The Allaqi-Heiani suture in southeastern Egypt represents the western part of
the main Allaqi-Heiani-Onib-Sol Hamed-Yanbu suture that is exposed in Egypt,
Sudan and Saudi Arabia as one of the Neoproterozoic ophiolite-decorated, arcarc
sutures in the Arabian-Nubian Shield (ANS). The Egyptian part of the suture
extends for ca. 250 km from the north-trending Hamisana shear zone in the east to
the Nile River in the west. It separates the ca. 750 Ma south Eastern Desert terrane
in the north from the ca. 830-720 Ma Gabgaba terrane in the south. The suture zone
is defined by a deformational belt made up of ophiolitic gabbros, serpentinites
and mafic volcanics, which are imbricated with syn-tectonic granitoids and
metasediments. The whole rock suite is intruded by post-tectonic granitoids and
gabbros. The suture zone suffered a poly-phase structural deformation that led to
a complex structural pattern.
For precise lithological mapping and delineation of geological structures along the
suture zone, we utilized digital image processing techniques to enhance Landsat
7 Enhanced Thematic Mapper Plus (ETM+) data to produce high quality images
suitable for photogeological interpretation. These techniques included false color
band composition (7, 4, 1 in R, G, B), principal component analysis (PC1, PC2,
PC3 in R, G, B) and band-ratios (5/7, 5/1, 5/4*3/4 in R, G, B and 5/7, 7/5, 5/
4*3/4 in R, G, B). Density slicing of the implemented four band ratios (5/7, 7/5,
5/1 and 5/4*3/4) has been used to produce a photogeological map. The mapped
rock units were checked in the field and the attitudes of both planer and linear
structures were measured and subsequently analyzed for better understanding of
the structural setting of the central Allaqi-Heiani suture zone. The serpentinites
and related ophiolitic rocks were followed along strike to identify the structural
continuity and changes in strike direction.
Photogeological interpretation and field studies indicate that the central part of the
Allaqi-Heiani suture zone is dominated by WNW-ESE striking low angle thrusts
that are associated with asymmetrical folds whose axial planes are parallel to
these thrusts. Folds are verging towards SSW. Additionally, a series of NNW-SSE
oriented parallel folds are dominated in the eastern part.
Structural analysis indicates that the central part of the Allaqi-Heiani suture zonehas undergone a poly-phase structural deformation involving, at least, two phases.
Each phase has its own structural style and stress regime. The first phase (D1)
was associated with an overall N-S or NNE-SSW shortening that produced SSWverging
folds and thrusts. The second phase (D2) was associated with an overall
ENE-WSW shortening, which produced NNW-SSE oriented folds in the central
and eastern parts of the study area and reactivated the older thrusts with obliqueslip
reverse fault movement.