Atlas of Deformed and Metamorphosed Rocks from Proterozoic Orogens

By T.R.K. Chetty and Wilbert Kehelpannala

Atlas of Deformed and Metamorphosed Rocks from Proterozoic Orogens is a richly illustrated reference book featuring over 660 full-color field images of a range of lithologies from some Proterozoic terrains that were subjected to multiple events of magmatism, deformation, metamorphism, and metasomatism. The Atlas focuses on amphibolite to granulite facies lithologies and associated ma?c-ultrama?c rocks from Proterozoic orogens of India, Sri Lanka, Botswana, South Africa, East Antarctica, and Western Australia. Each chapter in the book begins with a brief review of geology, including deformation and metamorphic history, along with a regional geological map to help readers to visualize the ?eld observations in the relevant geological context. Each image is accompanied by a concise description providing location, lithology, structural fabric, possible deformational history, metamorphic features, partial melting, metasomatism, and other important crustal processes. This Atlas is an important source of information for a broad range of earth scientists, graduate and undergraduate students, researchers, academicians, and other professionals. This book will form a great treasure to those geoscientists who never had an opportunity to visit any of the Proterozoic orogenic belts.

• Features over 660 full-color photographs representing typical lithologies and associated structural, metamorphic features, and other crustal processes from different Proterozoic orogens
• Highlights the significance of field photographs in advancing new knowledge which may provide pathways for new research
• Covers many important Proterozoic terranes of East Gondwana
• Presents regional geologic maps from each Proterozoic orogen

• Language: English
• Publisher: Elsevier Science
• Release date: Aug 20, 2021
• ISBN: 9780128179796

T.R.K. Chetty

Prof. T.R.K Chetty has made seminal contributions in understanding the structural architecture and tectonic evolution of Proterozoic orogens of India that transformed and revolutionized conventional thoughts with insightful modern concepts. His first book (August 2017, Elsevier) on “Proterozoic Orogens of India: A critical window to Gondwana” has been applauded nationally and internationally. Prof. Chetty is honoured with INSA-Royal Society Visiting Professor, 1987; INSA-JSPS Fellowship, CSIR-DAAD (Senior) Fellowship, 1997; Fellow of Andhra Pradesh Academy of Sciences; and visiting professor in many universities in India and abroad. Prof. Chetty is a recipient of National mineral Award (2006), Australian Endeavour Executive Award (2008) and is the first Indian to be elected as the President, International Association of Gondwana Research (2012-2014, IAGR).

Book preview

Atlas of Deformed and Metamorphosed Rocks from Proterozoic Orogens

T.R.K. Chetty

CSIR-National Geophysical Research Institute, Hyderabad, India

K.V. Wilbert Kehelpannala

Department of Geology, Faculty of Science, University of Botswana, Private Bag UB 00704, Gaborone, Botswana

Table of Contents

Cover image

Title page

Copyright

Preface

Acknowledgements

Chapter 1. Proterozoic orogens: introduction

1.1. Introduction

1.2. Orogenic evolution

1.3. Proterozoic high-grade rocks

1.4. Gondwana orogens

Chapter 2. Proterozoic orogens of Indian shield

Chapter 2.1. Proterozoic orogens of India

Chapter 2.2. Southern Granulite Terrane

Chapter 2.3. Eastern Ghats Mobile Belt

Chapter 2.4. Central Indian Tectonic Zone

Chapter 2.5. Aravalli-Delhi Orogenic Belt

Chapter 3. Proterozoic orogens of Sri Lanka

3.1. Introduction

3.2. The Wanni Complex

3.3. The Highland Complex

3.4. The Vijayan Complex

3.5. The Wanni Complex-Highland Complex Boundary Shear Zone (WHBSZ)

3.6. The Highland Complex/Vijayan Complex Boundary Shear Zone

Chapter 4. Proterozoic orogens of Southern Africa

4.1. Introduction

4.2. The Limpopo Belt

4.3. The Central Zone of the Limpopo Belt

4.4. The Mahalapye Complex

4.5. The Phikwe Complex

4.6. Beit Bridge Complex

4.7. The Magogaphate Shear Zone

Chapter 5. East Antarctica

5.1. Introduction

5.2. The Sør Rondane Mountains

5.3. The Maud Belt

5.4. The Muhlig-Hofmannfjella Mountains

5.5. The Lützow-Holm Complex

5.6. The Vestfold Hills

5.7. The Grove Mountains

5.8. The Bunger Hills

Chapter 6. Proterozoic orogens of Western Australia

6.1. Introduction

6.2. The Albany–Fraser orogen

6.3. The Pinjarra orogen

Index

Copyright

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Preface

In recent decades, there has been a significant shift of interest toward laboratory-centric research studies in geosciences, neglecting the importance of field geology, which forms a crucial element to the understanding of our planet Earth and its internal and external geological processes. Most of these processes are preserved in the form of rock records in the field, which can be considered as objects of beauty, kindling the imagination and stimulation of the uninitiated and experts alike and must be given their rightful place in geoscience education as well as in research studies.

