Earth's Oldest Rocks (eBook)

Vickie Bennett, Martin J. van Kranendonk, Hugh R.H. Smithies (Herausgeber)

eBook Download: EPUB

2007 | 1. Auflage
1330 Seiten
Elsevier Science (Verlag)
978-0-08-055247-7 (ISBN)

Infos

Earth's Oldest Rocks provides a comprehensive overview of all aspects of early Earth, from planetary accretion through to development of protocratons with depleted lithospheric keels by c. 3.2 Ga, in a series of papers written by over 50 of the world's leading experts. The book is divided into two chapters on early Earth history, ten chapters on the geology of specific cratons, and two chapters on early Earth analogues and the tectonic framework of early Earth. Individual contributions address topics that range from planetary accretion, a review of Earth meteorites, significance and composition of Hadean protocrust, composition of Archaean mantle and deep crust, all aspects of the geology of Paleoarchean cratons, composition of Archean oceans and hydrothermal environments, evidence and geological settings of early life, early Earth analogues from Venus and New Zealand, and a tectonic framework for early Earth.

* Contains comprehensive reviews of areas of ancient lithosphere on Earth, of planetary accretion processes, and of meteorites
* Focuses on specific aspects of early Earth, including oldest putative life forms, evidence of the composition of the ancient atmosphere-hydrosphere, and the oldest evidence for subduction-accretion
* Presents an overview of geological processes and model of the tectonic framework on early Earth

