The Atalla Shear Zone (ASZ) is one of the crucial megashears which are geometrically and kinematically akin to the Najd-Shear
Corridor in the central Eastern Desert of Egypt. The Landsat-8 and ASTER-based mapping techniques integrated with extensive
petrographic and structural-field investigations enhanced the geological and structural maps of the study area. The Neoproterozoic
basement complex in the study area discriminated into ditinctive rock suites: Meatiq Group, ophiolitic melange, arc assemblage,
syn- to late-tectonic granitoids, Dokhan Volcanics, Hammamat Sediments, post-Hammamat Felsites and post-tectonic granitoids.
The true color composites (TCC) (4 3 2 for Landsat-8; 3 2 1 for ASTER), false color composites (FCC) (1 6 4, 1 6 7 and 7 5 1 for
Landsat-8; 5 4 3 and 9 6 4 forASTER), principal component analysis (PCA) (1 2 3, 3 2 1 and 6 4 2 forLandsat-8; 1 2 3 and 5 4 2 for
ASTER),minimumnoise fraction (MNF) (1 2 3 and 3 5 1 for Landsat-8; 1 2 4 and 3 2 1 forASTER) and band ratios (BR) (6/2, 6/7,
6/5*4/3 and 7/6, 7/5, 5/3 for Landsat-8; 2/6, 7/5, 7/6 and 4/7, 3/4, 2/1 for ASTER besides the new created ratio 2/6, 7/5, 7/6) are the
best combinations that demonstrate efficiency in discrimination of lithologic contacts and structural elements, using the spectral
signature of different rock units.Moreover, the BR b7/b5, b5/b7 and b6/b4 of grey scale for Landsat-8 are used as a tool for mineral
detection along with the spectral indices created to detect muscovite (b7/b6), ferrous silicates b5/b4 (biotite, chlorite and amphiboles)
and ferrous iron b5/b3 (mafic minerals). The automatic lineament extraction utilizing the SRTM data advocated the role of
NE- to NNE-trending lineaments in the tectonic framework of the study area. The structural fabric of the study area is evaluated in
three main structural domains:Meatiq (MD), Atalla Shear Zone (ASZD) andWadi Hammamat (WHD). The pronounced structural
implication is the transposition of NE-oriented fabric in MD into NW-oriented penetrative shear-related fabric, fully in the ASZD
and partly in WHD. The combination of transcurrent shearing with ENE-directed shortening along the ASZ that was resulted in
noteworthy transpressive structures resemble in many respects those observed in the Ajjaj Shear Belt in Western Arabia. Among
these structures are shear zone-related folds, imbricated thrust sheets, antiformal stacks and thrust duplexes. The deformation history
of the investigated area proposed four phases of deformation (D1–D4). It depicts a long lasted deformational event covering themain
accretion-collision phases concurrent with the E-W assembly of Gondwana, and the subsequent post-collision Najd-related
transpressional phase which resulted in several major left-lateral transcurrent shear zones along with the exhumation of gneissic
core complexes in the Arabian-Nubian Shield. |
