Anorthosites (Minerals, Rocks and Mountains)

The idea for a book on anorthosites came to me in January of 1986 while returning to Houston after holiday festivities in Dallas. The original idea was a review paper on anorthosites, but by the time I reached Houston, the subject material I contemplated induding was obviously too extensive for a single paper. The Director of the Lunar and Planetary Institute, Kevin Burke, was receptive to the idea of a book, and suggested that I contact Peter Wyllie, who serves as Editor of the Springer-Verlag series Minerals and Rocks. This effort, which I originally expected would take about a year, has taken nearly 6. I have many excuses- indolence, moving to another continent, other commitments, etc.-but the basic truth is that writing a book is much larger an undertaking than can be anticipated. Many people are aware of this, and I was duly forewarned. . But why write a book on anorthosites? This is a very good question, which I have considered from many angles. One rationale can be expressed in terms of a comparison between anorthosite and basalt. A first-order understanding of basalt genesis has been extant for many years. By contrast, there is little agreement about the origin of anorthosite. There are good reasons for studying and writing about basalt: it is the most abundant rock type on the Earth’s surface, and is also plentiful on the surfaces of the other terrestrial planets. 1 Introduction.- 1.1 History and Nomenclature.- 1.2 Anorthosite Classification.- 1.3 The Anorthosite Problem.- 1.4 General Structure of this Volume.- 2 Archean Megacrystic Anorthosites.- 2.1 Introduction.- 2.2 General Features and Distribution.- 2.3 Geologic Environment.- 2.4 Form and Structure.- 2.5 Magmatic Textures and Structures.- 2.6 Megacryst-Bearing Mafic Dikes, Sills, and Flows.- 2.7 Metamorphic Textures and Structures.- 2.8 Mineralogy and Petrography.- 2.8.1 Plagioclase.- 2.8.2 Mafic Minerals.- 2.9 Chemical Composition.- 2.9.1 Major Element Chemistry.- 2.9.2 Trace Element Chemistry.- 2.9.3 Estimates of Bulk Compositions.- 2.10 Ore Deposits and Metallogeny.- 2.10.1 Fe-Ti Oxide Concentrations.- 2.10.2 Chromite Concentrations.- 2.10.3 Sulfide Mineralization.- 2.11 Ages and Isotopic Compositions.- 2.11.1 Direct Age Determinations of Archean Anorthosites.- 2.11.2 Isotopic Initial Ratios and Implications.- 2.12 Descriptions of Anorthosite Occurrences.- 2.12.1 Canada (Superior Province).- 2.12.1.1 The Bad Vermilion Lake Complex, Ontario.- 2.12.1.2 The Shawmere Complex, Ontario.- 2.12.1.3 The Bell River and Dore Lake Complexes, Quebec.- 2.12.1.4 Big Trout Lake, Ontario.- 2.12.1.5 Bird River Area, Manitoba.- 2.12.1.6 Upper Nelson River Area, Manitoba.- 2.12.2 Canada (Churchill Province).- 2.12.3 Canada (Labrador).- 2.12.4 Greenland.- 2.12.4.1 The Fiskensset Complex.- 2.12.4.2 Other Archean Anorthosites in Greenland.- 2.12.5 Scotland.- 2.12.6 U.S.S.R.