Table Of ContentGeochronological and Geochemical Constraints on the
Lithospheric Evolution of the Arabian Shield, Saudi
Arabia: Understanding Plutonic Rock Petrogenesis in
an Accretionary Orogen.
A thesis submitted for the
degree of Doctor of Philosophy
Frank Alexander Robinson
B.Sc. (Hons)
Department of Geology and Geophysics
The University of Adelaide
February 2014
Table of Contents
Abstract vi
Declaration viii
Acknowledgments ix
List of Figures x
List of Tables xv
Chapter 1: General Introduction 1
1.1 Granite Overview 1
1.2 Development of the A-type Classification 1
1.3 A-type Characteristics and Global Occurrences 2
1.4 Anorogenic Timing and Tectonic Significance 3
1.5 Petrogenetic Models for Generating Anorogenic Magmatism 4
1.6 The East African Orogen and its Relation to the Arabian-Nubian Shield 5
1.7 Arabian Shield Geological Overview 7
1.8 Aims 14
Chapter 2: Petrographic Constraints on Sampled Arabian Shield Plutons;
Subdivision of A-type Suites 15
2.1 Introduction 15
2.2 Sample Selection 16
2.2.1 Adopted Classification Nomenclature 18
2.3 Granitoid Petrography 19
2.3.1 Makkah Suite (dm) 20
2.3.2 Shufayyah Complex (su) 23
2.3.3 Kawr Suite (kw) 25
2.3.4 Abanat Suite (aa) 31
2.3.5 Malik Granite (kg) 33
2.4 Petrography Summary and Discussion 35
Chapter 3: Arabian Shield Pluton Geochronology; Subtle Changes in a
Homogeneous Juvenile Mantle 40
3.1 Introduction 40
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3.2 U-Pb Geochronology 41
3.2.1a Makkah Suite (dm): Gabbro-Diorite 41
3.2.1b Shufayyah Complex (su): Tonalite 43
3.2.1c Jar-Salajah Complex and Fara’ Trondhjemite (js): Granodiorite 46
3.2.1d Subh Suite (sf): Rhyolite 48
3.2.1e Kawr Suite (kw): Granodiorite 50
3.2.1f Al Hafoor Suite (ao): Alkali-Granite 53
3.2.1g Najirah Granite (nr): Granite 55
3.2.1h Wadbah Suite (wb): Alkali-Granite 57
3.2.1i Ibn Hashbal Suite (ih): Alkali-Granite 59
3.2.1j Ar Ruwaydah Suite (ku): Granite 61
3.2.1k Haml Suite (hla): Quartz-Monzonite 63
3.2.1l Kawr Suite (kw): Alkali-Granite 65
3.2.1m Idah Suite (id): Alkali-Granite 67
3.2.1n Al Khushaymiyah Suite (ky): Quartz-Monzonite 70
3.2.1o Malik Granite (kg): Granite 72
3.2.1p Admar Suite (ad): Syenite 74
3.2.1q Al Bad Granite Super Suite (abg): Alkali-Granite 76
3.2.1r Al Hawiyah Suite (hwg): Granite 78
3.2.1s Mardabah Complex (mr): Syenite 81
3.2.2 Arabian Shield U-Pb Geochronology Summary and Discussion 83
3.3 Hafnium (Hf) Isotopes 88
3.3.1 Western Shield 90
3.3.2 Eastern Shield 90
3.3.3 Nabitah Orogenic Belt 93
3.3.4 Hafnium Isotope Summary 95
Chapter 4: Geochemical Constraints on Arabian Shield Plutonic Rocks 97
4.1 Introduction 97
4.2 Whole Rock Major and Trace Element Geochemistry 98
4.2.1 Island Arc and Syncollisional Granitoids (IA+Syn) 99
4.2.2 Nabitah and Halaban Suture Granitoids (NHSG) 104
4.2.3 Post-Orogenic Perthitic Granitoids (POPG) 111
4.2.4 AnorogenicAegirine Perthitic Granitoids (AAPG) 119
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4.3 Whole Rock Isotope Geochemistry 125
4.3.1 Island Arc and Syncollisional Granitoids (IA+Syn) 126
4.3.2 Nabitah and Halaban Suture Granitoids (NHSG) 129
4.3.3 Post-Orogenic Perthitic Granitoids (POPG) 134
4.3.4 Anorogenic Aegirine PerthiticGranitoids (AAPG) 137
4.3.5 Shield Volcanics 139
4.3.6 Isotope Geochemistry Summary 142
4.4 Arabian Shield Granitoid Classification/Tectonic Discrimination 143
4.4.1 Post-Orogenic Perthitic Granitoids (POPG) and Anorogenic
Aegirine Perthitic Granitoids (AAPG) 143
4.4.2 Island Arc and Syncollisional Granitoids (IA+Syn) and Nabitah
and Halaban Suture Granitoids (NHSG) 148
4.4.3 Western Shield and Nabitah Suture Mafic Endmembers 154
4.4.4 Geochemistry Summary and Discussion 157
4.4.4a Subdivision of Arabian Shield A-type Granitoids 159
4.4.4b Differentiating Contaminated and Enriched Mantle 163
Chapter 5: Insights into Mantle Source from Zircon Geochemistry 167
5.1 Introduction 167
5.2 Island Arc and Syncollisional Granitoids (IA+Syn) 168
