STABLE ISOTOPE GEOCHEMISTRY

Transcription

1 IREVILEWS 3m MKNII&AIKDOT Editors: STABLE ISOTOPE GEOCHEMISTRY JOHN W. VALLEY DAVID R. COLE Department of Geology & Geophysics University of Wisconsin Madison, Wisconsin Chemical and Analytical Sciences Division Oak Ridge National Laboratory Oak Ridge, Tennessee COVER: Metamorphosed magnetite in a granulite fades marble. Oxygen isotope ratios, measured by ion microprobe from 8 nm spots within each pit, show homogeneity across the core of each crystal. However, depth profiles into crystal faces reveal low 8 18 O rims and gradients up to 9%o per 10 im. These results indicate slow cooling after the Grenville orogeny, explain the failure of conventional oxygen isotope thermometry for this sample, and document post-tectonic fluid infiltration. Correct interpretation of this sample would not be possible without spatially resolved microanalysis. See Valley & Graham (1991) Contributions to Mineralogy and Petrology 109: Series Editor for MSA: Paul H. Ribbe Virginia Polytechnic Institute and State University Blacksburg, Virginia MIINIBIRAL (BIICAL S C]IIETnr mi AMEIRIKCA SUB Gfittingen A 22387

2 STABLE ISOTOPE GEOCHEMISTRY Table of Contents 1 Equilibrium Oxygen, Hydrogen and Carbon Isotope Fractionation Factors Applicable to Geologic Systems Thomas Chacko, David R. Cole, Juske Horita INTRODUCTION 1 THEORETICAL BACKGROUND 2 Comparison of cation and isotope exchange reactions 2 Quantum mechanical reasons for isotopic fractionation 3 CALCULATING FRACTIONATION FACTORS 6 Theory 6 An example calculation 8 Calculation of fractionation factors for gases, liquids and fluids 11 Calculation of fractionation factors for minerals 12 VARIABLES INFLUENCING THE MAGNITUDE OF FRACTIONATION FACTORS 15 Temperature 15 Pressure 18 Mineral composition 21 Solution composition 24 METHODS OF CALIBRATING FRACTIONATION FACTORS 30 Semi-empirical bond-strength calibration 30 Natural sample calibration 33 Experimental calibration 35 SUMMARY OF FRACTIONATION FACTORS 40 Oxygen isotope fractionation factors 40 Carbon isotope fractionation factors 46 Hydrogen isotope fractionation factors 48 CONCLUSIONS 49 ACKNOWLEDGMENTS 50 REFERENCES 50 APPENDICES 62 2 Rates and Mechanisms of Isotopic Exchange David R. Cole, Sumit Chakraborty INTRODUCTION 83 Background 83 Objectives 84 GENERAL KINETIC CONCEPTS OF ISOTOPIC EXCHANGE 87 Concentration-dependent isotopic rate equation 87 Activity-dependent isotopic rate equation 89 Temperature-dependence of rate constants: activation energy and entropy 92 Compensation law and the isokinetic temperature 94

3 ISOTOPIC EXCHANGE IN GASEOUS AND AQUEOUS SYSTEMS 95 General background 95 Activity-dependent considerations 97 Rates of isotopic exchange between gases 98 Rates of isotopic exchange in aqueous solutions 105 REACTION-CONTROLLED MINERAL-FLUID ISOTOPE EXCHANGE 110 Chemical reaction versus diffusion 110 Rate models Ill Surface area, grain size and fluid-to-solid ratio 116 Influence of solution composition 119 Pressure effect 120 Activation parameters and empirical correlation with mineral chemistry 122 DIFFUSION-CONTROLLED MINERAL-FLUID ISOTOPE EXCHANGE 126 Fick'slaws 127 Diffusion coefficients 129 Determination of D 130 Factors influencing diffusion 143 Empirical methods 152 DIFFUSION-CONTROLLED MELT(GLASS)-VOLATILE ISOTOPE EXCHANGE 154 The mode of transport-diffusion versus percolation 155 Glasses versus melts: the glass transition 156 The diffusion equation in glasses/melts 157 Diffusion caused by gradients other than chemical: electrical, stress and thermal 160 Water diffusion in SiO 2 glass: a prototype for a wide range of behavior 160 Diffusion of water and other hydrogen-bearing species in natural molten systems 162 Diffusion of C and S related species '. 164 Diffusion of oxygen: new results 165 Pressure-dependence of diffusion rates 169 SUMMARY AND RECOMMENDATIONS 171 ACKNOWLEDGMENTS ; 172 REFERENCES 172 APPENDIX Tables Fractionation of Carbon and Hydrogen Isotopes in Biosynthetic Processes John M. Hayes ISOTOPE FRACTIONATION 225 Isotopes in reaction networks 226 Further general factors affecting isotopic compositions 230 Isotopic compositions of compound classes relative to biomass 231 Isotopic compositions of carbohydrates 234 Isotopic compositions of amino acids 246 Isotopic compositions of nucleic acids 256 Isotopic compositions of tetrapyrroles 257 Isotopic compositions of lipids 258 EPILOGUE 272 ACKNOWLEDGMENTS 273 REFERENCES 273

