Table of Contents Part I: The Geochemical Toolbox Chapter 1: Introduction...1 Geochemistry...1 This Book...2 The Philosophy of Science...4 Building Scientific Understanding...4 The Scientist as Skeptic...5 Elements, Atoms, and Chemical Bonds...6 The Periodic Table...6 Electrons and Orbits...7 Some Chemical Properties of the Elements...13 Chemical Bonding...16 A Brief Look at the Earth...18 Structure of the Earth...18 Plate Tectonics and the Hydrologic Cycle...19 Earth Materials...21 References and Suggestions for Further Reading...23 Chapter 2: Energy, Entropy and Fundamental Thermodynamic Concepts...24 The Thermodynamic Perspective...24 Thermodynamic Systems and Equilibrium...24 Fundamental Thermodynamic Variables...26 Equations of State...28 Ideal Gas Law...28 Equations of State for Real Gases...29 Critical phenomena...31 Equation of State for Other Substances...32 Temperature, Absolute Zero, and The Zeroth Law Of Thermodynamics...33 Energy and The First Law of Thermodynamics...34 Energy...34 Work...34 Path independence, Exact differentials, State functions, and the First Law...35 The Second Law and Entropy...37 Statement...37 Statistical Mechanics: A Microscopic Perspective of Entropy...38 Integrating Factors and Exact Differentials...44 Enthalpy...45 Heat Capacity...46 Constant Volume Heat Capacity...47 Constant Pressure Heat Capacity...47 Energy Associated with Volume Occupied and the Relationshp between C v and C p...47 Heat Capacity of Solids: A Problem in Quantum Physics...50 Relationship of Entropy to Other State Variables...57 Additive Nature of Silicate Heat Capacities...57 The Third Law and Absolute Entropy...58 Statement of the Third Law...58 Absolute Entropy...58 Calculating Enthalpy and Entropy Changes...59 Adiabatic Changes...59 Isobaric and Isothermal Changes in Enthalpy...59 Enthalpies of Formation, Vaporization and Fusion...60 Entropies of Reaction...61 i November 25, 1997
Free Energy...62 Helmholtz Free Energy...63 Gibbs Free Energy...64 Criteria for Equilibrium and Spontaneity...64 Temperature and Pressure Dependence of the Gibbs Free Energy...65 The Maxwell Relations...67 References and Suggestions for Further Reading...67 Problems...68 Chapter 3: Solutions and Thermodynamics of Multicomponent Systems...70 Introduction...70 Phase Equilibria...70 Some Definitions...70 The Gibbs Phase Rule...73 The Clapeyron Equation...75 Solutions...77 Raoult's Law...77 Henry's Law...77 The Chemical Potential...78 Partial Molar Quantities...78 Definition of Chemical Potential and Relationship to Gibbs Free Energy...79 Properties of the Chemical Potential...80 The Gibbs-Duhem Relation...80 Derivation of the Phase Rule...81 Ideal Solutions...82 Real solutions...84 Chemical Potential in Real Solutions...84 Fugacities...85 Activities and Activity Coefficients...86 Excess Functions...88 Electrolyte Solutions...90 The Nature of Water and Water-Electrolyte Interaction...90 Some Definitions and Conventions...92 Activities in Electrolytes...94 Solid Solutions and Their Activities...100 Ideal Solutions in Crystalline Solids...100 Equilibrium Constants...101 Derivation and Definition...101 K D Values, Apparent Equilibrium Constants and the Solubility Product...104 HenryÕs Law and Gas Solubilities...105 Temperature Dependence of Equilibrium Constant...106 Pressure Dependence of Equilibrium Constant...107 Practical Approach to Electrolyte Equilibrium...107 Chosing Components and Species...107 Mass Balance...108 Electrical Neutrality...108 Equilibrium Constant Expressions...109 Oxidation and Reduction...110 Redox in Aqueous Solutions...111 Redox in Magmatic Systems...119 References and Suggestions for Further Reading...120 Problems...120 Chapter 4: Applications of Thermodynamics to the Earth...124 Introduction...124 i i November 25, 1997
