REVIEWS in MINERALOGY 3 GEOCHEMISTRY

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1 SUB Gottingen "/ A19458 LjO ' \ ^ REVIEWS in MINERALOGY 3 and GEOCHEMISTRY Volume URANIUM-SERIES GEOCHEMISTRY EDITORS: Bernard Bourdon Gideon M. Henderson Craig C. Lundstrom Simon P. Turner Institut de Physique du Globe de Paris Paris, France University of Oxford Oxford, United Kingdom University of Illinois, Urbana-Champaign Urbana, Illinois, USA University of Bristol Bristol, United Kingdom FRONT COVER: The background of the front cover image is an exert from a paper published exactly 100 years before this volume. That paper was the first to calculate the half life for 234 Th, or U-X as this newly discovered radioactive substance was then called. Further details of the early history of U-series science can be found in the second preface to this volume. Superimposed on this background is the full series of radioactive nuclides produced by the initial decay of 238 U, and finally resulting in the formation of 206 Pb. Nuclides with half lives longer than a year are shown in red, while those with half lives between one day and one year are shown in blue. Series Editors: Jodi J. Rosso & Paul H. Ribbe GEOCHEMICAL SOCIETY MINERALOGICAL SOCIETY of AMERICA

2 RiMG Volume 52 U-series Geochemistry Table of Contents 1 Introduction to U-series Geochemistry Bernard Bourdon, Simon Turner, Gideon M. Henderson and Craig C. Lundstrom 1. NEW DEVELOPMENTS IN U-SERIES GEOCHEMISTRY 1 2. U AND TH RADIOACTIVE DECAY SERIES Basic concepts Disequilibrium between U-series nuclides Processes creating disequilibria between U-series nuclides 7 3. CHEMISTRY AND GEOCHEMISTRY OF THE U-SERIES NUCLIDES DETERMINATION OF THE HALF-LIVES OF U-SERIES NUCLIDES Methods for measurement of half-life Recommended half-lives for key nuclides OUTLINE OF THE VOLUME 16 REFERENCES 17 APPENDIX: GENERAL SOLUTIONS OF U-SERIES DECAY EQUATION USING LAPLACE TRANSFORMS 20 2 Techniques for Measuring Uranium-series Nuclides: Steven J. Goldstein and Claudine H. Stirling 1. INTRODUCTION SAMPLE PREPARATION Microwave digestion of solids Tracer addition and tracer/sample equilibration CHEMICAL SEPARATIONS Extraction chromatography resins/disks INSTRUMENTAL ANALYSIS METHODS Alpha spectrometry Gamma spectrometry Thermal ionization mass spectrometry (TIMS) Secondary ion mass spectrometry (SIMS) ICPMS and MC-ICPMS COMPARISON OF ANALYTICAL METHODS FOR U-SERIES NUCLIDES FUTURE DEVELOPMENTS 52 ACKNOWLEDGMENTS 53 REFERENCES 53 XI

3 3 Mineral-Melt Partitioning of Uranium, Thorium and Their Daughters Jonathan Blundy and Bernard Wood 1. INTRODUCTION :.:: r PARTITIONING PRELIMINARIES SOURCES OF PARTITIONING DATA THE IMPORTANCE OF PARTITIONING IN INTERPRETING U-SERIES DATA THE LATTICE STRAIN MODEL Proxies Derivation of proxy relationships ADDITIONAL CONSIDERATIONS Henry's Law Ingrowth MINERAL-MELT PARTITION COEFFICIENTS Clinopyroxene Orthopyroxene Olivine Garnet Amphibole Plagioclase Alkali-feldspar Phlogopite (biotite) Oxide minerals Ill Zircon Other accessory phases CONCLUSIONS 116 ACKNOWLEDGMENTS 118 REFERENCES Timescales of Magma Chamber Processes and Dating of Young Volcanic Rocks Michel Condomines, Pierre-Jean Gauthier, { and Olgeir Sigmarsson 1. INTRODUCTION GENERAL PRINCIPLES AND USEFUL DIAGRAMS Radioactive disequilibria as dating tools Isochron diagrams Diagrams showing the evolution of disequilibria vs. time TIMESCALES OF MAGMA TRANSFER AND MAGMA CHAMBER PROCESSES Preliminary comments and definitions Disequilibria in single volcanic samples Comparison of disequilibria in comagmatic lavas: timescales of differentiation 133 xii