4 4 Stable Isotope Variations in Extraterrestrial Materials Kevin D. McKeegan, Laurie A. Leshin INTRODUCTION 279 Isotope cosmochemistry of the light stable isotopes 280 Analysis methods 286 STABLE ISOTOPE RECORDS IN PRIMITIVE MATERIALS 287 Hydrogen 288 Oxygen 291 STABLE ISOTOPE RECORDS IN EVOLVED MATERIALS 305 Moon 305 Mars 306 UNRESOLVED ISSUES AND FUTURE DIRECTIONS 310 ACKNOWLEDGMENTS 311 REFERENCES...: Oxygen Isotope Variations of Basaltic Lavas and Upper Mantle Rocks John M. Eiler INTRODUCTION 319 GUIDING PRINCIPLES 319 EARLY STUDIES OF OXYGEN ISOTOPE VARIATIONS IN MAFIC IGNEOUS ROCKS..320 ISOTOPIC FRACTIONATIONS RELEVANT TO STUDY OF MANTLE ROCKS AND BASALTIC LAVAS 321 Experimental, theoretical and empirical constraints on fractionation factors 321 Oxygen-isotope systematics of crystallization, partial melting and degassing 326 Crystallization 327 Partial melting 329 Devolatilization 331 ISOTOPIC SIGNATURES OF CRUSTAL CONTAMINANTS AND SUBDUCTED LITHOSPHERE 332 Oceanic crust and sediments 332 Subduction-zone metamorphic rocks 334 Upper continental crust 334 Lower continental crust 335 OXYGEN ISOTOPE COMPOSITIONS OF MANTLE PERIDOTITES 336 MID-OCEAN RIDGE BASALTS 337 OCEANIC INTRAPLATE BASALTS 340 Survey of ocean islands 341 High'He^He 344 Detailed studies 345 CONTINENTAL INTRAPLATE BASALTS 352 ARC-RELATED LAVAS 352 SUMMARY AND FUTURE DIRECTIONS 357 View of the crust/mantle system through stable isotope geochemistry 357 Outstanding problems and future directions 358 ACKNOWLEDGMENTS 359 REFERENCES 359

5 6 Stable Isotope Thermometry at High Temperatures John W. Valley INTRODUCTION 365 REQUIREMENTS OF STABLE ISOTOPE THERMOMETRY 365 ANALYSIS OF STABLE ISOTOPE RATIOS 366 CALIBRATION OF ISOTOPE FRACTIONATION 368 KINETICS OF MINERAL EXCHANGE 369 Apparent temperature 369 Diffusion 370 Effect of deformation 372 Effect of water fugacity 372 DIFFUSION MODELS 373 Diffusion distance 373 Dodson's closure temperature 374 The Giletti model 375 The Fast Grain Boundary diffusion model (FGB) 376 The mode effect 377 STRATEGIES FOR SUCCESSFUL THERMOMETRY 379 Isotope exchange trajectories 379 RAM thermometers 380 Microscopic versus macroscopic models 381 TESTS OF THERMOMETRY 381 Concordance and 8-A diagrams 382 Imaging 382 The outcrop test 383 Microanalysis 384 Correlations to mode or crystal size 385 OXYGEN ISOTOPE THERMOMETRY 385 RAM thermometers 385 Aluminosilicate-quartz 386 Magnetite-quartz 388 Rutile-quartz 391 CARBON ISOTOPE THERMOMETRY 391 Calcite-graphite 391 Graphite crystallinity and morphology 393 Carbonate/graphite ratio 396 Contact and polymetamorphism 396 Fluid flow 397 Other minerals 398 Biogenic versus abiogenic graphite 398 Adirondack Mountains A case study 398 SULFUR ISOTOPE THERMOMETRY 399 SKARNS 400 ONE-MINERAL THERMOMETERS 400 ACKNOWLEDGMENTS 402 REFERENCES 402