Basic geological information and knowledge can be obtained through reading and reviewing of published geological maps and the available literature to understand the general geology, structural, metamorphic, and tectonic evolution of an area, which is possible only to a limited extent. It always remains superficial and can never substitute the personal experiences of field geologists on the nature and characteristics of rocks at outcrop scales in the field. It is in this context a record of field observations, descriptions, and interpretations in the form of a collection of high-quality field photographs will be of immense utility. These field photographs with brief and comprehensive description and interpretation in the form of an Atlas will form an important fundamental and essential requirement of the Earth Science community.

Almost all the rocks currently exposed in Proterozoic orogens have been deformed and metamorphosed under amphibolite- to granulite-facies conditions with some of them obtaining either ultrahigh pressure or ultrahigh temperature conditions. We have had the opportunity of studying such high-grade metamorphic rocks from several Proterozoic orogenic belts of Gondwana supercontinent in the field for over three  decades, making detailed sketches, measuring various structural elements, and mapping detailed geology. We have also conducted and participated in many international field workshops across some of the geologically important regions and had the benefit of interaction with many prominent earth scientists from all over the globe. During our long professional career with structural geology, tectonics, and metamorphic petrology being the focus, we have compiled and preserved innumerable number of field photographs, captured from some of the well-exposed areas of key orogenic belts of Gondwana supercontinent.

This Atlas forms a richly illustrated reference book with a long-lasting value that provides unique and comprehensive field images of a range of lithologies that were subjected to multiple events of magmatism, deformation, metamorphism, and metasomatism. Each chapter in the book begins with a brief review of geology, including deformation and metamorphic history, along with a regional geological map to help readers to visualize the field observations in the relevant geological context. The Atlas focuses on amphibolite to granulite facies rocks and associated mafic–ultramafic rocks from Proterozoic orogens of India, Sri Lanka, Botswana, South Africa, East Antarctica, and Western Australia. All the photographs have been sequentially organized considering the metamorphic complexes, tectonic divisions, and crustal units of respective individual orogens.

The present Atlas of selected photographs is an important source of information for a broad range of earth scientists, graduate and undergraduate students, researchers, academicians, and other professionals. The Atlas would be extremely useful, educative, and informative and would provide insights into the understanding of some of the mysteries of the earth's processes and its evolution. It will form a great treasure particularly to the younger generations and to those geoscientists who never had an opportunity to visit any of the Proterozoic orogenic belts.

In view of the above, we present here an Atlas of field photographs of deformed and metamorphosed rocks of varied rock compositions and structural geometry with a concise description providing location, lithology, structural fabrics, possible deformational history, metamorphic features, late metasomatism, and other important geological information. Its relevance and significance in understanding the geological and tectonic history and metamorphic evolution of a region are highlighted by providing relevant key references.

T.R.K. Chetty

K.V. Wilbert Kehelpannala

Acknowledgements

We are grateful to all our teachers, collaborators and students for their guidance, stimulating discussions and support during our professional journey. We also thank all those contributors for sparing their valuable photographs along with brief descriptions to the present Atlas. We appreciate and thank all those authors whose publications aided us in compiling the photographs published in literature, especially for the chapters on East Antarctica, Western Australia and some parts of the Limpopo Belt. We thank profusely the Geological Survey and Resource Strategy, Department of Mines, Industry Regulation and Safety, State of Western Australia, 2019, for permitting us to include some of the photographs from their field guides. We thank the following publishers and organisations for granting permission to reproduce some of their figures: The Geological Society of Sri Lanka, The Geological Society of London and the National Institute of Polar Research, Japan. We thank Prof. Yoshikuni Hiroi, Chiba, Japan, for sharing some spectacular photographs from East Antarctica.