4 3.4. Evolution of disequilibria during the eruptive history of a volcano: magma storage or residence times Studieson minerals and crystallization ages: timescales of crystallization Timescales of magma degassing DATING YOUNG VOLCANIC ROCKS Mineral isochrons ; Dating of whole-rocks SUMMARY AND CONCLUSIONS 167 ACKNOWLEDGMENTS 169 REFERENCES 169 D Uranium-series Disequilibria in Mid-ocean Ridge Basalts: Observations and Models of Basalt Genesis Craig C. Lundstrom 1. INTRODUCTION A primer on U-series disequilibria OBSERVED U-SERIES DISEQUILIBRIA IN MORB Analysis of U-series nuclides Observed U-series disequilibria in MORB relative to other tectonic settings Observed U-series disequilibria at specific ridge locations Applications: dating of MORB using U-series disequilibria Assessing secondary contamination in creating U-series disequilibria MODELS OF U-SERIES DISEQUILIBRIA GENERATION DURING MELTING Constraints on element partitioning Time-independent melting models Ingrowth melting models A review of U-series melting models RELATING MODELS TO OBSERVATIONS INTEGRATING U-SERIES DISEQUILIBRIA MODELS WITH CONSTRAINTS FROM OTHER GEOCHEMICAL TRACERS Comparison of melting at ridges to other tectonic settings The relationship between Th isotopes and long-lived isotope systems Reconciling U-series interpretations with other geochemical observations CONCLUDING REMARKS 207 ACKNOWLEDGMENTS REFERENCES 207 APPENDIX: TRANSPORT-BASED MODELS FOR CREATING U-SERIES DISEQUILIBRIA 212 xni

5 O U-series Geochemistry - Table of Contents U-series Constraints on Intraplate Basaltic Magmatism Bernard Bourdon and Kenneth W. W. Sims 1. INTRODUCTION DIFFICULTIES IN CONSTRAINING HOTSPOT MELTING PROCESSES Source composition and source heterogeneities Role of the lithosphere Complexities in the melting region THE ROLE OF SOURCE HETEROGENEITIES ON U-SERIES FRACTIONATION IN HOTSPOT MAGMATISM Identifying residual mineral phases Role of source heterogeneities on melting processes Tracing mantle sources MELTING PROCESSES AND RELATION TO CONVECTIVE STRUCTURE OF PLUME Time dependent melting models for hotspot magmatism Sources of uncertainty in these models Observational constraints SUMMARY AND PERSPECTIVES 244 ACKNOWLEDGMENTS 244 REFERENCES 244 APPENDIX: ANALYTICAL SOLUTIONS FOR TIME DEPENDENT MELTING MODELS 249 A.I. Dynamic melt transport 249 A.2. Chromatographic melt transport 249 A.3. Box-model for equilibrium melting Insights into Magma Genesis at Convergent Margins from U-series Isotopes Simon Turner, Bernard Bourdon and Jim Gill 1. INTRODUCTION CONVERGENT MARGIN MAGMATISM Geochemical signatures of source components The enriched component sediment or OIB? The fluid component Relative depletion of the mantle wedge U-SERIES ISOTOPES IN ARC LAVAS BEHAVIOUR OF THE U-SERIES NUCLIDES IN AQUEOUS FLUIDS General empirical evidence Empirical observations from arc lavas Experimental constraints on mineral/fluid partitioning Composition of fluids released from the subducting plate Chromatographic interaction with the mantle wedge SEDIMENT ADDITION, MASS BALANCE FOR Th AND TIME SCALES Mass balance for Th content and 23O Th/ 232 Th ratios 270 xiv

6 5.2. Mechanism of sediment transfer implications for the temperature of the wedge? Time scale of sediment transfer FLUID ADDITION TIME SCALES U addition time scales Ra addition time scales Reconciling the U and Ra time scales Single-stage fluid addition Two-stage fluid addition Continuous fluid addition Mechanisms of fluid addition PARTIAL MELTING AND MELT ASCENT RATES Pa- and 23o Th-excess evidence for a partial melting signature in the wedge Ra evidence for melt ascent rates Models to reconcile the Pa, Th and Ra data Batch and equilibrium porous flow melting models Dynamic melting Flux melting Partial melting of the subducting oceanic crust DISCUSSION OF U-SERIES TIME SCALE IMPLICATIONS FOR ARC LAVAS REAR ARC LAVAS MODIFYING PROCESSES Time since eruption Alteration and seawater interaction Magma chambers processes Radioactive decay Crystal fractionation or accumulation Magma recharge Crustal contamination TIME-INTEGRATED U-Th-Pb EVOLUTION OF THE CRUST-MANTLE FUTURE WORK 303 ACKNOWLEDGMENTS 303 REFERENCES 303 APPENDIX: EQUATIONS FOR SIMULATING MELTING AND DEHYDRATION MODELS IN ARCS 311 Al. Single-stage model 311 A2. Two stage-model for fluid addition 311 A3. Continuous dehydration and melting The Behavior of U-and Th-series Nuclides in Groundwater Donald Porcelli and Peter W. Swarzenski 1. INTRODUCTION NUCLIDE TRANSPORT IN AQUIFERS General modeling considerations Radon and the recoil rate of U-series nuclides 331 xv

