Regional geology of Africa

741 Pages·1991·44.11 MB·English

by  Sunday W. Petters

Lecture Notes in Earth Sciences 40
Editors:
S. Bhattacharji, Brooklyn
G. M. Friedman, Troy
H. J. Neugebauer, Bonn
A. Seilacher, Tuebingen
Sunday .W Petters
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Berlin Heidelberg NewYork
London Paris Tokyo
Kong Hong Barcelona
Budapest
Author
Sunday W. Petters
Department of Geology
University of Calabar
Calabar, Nigeria
"For all Lecture Notes in Earth Sciences published till now please see final page of the
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ISBN 3-540-54528-X Springer-Verlag Berlin Heidelberg New York
ISBN 0-387-54528-X Springer-Verlag New York Berlin Heidelberg
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Preface
This book represents the first attempt in three decades to marshall out
available information on the regional geology of Africa for advanced un-
dergraduates and beginning graduate students. Geologic education in
African universities is severely hampered by the lack of a textbook on
African regional geology. This situation is greatly exacerbated by the
inability of most African universities to purchase reference books and
maintain journal subscriptions. Besides, geologic information about
Africa is so widely dispersed that a balanced and comprehensive course
content on Africa is beyond the routine preparation of lecture notes by
university teachers. Since geology is a universal subject and Africa is
one of the largest landmasses on Earth with one of the longest continuous
records of Earth history, there is no doubt that geologic education in
other parts of the world will benefit from a comprehensive presentation
of African geologic case histories. The scope of this text also addresses
the need of the professional geologist, who may require some general or
background information about an unfamiliar African geologic region or age
interval.
Africa occupies a central position in the world's mineral raw materi-
als trade. Because of its enormous extent and great geologic age, the di-
versity and size of Africa's mineral endowment is unparalleled. Africa is
the leading source of gold, diamond, uranium, and dominates the world's
supply of strategic minerals such as chromium, manganese, cobalt, and
platinum. Consequently, African nations from Algeria to Zimbabwe depend
solely on mineral exports for economic survival. The geologic factors
which govern economic mineral deposits are stressed in this text.
The geological history of Africa spans 3.8 billion years, a record
that is unique both in duration and continuity. Few other parts of our
planet match the plethora of geologic phenomena and processes that are
displayed in the African continent. From the various stages of crustal
evolution decipherable from the Archean of southern Africa, through the
plate tectonics scenarios in the ubiquitous Late Proterozoic-Early Paleo-
zoic Pan-African mobile belts and in the Hercynian and Alpine orogenies
of northwest Africa, to the East African Rift Valley, Africa is replete
with excellent examples and problems for a course on regional tectonics.
Teachers of igneous and metamorphic petrology can hardly ignore
Africa's anorogenic magmatism (e.g.. layered ultramafic intrusives such
as the Great Dyke and the Bushveld Complex; the Tete gabbro-anorthosite
pluton; alkaline complexes; basaltic volcanism), or tantalizing high-
IIIV
grade metamorphic terranes such as the Limpopo belt, the Namaqua mobile
belt, and the Mozambique belt.
From the extensive Precambrian supracrustal sequences throughout the
continent with enormous thicknesses of sedimentary rocks that have hardly
been deformed or metamorphosed, to the stratigraphic evolution of
Africa's present-day passive continental margin, there is a complete
spectrum of facies models upon which to base a course on basin analysis
and stratigraphy.
To maintain its integrity a course on historical geology anywhere in
the world must address the theory of Continental Drift beyond invoking
past continuities between West Africa and South America. Past connections
between West Africa and eastern North America must equally be explored,
so also connections between northeast Africa and Arabia, and the paleo-
geography of southern Gondwana where Africa occupied centre stage. The
Precambrian fossil record, the transitions from reptiles to the earliest
mammals and dinosaurs, and the evolution of Man are among Africa's unique
contributions to the history of life and the story of organic evolution.
Although it lies today in the tropics Africa was the theatre of the
Earth's most-spectacular glaciations. Even after the scene of continental
glaciation had shifted to the northern continents only lately during the
Pleistocene, Africa still witnessed spectacular climatic fluctuations
during the Quaternary. Certainly students of archeology and paleoanthro-
pology cannot overlook the Quaternary paleoenvironmental record of the
Olduvai Gorge in Tanzania, the Lake Turkana basin in Kenya, the Nile val-
ley, the Sahara, and southern Africa.
