Structural evolution in the palaeoproterozoic basement (banded iron formation and related rocks) of SW Egypt [Elektronische Ressource] / vorgelegt von Mostafa Fahmy Mostafa Elkady

Elkady

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2003
• Nombre de lectures: 33
• Langue: English
• Poids de l'ouvrage: 14 Mo

Extrait

INAUGURAL – DISSERTATION
Zur
Erlangung der Doktorwürde
der
Naturwissenschaftlich-Mathematischen Gesamtfakultät
der
Ruprecht – Karls - Universität
Heidelberg
Deutschland



STRUCTURAL EVOLUTION IN THE PALAEOPROTEROZOIC
BASEMENT
(BANDED IRON FORMATION AND RELATED ROCKS)
OF SW EGYPT


Vorgelegt von
Mostafa Fahmy Mostafa Elkady
Aus Ägypten
2003



Gutachter : Prof. Dr. Reinhard O. Greiling
Prof. Dr. Wolfgang Dachroth







To the Memory of my Mother

My Father

And

My Family













IIAbstract
Structural evolution in the Palaeoproterozoic Banded Iron Formation of SW Egypt
M.F.Elkady
Geol.Pal.Inst.INF 234, D-69120 Heidelberg, Germany.Ruprecht-Karls-Universitaet
Heidelberg.
On leave from: Egyptian Geological Survey, 3 Slah Salem st., Abbassia Cairo Egypt.

The exposed basement of the Western Desert of Egypt is part of the pre-Pan-African
East Sahara Craton. The Gabel Uweinat-Bir Safsaf Aswan Uplift is situated at the
eastern fringe of this craton, and its high-grade metamorphic and granitoid rock
associations are markedly distinct from the metavolcanic-metasedimentary-ophiolitic
sequences of the Eastern Desert of Egypt (Nubian Shield). Crystalline basement
2rocks cover an area of some 40,000 km in SW Egypt.
The fieldwork and mapping of the basement rocks in the present area were carried
out during the winters 1998, 1999 and at last in 2001 for altogether about 10 months
of fieldwork. A detailed field geologic-structural map to the scale of 1:60,000 and two
cross sections, perpendicular to the regional structural trend for the whole area, are
prepared using vertical aerial photographs and Landsat images. Detailed
petrographic studies of the different rock units were carried out to determine their
compositional character and the effect of deformation on each rock unit. Some 125
rock specimens representing the different rock units were collected and more than
130 thin sections were examined petrographically using the polarizing microscope.
Microstructure studies and (analyses) attempted to determine the structural evolution
and possible transport direction from about 40 oriented thin sections parallel and
perpendicular to the foliation. Further structural data, from the anisotropy of the
magnetic susceptibility (AMS) was determined from 31 oriented samples, which were
cored and cut (200 cylinders). The magnetic susceptibility measurements were
analyzed with the Kappa bridge.
The BIF is exposed as an upper unit, while anatexite forms a middle one, underlain
by ultramafic-mafic units.
The BIF shows large quartz crystals with wavy extinction and undeformed
recrystallized quartz.
The Anatexite sequences were affected by granulite facies metamorphism, followed
by a retrograde metamorphism. The petrographic study shows some orthopyroxene
crystals altered to hornblende, biotite and chlorite.
The structural analysis of the area indicated that it was subjected to major tectonic
deformation including folding, overthrusting, shearing and faulting. The area is built
IIIup of thrust slices of the BIF and Anatexite, which extend for more than 25 km in
N15°E direction, dipping to the west with angles between 30° to 70°. The thickness of
slices horses is up to 4 km. The thrust sequence in this area has about 20 km width.
Thrust Faults have been derived from overturned folds, the shear surface replacing one of
the limbs of the fold. The structure is dominated by a series of nearly parallel, minor thrust
faults, or high angle reverse faults, which dissect the rock into slices, sheets, plates, blocks
or wedges that are approximately equidistant and have the same displacement and are all
steeply inclined to the WNW (285°).
Restoration of this thrust sequence shows that the anatexite forms a basement to the
overlying BIF. Both metamorphic banding in the anatexite and the layering in the BIF restore
to a horizontal primary orientation.