Inhalt

Front cover 1
Earth’S Oldest Rocks 4
Copyright page 5
Dedication 6
Contributing Authors 8
Contents 14
Preface: Aims, Scope, And Outline Of The Book 18
Part 1. Introduction 24
Chapter 1.1 Overview and History of Investigation of Early Earth Rocks 26
1.1-1. Granulite-Gneiss Belts 26
1.1-2. Greenstone-Granite Belts 28
1.1-3. The Hadean 29
1.1-4. Conclusions and Implications 29
Chapter 1.2 The Distribution of Paleoarchean Crust 32
1.2-1. Earth's Oldest Rocks and Minerals 32
1.2-2. Occurrences of Major Paleoarchean Rocks 34
1.2-3. Major Granitoid Events in the Paleoarchean 40
Part 2. Planetary Accretion and the Hadean to Eoarchean Earth – Building the Foundation 42
Chapter 2.1 The Formation of the Earth and Moon 44
2.1-1. The Solar Nebula 44
2.1-2. The Formation of The Giant Planets 45
2.1-3. Planetesimals 46
2.1-4. The Formation of the Terrestrial Planets 49
2.1-5. The Pre-Hadean State of the Earth 50
Acknowledgements 53
Chapter 2.2 Early Solar System Materials, Processes, and Chronology 54
2.2-1. Introduction 54
2.2-2. Early Solar System Materials 55
2.2-3. Early Solar System Events and Chronology 66
2.2-4. Summary 80
Chapter 2.3 Dynamics of the Hadean and Archaean Mantle 84
2.3-1. Introduction 84
2.3-2. Basic Principles Governing Tectonic Modes 85
2.3-3. Thermal State During Formation and the Hadean 87
2.3-4. Dynamical Stratification of the Mantle 89
2.3-5. Early Plate Tectonics and Early Mantle Cooling 93
2.3-6. Discussion 95
Acknowledgements 96
Chapter 2.4 The Enigma of the Terrestrial Protocrust: Evidence for Its Former Existence and the Importance of Its Complete Disappearance 98
2.4-1. Introduction 98
2.4-2. Evidence for Substantial > 4 Ga Differentiation of the Silicate Earth
2.4-3. Models for the Disappearance of the Hadean Crust 108
2.4-4. Summary 111
Chapter 2.5 The Oldest Terrestrial Mineral Record: A Review of 4400 to 4000 Ma Detrital Zircons from Jack Hills, Western Australia 114
2.5-1. Introduction 114
2.5-2. The Jack Hills 115
2.5-3. Jack Hills Zircons 120
2.5-4. Early Earth Processes Recorded in Jack Hills Zircons 132
Acknowledgements 134
Chapter 2.6 Evidence of Pre-3100 Ma Crust in the Youanmi and South West Terranes, and Eastern Goldfields Superterrane, of the Yilgarn Craton 136
2.6-1. Introduction 136
2.6-2. Evidence of Old (Pre-3100 Ma) Yilgarn Crust 138
2.6-3. Discussion 143
2.6-4. Conclusions 145
Acknowledgements 146
Part 3. Eoarchean Gneiss Complexes 148
Chapter 3.1 The Early Archean Acasta Gneiss Complex: Geological, Geochronological and Isotopic Studies and Implications for Early Crustal Evolution 150
3.1-1. Introduction 150
3.1-2. Geology 150
3.1-3. Geochronology 158
3.1-4. Constraints on the Provenance of the 4.2 Ga Zircon Xenocryst 160
3.1-5. Radiogenic Isotope Systematics 165
3.1-6. Tectonothermal Evolution of the Acasta Gneiss Complex 167
3.1-7. Implications for Early Crustal Evolution 169
Acknowledgements 170
Chapter 3.2 Ancient Antarctica: The Archaean of the East Antarctic Shield 172
3.2-1. Introduction 172
3.2-2. Overview of the Geology of the East Antarctic Shield 174
3.2-3. The Oldest Rocks: > 3400 Ma
3.2-4. Conclusions 208
Acknowledgements 209
Chapter 3.3 The Itsaq Gneiss Complex of Southern West Greenland and the Construction of Eoarchaean Crust at Convergent Plate Boundaries 210
Abstract 210
3.3-1. Introduction 211
3.3-2. Methods 213
3.3-3. Itsaq Gneiss Complex 218
3.3-4. Building of Itsaq Gneiss Complex Crust out of Tonalites 226
3.3-5. Eoarchaean Tectonic Intercalation of Unrelated Rocks in the Itsaq Gneiss Complex 233
3.3-6. Discussion 239
Acknowledgements 241
Chapter 3.4 The Geology of the 3.8 Ga Nuvvuagittuq (Porpoise Cove) Greenstone Belt, Northeastern Superior Province, Canada 242
3.4-1. Introduction 242
3.4-2. Geological Framework 243
3.4-3. Geology of the Nuvvuagittuq Belt 246