Activities in Non-Ideal Solid Solutions...124 Mathematical Models of Real Solutions...124 Exsolution Phenomena...127 Thermodynamics and Phase Diagrams...129 The Thermodynamics of Melting...131 Thermodynamics of Phase Diagrams for Binary Systems...132 Geothermometry and Geobarometry...138 Theoretical considerations...138 Practical Thermobarometers...139 Thermodynamic Models of Magmas...148 Structure of Silicate Melts...149 Magma Solution Models...150 Reprise: Thermodynamics of Electrolyte Solutions...155 Mean Ionic Quantities...155 Activities in High Ionic Strength Solutions...158 References and Suggestions For Further Reading...164 Problems...166 Chapter 5: Kinetics: The Pace of Things...169 Introduction...169 Reaction Kinetics...170 Elementary and Overall Reactions...170 Reaction Mechanisms...170 Reaction Rates...171 Rates of Complex Reactions...176 Steady-State and Equilibrium...179 Relationships between Kinetics and Thermodynamics...181 Principle of Detailed Balancing...181 Enthalpy and Activation Energy...183 Aspects of Transition State Theory...184 Diffusion...188 Diffusion Flux and Fick's Law...190 Diffusion in Multicomponent Systems and The Diffusion Coefficient...192 Diffusion in Solds and the Temperature Dependence of the Diffusion Coefficient...196 Diffusion in Liquids...198 Surfaces, Interfaces, and Inferface Processes...199 The Surface Free Energy...200 The Kelvin Effect...201 Nucleation and Crystal Growth...201 Adsorption...206 Catalysis...209 Kinetics of Dissolution and Leaching...211 Diagenesis...217 Compostional Gradients in Accumulating Sediment...217 References and Suggestions for Further Reading...221 Problems...223 Chapter 6: Aquatic Chemistry...227 Introduction...227 Acid-Base Reactions...227 Proton Accounting, Charge Balance, and Conservation Equations...228 The Carbonate System...230 Conservative and Non-Conservative Ions...233 Total Alkalinity and Carbonate Alkalinity...234 Buffer Intensity...237 i i i November 25, 1997
Complexation...238 Stability Constants...239 Water-Related Complexes...240 Other Complexes...242 Complexation in Fresh Waters...244 Dissolution and Precipitation Reactions...244 Dissolution of Carbonates by Ground and Surface Waters...244 Solubility of Mg...248 Solubility of SiO 2...249 Solubility of Al(OH) 3 and Other Hydroxides...250 Solubility of Silicates and Related Minerals...253 Clays and Their Properties...255 Clay Mineralogy...256 Ion-Exchange Properties of Clays...258 Mineral Surfaces and Their Interaction With Solutions...259 Adsorption...260 Development of Surface Charge and the Electric Double Layer...264 References and Suggestions for Further Reading...270 Problems...271 Chapter 7: Trace Elements in Igneous Processes...273 Introduction...273 What is a Trace Element?...274 Goldschmidt's Classification of the Elements...275 The Geochemical Periodic Table...277 The Volatile Elements...277 The Semi-Volatiles...278 The Alkali and Alkaline Earth Elements...279 The Rare Earth Elements and Y...280 The HFS Elements...283 The First Series Transition Metals...283 The Noble Metals...284 Other Elements...285 Distribution of Trace Elements Between Co-existing Phases...286 The Partition Coefficient...286 Factors Governing the Value of Parition Coefficients...288 Temperature and Pressure Dependence of the Partition Coefficient...288 Ionic Size and Charge...289 Compositional Dependency...292 Mineral-Liquid Partition Coefficients for Mafic and Ultramafic Systems...297 Crystal-Field Effects...298 Crystal Field Influences on Transition Metal Partitioning...303 Trace Element Distribution During Partial Melting...304 Equilibrium or Batch Melting...305 Fractional Melting...305 Zone Refining...306 Multiphase Solids...306 Continuous Melting...307 Constraints on Melting Models...308 Trace Element Distribution during Crystallization...314 Equilibrium Crystallization...314 Fractional Crystallization...314 In Situ Crystallization...315 Crystallization in Open System Magma Chambers...316 i v November 25, 1997