5.2.1 Major Element Geochemistry 169
5.2.2 Trace Element Geochemistry 170
5.3 Nabitah and Halaban Suture Granitoids (NHSG) 175
5.3.1 Major Element Geochemistry 178
5.3.2 Trace Element Geochemistry 180
5.4 Post-Orogenic Perthitic Granitoids (POPG) 186
5.4.1 Major Element Geochemistry 186
5.4.2 Trace Element Geochemistry 187
5.5 Anorogenic Aegirine Perthitic Granitoids (WPG) 189
5.5.1 Major Element Geochemistry 190
5.5.2 Trace Element Geochemistry 191
5.6 Zircon Geochemistry Summary 193
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Chapter 6: Discrete Crystallisation Ages within Granitoid Zircon
Populations 195
6.1 Introduction 195
6.2 Identification of Distinguished Zircon Morphologies 196
6.3 Identification of Non-Gaussian Probability Distributions 200
6.4 Discrete Ages Using Isoplot Software 203
6.5 Establishment of Three Discrete Zircon Ages 204
6.6 Relationships between Machine Error and Age Separation 207
6.7 Additional Evidence for Discrete Ages and Discussion 214
Chapter 7: Arabian Shield Post-Orogenic and Anorogenic Granitoids;
Petrogenetic Mechanisms for Distinct Contaminated and Enriched
Mantle Sources 216
7.1 Introduction 216
7.2 Geochemical Characteristics of Contaminated Granitoids 217
7.3 Magmatic Pulsing in a Contaminated MASH Zone 222
7.4 Subtle Differences in Primitive Syenites; Two Mantle Sources 228
7.5 Enriched Mantle Within Plate Granitoids; Key to Economic Deposits 233
7.6 Within Plate Granitoids; Products of Lithospheric Delamination 236
7.7 Generation of Crustal Melts 238
Chapter 8: A Tectonic Synthesis of the Arabian Shield; Implications
for Gondwana Assembly 241
8.1 Geochronological Overview 241
8.2 Island Arc Magmatism (950-750Ma) 243
8.3 Syncollisional Magmatism (730-636Ma) 250
8.4 Post-Orogenic Magmatism (636-600Ma) 251
8.5 Anorogenic Magmatism (<600Ma) 258
8.6 Evidence for Final Gondwana Assembly 265
8.7 Subtle Changes in Homogenous Juvenile Mantle Melts 270
8.8 Concluding Remarks 277
References 280
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Appendices
Appendix a Analytical Techniques 290
Appendix 1 Sample Catalogue from the Arabian Shield 303
1.1 Midyan Terrane 303
1.2 Jiddah Terrane 303
1.3 Hijaz Terrane 308
1.4 Ha’il Terrane 320
1.5 Ad Dawadimi Terrane 324
1.6 Tathlith Terrane 333
1.7 Afif Terrane 337
1.8 Asir Terrane 342
Appendix 2 Zircon U-Pb Geochronological Data 353
Appendix 3 Zircon Cathodoluminescence Images 396
Appendix 4 Zircon Hafnium Isotope Data 420
Appendix 5 Whole Rock Major and Trace Element Data; Ferrous Iron
Determination 444
Appendix 6 Whole Rock Sm-Nd and Sr Isotope Data 468
Appendix 7 Zircon Rare Earth Element Geochemistry 477
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Abstract
The Arabian-Nubian shield reflects the complex interplay between juvenile
oceanic and continental arc fragments accreted during the final stages of Gondwanian
super continental assembly. To date, much of the geochronological and geochemical
data from the Arabian Shield, Saudi Arabia, is absent or poorly constrained and
extrapolated from neighbouring Middle Eastern and African countries. Little attention
has been paid to the petrogenesis and tectonic significance of the plutonic rocks
pursuant to lithospheric orogenesis.
A total of 137 samples from 26 geological units were collected from the
Midyan, Hijaz, Asir, Tathlith, Afif, Ad Dawadimi and Ha’il terranes with particular
emphasis on accretionary suture zone and within plate setting relationships. Extensive
data bases are constructed using zircon U-Pb geochronology and Hf isotopes to evaluate
Gondwanian significance and whole rock major and trace element geochemistry, Nd,
Sm, Sr isotopes and zircon geochemistry to determine their petrogenetic properties.
These parameters provide new insight into changing mantle conditions beneath
collisional sutures (Yanbu, Nabitah and Halaban) and within plate asthenospheric
upwelling.