3.4-4. Discussion 263
3.4-5. Conclusions 273
Acknowledgements 273
Chapter 3.5 Eoarchean Rocks and Zircons in the North China Craton 274
3.5-1. Introduction 274
3.5-2. General Geology 274
3.5-3. Oldest Rocks and Zircons in the NCC 279
3.5-4. Discussion 294
Acknowledgements 296
Chapter 3.6 The Narryer Terrane, Western Australia: A Review 298
3.6-1. Introduction 298
3.6-2. Historical 298
3.6-3. Characteristics of the Narryer Gneiss Complex 305
3.6-4. Some Outstanding Issues 324
Acknowledgements 327
Part 4. The Paleoarchean Pilbara Craton, Western Australia 328
Chapter 4.1 Paleoarchean Development of a Continental Nucleus: the East Pilbara Terrane of the Pilbara Craton, Western Australia 330
4.1-1. Introduction 330
4.1-2. Geology of the Pilbara Craton 330
4.1-3. Geology of the East Pilbara Terrane 333
4.1-4. Tectonic Models, Old and New 355
Acknowledgements 360
Chapter 4.2 The Oldest Well-Preserved Felsic Volcanic Rocks on Earth: Geochemical Clues to the Early Evolution of the Pilbara Supergroup and Implications for the Growth of a Paleoarchean Protocontinent 362
4.2-1. Introduction 362
4.2-2. Regional geological summary 363
4.2-3. Analytical methods 363
4.2-4. Coonterunah Subgroup 363
4.2-5. Duffer Formation 374
4.2-6. Felsic Volcanic Units at Higher Stratigraphic Levels 377
4.2-7. Petrogenesis of mafic volcanic rocks 378
4.2-8. Petrogenesis of Felsic Volcanic Rocks 381
4.2-9. Implications for Early Pilbara Crustal Evolution 386
4.2-10. Conclusions 389
Acknowledgements 390
Chapter 4.3 Geochemistry of Paleoarchean Granites of the East Pilbara Terrane, Pilbara Craton, Western Australia: Implications for Early Archean Crustal Growth 392
4.3-1. Introduction 392
4.3-2. Regional geological summary 393
4.3-3. Granite Geochemistry and Petrology 394
4.3-4. Geochemistry 398
4.3-5. Granite Petrogenesis 410
4.3-6. Discussion 430
Acknowledgements 432
Chapter 4.4 Paleoarchean Mineral Deposits of the Pilbara Craton: Genesis, Tectonic Environment and Comparisons with Younger Deposits 434
4.4-1. Introduction 434
4.4-2. Paleoarchean Geological Evolution of the Pilbara Craton 436
4.4-3. Paleoarchean Mineral Deposits of the Pilbara Craton 436
4.4-4. Metallogenesis in Other Paleoarchean Terrains 463
4.4-5. A Comparison of Paleoarchean, Neoarchaean and Phanerozoic Metallogeny 464
4.4-6. Implications for Tectonic Processes During the Paleoarchean 469
4.4-7. Conclusions 473
Acknowledgements 473
Part 5. The Paleoarchean Kaapvaal Craton, Southern Africa 474
Chapter 5.1 An Overview of the Pre-Mesoarchean Rocks of the Kaapvaal Craton, South Africa 476
5.1-1. Introduction 476
5.1-2. Overview of the Pre-Mesoarchean Evolution of the Kaapvaal Craton 478
5.1-3. Conclusions 485
Chapter 5.2 The Ancient Gneiss Complex of Swaziland and Environs: Record of Early Archean Crustal Evolution in Southern Africa 488
5.2-1. Introduction 488
5.2-2. Field Relationships and Origin of Components of the AGC 493
5.2-3. Geochronology and Implications for Gneiss-Greenstone Relationships 495
5.2-4. Ngwane Gneiss 497
5.2-5. Dwalile Supracrustal Suite 498
5.2-6. Tsawela Gneiss 500
5.2-7. Discussion and Conclusions 502
Acknowledgements 503
Chapter 5.3 An Overview of the Geology of the Barberton Greenstone Belt and Vicinity: Implications for Early Crustal Development 504
5.3-1. Introduction 504
5.3-2. General Geology of the BGB 506
5.3-3. Tectono-Stratigraphic Suites 509
5.3-4. Structural Development of the BGGT 540
5.3-5. Evolution of the BGGT 545
5.3-6. Conclusions 548
Acknowledgements 549
Chapter 5.4 Volcanology of the Barberton Greenstone Belt, South Africa: Inflation and Evolution of Flow Fields 550
5.4-1. Introduction 550
5.4-2. Tectono-Volcanic History of Barberton Greenstone Belt (BGB) 551
5.4-3. Volcanology of the Barberton Greenstone Belt 553
5.4-4. Komati Formation 556
