Isotopic Constraints on Earth System Processes

Description

Using isotopes as a tool for understanding Earth processes From establishing the absolute age of the Earth to providing a stronger understanding of the nexus between geology and life, the careful measurement and quantitative interpretation of minor variations in the isotopic composition of Earth’s materials has provided profound insight into the origins and workings of our planet. Isotopic Constraints on Earth System Processes presents examples of the application of numerous different isotope systems to address a wide range of topical problems in Earth system science. Volume highlights include: examination of the natural fractionation of non-traditional stable isotopesutilizing isotopes to understand the origin of magmas and evolution of volcanic systemsapplication of isotopes to interrogate and understand Earth’s Carbon and Oxygen cyclesexamination of the geochemical and hydrologic processes that lead to isotopic fractionationapplication of isotopic reactive transport models to decipher hydrologic and biogeochemical processes The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals. Cover Title Page Copyright Page Contents List of Contributors Preface About the Companion Website Dedication Part I High-Temperature/Deep Earth Processes Chapter 1 High-Temperature Kinetic Isotope Fractionation of Silicate Materials 1.1. Introduction 1.2. Diffusion in Multi-Component Condensed Systems: Theory and Definitions 1.2.1. Fick’s Laws and the Diffusion Matrix 1.2.2. Effective Binary Diffusion Coefficients 1.2.3. Self-Diffusion Coefficients 1.2.4. Thermal (Soret) Diffusion Coefficients 1.3. Kinetic Isotope Fractionation During Diffusion Between Natural Melts 1.3.1. Laboratory Experiments Documenting Ca Isotope Fractionation by Diffusion Between Molten Rhyolite and Basalt 1.3.2. Isotope Fractionation between Melts from a Natural Setting 1.4. Isotope Fractionation by Soret Diffusion 1.4.1. The Soret Coefficient 1.4.2. Soret Isotope Fractionation in Silicate Liquids 1.5. Isotope Fractionation by Diffusion in Silicate Minerals 1.5.1. Experiments documenting Lithium Isotopic Fractionation by Diffusion in Pyroxene 1.5.2. Natural Examples of Lithium Zoning and Isotopic Fractionation by Diffusion in Pyroxenes 1.5.3. Lithium Isotopic Fractionation by Diffusion in Olivine 1.5.4. Fe-Mg zoning and Fe and Mg Isotopic Fractionation in Olivine 1.6. Isotope Fractionation by Evaporation from Silicate Melts 1.6.1. The Hertz-Knudsen Evaporation Equation 1.6.2. Rayleigh Fractionation 1.6.3. High-Temperature Vacuum Evaporation Experiments 1.6.4. Evidence of Evaporation in Natural CAIs from Chondritic Meteorites 1.7. Summary 1.8. Thoughts on Further Research References Chapter 2 Ca and K Isotope Fractionation by Diffusion in Molten Silicates: Large Concentration Gradients Are Not Required to Induce Large Diffusive Isotope Effects 2.1. Introduction 2.2. Methods 2.2.1. Experiments 2.2.2. Electron Microprobe Analyses 2.2.3. Ca Isotopic Measurements 2.2.4. K Isotopic Measurements 2.3. Results 2.3.1. Major Element Diffusion Profiles 2.3.2. Ca and K Isotopes 2.4. Discussion 2.5. Modeling 2.5.1. General Multicomponent Diffusion 2.5.2. The Zhang (1993) Modified Effective Binary Diffusion Model 