Summary of Trace Element Variations during Melting and Crystallization...318 References and Suggestions for Further Reading...320 Problems...323 Chapter 8: Radiogenic Isotope Geochemistry...325 Introduction...325 Physics of the Nucleus and the Structure of Nuclei...326 Nuclear Structure and Energetics...326 The Decay of Excited and Unstable Nuclei...330 Basics of Radiogenic Isotope Geochemistry...333 Geochronology...335 Decay Systems and Their Applications...336 Rb-Sr...336 Sm-Nd...338 Lu-Hf...343 Re-Os...344 La-Ce...348 U-Th-Pb...348 U and Th Decay Series Isotopes...352 Isotopes of He and Other Rare Gases...358 Cosmogenic and Fossil Isotopes...362 14 C...362 36 Cl in hydrology...363 10 Be in Subduction Zone Studies...364 Cosmic-Ray Exposure Ages of Meteorites...364 Fossil Nuclides...364 References and Suggestions for Further Reading...364 Problems...366 Chapter 9: Stable Isotope Geochemistry...370 Introduction...370 Scope of Stable Isotope Geochemistry...370 Notation...371 Theoretical Considerations...372 Equilibrium Isotope Fractionations...372 Kinetic Isotope Fractionations...378 Isotope Geothermometry...380 Isotope Fractionation in the Hydrologic System...383 Isotope Fractionation in Biological Systems...385 Carbon Isotope Fractionation During Photosynthesis...385 Nitrogen Isotope Fractionation in Biological Processes...387 Oxygen and Hydrogen Isotope Fractionation by Plants...388 Biological Fractionation of Sulfur Isotopes...389 Isotopes and Diet: You Are What You Eat...389 Paleoclimatology...393 The Marine Quaternary δ 18 O Record and Milankovitch Cycles...393 The Record in Glacial Ice...397 Soils and Paleosols...397 Hydrothermal Systems and Ore Deposits...399 Water-Rock Ratios...400 Sulfur Isotopes and Ore Deposits...402 Stable Isotopes in the Mantle and Magmatic Systems...404 Stable Isotopic Composition of the Mantle...404 v November 25, 1997
Stable Isotopes in Crystallizing Magmas...409 Combined Fractional Crystallization and Assimilation...411 Isotopes of Boron and Lithium...412 References and Suggestions for Further Reading...416 Problems...419 Part II: Understanding the Earth Chapter 10: The Big Picture: Cosmochemistry...421 Introduction...421 In the Beginning...Nucleosynthesis...421 Astronomical Background...421 The Polygenetic Hypothesis of Burbidge, Burbidge, Fowler and Hoyle...423 Cosmological Nucleosynthesis...425 Nucleosynthesis in Stellar Interiors...425 Explosive Nucleosynthesis...428 Nucleosynthesis in Interstellar Space...431 Summary...431 Meteorites: Essential Clues to the Beginning...432 Chondrites: The Most Primitive Objects...434 Differentiated Meteorites...441 Meteorite Mineralogy...443 Relationships among Meteorites and Meteorite Parent-Bodies...440 Time and the Isotopic composition of the Solar System...444 Meteorite Ages...444 Cosmic Ray Exposure Ages and the Origin of Meteorites...447 Isotopic Anomalies in Meteorites...449 Formation of the Solar System...453 Astronomical Observations and Theoretical Models of Star Formation...454 Formation of Chondritic Meteorites and Processes in the Solar Nebula...458 Formation of the Planets...464 The Moon: Its Chemistry and History...468 The Giant Impact Hypothesis...468 Geology and History of the Moon...469 References and Suggestions for Further Reading...471 Problems...472 Chapter 11: Geochemistry of the Solid Earth I: The Mantle and Core...474 