5.4-5. Hooggenoeg Formation 578
5.4-6. Kromberg Formation 582
5.4-7. Mendon Formation 586
5.4-8. Comparison of flow morphologies 589
5.4-9. Reconstructing flow fields 589
5.4-10. Flow Fields: Petrogenesis and Plate Tectonic Setting 590
5.4-11. Komati-Hooggenoeg Section: A Fore-Arc Ophiolite? 592
Acknowledgements 593
Chapter 5.5 Silicified Basalts, Bedded Cherts and Other Sea Floor Alteration Phenomena of the 3.4 Ga Nondweni Greenstone Belt, South Africa 594
5.5-1. Introduction 594
5.5-2. Geological Setting 595
5.5-3. Analytical Methods 600
5.5-4. Field Relationships and Geochemistry 601
5.5-5. Petrography 616
5.5-6. Discussion 620
5.5-7. Conclusions 627
Acknowledgements 628
Chapter 5.6 TTG Plutons of the Barberton Granitoid-Greenstone Terrain, South Africa 630
5.6-1. Introduction 630
5.6-2. Geological Setting 631
5.6-3. TTG Plutons of the BGGT 637
5.6-4. Geochemistry 644
5.6-5. Petrogenesis of TTG Rocks 665
5.6-6. Partial Melting of Amphibolites and Controls on the Melt Geochemistry 668
5.6-7. Summary and Geodynamic Implications 682
5.6-8. Discussion 687
5.6-9. Conclusions 689
Acknowledgements 690
Chapter 5.7 Metamorphism in the Barberton Granite Greenstone Terrain: A Record of Paleoarchean Accretion 692
5.7-1. Evidence for Accretionary Orogeny in the BGGT 694
5.7-2. Metamorphic History of the Eastern Terrane 696
5.7-3. Metamorphism in the Western Domain 702
5.7-4. Inyoni Shear Zone 707
5.7-5. Discussion and Conclusions 709
Chapter 5.8 Tectono-Metamorphic Controls on Archean Gold Mineralization in the Barberton Greenstone Belt, South Africa: An Example from the New Consort Gold Mine 722
5.8-1. Introduction 722
5.8-2. Geological Setting 724
5.8-3. Characteristics of Greenschist Facies Gold Deposits 727
5.8-4. The New Consort Gold Mine 729
5.8-5. Constraints on the Timing of Deformation, Metamorphism and Mineralization 742
5.8-6. Onset of Extensional Tectonics - 3230 Ma, 3100 Ma, or Multistage? 748
5.8-7. Conclusion 749
Acknowledgements 750
Part 6. Paleoarchean Gneiss Terranes 752
Chapter 6.1 Paleoarchean Gneisses in the Minnesota River Valley and Northern Michigan, USA 754
6.1-1. Introduction 754
6.1-2. Regional Setting 754
6.1-3. Geologic Setting 756
6.1-4. Geochronology 761
6.1-5. Discussion 769
Acknowledgements 773
Chapter 6.2 The Assean Lake Complex: Ancient Crust at the Northwestern Margin of the Superior Craton, Manitoba, Canada 774
6.2-1. Introduction 774
6.2-2. Principal Geological Elements of the Northwestern Superior Craton Margin 775
6.2-3. Geology of the Assean Lake Complex 780
6.2-4. Extent of the Mesoarchean Assean Lake Complex 792
6.2-5. Conclusions 796
Acknowledgements 796
Chapter 6.3 Oldest Rocks of the Wyoming Craton 798
6.3-1. Introduction 798
6.3-2. Known Occurrences of Eo- and Paleoarchean Rocks and Minerals 800
6.3-3. Isotopic Evidence of Ancient Crust in Meso- to Neoarchean Plutons and Sedimentary Rocks 807
6.3-4. Discussion 811
6.3-5. Conclusions 814
Chapter 6.4 The Oldest Rock Assemblages of the Siberian Craton 816
6.4-1. Introduction 816
6.4-2. Sharyzhalgay Uplift 819
6.4-3. Aldan Shield 842
6.4-4. Anabar Shield 850
6.4-5. Discussion 858
Acknowledgements 861
Part 7. Life on Earl Yearth 862
Chapter 7.1 Searching for Earth's Earliest Life in Southern West Greenland - History, Current Status, and Future Prospects 864
7.1-1. Introduction 864
7.1-2. Claims for Early Terrestrial Life 866
7.1-3. Significance of Banded Iron Formation (BIF) 875
7.1-4. Prospects for the Discovery of Early Life Signatures 876
Chapter 7.2 A Review of the Evidence for Putative Paleoarchean Life in the Pilbara Craton, Western Australia 878
7.2-1. Introduction 878
7.2-2. Geological Setting 881
7.2-3. Use of Morphology as an Indicator of Biogenicity 882
7.2-4. Dresser Formation Stromatolites 883
7.2-5. Strelley Pool Chert Stromatolites 888