7 U-series Geochemistry- Table of Contents 2.3. Ra isotopes Th isotopes U isotopes Pb GROUNDWATER DISCHARGE INTO ESTUARIES Background Tracing groundwater using 222 Rn and the Ra quartet OPEN ISSUES The effects of well construction and sampling Quantification of model, parameters Interpreting model-derived information Inputs at the water table Applications to pollutant radionuclide migration studies Tracing groundwater discharges 355 ACKNOWLEDGMENTS 355 REFERENCES Uranium-series Dating of Marine and Lacustrine Carbonates R.L. Edwards, CD. Gallup, and H. Cheng 1. HISTORICAL CONSIDERATIONS THEORY Decay chains Secular equilibrium and uranium-series dating Th, 23l Pa, and 23O Th/ 231 Pa age equations Tests for 231 Pa- 230 Th age concordancy TESTS OF DATING ASSUMPTIONS Are initial 23O Th/ 238 U and 231 Pa/ 235 U values equal to zero? Tests of the closed-system assumption SOURCES OF ERROR IN AGE Errors in half-lives and decay constants Errors in measurement of isotope ratios Error in initial 23o Th/ 232 Th LATE QUATERNARY SEA LEVELS FROM CORAL DATING Deglacial sea level Sea level during the last interglacial/glacial cycle and earlier DATING OF OTHER MARINE AND LACUSTRINE MATERIALS Deep sea corals Carbonate bank sediments Mollusks and foraminifera Lacustrine carbonates CONCLUSIONS 399 ACKNOWLEDGMENTS 399 REFERENCES 400 xvi

8 10 Uranium-series Chronology and Environmental x Applications of Speleothems David A. Richards and Jeffrey A. Dorale 1. INTRODUCTION 1. : BASIC GEOCHRONOLICAL PRINCIPLES AND ASSUMPTIONS General principles of 23O Th- 234 U- 238 U and 23l Pa- 235 U dating Initial conditions Closed system decay U/ 238 U dating methodology U-Th-Pb dating of secondary carbonates of Quaternary age SPELEOTHEM GEOCHRONOLOGY IN PRACTICE Speleothem sampling strategy Treatment of U-series ages SPELEOTHEM CHRONOLOGY AND ENVIRONMENTAL CHANGE Applications based on the presence/absence or growth rate of speleothems Applications based on proxy evidence for environmental change contained within speleothems CONCLUDING REMARKS 449 ACKNOWLEDGMENTS 450 REFERENCES Short-lived U/Th Series Radionuclides in the Ocean: Tracers for Scavenging Rates, Export Fluxes and Particle Dynamics /. K. Cochran and P. Masque 1. INTRODUCTION MEASUREMENT TECHNIQUES SCAVENGING FROM SEA WATER Early observations of Th scavenging Development of scavenging models based on Th The role of colloids in Th scavenging Scavenging of Po THORIUM AND POLONIUM AS TRACERS FOR ORGANIC CARBON CYCLING IN THE OCEANS Basis, approach and early results Results of the past decade: JGOFS and other studies Unresolved issues Th AS A TRACER FOR PARTICLE TRANSPORT AND SEDIMENT PROCESSES IN THE COASTAL OCEAN Sediment mixing rates Th as a tracer of particle transport in shelf and estuarine environments CONCLUDING REMARKS 486 ACKNOWLEDGMENTS 487 REFERENCES 487 xvii