6 7 Stable Isotope Transport and Contact Metamorphic Fluid Flow Lukas P. Baumgartner, John W. Valley INTRODUCTION 415 Abbreviations and symbols 416 "CLOSED SYSTEM" METAMORPHIC VOLATILIZATION 417 BATCH VOLATILIZATION..: 417 Rayleigh volatilization 419 Dehydration 420 Mixed volatile reactions 420 COUPLED O-C DEPLETIONS 421 OPEN SYSTEM FLUID-ROCK INTERACTION: CONTINUUM MECHANICS MODELS OF STABLE ISOTOPE TRANSPORT IN HIGH TEMPERATURE CRUSTAL SYSTEMS 423 The mass balance equation for stable isotope transport 427 MATHEMATICAL FORMULATION OF THE TRANSPORT MECHANISMS 430 The transport equation 433 FLUID-ROCK INTERACTION: THE TIME DEPENDENCE OF THE SYSTEM'S ISOTOPIC COMPOSITION 434 Geologically relevant insights from simple analytical solutions to the stable isotope transport equations 438 CONTINUUM MECHANICS AND FLUID-ROCK RATIOS 450 CONTACT METAMORPHISM 453 Volatilization during contact metamorphism 453 Fluid infiltration during contact metamorphism 454 An example: The Alta contact aureole 456 FUTURE WORK: MERGING THE RESULTS OF MODELING AND MICROANALYSIS 459 ACKNOWLEGMENTS 460 REFERENCES Stable Isotopes in Seafloor Hydrothermal Systems: Vent fluids, hydrothermal deposits, hydrothermal alteration, and microbial processes W. C. Shanks, III INTRODUCTION 469 METHODS 472 GEOLOGIC SETTING OF SEAFLOOR HYDROTHERMAL SYSTEMS 478 SEAFLOOR HYDROTHERMAL VENT FLUIDS 481 Oxygen and hydrogen isotopes in vent fluids 483 Sulfur isotopes in vent fluids 484 Carbon isotopes in vent fluids 486 STABLE ISOTOPE SYSTEMATICS OF SELECTED SEAFLOOR HYDROTHERMAL SYSTEMS 488 Bare volcanic ridges: 21 N, 9-10 N, and S EPR 489 Deep reaction zones: 504B 496 Oceanic gabbros: Hess Deep and Southwest Indian Ridge 499 Shallow alteration zones and seawater entrainment: TAG 499

7 Serpentinization 502 Sedimented ridges 506 Rifted continental settings 510 Convergent margins 513 SUMMARY AND CONCLUSIONS 516 Eruptive events 516 Magmatic components Phase separation 516 Deep biosphere 517 ACKNOWLEDGMENTS 517 REFERENCES Oxygen- and Hydrogen-Isotopic Ratios of Water in Precipitation: Beyond Paleothermometry Richard B. Alley, Kurt M. Cuffey INTRODUCTION 527 BASIS OF PALEOTHERMOMETRY USING OXYGEN- AND HYDROGEN-ISOTOPIC RATIOS OF WATER 528 COMPLICATIONS 534 Source effects on 8' 8 O or 8D of precipitation 534 Path effects on 8 18 O or 8D of water in precipitation 537 Sampling and other site effects 538 CASE STUDIES 539 Central Greenland 539 Southern Africa 547 DISCUSSION 548 ACKNOWLEDGMENTS 549 REFERENCES Isotopic Evolution of the Biogeochemical Carbon Cycle During the Precambrian David J. Des M arais INTRODUCTION 555 THE PRESENT-DAY CARBON CYCLE 556 The hydrosphere-atmosphere-biosphere (HAB) sub-cycle 556 The sedimentary (SED) sub-cycle 557 The metamorphic (MET) sub-cycle 558 The mantle-crust (MAN) sub-cycle 558 ISOTOPIC INDICATORS OF CARBON BUDGETS AND PROCESSES 559 Biological isotopic discrimination 559 Isotopic mass balance and the sedimentary cycle 559 Preservation of the carbon isotopic record 560 THE ARCHEAN RECORD 564 Planetary processes, climate and the carbon cycle 564 Archean biosphere 564