7.2-6. Origin of Carbonaceous Material/Microfossils in Hydrothermal Silica Veins 898
7.2-7. Conclusions 900
Acknowledgements 900
Chapter 7.3 Stable Carbon and Sulfur Isotope Geochemistry of the ca. 3490 Ma Dresser Formation Hydrothermal Deposit, Pilbara Craton, Western Australia 902
7.3-1. Introduction 902
7.3-2. Hydrothermal Deposits in the North Pole Area 903
7.3-3. Carbon and Sulfur Isotope Geochemistry of the Dresser Formation 909
7.3-4. Conclusions 917
Acknowledgements 919
Chapter 7.4 Organic Geochemistry of Archaean Carbonaceous Cherts from the Pilbara Craton, Western Australia 920
7.4-1. Introduction 920
7.4-2. Petrography of typical carbonaceous material in Warrawoona and Kelly Group cherts 922
7.4-3. Carbon Isotope (delta13C) Measurements 922
7.4-4. Raman Spectroscopy 925
7.4-5. Pyrolysis Gas Chromatography Mass Spectrometry (py-GC/MS) 931
7.4-6. Other Structural Elucidation Analytical Techniques Applied to Pilbara Kerogens 939
7.4-7. Implications for the Interpretation of Signals from Early Life in the Strelley Pool Chert 940
7.4-8. Conclusions 942
Acknowledgements 944
Chapter 7.5 Sulphur on the Early Earth 946
7.5-1. Introduction 946
7.5-2. Origin of Sulphur to the Earth 949
7.5-3. Extraterrestrial Inputs to the Sulphur Cycle on the Early Earth 959
7.5-4. Sulphur and the Hadean Earth Surface State 962
7.5-5. Sulphur and the Early Archaean Atmosphere 967
7.5-6. Sulphur and Early Life 969
7.5-7. Sulphur Isotopes in Early Archaean Rocks 980
7.5-8. Concluding Remarks: Banded Iron-Formations, Sulphur and Life on the Early Earth 991
Acknowledgements 993
Chapter 7.6 The Marine Carbonate and Chert Isotope Records and Their Implications for Tectonics, Life and Climate on the Early Earth 994
7.6-1. Introduction 994
7.6-2. The Sr Isotope Composition of the Early Ocean 996
7.6-3. The C Isotope Composition of Early Marine Carbonate Rocks 997
7.6-4. The O Isotope Composition of Early Marine Sedimentary Rocks 1001
7.6-5. Summary 1006
Part 8. Tectonicson Early Earth 1008
Chapter 8.1 Venus: A Thin-Lithosphere Analog for Early Earth? 1010
8.1-1. Introduction 1010
8.1-2. Venus Overview 1012
8.1-3. Thin Lithosphere Tectonomagmatic Features 1019
8.1-4. Early Earth Analogues 1032
8.1-5. Summary 1035
Chapter 8.2 The Earliest Subcontinental Lithospheric Mantle 1036
8.2-1 Introduction 1036
8.2-2. SCLM Composition 1036
8.2-3. Archean SCLM 1039
8.2-4. Is There More Archean SCLM Than We Think? 1055
8.2-5. Implications for Crustal Evolution 1057
Acknowledgements 1057
Chapter 8.3 Ancient to Modern Earth: The Role of Mantle Plumes in the Making of Continental Crust 1060
8.3-1. Introduction 1060
8.3-2. The Continental Crust 1061
8.3-3. Mantle Plumes 1065
8.3-4. The Archaean 1069
8.3-5. The Proterozoic 1076
8.3-6. The Phanerozoic 1079
8.3-7. Concluding Remarks 1084
Acknowledgements 1087
Chapter 8.4 Eo- to Mesoarchean Terranes of the Superior Province and Their Tectonic Context 1088
8.4-1. Introduction 1088
8.4-2. Tectonic Framework 1088
8.4-3. Microcontinental Fragments 1091
8.4-4. History of Tectonic Assembly 1103
8.4-5. Influence of Microcontinental Terranes on Tectonic Style 1106
Acknowledgements 1107
Chapter 8.5 Early Archean Asteroid Impacts on Earth: Stratigraphic and Isotopic Age Correlations and Possible Geodynamic Consequences 1110
8.5-1. Introduction 1110
8.5-2. 3.47 Ga Impact Events 1111
8.5-3. The 3.26-3.24 Ga Barberton Impact Cluster 1113
8.5-4. Stratigraphic and Isotopic Age Correlations Between the 3.26-3.24 Ga Impacts 1117
8.5-5. Possible Geodynamic Consequences 1119
8.5-6. Lunar correlations 1123
8.5-7. Summary 1124
Chapter 8.6 Tectonics of Early Earth 1128
8.6-1. Patterns of Crust Formation 1129
8.6-2. Tectonic Evolution of Early Earth 1130
8.6-3. Timescale Divisions 1138
Acknowledgements 1139
References 1140
Subject Index 1314

