Download Table of Contents 1 An Overview of Noble Gas Geochemistry and

Table of Contents
Noble Gases in Geochemistry and Cosmochemistry
Reviews in Mineralogy and Geochemistry, Vol. 47
1
An Overview of Noble Gas Geochemistry and Cosmochemistry
D. Porcelli, C. J. Ballentine, R. Wieler
INTRODUCTION ........................................................................................................................... 1
NOBLE GAS MASS SPECTROMETRY ...................................................................................... 2
THE ATMOSPHERIC STANDARD ............................................................................................. 2
PRODUCTION OF NOBLE GAS ISOTOPES .............................................................................. 4
BEHAVIOR OF THE NOBLE GASES.......................................................................................... 5
Water, natural gas, and oil partitioning ......................................................................................6
Silicate melt solubilities ............................................................................................................. 6
Crystal-melt partitioning ............................................................................................................ 6
Iron-silicate partitioning............................................................................................................. 6
Adsorption ................................................................................................................................. 6
Diffusion .................................................................................................................................... 7
Atmosphere losses ..................................................................................................................... 7
NOBLE GASES IN COSMOCHEMICAL AND GEOCHEMICAL STUDIES ............................ 7
Noble gases in cosmochemistry ................................................................................................. 8
Noble gases in the mantle ........................................................................................................ 10
Noble gases in surface reservoirs ............................................................................................. 11
Noble gases and geochronology .............................................................................................. 13
END NOTE ................................................................................................................................... 14
ACKNOWLEDGMENTS ............................................................................................................. 14
REFERENCES .............................................................................................................................. 14
APPENDIX I ................................................................................................................................. 18
Noble Gases in the Solar System
2
71
Noble Gases in the Solar System
Rainer Wieler
INTRODUCTION ..........................................................................................................................21
ANALYTICAL TECHNIQUES ....................................................................................................21
THE SUN .......................................................................................................................................23
Solar noble gas abundances .....................................................................................................23
Helium in the Sun ....................................................................................................................26
Noble gases in the solar corpuscular radiation.........................................................................27
THE GIANT PLANETS ................................................................................................................36
The He abundances ..................................................................................................................36
The Ne-Xe abundances in Jupiter ............................................................................................39
Isotopic ratios in Jupiter ...........................................................................................................40
VENUS...........................................................................................................................................42
THE MOON ...................................................................................................................................43
Trapped solar (and other) noble gases in the lunar (and asteroidal) regoliths .........................43
Nitrogen in lunar samples ........................................................................................................52
Cosmogenic noble gases in lunar samples ...............................................................................53
THE EXOSPHERES OF THE MOON AND MERCURY............................................................55
Sources and sinks .....................................................................................................................57
COMETS ........................................................................................................................................58
INTERPLANETARY DUST PARTICLES AND MICROMETEORITES ..................................59
ELEMENTARY PARTICLES IN INTERPLANETARY SPACE ................................................61
Galactic cosmic rays ................................................................................................................61
Interstellar and interplanetary pick-up ions .............................................................................62
Anomalous cosmic rays ...........................................................................................................63
ACKNOWLEDGMENTS ..............................................................................................................63
REFERENCES ...............................................................................................................................63
3
Noble Gases in Meteorites – Trapped Components
Ulrich Ott
OVERVIEW AND HISTORICAL ............................................................................................... 71
ELEMENTAL ABUNDANCE PATTERNS ................................................................................ 73
ISOTOPIC COMPOSITIONS....................................................................................................... 74
Helium .................................................................................................................................... 75
Neon ........................................................................................................................................ 76
Argon ...................................................................................................................................... 77
Krypton ................................................................................................................................... 78
Xenon ...................................................................................................................................... 80
ORIGINS AND HISTORY ........................................................................................................... 82
Q(P1)-gases ............................................................................................................................. 83
Gases in presolar silicon carbide and graphite ........................................................................ 84
Gases trapped in presolar diamond (HL, P3 and P6 components) .......................................... 87
Ureilite gases........................................................................................................................... 89
Subsolar and sub-Q gases ....................................................................................................... 89
Sitings ..................................................................................................................................... 90
Other (lesser) components ...................................................................................................... 90
RELATIONS ................................................................................................................................. 91
Relationship between Q and solar gases ................................................................................. 91
A more primitive component (in Xe and only in Xe?) ........................................................... 94
CONCLUDING REMARKS ........................................................................................................ 96
ACKNOWLEDGMENTS ............................................................................................................. 96
REFERENCES .............................................................................................................................. 96
4
Noble Gases in the Moon and Meteorites:
Radiogenic Components and Early Volatile Chronologies
Timothy D. Swindle
INTRODUCTION ....................................................................................................................... 101