But since African examples have already been cited in standard geo-
logic textbook, I have often been asked why it has become necessary to
revive the idea of a full-length textbook on African geology, 30 years
after this idea was abandoned by the geologic community. My simple an-
swer, as already stated, is that the wealth of available geologic infor-
mation about Africa is so enormous and fascinating, but so diffuse, that
an attempt must be made to assemble and pass on this knowledge.
Berlin, May 1991 Sunday W. Petters
Acknowl edgemen ts
I would like to acknowledge the unique opportunity afforded me by two
German institutions to write this text. This text was prepared during
eleven months of residence at the Wissenschaftskolleg zu Berlin
(Institute for Advanced Study Berlin). I thank this institution for fel-
lowship support, and excellent bibliographic and secretarial assistance
through which I enjoyed limitless access to geologic literature on
Africa, and equally important, had the manuscript typed. Secondly, I wish
to thank Prof. Dr. Eberhard Klitzsch of the Technical University Berlin
who is the project leader of Special Research Project "Geoscientific
Problems in Arid and Semiarid Areas" (Sonderforschungsbereich 69) funded
by the German Research Foundation (DFG). Special Project 69 is devoted to
geoscientific research in northeast Africa (Egypt, Sudan, Somalia,
Ethiopia) and has graduate students from various parts of Africa. My
visit to the Wissenschaftskolleg was through the recommendation of Pro-
fessor Klitzsch. During the preparation of the manuscript I benefited
enormously from discussions with and suggestions from the geologists in
Special Project 69.
The idea of writing a textbook on the regional geology of Africa was
conceived during my 15 years of teaching various geology courses at five
Nigerian universities. During this period I sought to enrich my course
contents by visiting several European libraries and museums. In this res-
pect I wish to thank Dr. M.C. Daly and his wife and Dr. C.S. Orereke for
their hospitality during my visit to the University of Leeds in 1984. Dr.
M. Oden was my host in London that year during my visit to the British
Museum of Natural History, the Geological Museum, and the Imperial Col-
lege library. I thank Prof. P. Bowden and Dr. J.A. Kinnaird for their
hospitality during the colloquium on African geology at St. Andrews Uni-
versity in 1985. Professor H.P. Luterbacher was very helpful during my
visit to the University of T~bingen in 1987.
I am generally greatly indebted to all geologists who have worked in
Africa, from whose publications I have drawn the material for this text.
I would also like to thank especially all those who sent very important
books, reprints, and pre-prints of their publications on Africa. These
include Profs. J.B Wright, S.J. Culver, R. Caby, B.-D. Erdtmann,
L.B. Halstead, V. Jacobshagen, J.A. Peterson, P. Wilde, C.O. Ofoegbu,
J.D. Fairhead, I. Valeton, J.R. Vail, and N.J. Jackson. Professors
E. Buffetaut and L.L. Jacobs supplied illustrations of African verte-
brates.
I am greatly indebted to Prof. Rushdi Said who was also in residence
at the Wissenschaftskolleg during the 1989/90 session. Professor Said's
constant advice and encouragement kept up my spirits. I thank Profs. R.K.
Olsson, R.C. Murray and B.W. Andah for encouraging me to pursue this pro-
ject over the years.
I am very grateful to Drs. M.C. Daly and G. Matheis who read through
the Precambrian chapters and offered very useful suggestions. I als0
thank Drs. S. Muhongo and H. Schandelmeier for their comments on some of
the Precambrian chapters. Dr. Muhongo greatly improved my coverage of
East Africa. Professor N. Rutter kindly reviewed the Quaternary chapter.
My special thanks go to Ms R. Plaar for the preparation of the
manuscript, and all the secretarial staff of the Institute for their
invaluable help. Special appreciation goes to Mrs Maria A. Gowans and Ms
Linda O'Riordan who prepared the final camera-ready manuscript, for their
patience and hard work. I would also like to acknowledge Mr Reinhard
Prasser, who, in addition to his great hospitality, served at the final
moment as the liaison with the publisher. Excellent bibliographic
assistance was provided by Mrs Gesine Bottomley and her staff at the
Wissenschaftskolleg and by Mrs Evelyn Kubig of the Geology Library of the
Technical University, Berlin. Messrs Umo Harrison, E. Umo, Joe Sams, and
Richard Ingwe and his colleagues rendered cartographic assistance.