We are very grateful to Elsevier publishers for accepting our proposal for the Atlas and for working with us on this project. We highly appreciate and wish to acknowledge the high quality and prompt support rendered by the Elsevier team (Emerald, Sruthi and their team members) in transforming field photographs and the manuscript to its present shape of the Atlas.

TRK owes gratitude and appreciation to the CSIR-National Geophysical Research Institute (NGRI), for making his entire four-decade scientific career fully satisfying, exciting and meaningful, by providing excellent infrastructural facilities and a congenial atmosphere for his scientific pursuits. TRK owes a sense of gratitude to all the directors of CSIR-NGRI for their encouragement and support throughout his career and after superannuation till 2020. TRK is thankful to Dr. P. Rama Rao (CSIR-NGRI) for sparing his valuable time in critically going through Chapters 2 and 6. He appreciates and acknowledges Prof. T.K. Biswal (Mumbai); Prof. Dilip Saha (Kolkata); Prof. J.K. Nanda (Bhubaneswar); Dr. Mahapatro (GSI); Dr.Sesha Sai (GSI) for sharing some of their valuable pictures to Chapter 2. TRK thanks his former colleagues Drs. D.S.N. Murthy, Y.J. Bhaskar Rao, B.L.Narayana, and international collaborators Profs. M. Santosh (China), Alan Collins (Australia), T. Tsunogae (Japan) for their valuable discussions both in the field and laboratory. We also thank Prof. Larry Brown (USA), Dr. Chris Clark (Australia); Dr. Teale (Australia) for sparing some of their pictures captured during the International Field workshop across the Southern Granulite Terrane, organised by TRK, in 2004.

TRK is indebted to his late parents Sri. T. Chinnagangulaiah and Smt. T. Subbamma; his life partner Smt. Rama Devi; and daughters (Sreesusudha, Sowmya and Sujani) and their families for their love and affection, and for making his life exciting and enjoyable.

KVWK would like to thank his long-time collaborator late Prof. Alfred Kröner, for his valuable discussions in the field and encouragement. He also acknowledges Dr. K. Laletsang, Head of the Geology Department, University of Botswana, and Prof. Read Mapeo, the former Head, for their support in providing facilities. Most of the photographs from the Limpopo Belt in Botswana, published in this Atlas, were taken during field excursions and B.Sc. final year field research projects funded by the Faculty of Science, University of Botswana. KVWK acknowledges that the photographs from Sri Lanka included in this Atlas were taken by him during many of his field visits to his home country and also during his time as a researcher at the former Institute of Fundamental Studies. KVWK expresses his love and affection to his wife Benedicta and children (Thisura, Kithma and Gimhanie) for their unstinted support in various ways during the compilation of this Atlas.

Chapter 1: Proterozoic orogens

introduction

Abstract

This chapter provides a brief introduction about definition, characteristics, classification, and significance of deeply eroded Proterozoic orogenic belts in Gondwana supercontinent. The study of complex lithological associations and structural patterns associated with orogens, involving several phases of ductile deformation, recrystallization, and partial melting processes, poses challenges to geoscientists. The rock records preserving such processes in the form of field photographs and their importance in understanding the orogenic evolution are the essential elements in bringing out the present Atlas. This chapter also presents a map of distribution of ancient orogenic belts in Gondwana supercontinent that include India, Sri Lanka, southern Africa, East Antarctica, and Western Australia.

Keywords

Atlas; Deformation; Field photographs; Geodynamics; Gondwana supercontinent; Metamorphism; Proterozoic orogens

1.1. Introduction

Orogens in space and time are the potential sources of information in understanding the mechanism of episodic global material circulation on a whole-mantle-scale. They represent the hallmarks of the interaction among lithospheric plates. The word orogen is derived from Greece (oros for mountain, genesis for origin). The term orogen or orogenic belt has been traditionally described as a mountain belt composed of different types of rocks or rock strata forming a complex of variable size, typically tens to hundreds of kilometres wide and several thousand kilometre long, later fragmented during younger geological time due to various processes (e.g., Miashiro, 1961). In modern terminology, an orogen can be defined as a major linear deformed zone, sandwiched between cratons with prolonged deformational history, repeatedly reactivated and associated with different events of magmatic pulses and metamorphic episodes in space and time (Dewey and Bird, 1970). An orogen or orogenic belt develops when a continental plate crumples and is pushed upwards to form one or multiple mountain ranges. This involves a series of geological processes called orogenesis.

