pliocene of Africa. In regard to the Miocene fossil aardvarks, this new taxon, Orycteropus djourabensis nov. sp., shows more affinities with the extant O. afer. The main differences are the larger teeth and the shorter hand in the fossil form. Kossom Bougoudi and Kollé represent a chronological series that gives a unique opportunity for studying the evolution of the African Tubulidentata around the Mio-Pliocene boundary (5.5-4 My). The new species is distinct from the older Chadian Orycteropodid from KB and it embodies the taxonomic turnover that took place within the order Tubulidentata around this boundary in Africa. Moreover, this new species is the oldest known Orycteropus species that clearly belongs to the modern forms including the extant aardvark.
The Asu River Group (middle-late Albian), exposed in the Nkalagu area of the southern Benue trough, consists of two formations, viz: the Abakaliki Formation at the base overlain by the Ebonyi Formation (new name). The Abakaliki Formation is composed mainly of illitic and kaolinitic black shales and mudstones interbedded with black micritic limestone, siltstone adn minor feldspathic sandstones. The limestone is composed of grapestones, infralimeclasts and brown algal remains. These together with the pyritic and fossiliferous chale, suggest oscillatory deposition of argillaceous sediment in a shallow but anoxic subsiding bottom and marine facies.Rapid alternations of sandstone, siltstone, shales, mudstones, oolitic and serpulid grainstones and packstone-wackestone indicative of transitional environment of deposition characterise the Ebonyi Formation. The thick horizontal strata and interference ripple marks suggest lower flow regime of deposition while the thin evaporite laminite indicate locally short-term aridity during the Cretaceous in the southern Benue trough.
The Middle Jurassic (Bathonian) rocks of the Ras El Abd area include three main shell concentrations: a molluscan shell bed, the lower rhynchonellid bed, and the upper rhynchonellid bed. Analysis of the taphonomic signatures indicates that; the molluscan shell bed represents a proximal tempestite, the lower rhynchonellid bed corresponds to a primary biogenic concentration sensu [Fürsich, F.T., Oschmann, W., 1993. Shell beds as tools in basin analysis: the Jurassic of Kachchh, western India. Journal of the Geological Society 150, 169–185], and the upper rhynchonellid bed a proximal storm-flow concentration. The shell concentrations formed below fair-weather wave-base in shallow, relatively high energy environments.
Outcrops in the Cretaceous Abeokuta Group of the Dahomey (Benin) Basin in southwestern Nigeria are described. Based on detailed sedimentological logging, 13 lithofacies were delineated. They are: massive and loose sand; cross-bedded loose sand; normally graded sandstone (upward fining sandstone); laminated silt; clay; laminated sandstone; clay with sandstone injections and clasts (sandstone boulders); clayey sand with sandstone boulders; silty clay with intraformational folds and breccias; highly contorted conglomerate/clayey silt; and channel infills. The association of the lithofacies and their sedimentary structures support that these lithologies were deposited by turbidity current, grain flow, debris flow, liquefied flow and fluidized flow. Since these depositional features are diagnostic of slope environments, the Cretaceous Abeokuta Group was concluded to have been deposited in slope environments.
The discovery of Upper Miocene marine layers in a water-borehole in Abidjan, to the north of the great tectonical fault zone dividing lengthwise the terrestrial part of the Ivory Coast sedimentary basin, incited us to study their microfauna, palynoflora and nannoflora in detail. To our knowledge it is for the first time that fossils of the two last named groups of such age have been studied in Ivory Coast and none of the characteristic species of the three groups illustrated up to now. The study has been carried out within the geological and sedimentological framework of the borehole.
