الفهرس 
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Abstract
The present thesis deals with the geology of the Pan- African basement
rocks in Wadi Kreiga - Wadi Kurbiyay area. This area is located in the South
Eastern Desert of Egypt between latitudes 22° 45’ 00” and 22° 55’ 00” Nand
longitudes 35° 00’ 00” and 3520’ 00” E, covering approximately 690 Kms’’,
This work is an attempt to clarify; the relationships between the different
rock units in order to determine their metamorphic grade and to define their
petrogenesis and tectonic setting.
The area was mapped on the scale 1 : 50,000 using aerial photographs
scale 1 :40,000, photomosaics scale 1 : 50,000 and supported by landsat images.
Intrusive and structural relations within the mapped area show the following
relative age succession of the exposed rock units. It is more convenient to
review the sequence of the rock units and their inferred tectonic setting (see
table. 9).
Table (9) : The rock units sequence and their inferred tectonic settings • Rock Unit . Tectonic Setting
Dykes The last magmatic activities and filling the fractures of
the tensional environment.
Post-tectonic Emplaced during the waning of the Pan-African orogeny
granites (Late orogenic granites): show calc- alkaline affinity and
have been formed in an environment of compression,
probably belonging to collision-related granites.
Table (9) Continued
Rock Unit Tectonic Setting
8yn-tectonic
Syn-tectonic, calc-alkaline plutonism, were formed under
granitoids compressional environment, above subduction zone arid
pertain to I-type volcanic arc granite.
8yn-tectonic Syn-tectonic plutonism, they are transitional in
intrusive composition from calc-alkaline to tholeiitic and pertain to
metagabbros an island arc tectonic setting.
These rocks have calc-alkaline nature and similar to
Metavolcanics island arc lavas evolving in an intra-oceanic
and volcaniclastic environments.
metasediments The volcaniclastic metasediments were deposited in an
oceanic back-arc basins.
8erpentinites and
talc carbonate Dismembered ophiolitic sequence
rocks
The serpentinite and talc carbonate roc~ occur at the central part of the
southern border of the mapped area, where they constitute a huge conspicuous
mountainous mass of Gabal Kurbiyay which follow a roughly NW-SE direction.
The serpentinite rocks have been emplaced tectonically where they found as
allochtonous remnants of an old oceanic crust. They are thrusted over the
surrounding island arc metavolcanics and volcaniclastic metasediments.
Scattered slices and thrust lenses of serpentinites are tectonically incorporated
within the metavolcanic and volcaniclastic metasediments. On the other hand,
these serpentinites were intruded by syn-tectonic metagabbros and granitoid
rocks.
The mode of occurrence of the present serpentinites and their geological
features are quite similar to those pertaining to Fransciscan ophiolites and Bay
islands which were described by several authors (e.g, Loney et al., 1971; Bailey
et al., 1970; Coleman, 1971 and 1977).
” Extreme tectonic dismembering of ophiolites is common within the
Fransciscan of California, this produce tectonic blocks of metamorphic
peridotite within a melange.” (Loney et al., 1971).
” where ophiolites have been incorporated into orogenic zones, their
peridotites become serpentinized and are often detached into isolated tectonic
lenses separated from the mafic rocks” (Coleman, 1977).
Petrographically, the investigated serpentinites consist mainly of antigorite
shreds replaced by talc, carbonate, tremolite, magnetite and chlorite.
Geochemical investigations of the present serpentinites were carried by
several authors (~.g. Aly et al.’,199~; Zimmer et al., 1995 and Abdel Kariem
et al., 2001) and concluded that they are pertaining to an o.E!Iiolitic assemblag~
within MORB-like affinity.
The mode of occurrence, -petrographic criteria and further contributions of
geochemical results indicated that .these serpentinites are derived from
peridotites essentially harzburgite and belonging to an ophiolitic assemblage.
The metavolcanic rocks cover mainly the southwestern part of the
mapped area, and surrounding the whole exposure of Gabal Kurbiyay except its
northern side. They comprise metamorphosed basic to intermediate rocks
including metabasalt, basaltic meta-andesites and predominantly meta-andesites.
In places, these rocks are transformed to actinolite-tremolite-chlorite
a
-sc-h-is-ts. Meta tuffs and volcaniclastic metasediments are also encountered.
Metavolcanic rocks exhibit tectonic contac~ with serpentinites whereas; they
are intruded by the syn-tectonic metagabbros and granitoids.