Textauszug

Developments in Precambrian Geology, Vol. 15, Number Suppl (C), 2007

ISSN: 0166-2635

doi: 10.1016/S0166-2635(07)15092-1

Preface: Aims, Scope, and Outline of the Book

Martin J. Van Kranendonk, R. Hugh Smithies, Vickie C. Bennett

The geological history of early Earth holds a certain ineluctable fascination, not just for professional Earth Scientists and geology students, but for scientists in other disciplines, as well as many in the general public. This fascination with early Earth is compelling, not least because we know so little about it, but also because – as with the search for life on ancient Earth and elsewhere in the solar system – it casts light on the fundamental issues of our existence: who are we; how are we here?

To facilitate a better understanding of these questions, we need to know how our home planet formed, what it was like in its early history, how it was able to foster the development of life, and how it evolved into the planet we live on today.

We had two main aims in mind when inviting authors to contribute papers to this book. The first aim, reflected in the main title of the book, was to compile a geological record of Earth’s Oldest Rocks, with thorough descriptions of as much of the oldest continental crust as possible, and with a focus on the rocks. The second aim was to gain a better understanding of the tectonic processes that gave rise to the formation and preservation of these oldest pieces of continental crust, and when and how early tectonic processes changed to a plate tectonic Earth operating more or less as we know it today. It is the latter part of this last sentence that explains why 3.2 Ga was chosen as the upper time limit for this book, for this is the time when evidence from geological studies strongly supports the operation (at least locally) of modern-style plate tectonics on Earth (Smithies et al., 2005a). After 3.2 Ga, the geological evidence in support of some form of plate tectonics operating on Earth is compelling, although there were significant differences in how this process operated compared with plate tectonics on Proterozoic to recent Earth, but that is another story (see Van Kranendonk, 2004a, and references therein).

When considering the evolution of early Earth, it is important to keep in mind the concept of Secular Change, and to “… stretch ones’ tectonic imagination with respect to non-plate tectonic processes of heat transfer , providing for means to test geologic histories against multiple hypotheses, aimed at understanding possible early Earth”, as Vicki Hansen so nicely states in her paper on Venus towards the end of this volume. Indeed, we suggest that Secular Change be regarded as a guiding principle for studies of early Earth evolution, in the same way that Lyell’s (1758) Principle of Uniformitarianism (the present is the key to the past) has guided our understanding of the more recent geological past, when Earth’s primary heat loss mechanism was through plate tectonics.

Secular Change is important for early Earth studies for two main reasons. First, planetary studies have shown that Earth had a violent accretionary history starting at 4.567 Ga, and was a molten ball at 4.50 Ga due to the heat of accretion and heat from the decay of short-lived radiogenic nucleides. This contrasts dramatically with modern Earth, which is differentiated into a core, mantle, crust, hydrosphere and atmosphere, has a rapidly spinning core, a convecting and melting mantle, two types of crust, a rigid lithosphere that is divided into several plates that are moving across the planet’s surface through a process we call plate tectonics, is host to a thriving biosphere, and has an oxygen-rich atmosphere. We use this contrast to directly infer secular change. What remains unanswered is the rate of secular change, including the rate of growth of continental crust and the time of onset of plate tectonics. Opinions in regard to these issues vary markedly. Whereas some maintain that much of this change occurred very early and that Earth has been operating in a similar fashion since 4.2 Gyr ago (e.g., Cavosie et al., this volume), others maintain that change has occurred more gradually, and that modern plate tectonics did not commence until the Neoproterozoic (Hamilton, 1998, 2003; Stern, 2005; Brown, 2006).