Phosphorites in Egypt occur in the Eastern Desert, the Nile Valley and the Western Desert at Abu Tartur area and present in Duwi Formation as a part of the Middle Eastern to North African phosphogenic province of Late Cretaceous to Paleogene age (Campanian–Maastrichtian). The Maghrabi-Liffiya phosphorite sector is considered as the most important phosphorite deposits in the Abu Tartur area due to its large reserve thickness and high-grade of lower phosphorite bed beside high content of REE. Back scattered electron (BSE) images show framboidal pyrite filling the pores of the phosphatic grains, suggesting diagenetic reducing conditions during phosphorites formation.Electron Probe Micro Analyzer (EPMA) chemical mapping was conducted to examine the variation and distributions of selected elements (P, F, La, Fe, Yb, Si, Ce, W, Eu, S, Ca, Y and Er) within the shark teeth, coprolites and bone fragments. In the teeth W, S, Fe are concentrated along the axis of the teeth, the bone fragments show high concentration of W, Yb, Er and Eu, whereas coprolites are nearly homogenous in composition contains S, Er with some Si as micro-inclusions. Fluorapatite is considered as main phosphate mineral whereas pyrite occurs as pore-filling within the phosphatic grains and cement materials. Maghrabi-Liffiya samples show a wide range in the P2O5 content, between 19.8 wt.% and 29.8 wt.% with an average of 24.6 wt.% and shows low U content ranging from 15 ppm to 34 ppm with an average of 22 ppm. The total REE content in nine samples representing the Maghrabi-Liffiya ranges from 519 to 1139 ppm with an average of about 879 ppm. The calculation of LREE (La–Gd) show indeed a marked enrichment relative to the HREE (Tb–Lu) where LREE/HREE ratio attains 8.4 indicating a strong fractionation between the LREE and HREE. Chondrite-normalized REE patterns of the studied phosphorite samples show a negative Eu anomaly.
Abu Hamamid (AH) Neoproterozoic (Sm/Nd model age of ∼770 ± 20 Ma) mafic–ultramafic intrusion lies along a NE–SW fracture zone in the Shadli Metavolcanic Belt, south Eastern Desert, Egypt. AH intrusion is concentrically zoned with cumulate clinopyroxene-bearing dunite core mantled by olivine clinopyroxenite, hornblende clinopyroxenite and hornblende gabbroic rim. The observed crystallization sequence is olivine (+spinel)-clinopyroxene–hornblende. Orthopyroxene is an extremely rare phase in the core rocks. Clinopyroxene is Ca-rich diopside and spinel shows wide range of Cr# (38–85) and Fe3+# (22–95) ratios. Olivine ranges from Fo74 to Fo81. The ferromagnesian minerals from the AH intrusion show a consistent decrease in the Mg# of olivine (81–74), clinopyroxene (89–81), and hornblende (87–66) from core to rim. The gradational contact between the different rock types of the AH mafic–ultramafic rocks, their cumulate nature, the recognition of small-scale layering together with the systematic modal and compositional variations of rock-forming minerals all point to generation by fractional crystallization from a common parental magma. Petrography and mineral compositional data suggest that the AH complex crystallized from fractionated hydrous tholeiitic magma with no significant crustal contamination.AH intrusion shares many important field, petrographic and mineralogical features with Phanerozoic Alaskan-type intrusions formed above subduction zones, suggesting that the AH rocks formed in a similar tectonic environment. Clinopyroxene and spinel chemistry support the subduction-related (island-arc) tectonic environment of origin for the AH complex. This revives interests in models involving subduction-related (island-arc), and possibly plume-interaction origin for the Shadli Metavolcanic Belt.
Abu Zawal area is located north of the Qena-Safaga road. It consists of igneous and metamorphic rocks of late Precambrian age.It has been subjected to geological, radiometric and structural investigations to reveal the structural setting of the area and its relation to the trends of mineralization, as well as the distribution of the radioactivity in the different rock units. Each rock units has been characterized statistically by a certain radiometric background through the radiometric survey traverses. Application of certain statistical inference tests found the relation between the different rock types of Abu Zawal area and their equivalents in other studied areas.It is found that least radioactivity is associated with basic metavolcanic rocks, while the highest values are associated with the late orogenic plutonites and related rocks, while granodiorites have moderate levels of radioactivity. The study suggests that the late orogenic plutonites of Abu Zawal area may be younger than plutons of similar composition in the north of the Eastern Desert.