The petrochemical characters of these metavolcanics revealed that, they
are predominantly low-potassic in character and mostly calc-alkaline in nature
with a few samples having tholeiitic affinity. These metavolcanics follow the
Cascade trend that common in island arc environments.
In general, the results reached here indicate that, these rocks are similar to
island arc lavas evolving in an intra-oceanic environment, and conformable with
the data obtained by Stern (1981) on the Egyptian younger metavolcanic rocks.
The present volcaniclastic metasediments occupy small area (south Bir
Madi). Detailed field and petrographic investigations revealed that, these rocks
including metasiltstones, metagreywackes, spotted phyllite, gamet-biotite schist
and garnet-cordierite-biotite schist. These rocks have been subjected to various
degree of metamorphism ranging from greenschist to lower amphibolite facies.
An the light of the above mentioned data, the author can proposed that the
principle source of the volcaniclastic metasediments is the arc derived material
related to the arc volcanism and have been deposited in a back arc basin which
floored by an old oceanic crust.
Syn-tectonic intrusive metagabbros are exposed in the central part of the
mapped area, where they constitute a huge mountaineous mass of Gabal
Meneiga. Along Wadi Atluk and Wadi Shallal El Gharbi small-scattered masses
of these rocks are also encountered. They intruded within serpentinites and
metavolcanics, while these rocks are intruded bysyn-tectonic granitoids.
Petrochemical characters point out that, these rocks are transitional in
composition from calc-alkaline to tholeiitic and pertain to an island arc tectonic
setting which evolved in oceanic environment prior to cratonization.
Syn-tectonic granitoids are widespread throughout the area and they
possess intrusive contacts with the surrounding rocks.
Petrochemical studies revealed that, these rocks are mainly peraluminous,
and calc-alkaline in nature. They were formed under an environment of
compression above subduction zone and conformable with l-type and volcanic
arc granites. Most of their characteristics are comparable with those of G1
granites of Hussein et al, (1981).
-Post-tectonic granites are less distributed throughout the study area and occur as small intrusions near Bir Madi. They are considered to be the youngest
rock unit in the study area, where they have sharp intrusive contact with the
surrounding rocks.
These granites are pink in colour, porphyritic in places and composed of
quartz, perthite, plagioclase and minor biotite.
The field relations and the petrographic investigation of these rocks may
indicate that, they are belonging to G2 granite (collision related granites) of
Several dykes and vein~ that invade all rock units in the area represent the
last magmatic activities in the present area. These dykes are belonging to post
granitic dykes and have trending to E-W and NE-SW directions.
The present area was subjected to polyphases of deformation, they are
grouped into th[ee major events namely (Dr) including thrusting and F) and F2
folds; (02) including F3 folds and (03) resulting in the development of right and
left lateral strike-slip faults (EI Amawy et al., 2001).;()
l =::c::=5iiii=:S:::’
Field and petrographic studies indicate that, most of the exposed rocks in
the mapped area were subjected to polymetamorphic events including three
episodes which are, regional, contact and retrograde metamorphism.
The regional metamorphism is the most widespread and its imprints are
quite visible especially, in the volcaniclastic metasediments. It ranges from
greenschist to lower amphibolite facies with the mineral assemblages (quartz +
albite + chlorite + sericite + epidote) and (quartz + biotite + plagioclase +
garnet) respectively.
The contact metamorphism is regarded as the result of the thermal effects
of the intrusion of syn-tectonic granitoids and are best recognized along its
contact with volcaniclastic metasediments. On closer approach to the contact
cordierite-garnet-biotite schist were developed, whereas; the volcaniclastic
metasediments in the outer parts are characterized by spotted phyllite.
Actually, it is not known whether the thermal effect of the syn-tectonic
granitoids is the reason that produces a new generation of garnet or the garnet
which occurs within the aureole, represents pre-pluton regional metamorphism.
The last stage assemblages of contact metamorphism were obliterated
through retrograde metamorphism. Thus pseudomorphs of fine-grained chlorite
(pennine) replaced cordierite and transformation of garnet porphyroblasts into
chlorite especially along their margins and cracks.
Generally, the field, petrographic, metamorphic and geochemical studies
that presented in this thesis and the published geochemical data indicate that
there is no conclusive evidence for the existence of Archaean or even Early-
Proterozoic crust in Gabal Gerf area.
Accordingly, a Pan-African age can. be assigned to the rocks of the
studied area.