2.5.3. Comparison to Previous Studies 2.6. Conclusions and Possible Future Applications Appendix Linear versus exponential dependence of activity on SiO2 Acknowledgments References Chapter 3 Calcium Isotope Constraints on Recycled Carbonates in Subduction-Related Magmas 3.1. Introduction 3.2. Analytical Methods and Samples 3.2.1. Double-spike Thermal Ionization Mass Spectrometry Calcium Isotope Measurements 3.2.2. Igneous Samples Characterized for Calcium Isotope Composition 3.3. Results 3.4. Discussion 3.4.1. Calcium Isotopic Record of Marine Carbonates 3.4.2. Calcium Isotopic Record of Mantle-Derived Rocks 3.4.3. Calcium Isotopes Exhibit no Evidence for Carbonate Sediment Recycling at Subduction Zones 3.4.4. Mantle Source(s) of Calcium in Carbonatite Magmas 3.4.5. Origin of the Light Calcium Isotope Composition of Laacher See and other Intrusive Carbonatites 3.5. Conclusions Acknowledgments References Chapter 4 Reassessing the Role of Continental Lithospheric Mantle in Cenozoic Magmatism, Southwestern North America 4.1. Introduction 4.2. Geologic Background & General Terminology 4.2.1. Cenozoic Geologic History of SWNA 4.2.2. Definition of Continental Lithospheric Mantle 4.3. Methods/Data 4.4. Results 4.5. Discussion 4.5.1. Do Nd Isotope Data Support a CLM Source for Mafic Volcanic Rocks in SWNA? 4.5.2. Isotopic Composition of CLM from Xenolith Studies 4.5.3. Cenozoic Metasomatism of CLM 4.5.4. Physical Evolution of Deep Lithosphere 4.6. Conclusions Acknowledgments References Chapter 5 Rhyolite Ignimbrite Generation in the Northern Andes: The Chalupas Caldera, Ecuador 5.1. Introduction 5.2. Geological Setting and Age of the Chalupas Caldera 5.3. Geochemical Results 5.3.1. Analytical Techniques 5.3.2. Major Element Geochemistry 5.3.3. Trace Element Geochemistry 5.3.4. Isotope Geochemistry 5.3.5. Metamorphic Basement Rocks of the Eastern Cordillera 5.4. Evolution of the Chalupas Magmatic System 5.4.1. Role of Fractional Crystallization 5.4.2. The Role of Crustal Assimilation 5.4.3. Modeling Results 5.4.4. Model Discussion 5.4.5. Assimilation and Crustal Thickness 5.5. Crustal Structure, Magma Supply, and Transport 5.5.1. Crustal and Magma Density 5.5.2. Temperature Considerations 5.5.3. Subduction Zone Magma Supply and Magmatic Timescales 5.5.4. Timescales of Transport and Assimilation 5.6. Chalupas Eruption Volume and Magma Supply 5.7. Summary and Conclusions Appendix 5A Ar-Ar Geochronology Pre-Caldera Lavas Chalupas Ignimbrite Post-Caldera Lavas Summary of Age Data Appendix 5B Mineral Chemistry and Petrographic Descriptions 5B.1. Pre-Caldera Lavas 5B.2. Post-Caldera Lavas 5B.3.Chalupas Ignimbrite 5B.4. Lithics from the Chalupas Ignimbrite Appendix 5C Models for Crystal Fractionation, Assimilation-Fractional Crystallization, and Magma Fluxes 5C.1. Quantitative Estimation of Crystal Fractionation Effects 5C.2. Assimilation-Fractional Crystallization (AFC) Model Details 5C.3. Relationship between f and Crustal Fraction (fc) in the AFC Model 5C.4. Magma Supply Considerations 5C.5. Magma Supply Requirements 5C.6. Diapir Formation and Transport through the Lower and Mid-Crust ACKNOWLEDGMENTS REFERENCES Chapter 6 Xenolith Constraints on “Self-Assimilation” and the Origin of Low 18O Values in Mauna Kea Basalts 6.1. Introduction 