The Proterozoic orogenic belts occur wrapping around Precambrian cratons and expose essentially high-grade rocks metamorphosed under amphibolite to granulite facies conditions. They represent not only important loci of mineral wealth but also manifest past convergent plate tectonics that provide insightful clues to the processes of deep crustal evolution, such as subduction, obduction, accretion, magmatism, and collision. They occur as mountain belts developed through crustal thickening, magmatism, and metamorphism during more than one tectonothermal event (orogenies) through time. The orogens constitute pronounced linear structural forms displaying terranes or blocks of deformed rocks, separated by suture/shear zones or dipping thrust faults. The thrust faults carry relatively thin slices of rock (which are called nappes or thrust sheets and differ from tectonic plateaus) from the core of the shortening orogen out toward the margins and are intimately associated with folds and development of metamorphism. Orogens are significant in revealing the processes of continental growth and deformation including terrane accretion, ophiolite obduction, terrane amalgamation, terrane dispersal, and crustal reactivation.

The orogens can broadly be grouped into collisional and acccretional types (Windley, 1995). The orogens that occur at plate margins with continuing subduction and accretion are known as accretionary orogens (also known as Pacific type) and appear to have been active throughout much of Earth's history and constitute major sites of continental growth (Cawood et al., 2009). Examples include Cordilleran, Pacific, Andean, Miyashiro, and Altaid-type orogens. Accretionary orogenic systems are formed through ongoing plate convergence during the period of supercontinent break-up and continental dispersal. Collisional orogenic systems (Himalayan-type) are generated when the ocean is closed during continental assembly and formation of supercontinents. Collisional orogenic systems may be superimposed on accretionary systems, which can be described as subduction-to-collision orogenesis (e.g., Liou et al., 2004).

Plate tectonics has been considered as an active component of the Earth's processes possibly since the formation of the first continental crust at >4.3  Ga (Ernst, 2005). Several distinct lines of evidence, in concert, established that the process of plate tectonics has been active since at least 3.1  Ga. At least four types of collisions are presently recognized: continent-continent (Alpine/Himalayan), continent-arc (Andean), arc-arc (Alaskan) collisions, and the fourth is a special category (Turkic-type) where there is a progressive accretion of small island arcs and migration of magmatic front that may produce sutures (Sengör and Natal'in). Large strike-slip faults, which juxtapose assemblages formed in distant regions and metamorphosed at different structural levels, can also be erroneously reckoned as sutures. Absence or rarity of blue schist- and eclogite-facies (high-P) metamorphic rocks in Precambrian subduction-accretion complexes may be attributed to elevated thermal gradients and shallow-angle subduction (Brown, 2009). High-T metamorphism and slab melting would be significant during the subduction of hotter, less viscous, more buoyant, thicker and faster movement of Precambrian oceanic crust (Polat and Kerrich, 2004).

While Alpine-Himalayan chain represents modern orogens, Appalachians–Caledonian, Grenville, Trans-Hudson, Capricorn, and Limpopo are some of the well-known examples of ancient orogens. The present Atlas is confined to Proterozoic orogens with special focus on east Gondwana. The Proterozoic period spans nearly 2 billion years, which can be divided into three eras: Palaeoproterozoic (2500–1600  Ma); Mesoproterozoic (1600–1000  Ma); and Neoproterozoic (1000–540  Ma). The Proterozoic is considered to be important because of great crustal stabilization marked by the development of global-scale orogens.

1.2. Orogenic evolution

Tectonic evolution of orogenic systems is a fundamental research problem in understanding the Earth's evolution, which in turn helps in better comprehension of mineral resources, seismicity patterns, and various geological hazards. There are primarily two types of orogenic systems in the Earth's history from the Archaean through to modern Earth: accretionary orogenic systems and collisional systems. Some of the best studied orogenic systems in the world such as Grenville orogen showed that the Greenville province resulted from a Mesoproterozoic continental collision and consists of tectonically stacked slices of Archean, Paleozoic, Mesoproterozoic rocks that are exposed at various crustal levels. Features such as deformation, metamorphism, and magmatism may vary in intensity along and across the length and breadth of the orogens. In general, orogens are characterized by the presence of complex zones of transpressive deformation displaying complex styles of structures and metamorphism.

Recent decades of research reveal that deeply eroded ancient orogens provide insights into the hidden roots of modern orogens. Further advanced analytical techniques and modern concepts in fields like geodynamics, provided fresh insights that led to the application of realistic modern analogies into the evolution of ancient orogenic belts. Broadly, orogens also offer the realms of natural laboratory to address the nature of large Earth's processes such as the behavior of lithosphere, crust-mantle interaction, supercontinent formation, different geodynamic processes, and ultimately the Earth's history.