9 12 The U-series Toolbox for Paleoceanography Gideon M. Henderson and Robert F. Anderson 1. INTRODUCTION U-SERIES ISOTOPES IN THE OCEAN ENVIRONMENT The ocean uranium budget Chemical behavior of U-series nuclides in the oceans HISTORY OF WEATHERING - ( 234 U/ 238 U) SEDIMENTATION RATE- 230 Th xs :, The downward flux of 230 Th Seafloor sediments Mn crusts PAST EXPORT PRODUCTIVITY - ( 231 Pa xs / 230 Th xs ) Chemical fractionation and boundary scavenging ( 231 Pa xs / 230 Th xs ) ratios as a paleoproductivity proxy The role of particle composition Prospects for future use RATES OF PAST OCEAN CIRCULATION - ( 231 Pa xs / 230 Th xs ) HOLOCENE SEDIMENT CHRONOLOGY- 226 Ra SEDIMENT MIXING Pb CONCLUDING REMARKS 522 ACKNOWLEDGMENTS 523 REFERENCES 523 APPENDIX U-Th-Ra Fraetionation During Weathering and River Transport F. Chabaux, J. Riotte and O. Dequincey 1. INTRODUCTION ORIGIN OF RADIONUCLIDE FRACTIONATION DURING WEATHERING AND TRANSFERS INTO SURFACE WATERS Chemical fractionation arid mobilization factors Alpha recoil RADIOACTIVE DISEQUILIBRIA IN WEATHERING PROFILES: DATING AND TRACING OF CHEMICAL MOBILITY Dating of pedogenic concretions Characterization and time scale of chemical mobility in weathering profiles TRANSPORT OF U-Th-Ra ISOTOPES IN RIVER WATERS Transport of uranium isotopes in river waters Transport of thorium and radium isotopes ESTIMATES OF WEATHERING MASS BALANCE FROM U-SERIES DISEQUILIBRIA IN RIVER WATERS : : CONCLUDING REMARK 568 ACKNOWLEDGMENTS 569 REFERENCES 569 xviii

10 14 The Behavior of U- and Th-series Nuclides in the Estuarine Environment Peter W. Swarzenski, Donald Porcelli, Per S. Andersson and Joseph M. Smoak 1. INTRODUCTION Estuarine mixing Estuary fluxes Colloids URANIUM U in seawater River water U inputs U behavior in estuaries.' Uranium removal to anoxic sediments ; Importance of particles and colloids for controlling estuarine uranium The ( 234 U/ 238 U) activity ratios in estuaries THORIUM Th Th Long-lived Th isotopes Th and 230 Th RADIUM : RADON LEAD AND POLONIUM CONCLUSIONS 599 REFERENCES U-series Dating and Human Evolution A. W. G. Pike and P. B. Pettitt 1. INTRODUCTION U-SERIES DATING OF BONES AND TEETH The diffusion-adsorption (D-A) model U-series combined with electron spin resonance dating Non-destructive U-series dating by gamma spectrometry Future developments APPLICATIONS The issue of chronology in hominid evolution Neanderthals and modern humans in Israel Homo erectus and Homo sapiens in Java Homo erectus and Homo sapiens, in China The "Pit of the Bones" and a new species of hominid in Spain The earliest Australian human remains CONCLUSION 625 ACKNOWLEDGMENTS 626 REFERENCES 626 APPENDIX: FURTHER DETAILS OF THE D-A MODEL 630 xix

11 16 Mathematical-Statistical Treatment of Data and Errors for 23O Th/U Geochronology K. R. Ludwig 1. INTRODUCTION WHY ERROR ESTIMATION IS IMPORTANT ; ERRORS OF THE MEASURED ISOTOPIC RATIOS ERROR CORRELATIONS FIRST ORDER ESTIMATION OF ERRORS WHEN FIRST ORDER ERROR ESTIMATION IS INADEQUATE Improving the first order estimate analytically Error estimation by Monte Carlo CORRECTING A SINGLE ANALYSIS FOR DETRITAL THORIUM AND URANIUM ISOCHRONS Isochron representations for the general 23O Th/U system Error-weighted regressions and isochrons forx-y data dimensional error-weighted regressions and isochrons Isochrons with excess scatter Beyond error-weighted least-squares isochrons Robust and resistant isochrons PITFALLS IN DATA PRESENTATION NOTE ON IMPLEMENTATION OF ALGORITHMS 651 ACKNOWLEDGMENTS 651 REFERENCES 651 APPENDIX I: ESTIMATING ERROR CORRELATIONS 653 APPENDIX II: WORKED EXAMPLE OF DETRITAL CORRECTION AND ERROR PROPAGATION 655 APPENDIX III: FUNCTIONS/ROUTINES FOR 23O Th/U DATING PROVIDED BY ISOPLOT 656 xx