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

Abstract

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.

Structural interpretation of the Wadi Hafafit culmination: A Pan-African gneissic dome in the central Eastern Desert, Egypt

“…At the end of the Pan-African orogeny, the Arabian-Nubian shield was covered with molasse-type terrestrial sedimentary rocks. During its Phanerozoic evolution, these sedimentary rocks were largely removed by erosion, but they are preserved in small molasse basins that are often conspicuously linked to the metamorphic domes (Fritz and Messner, 1999;Abd El-Wahed, 2010). Conglomerates in these basins are occasionally highly deformed, but overall these sedimentary rocks are partially deformed and largely unmetamorphosed.…”

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

“…The largest and best examples are found in the CED, for example, Wadi Hammamat, El Qash, Zeidun, Arak, Um Esh–Um Seleimat, El Kareim, El Mayah, and Igla basins. Their thickness varies from about 4,000 m thick (Abd El‐Wahed, ) to about 7,500 m (Fritz & Messner, ). Hammamat series are divided into two main subdivisions (Akaad & El‐Ramly, ): Igla Formation (the lower one), at the type locality of Wadi Igla, is mainly composed of sandstones, siltstones, and mudstones with basal conglomerates.…”

“…Hammamat series are divided into two main subdivisions (Akaad & El‐Ramly, ): Igla Formation (the lower one), at the type locality of Wadi Igla, is mainly composed of sandstones, siltstones, and mudstones with basal conglomerates. They are represented by a clastic bedded succession of a characteristic brick red to purple colour, (Fowler & Osman, ; Genna, Nehlig, Le Goff, Guerrot, & Shanti, ; Wilde & Youssef, ) exposed in several molasse basins such as Wadi El‐Qash, Wadi Queih, and El Kareim basin (Abd El‐Wahed, ). Shihimiya Formation (the upper one) includes conglomerates, greywackes, arenites, and mudstones with greenish colour due to chloritization and epidotization (Akaad, ; Akaad & El‐Ramly, ; Rice, Osman, Abdeen, Sadek, & Ragab, ; Samuel, Roufaiel, Hilmy, & Moussa, ). The Shihimiya formation is diverse and includes clasts of ophiolites, arc metavolcanics, arc granitoids, metasediments, Dokhan volcanics, and pink and red granites (Akaad & Noweir, ; Hassan & Hashad, ; Messner, , b; Ries et al, ). …”

Provenance of the heavy mineral-enriched alluvial deposits at the west coast of the Red Sea. Implications for evolution of Arabian–Nubian crust

“…The Dokhan volcanics and Hammamat Group crops out in post amalgamation basins of Eastern Desert. Both units are of variable thicknesses with a maximum of 1300 m and 7000 m, respectively (e.g., Eliwa et al, 2006;Abd El-Wahed, 2010). …”