8 THE LATE ARCHEAN TO PROTEROZOIC TRANSITION 568 Changes in the carbon cycle 568 Marine sedimentation on the Kaapvaal Craton: a glimpse of carbon isotopic patterns at the dawn ( Ga) of the Proterozoic Eon 568 Isotopic change from late Archean to Mesoproterozoic ( Ga) 570 THE MESOPROTEROZOIC RECORD ( Ga) 572 THE NEOPROTEROZOIC RECORD ( Ga) i 572 THE C CYCLE, O 2 AND THE EVOLUTION OF EUKARYA 573 FUTURE WORK 574 ACKNOWLEDGMENTS 574 REFERENCES Isotopic Biogeochemistry of Marine Organic Carbon Katherine H. Freeman INTRODUCTION 579 MARINE INORGANIC CARBON 579 PRODUCTION OF MARINE ORGANIC MATTER 583 The photosynthetic isotope effect 583 The photosynthetic isotope effect and studies of paleoenvironmental change 585 Organic carbon in marine surface waters 587 Trophic effects and ecosystem studies 588 MARINE SEDIMENTARY ORGANIC MATTER 590 Alteration of primary isotopic signatures 590 The bulk of sedimentary organic matter: an unresolved issue 592 Microbial influences on marine sedimentary organic matter 8' 3 C values 593 SEDIMENTARY RECORDS OF PAST ENVIRONMENTS 595 ACKNOWLEDGMENTS 597 REFERENCES Biogeochemistry of Sulfur Isotopes D. E. Canfield INTRODUCTION 607 MICROBIAL PROCESSES 609 Assimilatory sulfate reduction 609 DISSIMILATORY SULFATE REDUCTION 610 Ecological and phylogenetic diversity of sulfate reducers 610 Principles governing the extent of fractionation 611 Magnitude of fractionation during sulfate reduction by pure cultures 614 Fractionation at high temperatures 615 Isotope fractionation during sulfate reduction in nature 616 SULFIDE OXIDATION 618 Fractionations during sulfide oxidation 618 Disproportionation of sulfur intermediate compounds 620 Isotope fractionation during disproportionation 621

9 ISOTOPIC COMPOSITION OF SEDIMENTARY SULFIDES 623 Minor sulfur isotopes 627 FRACTIONATION CALCULATIONS 627 A FEW SPECIFIC APPLICATIONS, 629 The isotope record of sedimentary sulfides 629 Biogenic sulfides and microscale isotope analysis 631 Organic sulfur 632 CONCLUDING REMARKS 632 ACKNOWLEDGMENTS 633 REFERENCES Stratigraphic Variation in Marine Carbonate Carbon Isotope Ratios Robert L. Ripperdan INTRODUCTION 637 THE MARINE CARBON CYCLE 639 The short-term carbon cycle 640 The long-term carbon cycle 641 ISOTOPIC VARIATION WITHIN THE LONG-TERM MARINE CARBON CYCLE 642 General principles 642 The general mass balance model for marine carbon 643 Variation in the burial flux of marine organic carbon 645 Continental weathering of carbon 646 Silicate weathering 647 Volcanic and metamorphic emissions of CO Clathrate hydrates and sedimentary methane 650 Stratigraphic variation by other means: confounding factors 651 A DETAILED LOOK AT A LARGE TRANSIENT A 13 C EVENT: 653 THE LATE ORDOVICIAN GLACIATION AND MASS EXTINCTION 653 Late Ordovician 8 13 C variation in the Hanson Creek Formation, central Nevada 654 Models for the Late Ordovician positive 8 13 C excursion 657 SUMMARY 658 ACKNOWLEDGMENTS 658 REFERENCES 658