- 2.12.6.1 Kola Peninsula.- 2.12.6.2 Anabar Shield.- 2.12.7 India.- 2.12.7.1 The Chimalpahad Complex.- 2.12.7.2 The Sittampundi and Bhavani Complexes.- 2.12.8 Africa.- 2.12.8.1 The Messina Complex, Limpopo Mobile Belt.- 2.12.8.2 Anorthosites of the Kaapvaal Craton, South Africa.- 2.12.8.3 Other Archean Anorthosites in Africa.- 2.12.9 Madagascar.- 2.12.10 Australia.- 2.12.11 South America.- 2.12.12 Antarctica.- 2.13 Origin of Archean Megacrystic Anorthosites.- 2.13.1 Early Ideas.- 2.13.2 A Multiplicity of Analogs.- 2.13.3 Parental and Primary Magmas.- 2.13.4 Emplacement as Mushes?.- 2.13.5 Low-Pressure Crystallization of Plagioclase Megacrysts?.- 2.13.6 Tectonic Setting.- 2.14 Summary.- 3 Proterozoic Massif-Type Anorthosites.- 3.1 Introduction.- 3.1.1 Semantics.- 3.1.2 General Characteristics.- 3.1.3 Transitional Occurrences.- 3.2 Distribution.- 3.2.1 Major Concentrations.- 3.2.2 Anorthosite Belts.- 3.3 Geologic Setting.- 3.3.1 Crustal Basement Ages.- 3.3.2 Metamorphic Grade of Country Rocks.- 3.3.3 Crustal Basement Lithologies.- 3.3.4 Depth of Emplacement.- 3.4 Form and Structure.- 3.4.1 Inferences from Geology.- 3.4.2 Inferences from Geophysics.- 3.5 Lithologies.- 3.5.1 The Anorthosite “Suite”.- 3.5.2 Relative Volumes of Rock Types.- 3.5.3 Varietal Terminology.- 3.5.4 Andesine- vs. Labradorite-Type Anorthosites.- 3.6 Magmatic Features.- 3.6.1 Igneous Structures.- 3.6.1.1 Massive vs. Layered Bodies.- 3.6.1.2 Types of Igneous Layering.- 3.6.1.3 Block Structure.- 3.6.1.4 Anorthositic Dikes.- 3.6.1.5 Pillow Structures.- 3.6.2 Igneous Textures.- 3.7 Metamorphic Structures and Textures.- 3.8 Mineralogy.- 3.8.1 Plagioclase.- 3.8.1.1 Morphology and Internal Features.- 3.8.1.2 Composition.- 3.8.1.3 Metamorphic Effects.- 3.8.2 Mafic Silicates.- 3.8.2.1 Pyroxenes.- 3.8.2.2 Olivines.- 3.8.2.3 Hydrous (?) Mafic Silicates.- 3.8.3 Fe-Ti Oxides.- 3.8.4 Other Accessory Minerals.- 3.8.5 Al-Rich Pyroxene Megacrysts.- 3.8.6 Metamorphic Mineralogy and Thermobarometry.- 3.9 Chemical Composition.- 3.9.1 Major Element Chemistry.- 3.9.1.1 Anorthosite Suite.- 3.9.1.2 Gabbroic Rocks.- 3.9.1.3 Ferrodiorites and Related Rocks.- 3.9.2 Trace Element Chemistry.- 3.9.2.1 Sr and Other Trace Elements.- 3.9.2.2 Rare Earth Elements.- 3.9.3 Estimates of Bulk Composition.- 3.10 Ore Deposits and Metallogeny.- 3.10.1 Fe-Ti Oxide Ores.- 3.10.2 Building and Dimension Stone.- 3.10.3 Anorthosite as an Al Ore?.- 3.11 Associated Silicic Rocks.- 3.11.1 General Characteristics.- 3.11.2 Relationship to the Anorthosite Suite.- 3.11.3 Petrogenesis.- 3.12 Layered Intrusions Related (?) to Massif-Type Anorthosite.- 3.12.1 The Kiglapait Layered Intrusion, Labrador.- 3.12.2 The Michikamau Intrusion, Labrador.- 3.12.3 The Duluth Complex, Minnesota.- 3.12.4 The Glen Mountains Layered Complex, Oklahoma.- 3.12.5 The Bjerkreim-Sokndal Lopolith, Norway.- 3.13 Ages and Isotopic Compositions.- 3.13.1 Direct Determination of Anorthosite Ages.