6.2. Samples and Analytical Methods 6.2.1. EPMA Analysis of Mineral Major Element Composition 6.2.2. Clinopyroxene Trace Element Analysis by LA-ICP-MS 6.2.3. Oxygen Isotope Analysis by Laser Fluorination Gas Source Mass Spectrometry 6.2.4. Strontium-Nd-Pb Isotope Analysis by TIMS and MC-ICP-MS 6.3. Results 6.4. Discussion 6.4.1. Constraints on Parental Melts of Mauna Kea Xenoliths 6.4.2. Constraints on The P-T Conditions Of Xenolith Formation and Later Re-Equilibration 6.4.3. Role of Pacific Crust Assimilation and Edifice Self-Assimilation 6.4.4. Oxygen Isotope Compositional Variability in the Hawaiian Plume? 6.4.5. Significance of Self-Assimilation for Interpretation of Geochemical Signatures in Hawaiian Basalts 6.5. Conclusions Acknowledgments References Chapter 7 Monitoring Volcanic Activity Through Combined Measurements of CO2 Efflux and (222Rn) and (220Rn) in Soil Gas: An Application to Mount Etna, Italy 7.1. Introduction 7.2. Background 7.2.1. Mt. Etna Volcanic Activity During 2006 to 2009 7.2.2. Prior Work Utilizing Coupled 220Rn/222Rn and CO2 Efflux Measurements on Mt. Etna 7.3. Sampling Strategy and Analytical Methods 7.3.1. Sampling Strategy 7.3.2. Soil 222Rn and 220Rn Measurements 7.3.3. Soil CO2 Concentration and Efflux Measurements 7.3.4. Carbon Isotope Measurements 7.4. Synopsis of This Study’s Results 7.4.1. Coupled CO2 Efflux and (220Rn/222Rn) 7.4.2. Carbon Isotopes 7.5. The Soil Gas Disequilibrium Index (SGDI) 7.6. Relationship Between Filtered SGDI Data and Volcanic Activity of Mt. Etna 7.6.1. Modelling 7.6.2. Comparison of SGDI to Other Monitoring Proxies 7.7. Summary Appendix Statistical Treatment of SGDI Data Cluster Analysis and Spatial Distributions Analysis of SGDI Time Series Definition of Anomalies in the SGDI Time Series Acknowledgments References Part II Low-Temperature/Shallow Earth Processes Chapter 8 The Carbon Isotope Record and Earth Surface Oxygenation 8.1. Introduction 8.2. The Carbon Isotope Budget 8.3. forg and the Oxygen Budget 8.4. Oxygen Sinks in a Low-Oxygen World 8.4.1. Carbon as a Precambrian Oxygen Sink 8.4.2. Sulfur as a Precambrian Oxygen Sink 8.4.3. Iron as a Precambrian Oxygen Sink 8.4.4. Other Precambrian Oxygen Sinks 8.5. Resolving the pO2 – forg Paradox 8.6. Predictions of the Authigenic Feedback Hypothesis 8.7. Conclusions References Chapter 9 Detrital Garnet Geochronology: A New Window into Ancient Tectonics and Sedimentary Provenance 9.1. Introduction and Motivation 9.2. Theoretical Feasibility of Detrital Garnet Geochronology 9.2.1. Age Precision vs. Single Garnet Grain Diameter 9.2.2. Age Accuracy: Blanks 9.2.3. Age Accuracy: Second Point on the Isochron 9.3. Detailed Methodology 9.3.1. Sample Processing Prior to Chemical Analysis 9.3.2. Partial Dissolution: Leaching out the Inclusions 9.3.3. Full Dissolution of Pure Garnet Residue 9.3.4. Column Chemistry 9.3.5. Thermal Ionization Mass Spectroscopy 9.3.6. Blank Correction 9.3.7. Age Determination 9.4. Case Studies 9.4.1. Preliminary Work: Multi-Grain Detrital Garnet Ages in Beach Sand from Hampton Beach, New Hampshire 9.4.2. Bulk vs. Detrital Garnet Methodology Test: Townshend Dam, Vermont 9.4.3. Single-Grain Detrital Garnet Ages in Stream Alluvium: Townshend Dam, Vermont 9.4.4. Single-Grain Detrital Garnet in Stream