The orogens, on a whole-Earth scale, represent the surface manifestations of the motion of Earth's lithosphere and contribute to the generation of new continental crust through plate tectonics that is horizontally transported and eventually destroyed at subduction zones prior to orogenic suturing. The subducted material accumulates at 660  km depth, being transformed from a curtain-like sheet to a large blob that drops vertically to the Core–Mantle Boundary (CMB) (Maruyama et al., 1994). The involvement of plate tectonics through a variety of associated processes like subduction zones after the consumption of oceanic crust produces volcanoes and builds island arcs magmatism. The other important associated processes include magmatism, metamorphism, crustal melting, and thickening. However, these are dependent on the strength and rheology of the continental lithosphere and the change in their properties during orogenesis. The process of orogeny may take tens of millions of years to build mountains from plains or the ocean floor, and the topography is related to the principle of isostasy.

In summary, the orogenic processes include continental rifting and ocean opening, oceanic and continental subduction, late to post-orogenic extension, sedimentation, magmatism and metamorphism, exhumation of deep seated rocks, back-arc opening and microcontinent rotation, etc. The interfering orogenic scale tectonics such as thrusting, folding, and shearing processes and deformation histories within orogenic belts can be treated as second order processes.

1.3. Proterozoic high-grade rocks

The Proterozoic orogenic belts constitute essentially high-grade rocks metamorphosed under amphibolite to granulite facies conditions. The Precambrian high-grade rocks occur in the form of thick sequences of interlayered and intercalated bands, layers, lenses, etc., with complex metamorphic histories and structures with different geometries and interrelationships. These rocks are, in general, dominated by quartzo-feldspathic gneisses with varied amounts of biotite, hornblende, both clino- and orthopyroxenes, garnet, opaque minerals, and accessory zircon. In addition, metapelitic rocks with variable amount of biotite, garnet, Al-silicates, cordierite, sapphirine, and spinel make an important lithology in orogenic belts. Enclaves of other rock types (both sedimentary and igneous origins) are also common defining them more generally as migmatitic gneisses. The other dominant rocks include metasedimentary rocks such as quartzite, marble, calc-silicate rocks, metaigneous rocks like metabasite and ultramafic rocks. In some orogenic belts, the occurrence of metamorphosed and deformed layered igneous rocks is also reported. In general, the rocks witness amphibolite-granulite facies metamorphic conditions.

The structures and their interrelationships preserved in high-grade rocks are usually complex, because of prolonged metamorphic recrystallization, mineral reactions, and polyphase deformation through multiple events, which are often complicated and masked by different magmatic and metamorphic episodes. These rocks have further been subjected to several phases of ductile deformational processes involving recrystallization and partial melting, resulting in complex lithological associations and structural patterns. Identification of such complex rock records and their geometries in the field is important and challenging to all geoscientists. This forms the first crucial step for understanding the true geological relationships, protolith characteristics, structural features, deformational history, metamorphism, and tectonic evolution. The difference in lithology and metamorphic grade among the rocks in orogens has been commonly attributed to the difference in the level of exposure. In the light of above, field observations are extremely important before selection and collection of rock samples for further laboratory studies.

1.4. Gondwana orogens

Gondwanaland or Gondwana is the name described for the southern half of the Pangaean supercontinent (~300 Ma) constituting major continental blocks of South America, Africa, Arabia, Madagascar, Sri Lanka, India, Antarctica, and Australia (Fig. 1.1). The name Gondwana is derived from a tribe in India (Gonds) and wana means land of. Gondwanaland is superficially divided into a west Gondwana (Africa and South America) and an east Gondwana (India, Sri Lanka, Madagascar, Antarctica, and Australia). The orogens in the continents of east Gondwana resulted from a complex series of orogenic events during the Proterozoic period (Yoshida, 1995).

Two main periods of orogenesis were identified within east Gondwana (see Fig. 1.1). The first episode resulted from the amalgamation of arc-terranes in the Arabian-Nubian shield region and oblique continent-continent collision between eastern Africa and ill-defined collage of continental blocks including parts of Madagascar, Sri Lanka, Seychelles, India, and East Antarctica (750–620  Ma). This is referred to as the East Africa Orogen (EAO) and the second major episode of orogenesis is considered as Kuunga Orogeny that took place between 570 and 530  Ma (Meert et al., 1995). This episode