- 3.13.1.1 Rb-Sr.- 3.13.1.2 Sm-Nd.- 3.13.1.3 Pb-Pb.- 3.13.1.4 U-Pb.- 3.13.2 Initial Isotopic Ratios and Implications.- 3.13.2.1 Constraints on Mantle Source(s).- 3.13.2.2 Isotopic Provinciality.- 3.13.2.3 Crustal Contamination.- 3.13.2.4 Enriched Mantle?.- 3.13.2.5 Constraints on Relations between Anorthosite and Granitoid Suites.- 3.13.3 Stable Isotopes.- 3.14 Descriptions of Selected Anorthosite – Bearing Terranes.- 3.14.1 The Grenville Province.- 3.14.2 The Nain/Churchill Provinces.- 3.14.3 The Rogaland Complex, South Norway.- 3.14.4 The Eastern Ghats Belt, India.- 3.14.5 Anorthosites of Africa and Madagascar.- 3.14.5.1 The Kunene Complex, Angola/Namibia.- 3.14.5.2 The Ar Massif, Niger.- 3.14.5.3 Anorthosites of Madagascar.- 3.14.6 Anorthosites of the U.S.S.R.- 3.14.6.1 Kola Peninsula.- 3.14.6.2 East European Platform.- 3.14.6.3 Aldan Shield.- 3.14.7 Anorthosites of Mongolia.- 3.15 Petrogenesis of Massif-Type Anorthosites.- 3.15.1 Early Ideas.- 3.15.1.1 Neptunism.- 3.15.1.2 “Anorthositization”.- 3.15.1.3 Anatectic Residues.- 3.15.2 Parental Magmas: the Holy Grail.- 3.15.2.1 Granitoid Suite: Consanguineous or Not?.- 3.15.2.2 Anorthositic Melts?.- 3.15.2.3 Basaltic Melts?.- 3.15.3 Crystallization and Emplacement.- 3.15.3.1 Crystallization Histories.- 3.15.3.2 Polybaric Crystallization?.- 3.15.3.3 Did Plagioclase Sink or Float?.- 3.15.3.4 Emplacement as Mushes?.- 3.15.4 A Plausible Petrogenetic Model.- 3.16 Tectonic Setting: the Frontier of Anorthosite Research.- 3.16.1 An Anorthosite “Event”? No!.- 3.16.2 Convergent Plate Margin-Settings.- 3.16.2.1 Continental Collision.- 3.16.2.2 Subduction.- 3.16.3 Divergent Plate Margin-Settings.- 3.16.3.1 Rifts.- 3.16.4 Intra-Plate Settings.- 3.16.4.1 Plumes.- 3.16.4.2 Thermal Insulation by a Supercontinent.- 3.17 Summary.- 4 Anorthosites in Layered Mafic Intrusions.- 4.1 Introduction.- 4.2 Stratigraphic Position of Anorthosites.- 4.3 Structural Varieties of Anorthosite.- 4.3.1 Layering.- 4.3.1.1 Thick Anorthosite Layers.- 4.3.1.2 Modally Graded and Rhythmic Layering.- 4.3.1.3 Microrhythmic (“Inch-Scale”) Layering.- 4.3.2 Syn- and Post-Layering Structures.- 4.3.2.1 Trough Structures.- 4.3.2.2 Potholes.- 4.3.2.3 Cognate Xenoliths.- 4.3.2.4 Irregular Bodies.- 4.3.2.5 Anorthosite-Chromitite Relations.- 4.4 Textural Varieties of Anorthosite.- 4.5 Mineralogy.- 4.5.1 Plagioclase Composition.- 4.5.2 Cryptic Variations.- 4.5.3 Plagioclase-Mafic Silicate Relationships.- 4.6 Chemical Composition.- 4.6.1 Major Element Chemistry.- 4.6.2 Trace Element Chemistry.- 4.7 Isotopic Systematics.- 4.8 Petrogenesis.- 4.8.1 Early Ideas.- 4.8.2 Single Parental Magma Theories.- 4.8.3 Multiple Parental Magmas.- 4.8.4 Emplacement as Mushes.- 4.9 Ore Deposits and Metallogeny.- 4.9.1 Chromite.- 4.9.2 Platinum Group Elements.- 4.9.3 Fe-Ti Oxides.- 4.10 Descriptions of Some Anorthosite-Bearing Layered Mafic Intrusions.- 4.10.1 Bushveld Complex, South Africa.