The El Mayah molasse basin in the Eastern Desert of Egypt

Shalaby, Ahmed; Stüwe, Kurt; Fritz, Harald; Makroum, Farid Mahmoud

doi:10.1016/j.jafrearsci.2006.01.004

Cited by 72 publications

(36 citation statements)

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“…Several of the molasse basins occur adjacent to the metamorphic core complexes in the CED (Fig. 2), and their formation is usually attributed to the extension that allowed the exhumation of core complexes during the final stage of the East African Orogeny (650-550 Ma; Greiling et al 1994;Fritz et al 2002;Shalaby et al 2006).…”

Section: Tectonic Setting Of the Molasse Basinsmentioning

confidence: 99%

“…molasse basins includes Wadi Igla, Wadi Kareim, Wadi Queih, Wadi Hammamat, and Wadi El-Miyah basins (Abdeen et al 1992(Abdeen et al , 1997Rice et al 1993;Messner 1996;Fritz and Messner 1999;Fowler and Osman 2001;Abdeen and Greiling 2005;Shalaby et al 2006;Abd El-Wahed 2007). This contribution presents detailed structural and strain analysis of eight molasse basins from the CED and one from the Northern Eastern Desert (NED) and discusses the role of thrusting events and sinistral shearing along the Najd Fault System in the deformation history of these basins.…”

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confidence: 99%

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The role of the Najd Fault System in the tectonic evolution of the Hammamat molasse sediments, Eastern Desert, Egypt

El‐Wahed

2009

Arab J Geosci

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The Hammamat molasse sediments of the Eastern Desert of Egypt were deposited in isolated basins formed during an initial stage of orogen parallel N-S extension (650-580 Ma) in the Neoproterozoic time. Supply of sediments to the molasse basins began after the eruption of Dokhan volcanics (602-593 Ma), exhumation of core complexes (650-550 Ma), and intrusion of late tectonic granites (610-550 Ma). The late Neoproterozoic structures in the molasse sediments include: (1) NNWdirected thrusts due to NNW-SSE shortening (650-640 Ma), indicated by the presence of NE-, ENE-, and WSW-trending folds and NNW-directed thrusts.(2) SWand NE-directed thrusts due to ENE-WSW constriction during oblique convergence and arc accretion at around 640-620 Ma. Many of the map-and mesoscopic-scale NWtrending folds in the core complexes, the molasse sediments, and the Neoproterozoic nappes in the Eastern Desert are related to this event. Sinistral shearing along the Najd Fault System (650-540 Ma) resulted in the development of subvertical foliation, subhorizontal stretching lineation, and NW-trending tight folds overprinting earlier folds. Stretched pebbles are oriented NW-SE and WNW-ESE in the molasse basins localized within the Najd Fault System, and NE-SW in the basins outside the influence zone of this NW-trending fault system. Strain estimated using pebbles from nine molasse basins indicate that the amount of strain differs from one basin to another and from one place to another within the same basin. Weak tectonic strain (Rs=2.16-2.24) is obtained from post-orogenic basins; moderate strains are reported from foreland basins (Rs=2.37-3.18), whereas moderate to high tectonic strains are recorded from the intermontane basins (Rs=2.40-4.36). The obtained tectonic strain and K values indicate that the flattening strain prevails in the post-orogenic and foreland basins, whereas as both constrictional and flattening strains are recorded in intermontane basins. Strain variation from one basin to another and within the individual basin is attributed to presence of thrust and sinistral shear zones. Away from the deformed zones, the pebbles show no significant stretching. Two phases of thrusting and an episode of transpressional sinistral shearing are the latest structure features of the East African orogeny in the Arabian-Nubian Shield.

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Section: Tectonic Setting Of the Molasse Basinsmentioning

confidence: 99%

mentioning

confidence: 99%

The role of the Najd Fault System in the tectonic evolution of the Hammamat molasse sediments, Eastern Desert, Egypt

El‐Wahed

2009

Arab J Geosci

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“…These shear zones mark the external boundaries of the core complexes (e.g., Sibai, Meatiq, Hafafit) and control the main deformation events in the CED (Fritz et al 1996Shalaby et al 2005Shalaby et al , 2006Abd El-Wahed 2006. Sinistral shearing along the NFS was active in the period 650-540 Ma.…”

Section: Relation Between Wfsz and The Najd Fault Systemmentioning

confidence: 99%

“…Sinistral shearing along the NFS was active in the period 650-540 Ma. This was accompanied by intrusion of syntectonic older granite around 650-615 Ma (Loizenbauer et al 2001;Bregar et al 2002;Fritz et al 2002;Shalaby et al 2006). The shear zones pertaining to the NFS are concentrated mainly in the CED and completely disregarded or treated with lack of concern in the NED.…”

Section: Relation Between Wfsz and The Najd Fault Systemmentioning

confidence: 99%

“…The first model considers the gneiss-cored domes as metamorphic core complexes formed during transpression combined with lateral extrusion along the NW trending zones bounded by sinistral strike-slip shears of the NFS with the formation of synextensional plutonism (e.g., Fritz et al 1996 andBregar et al 2002;Abd El-Wahed 2008). This model highlights the importance of the NFS during the tectonic evolution of the Eastern Desert of Egypt (e.g., Fritz and Messner 1999;Unzog and Kurz 2000;Loizenbauer et al 2001;Makroum 2001;Abdeen and Greiling 2005;Shalaby et al 2005Shalaby et al , 2006Abd El-Wahed 2006Abdeen et al 2008). The second model argues against the presence of core complexes in the Eastern Desert of Egypt and explains the development of gneiss-cored domes by an overlap between NW-SE complex folding and NW-SE extension parallel to the fold hinges (e.g., Fowler and Osman 2001;Fowler et al 2007;Andresen et al 2008).…”

