Gravitational collapse origin of shear zones, foliations and linear structures in the Neoproterozoic cover nappes, Eastern Desert, Egypt

Fowler, Abdel-Rahman; Kalioubi, Baher El

doi:10.1016/j.jafrearsci.2003.09.003

Cited by 61 publications

(36 citation statements)

References 39 publications

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“…The pebble long axes in the molasse sediments plunge gently NW or SE. The early developed Folding of mylonitic foliation and NNW-directed thrusts creates opposite senses of shearing on the mylonites (Fowler and El-Kalioubi 2004). The same conclusion was obtained by Wallbrecher et al (1996) in their analysis of apparent dextral and sinistral shear zones along the SW margin of the Meatiq dome.…”

Section: Wadi Um Seleimat Basinsupporting

confidence: 69%

“…Akaad (1996) has described this area as a "formidable shear zone". Fowler and El-Kalioubi (2004) assigned the strong shearing to the NW-ward shear translation of the ophiolite and molasse cover nappes which resulted from gravitational collapse following arc collision and crustal thickening.…”

Section: Wadi Um Seleimat Basinmentioning

confidence: 99%

“…The ophiolitic mélange of the Um Esh-Um Seleimat area consists of grayish metagabbro, metadolerite, and metabasalt blocks (Fig. 9a), which exist as elongate or lenticular bodies incorporated within foliated serpentinite and dark gray pelite (Fowler and El-Kalioubi 2004). In this area, Akaad et al (1996) and Akaad (1996) Akaad et al (1993), the other structures are identified in this study, b Equal area, lower hemisphere stereographic presentation of bedding and fracture cleavage, foliation associated with sinistral shearing, and long axis of pebbles from Wadi Igla basin.…”

Section: Wadi Um Seleimat Basinmentioning

confidence: 99%

“…Presence of moderately NW-plunging open folds in the NE-and SW-directed thrust slices and stretching of pebbles in the molasse sediments can be related directly to sinistral shearing. Change in strike of foliation from NNW to WNW along the southern branches of Wadi Um Seleimat may be due to block rotation during movement along the strike-slip faults (Fowler and El-Kalioubi 2004).…”

Section: Wadi Um Seleimat Basinmentioning

confidence: 99%

“…The suprastructural sequence in the Eastern Desert was intensely deformed during nappes emplacement which accompanied accretion of island arcs onto the Saharan Metacraton (Abdelsalam et al 2002) during an oblique collision event in the late stage of the East African orogeny (Gass 1982;Wallbrecher et al 1993;Fowler and El-Kalioubi 2004). It consists of low-grade metamorphosed ophiolite fragments, volcano-sedimentary rocks, and metavolcanics (Akaad and Noweir 1980).…”

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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: Wadi Um Seleimat Basinsupporting

confidence: 69%

Section: Wadi Um Seleimat Basinmentioning

confidence: 99%

Section: Wadi Um Seleimat Basinmentioning

confidence: 99%

Section: Wadi Um Seleimat Basinmentioning

confidence: 99%

mentioning

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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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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Volcanogenic talc‐copper deposits of Darhib‐Abu Jurdi area, Egypt: Petrogenesis and remote sensing characterization

2020

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Economic talc deposits were developed as an integral part of a volcanogenic massive sulfide system in Darhib‐Abu Jurdi bimodal‐mafic type submarine volcanics in the South Eastern Desert of Egypt. These Pan‐African metavolcanics were erupted in a rift‐related environment and experienced low‐grade greenschist metamorphism. They host talc‐malachite mineralization, mainly within E–W trending alteration zones along the major latitudinal shear planes. These mineralized alteration zones contain economic talc deposits as well as averages of 1.7% Cu and 0.46% Zn; the maximum may exceed 11% Cu. Sentinel‐2, ASTER, and Landsat‐8 dataset in conjunction with a portable TerraSpec Halo mineral identifier device (ASD) were employed in detecting and mapping these mineralized alteration zones within the Darhib‐Abu Jurdi metavolcanics. Petrography, mineralogy, and geochemistry of these deposits and host volcanics enabled to put constraints on their petrogenesis and evolution as a submarine hydrothermal vent system. Mineralogical characteristics of pervasive chloritization stringer zone, hypogene primary sulfide ore zone, and supergene oxidized zone are addressed and discussed. Talc deposits were formed at Darhib‐Abu Jurdi area as the main gangue phase via (a) direct precipitation on seafloor by interaction of silica‐saturated hydrothermal fluids with Mg‐rich seawater, (b) precipitation with actinolite/tremolite at shallow depth beneath the sulfide ore lenses due to penetration of Mg‐rich seawater into hydrothermal conduit, and (c) replacement of pre‐existing tremolite, actinolite, chlorite, and septechlorite.

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Gravitational collapse origin of shear zones, foliations and linear structures in the Neoproterozoic cover nappes, Eastern Desert, Egypt

Cited by 61 publications

References 39 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

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

Volcanogenic talc‐copper deposits of Darhib‐Abu Jurdi area, Egypt: Petrogenesis and remote sensing characterization

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