- 4.10.2 Stillwater Complex, Montana.- 4.10.3 Dufek Complex, Antarctica.- 4.10.4 Sept Iles Complex, Quebec.- 4.10.5 Giles Complex, Australia.- 4.11 Summary.- 5 Anorthosites of Oceanic Settings.- 5.1 Introduction.- 5.2 Anorthosites of the Ocean Basins.- 5.2.1 Sampling.- 5.2.2 Lithologies.- 5.2.3 Mineralogy.- 5.2.4 Textures.- 5.2.5 Mineral Chemistry.- 5.2.6 Geochemistry.- 5.2.7 Petrogenesis.- 5.2.8 Comparisons with Other Anorthosite Types.- 5.2.9 Summary.- 5.3 Anorthosites in Ophiolite Complexes.- 5.3.1 Introduction.- 5.3.2 Lithologies and Mineralogy.- 5.3.3 Structural Features.- 5.3.4 Petrography.- 5.3.5 Mineral Chemistry.- 5.3.6 Geochemistry.- 5.3.7 Petrogenesis.- 5.3.8 Comparison with Oceanic and Other Anorthosite Types.- 5.3.9 Summary.- 6 Anorthosite Inclusions in Other Igneous Rocks.- 6.1 Introduction.- 6.2 Cognate Inclusions.- 6.2.1 Gardar Dikes, South Greenland.- 6.2.2 Inclusions on Oceanic Islands.- 6.2.2.1 Iceland.- 6.2.2.2 Hawaii.- 6.2.3 Inclusions in Island Arcs.- 6.2.4 Inclusions in Continental Arcs.- 6.3 Xenolithic Inclusions.- 6.3.1 Beaver Bay Complex, Minnesota.- 6.3.2 Anorthosite Inclusions in Kimberlite.- 6.3.3 Grospydites.- 6.3.4 Anorthosite Inclusions in Granitoids.- 7 Extraterrestrial Anorthosites.- 7.1 Lunar Anorthosites.- 7.1.1 Introduction.- 7.1.2 Lithologies.- 7.1.2.1 Pristine vs. Nonpristine Samples.- 7.1.2.2 Lithological Classification of Lunar Highlands Samples.- 7.1.3 Textures.- 7.1.3.1 Igneous Textures?.- 7.1.3.2 Monomict Breccias.- 7.1.3.3 Dimict Breccias.- 7.1.3.4 Polymict Breccias.- 7.1.3.5 Granulitic Breccias.- 7.1.3.6 Effects of Shock Metamorphism.- 7.1.4 Mineralogy.- 7.1.5 Chemical Composition.- 7.1.5.1 Major Elements.- 7.1.5.2 Trace Elements.- 7.1.6 Ages and Isotopic Compositions.- 7.1.7 Amount and Distribution of Anorthositic Rocks in the Lunar Highlands Crust.- 7.1.7.1 Surface Variations.- 7.1.7.2 Variations with Depth.- 7.1.8 Origin of Lunar Anorthosites.- 7.1.8.1 Petrogenesis.- 7.1.8.2 Parental Magma(s).- 7.1.8.3 Crystallization from a Magma Ocean.- 7.1.8.4 Serial Magmatism ?.- 7.1.9 Comparison with Terrestrial Anorthosites.- 7.2 Anorthositic Meteorites from the Moon.- 7.2.1 Introduction.- 7.2.2 Evidence for a Lunar Origin of Anorthositic Meteorites.- 7.2.2.1 Lithology and Petrography.- 7.2.2.2 Mineralogy.- 7.2.2.3 Geochemistry.- 7.2.2.4 Ages and Isotopic Compositions.- 7.2.3 Differences Between Lunar Meteorites and Apollo Samples.- 7.2.4 Transfer of Lunar Meteorites to Earth.- 7.3 Anorthosites on the Other Terrestrial Planets?.- 7.3.1 Mercury.- 7.3.2 Venus.- 7.3.3 Mars.- 7.4 Summary.- 8 Synthesis and Summary.- 8.1 Classification and Characteristics.- 8.2 Petrogenesis.- 8.3 Timing of Anorthosite Formation.- 8.3.1 Isotope Systematics.- 8.3.2 Temporality.- 8.3.3 An Content as a Geochronometer?.- 8.4 Research Frontiers.- 8.4.1 Magma Composition.- 8.4.2 Magma Crystallization.- 8.4.3 Magma Generation.- 8.4.4 Magma Emplacement.- References.- Locality Index.