LONG-LIVED NUCLIDES: CHRONOLOGY OF SOLAR SYSTEM EVOLUTION ............. 102
Solar system impact history ................................................................................................... 103
Extinct radionuclides: Chronology of solar system formation .............................................. 108
Iodine-xenon .......................................................................................................................... 109
244
Plutonium ........................................................................................................................... 117
Other fissioning nuclides?...................................................................................................... 120
Other radiogenic noble gases ................................................................................................. 120
ACKNOWLEDGMENTS ........................................................................................................... 121
REFERENCES ............................................................................................................................ 121
5
Cosmic-Ray-Produced Noble Gases in Meteorites
Rainer Wieler
INTRODUCTION ........................................................................................................................125
THE PRODUCTION OF COSMOGENIC NUCLIDES IN METEORITES ..............................126
Fundamentals ......................................................................................................................... 126
Production systematics........................................................................................................... 128
Cosmogenic noble gases produced by capture of low-energy neutrons ................................ 139
Isotopic abundances of cosmogenic noble gases ................................................................... 141
EXPOSURE AGE DISTRIBUTIONS OF METEORITES .........................................................144
Undifferentiated meteorites ................................................................................................... 146
Differentiated meteorites ....................................................................................................... 149
Exposure ages and dynamical models of meteorite delivery ................................................. 153
COMPLEX EXPOSURE HISTORIES ........................................................................................155
THE COSMIC RAY FLUX IN TIME .........................................................................................159
TERRESTRIAL AGES ................................................................................................................161
COSMOGENIC NOBLE GASES PRODUCED BY SOLAR COSMIC RAYS (SCR)..............162
ACKNOWLEDGMENTS ............................................................................................................162
REFERENCES .............................................................................................................................163
6
Martian Noble Gases
Timothy D. Swindle
STUDYING MARS AS ANOTHER PLANET .......................................................................... 171
DISCOVERY OF MARTIAN METEORITES........................................................................... 171
MARTIAN ATMOSPHERE ....................................................................................................... 175
OTHER MARTIAN NOBLE GAS RESERVOIRS ................................................................... 180
Martian interior (Chassigny) ................................................................................................. 180
Other reservoirs I: Nakhlite (and ALH84001) Xe ................................................................ 181
Other reservoirs II: Shergottite Ar ........................................................................................ 182
Paleoatmosphere ................................................................................................................... 182
MARTIAN CHRONOLOGY ..................................................................................................... 183
40
Ar-39Ar dating..................................................................................................................... 184
Cosmic-ray exposure ages .................................................................................................... 185
ACKNOWLEDGMENTS ........................................................................................................... 187
REFERENCES ............................................................................................................................ 187
7
Origin of Noble Gases in the Terrestrial Planets
Robert O. Pepin, Donald Porcelli
INTRODUCTION ....................................................................................................................... 191
CHARACTERISTICS OF PLANETARY NOBLE GASES ...................................................... 193
Planetary noble gas abundance patterns ............................................................................... 193
Terrestrial noble gases .......................................................................................................... 196
Noble gases on Venus ........................................................................................................... 205
Noble Gases on Mars ............................................................................................................ 206
ACQUISITION OF PLANETARY NOBLE GASES ................................................................. 208
Early post-nebular solar wind ............................................................................................... 209
Adsorption on pre-planetary grains or protoplanetary bodies .............................................. 210
Gravitational capture ............................................................................................................. 210
Accretion of volatile-rich planetesimals ............................................................................... 213
LOSSES AND MODIFICATIONS OF PLANETARY NOBLE GASES .................................. 216
Losses during accretion......................................................................................................... 216
Sputtering .............................................................................................................................. 217
Hydrodynamic escape ........................................................................................................... 218
Primordial xenon................................................................................................................... 231
OUTSTANDING ISSUES .......................................................................................................... 235
ACKNOWLEDGMENTS ........................................................................................................... 239
REFERENCES ............................................................................................................................ 239
8
Noble Gas Isotope Geochemistry of
Mid-Ocean Ridge and Ocean Island Basalts:
Characterization of Mantle Source Reservoirs
David W. Graham
INTRODUCTION ....................................................................................................................... 247
BACKGROUND ......................................................................................................................... 249
Noble gas chemical behavior ................................................................................................ 249
Mantle structure and noble gases .......................................................................................... 252
HELIUM ..................................................................................................................................... 254
Significance .......................................................................................................................... 254
Radiogenic production .......................................................................................................... 255
Mid-ocean ridge basalts ........................................................................................................ 255
Ocean island basalts .............................................................................................................. 265
NEON .......................................................................................................................................... 279
Significance .......................................................................................................................... 279
Nucleogenic production ........................................................................................................ 279
Mid-ocean ridge basalts ........................................................................................................ 281
Ocean island basalts .............................................................................................................. 283
ARGON ....................................................................................................................................... 284