Section: Introductionmentioning

confidence: 99%

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Synoblique convergent and extensional deformation and metamorphism in the Neoproterozoic rocks along Wadi Fatira shear zone, Northern Eastern Desert, Egypt

El‐Wahed

Anbar

2008

Arab J Geosci

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The Wadi Fatira area occurs at the southern margin of the Northern Eastern Desert (NED) of Egypt and is occupied by highly sheared metavolcanics tectonically alternated with banded iron formations and intruded by Barud tonalite-granodiorite, post-tectonic gabbroic and granitic intrusions. Detailed structural investigation showed that the schists and migmatitic amphibolites are formed by shearing in metavolcanics and syntectonic Barud tonalitegranodiorite due to movement along the Wadi Fatira shear zone (WFSZ). This shear zone starts as a NW-SE striking fault along Wadi Barud Al Azraq and the Eastern part of Wadi Fatira and turns to a E-W trending fault to the north of Wadi Fatira. Microstructural shear sense indicators such as asymmetric geometry of porphyroclasts such as σ-type and asymmetric folds deforming fine-grained bands which are frequently found around porphyroclasts indicate sinistral sense of shearing along the WFSZ. This shear zone is characterized by transitions from local convergence to local extension along their E-W and NW-SE trending parts, respectively. The NW-SE part of the WFSZ is of about 200 m in width and characterized by synmagmatic extensional features such as intrusion of synkinematic tonalite, creation of NE-SE trending normal faults, and formation of migmatitic amphibolites and schlieric tonalites. This part of the shear zone is metamorphosed under synthermal peak metamorphic conditions (725°C at 2-4 kbar). The E-W compressional part of the WFSZ is up to 3 km in width and composed of hornblende, chlorite, actinolite, and biotite schists together with sheared intermediate and acidic metatuffs. Contractional and transpressional structures in this part of the WFSZ include E-W trending major asymmetrical anticline and syncline, nearly vertical foliation and steeply pitching stretching lineations, NNE dipping minor thrusts, and minor intrafolial folds with their hinges parallel to the stretching lineation. P-T estimates using mineral analyses of plagioclase and hornblende from schists and foliated metavolcanics indicate prograde metamorphism under medium-grade amphibolite facies (500-600°C at 3-7 kbar) retrogressed to low-grade greenschist facies (227-317°C). The foliation in Barud tonalite-granodiorite close to the E-W part of the WFSZ runs parallel to the plane of shearing and the tonalite show numerous magmatic flow structures overprinted by folding and ductile shearing. The WFSZ is similar to structures resulted from combined simple shear and orthogonal shortening of oblique transpressive shear zones and their sense of movement is comparable with the characteristics of the Najd Fault System.

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Egyptian Hammamat molasse basins and their relations to arc collision stages: Implications for radioactive elements mineralization potential

2018

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Our understanding of the formation style and tectonic setting of Hammamat molasse sedimentary rocks (HMSR) as well as their chronological situation in the legend of the geologic maps is as yet deficient. The purpose of the work is to decipher the misinterpretation of the HMSR genesis. As such, we present a new classification for HMSR that provides answers about its significant field relationships with the mature island arc volcanics that obviously explains the changes in the depositional environments of HMSR, tectonic setting in addition to the shape and type of their constituents. In the light of our suggested thematic evolution model, the HMSR have been deposited in 3 different tectonic settings: (a) fore‐arc, intra‐arc, and back‐arc basins during pre‐collision stage; (b) fore‐arc basins and low land basins in accretionary prism during syn‐collision stage; and (c) low land and intramontane basins during late‐collision stage. The characteristics of HMSR in each stage differ according to the shape and type of basin and the source of sediments supplying. Thus, they show different types and sizes of clasts, mineralization, and radioactivity. The low radioactive potentiality of HMSR is entirely related to their composition, nature, and source of sediments. Generally, any radioactive anomalies are not related to HMSR themselves, but to the surrounding U‐rich rocks and/or the hydrothermal and super‐heated solutions. Siltstones of HMSR with their recognizable low permeability could be a good barrier for solutions carrying uranium and probably form visible uranium mineralization. Spots of visible uranium mineralization are scattered at the contact between HMSR and late‐collision granites within the southern periphery of Um Tawat Basin and at the contact between trachytes and HMSR within Wadi El Kareim Basin; the extension of this mineralization does not exceed more than few centimetres away from the contact.

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The El Mayah molasse basin in the Eastern Desert of Egypt

Cited by 72 publications

References 16 publications

The role of the Najd Fault System in the tectonic evolution of the Hammamat molasse sediments, Eastern Desert, Egypt

The role of the Najd Fault System in the tectonic evolution of the Hammamat molasse sediments, Eastern Desert, Egypt

Synoblique convergent and extensional deformation and metamorphism in the Neoproterozoic rocks along Wadi Fatira shear zone, Northern Eastern Desert, Egypt

Egyptian Hammamat molasse basins and their relations to arc collision stages: Implications for radioactive elements mineralization potential

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