I thank Professor Charles Effiong, Vice-Chancellor of the University
of Calabar for moral and material support. Dr. Alfred Koch, chairman and
managing director of Mobil Producing Nigeria and Mr. Wande Sawyerr, ex-
ploration manager of Mobil, also encouraged this project.
Finally, on behalf of my wife Janet, and my children, Mfon, Emem,
Ekanga and Unwana, who were with me in Berlin, I wish to express profound
gratitude to the Rektor of the Wissenschaftskolleg, Prof. Dr. Wolf Lepe-
nies and his wife for their hospitality. All the staff of the Wis-
senschaftskolleg were very friendly to us, and for this we are very
grateful.
TABLE OF CONTENTS
CHAPTER 1 INTRODUCTION
i.i The Physical Setting of Africa
1.2 Geological History and Mineral Deposits of Africa
CHAPTER 2 THE PRECAMBRIAN OF AFRICA: AN INTRODUCTION
2.1 Tectonic Framework 8
2.2 The Precambrian Time-Scale 13
2.3 Orogenic Cycles in Africa 16
2.4 Dominant Rock Types 19
C~PTER 3 THE ARCHEAN
3.1 Introduction 21
3.2 Kalahari Craton 23
3.2.1 Kaapvaal Province 25
Ancient Gneiss Complex 26
The Barberton Greenstone Belt 28
Structure of the Barberton Greenstone Belt 38
Granitoid Emplacement and Cratonization 39
Other Greenstone Belts in the Kaapvaal Province 41
3.2.2 Pongola Basin 42
3.2.3 .Zimbabwe Province 44
Gwenoro Dam Basement Gneisses 45
Older Greenstone Belt (Sebakwian Group) 47
Bulawayan Greenstones 48
Structure of the Bulawayan Greenstone 54
Igneous Intrusion and Cratonization 54
3.2.4 Limpopo Province 56
Northern Marginal Zone (N.M.Z.) 56
Central Zone in the Limpopo Valley 57
Central Zone in Botswana 58
Southern Marginal Zone (S.M.Z.) 59
Tectonic Models 60
3.2.5 Archean Mineralization on the Kalahari Craton 64
Gold 65
Chrome 68
Massive Base-Metal Sulphides 68
Iron Ore 69
Pegmatite Mineralization 69
Corundum 69
Asbestos 7O
IIX
3.3 Zaire Craton 17
3.3.1 Kasai-NE Angola Shield 72
3.3.2 NW Zaire Craton 74
3.3.3 NE Zaire Craton 76
Bomu Gneiss Complex 77
West Nile Gneissic Complex 79
Ganguan Greenstone and Schist Belt 80
Kibalian Greenstone Belts 81
Granitoids 82
Gold Mineralization 83
3 4 Tanzania Craton 84
34.1 Geologic Framework 84
34.2 Dodoma Schist Belt 86
34.3 Nyanzian-Kavirondian Schist Belts 86
3 4.4 Gold Mineralization on the Tanzania Craton 87
3 5 West African Craton 90
35.1 Guinea Rise 90
Granitic Gneiss Basement 91
Greenstone Belts 92
3.5.2 Archean Mineralization on the Guinea Rise 98
3.5.3 Reguibat Shield 99
3.6 Other Archean Terranes in Africa 102
3.6.1 East Saharan Craton 102
Jebel Uweinat 102
Tuareg Shield 104
3.6.2 Madagascar 105
3.7 Archean Tectonic Models 105
3.7.1 Classical Models 105
3.7.2 Back-arc-Marginal Basin Models 107
3.7.3 Archean Plate Tectonics 107
CHAPTER 4 EARLY PROTEROZOIC CRATONIC BASINS
AND MOBILE BELTS
4.1 Introduction 113
4.2 Kalahari Cratonic Basins 115
4.2.1 Introduction 115
4.2.2 Witwatersrand Basin 119
Stratigraphy 121
Mineralization 124
4.2.3 Ventersdorp Basin 126
4.2.4 Transvaal-Griqualand West Basins 127
Stratigraphy 127