The Deformational Evolution
Three major deformation phases can be discerned in the study area (D1, D2 and
D3), the three phases D1, D2 and D3 affected only the basement rocks and are
followed by Phanerozoic brittle deformation affecting both the basement and the
overlying sedimentary rocks in the investigated area.
The D1 structures indicate a crustal thickening followed by crustal thinning and
developed the melano- and leucosome in the Anatexite sequences. A foliation (S1)
observed in the thin section of the BIF as simple shear mylonitization zones.
Generally in (D1) the Anatexite bands are parallel with the mylonitic shear zones in
the BIF.
The D2 structures dominate in the BIF as a micro and macro folding (F2) associated
with low angle thrust or shear zones (S2). In the Anatexite and the Ultramafic-mafic
sequences minor folds with the same characters as in the BIF are observed.
Generally in (D2) the BIF and Anatexite bands had E-W strike and dipped shallowly
to the south (S2), and contain minor folds (F2) with E-W axial surfaces.
The D1 and D2 deformations are both of them overprinted by the D3 structures,
which refolded the F2 at a perpendicular direction of the fold axes by F3. The D3
affected refolding and thrusting at the BIF, Anatexite sequences and Ultramfic-mafic
bands as F3 and S3. The F3 has NNE trend and plunge with an angle of 15°. The
foliation S3, is parallel to the fold axial surfaces and thrust surfaces. The dip angle
ranges between 30° and 70° to the WWN (285°).



IVACKNOWLEDGEMENT
This dissertation is contribution to a project between the Egyptian Geological Survey,
Cairo (Mr. Aboul Hassan Abdolraouf) and the Geolgisches-Palaeontologisches
Institute, Heidelberg University, Germany (Prof R.O.Greiling). Funding by BMFT/KFA
Jülich and logistic support and field facilities by the Egyptian Geological Survey are
gratefully acknowledged.
I wish to express my deep sense of gratitude to the scientists who supervised this
work namely Prof. R.O.Greiling, Professor of Structural Geology and Director of the
Geolgisches-Palaeontologisches Institute, Heidelberg University for guidance in the
field, valuable suggestions and discussions, continuous help during the progress of
the work and critical reading of the manuscript. Prof. A.A. Dardir, Chairman of the
Egyptian Company for Salt “Amesal”, and former Chairman of the Egyptian
Geological Survey for his continuous advice and encouragement. Prof. H. Flick, in
the Geolgisches-Palaeontologisches Institute, Heidelberg University for his kindness,
invaluable and continuous advice and discussions as well as reading the manuscript,
Dr. A. Kontny Assistance Professor in the Geolgisches-Palaeontologisches Institute,
Heidelberg University for her kindness, invaluable and continuous advice and
discussions, Prof. W. Dachroth, the Professor of Applied and Engineering Geology in
the Geolgisches-Palaeontologisches Institute, Heidelberg University for his kindness,
invaluable and continuous advice and discussions, Dr Z. El Alfy the Director of the
Egyptian Geological Survey for his continuous advice, discussions, encouragement
and reading of the manuscript.
The conclusion and results of the work have improved much due to critical and
constructive discussions both in the field and during the office work. Field and office
discussions were carried out with Drs. A. Khaled, M.F. Sadek, W. Ghebr.eab, M.M.
Abdeen and Geologests M. Khattab, A. Salem, G. Shaban, colleagues in EGSMA.
The author is greatly indebted to Dr. W. Janiesch the Chairman of SAS Institute
Germany, Mrs A. Dörrhofer the Director of the SAS-Germany, Mr. K. Hessenauer,
the former Manager in SAS-Germany, for bestow him a part time Job to finance my
study and live during my stay in Heidelberg, and my kind-heartedly thanks for all the
staff of SAS Germany for their kindly relationship, tolerance, sympathies,
encouragement and advices during my work with them.
The author is thankful to Mr Abol Hassan Abel Raouf, the Chairman of Egyptian
Geological Survey for his advices tolerance and support to finish this work, Mr. G.
VNaim and Mr .M. El Hinnawy the former Chairman’s of Egyptian Geological Survey
for their agree to continue this work in Geological Institute of Heidelberg University.
I greatfully acknowledge the Mr. R. Koch the PC graphic in geological Institute,
librarians Mr. M. Bühler, Mrs K. Seehaus, and technical assistance of the geological
Institute in Heidelberg Mr. Will (Photo-Lab.) and Mrs O. Wallerath for preparing the
thin sections, the help of the colleagues Dipl. Geol. F Cueto, and L. Nano for their
kind help in the Computer soft and hardware in the Geolgisches-Palaeontologisches
Institute, Heidelberg University.
Thanks are also rendered to the Secretary Staff in the Geolgisches-
Palaeontologisches Institute, Heidelberg University Mrs G. Froelich, J. Kontny and A.
Hoffman for their kindness helps.