19 granitic units are subdivided into metaluminous, peraluminous and
peralkaline groups that possess distinguished island arc (~950-730Ma), syncollisional
(~<730-636Ma), post tectonic (~<636-600Ma) and anorogenic (<600Ma) U-Pb
geochronology. These magmatic phases represent accretionary cycles initiating from the
dismantlement of Rodinia, closure of the Mozambique Ocean and final Gondwana
amalgamation. Evidence for final assembly is recorded at ~525Ma (Najd fault
reactivation) which is now the youngest dated magmatism in the Arabian-Nubian Shield
and warrants repositioning of the regional unconformity at ~542Ma.
Emplacement of sampled Arabian Shield classic A-type post-tectonic and
anorogenic granitoids falls into three categories: 1) Intrude sutures immediately
following collision which contain extensive mafic cumulate fractionation and N-MORB
affiliation. 2) Plate boundary juxtaposed suites without obvious mafic cumulates, but
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posses contaminated N-MORB geochemistry. 3) Within plate granitoids isolated from
plate boundaries and also without obvious mafic cumulates, but with a distinctive
enriched (OIB) like asthenospheric mantle source. All categories produce similar felsic
endmembers, but contain isotopically distinct mantle source. These are differentiated
using a newly developed geochemical scheme (contaminated and enriched mantle
granitoids) that is successfully applied to regional Arabian-Nubian examples.
The diachronous Nabitah Orogenic Belt symbolises collision and subduction
between western oceanic and eastern continental terranes that was terminated by the
appearance of category 1 post-tectonic granitoids. This long lived (~50Ma) granitic
magmatism contains mingling textures, discrete crystallisation ages, distinguished
zircon morphologies and isotopically less juvenile mafics that geochronologically and
geochemically reflect magmatic pulsing from a contaminated lower crustal MASH
zone. The transition from N-MORB like mafics to isotopically enriched granitoids
(isotopically similar to category 3 suites) reflects subduction magmatism followed by
slab tear and asthenospheric influx.
Conversely, the appearance of category 3 anorogenic plutons is characterised by
widespread, tightly constrained (<10Ma) magmatism that is geochemically enriched,
economic and symbolic of lithospheric delamination and asthenospheric (OIB like)
upwelling. Differences between category 1, 2 and 3 zircon geochemistry constrain
further contaminated and enriched mantle source behaviour that produces similar felsic
products from distinguished petrogenetic processes.
In summary, the work presented in this thesis establishes clear distinctions
between accretionary syncollisional suites and anorogenic suites, but more significantly,
post-orogenic plutons confined to suture zones from those confined to within plate
settings. This allows new petrogenetic insights into changing juvenile mantle beneath
the Arabian Shield.
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Declaration
I certify that this work contains no material which has been accepted for the
award of any other degree or diploma in any university or other tertiary institution in my
name and, to the best of my knowledge and belief, contains no material previously
published or written by another person, except where due reference has been made in
the text. In addition, I certify that no part of this work will, in the future, be used in a
submission in my name, for any other degree or diploma in any university or other
tertiary institution without the prior approval of the University of Adelaide and where
applicable, any partner institution responsible for the joint-award of this degree.
I give consent to this copy of my thesis, when deposited in the University
Library, being made available for loan and photocopying, subject to the provisions of
the Copyright Act 1968.
I also give permission for the digital version of my thesis to be made available
on the web, via the University’s digital research repository, the Library catalogue and
also through web search engines, unless permission has been granted by the University
to restrict access for a period of time
…………………………..
Frank Alexander Robinson
…………………………..
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Acknowledgements
Firstly, I would like to throw out a big thank you to my supervisors Professor
John Foden and Associate Professor Alan Collins for their endless support, knowledge
and enthusiasm throughout this project. I appreciate them allowing me the freedom to
determine the direction of my thesis.
A special thank you must be awarded to the Saudi Arabian Geological Survey
for providing me with the opportunity and support to carry out this project. In particular,
Khalid Kadi, Mubarak Al-Nahdi, Fayek Kattan and Abdullah Yazidi must be thanked
for their gracious hospitality and support in Saudi Arabia. Their ongoing friendship has
been invaluable for the completion of this project.
This project would not have been possible without the tireless efforts of the
technical support staff from Adelaide Microscopy. Ben Wade, Angus Netting and Aoife
McFadden must be recognised for their help and support in obtaining geochronological
and geochemical data. David Bruce and John Stanley from the Adelaide Geology
Department must also take the stage for their help and advice in obtaining geochemical
data. Dr Justin Payne has also provided invaluable help and support throughout this
project. Paolo Sossi must also be thanked for his help with whole rock wet chemistry
and iron determination.
To the many geology friends I have made along the way, in particular Ben
Vanderhoek, Russell Smits, Jade Anderson and Alec Walsh, I thank you all for the
much needed coffees and lunches we had together. Without these I probably would not
have made it through to the end. I would like to thank my family, especially my mother
and father for putting up with my various moods and coaching me through to
submission. Max and Zen must also be thanked for keeping me sane by baking
brownies and letting me win at Catan. Finally, a big thanks to all my brothers and
sisters, but in particular that big lug Tony for keeping things light hearted all the way to
the end.
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