Introduction...474 Composition of the EarthÕs Mantle...474 Cosmochemical Constraints on the EarthÕs Composition...474 Upper Mantle Composition...475 Phase Transitions in the Mantle...480 The Transition Zone...481 Composition of the Lower Mantle...482 The Primitive Mantle...484 Magma Ocean and Mantle Differentiation...486 The Core and Core Formation...487 Mantle Geochemical Reservoirs...490 Evidence from Oceanic Basalts...490 Evolution of the Depleted Upper Mantle...493 Geochemical Evolution of Mantle Plume Reservoirs...500 The Subcontinental Lithosphere...505 References and Suggestions for Further Reading...508 vi November 25, 1997
Problems...510 Chapter 12: Geochemistry of the Solid Earth II: The Crust...512 Introduction...512 The Oceanic Crust...512 Processes in Subduction Zones and Island Arc Geochemistry...517 Major Element Composition...517 Trace Element Composition...519 Isotopic Composition and Sediment Subduction...521 Magma Genesis in Subduction Zones...523 CrustÑMantle Interaction: Assimilation...526 Geochemistry of Two-Component Mixtures...526 AssimilationÐFractional Crystallization...529 Composition of the Continental Crust...530 The Upper Crust...531 The Middle and Lower Crust...534 The Total Continental Crust...538 Growth of the Continental Crust...540 The Pace of Crustal Growth...541 Mechanisms of Crustal Growth...544 Crustal Growth in the Archean...546 References and Suggestions for Further Reading...550 Problems...553 Chapter 13: Reactions at the EarthÕs Surface: Weathering, Soils, and Stream Chemistry...555 Introduction...555 Redox in Natural Waters...555 Biogeochemical Reodox Reactions...557 Redox Buffers and Transition Metal Chemistry...559 Weathering, Soils, and Biogeochemical Cycling...563 Soil Profiles...564 Chemical Cycling in Soils...567 Biogeochemical Cycling...568 Weathering Rates and Reactions...570 The Watershed Approach...568 Thermodynamic and Kinetic Assessment of Stream Compositions...575 Factors Controlling Weathering Rates...577 The Composition of Rivers...580 Continental Saline Waters...584 References and Suggestions for Further Reading...587 Problems...588 Chapter 14: Organic Geochemistry...589 Introduction...589 A Brief Biological Background...589 Organic Compounds and Their Nomenclature...590 Hydrocarbons...591 Functional Groups...593 Biologically Important Organic Compounds...596 The Chemistry of Life: Important Biochemical Processes...602 Photosynthesis...602 Respiration...604 Organic Matter in Soils and Natural Waters...606 Dissolved Organic Substances...606 vii November 25, 1997
Organic Matter in Soils...613 Chemical Properties of Organic Molecules...615 Acid-Base Properties...615 Complexation...616 Adsorption Phenomena...622 Sedimentary Organic Matter and Coal and Oil Formation...626 Formation and Diagenesis of Organic-Rich Sediments...627 Kerogen and Bitumen...631 Thermal Evolution of Organic Matter and Petroleum Generation...633 Compositional Evolution of Coal...637 Isotopic Composition of Hydrocarbons...638 References and Suggestions for Further Reading...640 Problems...642 Chapter 15: The Oceans as a Chemical System...645 Introduction...645 Some Background Oceanographic Concepts...645 Salinity, Chlorinity, Density, and Temperature...645 Circulation of the Ocean and the Structure of Ocean Water...646 Composition of Seawater...650 Conservative Elements...654 Dissolved Gases...654 Nutrient Elements...663 Particle-Reactive Elements...666 Sources and Sinks of Dissolved Matter in Seawater...670 Residence Time...671 The Riverine Source...672 Ridge Hydrothermal Systems...677 The Atmospheric Source...688 Sedimentary Sinks and Sources...689 References and Suggestions for Further Reading...696 Problems...700 vi i i November 25, 1997