The second main reason why Secular Change is important when considering early Earth is based on geological evidence from Earth’s oldest rocks, which shows that there are many differences between early Earth rocks and those of Proterozoic to recent Earth (e.g., Hamilton, 1993, 1998, 2005; Stern, 2005; Brown, 2006). Some of these differences include:

• Archean Earth erupted unique komatiitic magmas (Viljoen and Viljoen, 1969) from a hotter mantle (Herzberg, 1992; Nisbett et al., 1993; Arndt et al., 1998);

• Archean crust is characterised by granite-greenstone terranes, a type of crust found much less commonly in younger terrains;

• Granite-greenstone terranes are characterised by a dome-and-keel architecture that is unique to Archean and Paleoproterozoic crust (e.g., MacGregor, 1951; Hickman, 1984);

• The average composition of Archean continental crust was different (Taylor and McLennan, 1985);

• The average composition of early Archean granitic rocks is dominated by sodic (TTG) compositions, in contrast to the more potassic composition of most younger granitic rocks;

• The composition of Archean TTG is not the same as Phanerozoic adakites formed in subduction zones (Smithies, 2000);

• Archean sedimentary rocks are predominantly chert and banded iron-formation, and generally lack continental-type sedimentary rocks before ∼3.2 Ga, although there are local exceptions;

• Sr-isotope data show that the chemistry of Archean seawater was essentially mantle buffered, contrasting with a riverine buffered signature after ∼2.7 Ga;

• Many of the characteristic products of subduction are lacking in Archean rocks, including blueschists, ophiolites, and ultra-high pressure metamorphic terranes (Stern, 2005; Brown, 2006), and accretionary complexes with exotic blocks in zones of tectonic melange (McCall, 2003);

• Ophiolites >1 Ga are fundamentally different than younger ophiolites, according to Moores (2002).

These differences tell us that early Earth was a vastly different planet than that of today, primarily due to a higher mantle temperature. Follow-on effects from this include a higher geothermal gradient, which in turn resulted in greater degrees of partial melting of upwelling mantle, a thicker, but softer crust, and a softer, weaker lithosphere. A more detailed review of these differences is presented in the final paper of this book.

A note regarding terminology. For the purposes of this book, we have adopted the IUGS International Commission on Stratigraphy convention for sub-divisions of the Archean Eon into the Neoarchean Era (2.5–2.8 Ga), Mesoarchean Era (2.8–3.2 Ga), and Paleoarchean Era (3.2–3.6 Ga) (Gradstein et al., 2004). We have also used the Eoarchean Era for rocks older than 3.6 Ga as suggested by these authors, but have placed a lower limit on this sub-division at 4.0 Ga and refer to the period of time older than this as the Hadean Eon (4.0–4.567 Ga).

This book is organised into eight parts, including an Introduction, five parts describing the geology of Earth’s oldest rocks, a part on early life, and a final part on the tectonics of early Earth. In Part 1, Brian Windley provides an overview of the history of discovery of ancient rocks on Earth, which started with publications in 1951 and was followed by seminal discoveries using advanced analytical techniques up to the present day. This is followed by Kent Condie’s overview of the distribution of ancient rocks on Earth.

Parts 2–6 describe the geology of Earth’s oldest rocks, and are divided on the basis of successive stages of early Earth evolution. Part 2 outlines the beginnings of Earth history, with a review of planetary accretion processes in the formation of the Earth and Moon by Stuart Ross Taylor, and an investigation of early solar system materials as represented by the meteorite record on Earth, by Alex Bevan. This is followed by a theoretical consideration of the dynamics of the mantle of early Earth by Geoff Davies and a review of the evidence in favour of an early terrestrial protocrust by Balz Kamber. Thereafter are two papers by Cavosie and others and Stephen Wyche that review the distribution and characteristics of Eoarchean zircon grains from Western Australia and their significance in terms of early Earth evolution.

Part 3 presents a series of papers that describe the geology of Eoarchean gneiss complexes from different cratons around the world. These include a description of the oldest rocks in the world from the Acasta Gneiss Complex in the Slave Craton in northwestern Canada by Iizuka and others. Other ancient, high-grade and strongly deformed rocks are described from Antarctica by Harley and Kelly, from the North China Craton by Liu and others, and from the Narryer Terrane of the Yilgarn Craton in Western Australia by Wilde and Spaggiari. O’Neil and others describe the ancient supracrustal rocks of the Nuvvuagittuq Greenstone Belt in the Superior...

Produkt-Details

• Erscheint lt. Verlag: 26.10.2007
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geophysik
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik ► Bergbau
• Themenwelt: Wirtschaft
• ISBN-10: 0-08-055247-1 / 0080552471
• ISBN-13: 978-0-08-055247-7 / 9780080552477