Alluvium: Southern Appalachians 9.4.5. Dating Detrital Garnet in Sedimentary Rocks: Scotland 9.5. Conclusion Acknowledgments References Chapter 10 A Review of the Development of Cr, Se, U, Sb, and Te Isotopes as Indicators of Redox Reactions, Contaminant Fate, and Contaminant Transport in Aqueous Systems 10.1. Introduction 10.2. Mass Spectrometry and Sample Preparation Methods 10.2.1. Mass Spectrometry 10.2.2. Sample Preparation 10.3. Current Understanding of Isotopic Fractionation 10.3.1. Equilibrium Fractionation Theory and Calculations 10.3.2. Kinetic Fractionation 10.3.3. Time Scales for Attainment of Equilibrium 10.3.4. Experimental Determinations of Isotopic Fractionation 10.4. Applications of Cr, U, and Se isotope measurements 10.4.1. Chromium Isotopes 10.4.2. Uranium Isotope Applications 10.4.3. Selenium Isotope Applications 10.4.4. Te and Sb Isotope Field Data 10.5. Reactive Transport Models: An Essential Part of the Science 10.5.1. Rayleigh Distillation Models and their Limitations 10.5.2. Application to Heavy Isotopes in Laboratory and Natural Environments 10.5.3. Beyond Rayleigh: Heavy Isotopes in Reactive Transport Frameworks 10.6. Conclusions and Outlook Acknowledgments References Chapter 11 The Effects of Reactive Transport on Sulfur Isotopic Compositions in Natural Environments 11.1. Motivation 11.2. Sulfur Isotope Introduction 11.2.1. Constraining the Sulfur Isotope Fractionation Factor 11.2.2. Variation in the Sulfur Isotope Fractionation Factor 11.2.3. A Case Study 11.3. Reactive Transport Effects on Sulfur Isotope-Signatures 11.3.1. An Example of Marine Sedimentary Profiles 11.3.2. An Example of Aquifers 11.4. Summary References Chapter 12 A Reactive Transport Framework Describing Covariation in the Isotopic Ratios of Multiple Elements in Natural Systems 12.1. Motivation 12.1.1. Open Systems 12.1.2. Multi-Isotope Analysis 12.1.3. Multi-Isotopic Reactive Transport Modeling 12.2. A Synthetic Model Study of Paired Isotope Signatures 12.2.1. Basic Model Setup 12.2.2. Structurally Heterogeneous Flow Fields 12.2.3. Point Sources 12.2.4. Point Sources with Dilution 12.3. Summary References Chapter 13 Stable Ca Isotope Fractionation in Cenozoic Marine Mammals: Beyond Biomineralization and Trophic Positioning 13.1. Introduction 13.2. Background 13.2.1. Stable Ca Isotope Fractionation in Nature 13.2.2. Bowhead Whales: Evolution, Ontogenesis, and Ecology 13.3. Methods 13.3.1. Sample Collection 13.3.2. Structural Material Analytical Techniques 13.3.3 Baleen Material Analytical Techniques 13.3.4. Defining the Window of Trophic Discrimination 13.4. Results 13.4.1. Marine Mammal Bone Material 13.4.2. Bowhead Whale Baleen Material 13.5. Discussion 13.5.1. Fossil Marine Mammal Excursion 13.5.2. Modern Odontocete Excursion 13.5.3. Modern Mysticete Excursion 13.6 Conclusions Appendix 13A Marine Mammal Bone Analysis 13A.1. Structural Material Sample Preparation 13A.2. Sample Purification and Matrix Separation 13A.3. Sample Introduction and Analysis Appendix 13B Baleen Analysis I 13B.1. Baleen Material Sample Preparation 13B.2. Sample Purification and Matrix Separation 13B.3. Sample Introduction and Analysis 13B.4. Initial Measurement of Sample 2012-B5 Appendix 13C Baleen Analysis II Acknowledgments References Index EULA