Significance .......................................................................................................................... 284
Radiogenic production .......................................................................................................... 284
Atmospheric contamination .................................................................................................. 284
Mid-ocean ridge basalts ........................................................................................................ 285
Ocean island basalts .............................................................................................................. 288
KRYPTON .................................................................................................................................. 289
XENON ....................................................................................................................................... 289
Significance .......................................................................................................................... 289
Radiogenic production .......................................................................................................... 290
Mid-ocean ridge basalts ........................................................................................................ 291
Ocean island basalts .............................................................................................................. 292
COUPLED RADIOGENIC/NUCLEOGENIC PRODUCTION ................................................. 293
Neon-helium systematics ...................................................................................................... 293
Argon-helium systematics .................................................................................................... 297
Xenon-neon-helium systematics ........................................................................................... 300
MANTLE ABUNDANCE PATTERNS OF NOBLE GASES ................................................... 301
PRINCIPAL OBSERVATIONS ................................................................................................. 302
SUMMARY ................................................................................................................................ 303
ACKNOWLEDGMENTS ........................................................................................................... 305
REFERENCES ............................................................................................................................ 305
9
Noble Gases and Volatile Recycling at Subduction Zones
David R. Hilton, Tobias P. Fischer, Bernard Marty
INTRODUCTION ....................................................................................................................... 319
SAMPLING FOR NOBLE GASES ............................................................................................ 320
Volcanic and geothermal fluids ............................................................................................ 320
Hot spring waters and groundwaters..................................................................................... 321
Geothermal wells .................................................................................................................. 322
Natural gases ......................................................................................................................... 322
Mafic phenocrysts and xenoliths .......................................................................................... 322
Submarine glasses ................................................................................................................. 323
Problematic issues of noble gas analysis .............................................................................. 323
NOBLE GAS SYSTEMATICS OF ARC-RELATED VOLCANISM ....................................... 324
Helium isotope systematics of arc-related volcanism ........................................................... 325
Neon and argon isotope systematics of arc-related volcanism ............................................. 330
Krypton and xenon isotope systematics of arc-related volcanism ........................................ 333
Relative noble gas abundance systematics of arc-related volcanism .................................... 333
NOBLE GASES IN BACK-ARC BASINS ................................................................................ 334
Helium isotopes in back-arc basins ....................................................................................... 334
Neon isotopes in back-arc basins .......................................................................................... 337
Argon, krypton and xenon isotopes in back-arc basins ........................................................ 338
RECYCLING OF VOLATILES AT SUBDUCTION ZONES:
A MASS BALANCE APPROACH ......................................................................................... 340
The global volatile output at arc volcanoes: The 3He approach............................................ 340
Volatile output at individual arcs—SO2 and the power law distribution .............................. 341
Using helium to resolve volatile provenance ........................................................................ 349
Problematic issues regarding estimates of volatile output at arcs ......................................... 351
Volatile output at the back-arc and fore-arc regions ............................................................. 352
The volatile input via the trench ........................................................................................... 353
Volatile mass balance at subduction zones ........................................................................... 355
Global implications of volatile recycling at subduction zones ............................................. 358
SUMMARY AND FUTURE WORK ......................................................................................... 361
ACKNOWLEDGMENTS ........................................................................................................... 362
REFERENCES ............................................................................................................................ 362
10
Storage and Transport of Noble Gases
in the Subcontinental Lithosphere
Tibor J. Dunai, Donald Porcelli
INTRODUCTION ....................................................................................................................... 371
SUBCONTINENTAL MANTLE AS GEOCHEMICAL RESERVOIR .................................... 372
Thickness of the lithosphere ................................................................................................. 372
Composition of the lithosphere ............................................................................................. 373
Age of the lithosphere ........................................................................................................... 374
Possible xenolith noble gas components............................................................................... 374
NOBLE GASES IN ULTRAMAFIC XENOLITHS AND PHENOCRYSTS............................ 377
Fluid inclusions as hosts for noble gases .............................................................................. 377
Helium isotopic variations .................................................................................................... 381
He-Sr relationships ............................................................................................................... 382
He-C relationships ................................................................................................................ 384
The heavier noble gases ........................................................................................................ 386
Regional studies of the sources of xenolith mantle rare gases .............................................. 388
The mantle sources of xenolith He ....................................................................................... 394
Introducing He into the lithosphere ...................................................................................... 396
DIAMONDS ............................................................................................................................... 397
Ancient He ............................................................................................................................ 398
Ancient Xe ............................................................................................................................ 399
Mantle sources of diamond rare gases .................................................................................. 399
MANTLE VOLATILES IN THE CONTINENTAL CRUST .................................................... 400
CONCLUSIONS ......................................................................................................................... 400
ACKNOWLEDGMENTS ........................................................................................................... 401
REFERENCES ............................................................................................................................ 401
11
Models for Distribution of Terrestrial Noble Gases
and Evolution of the Atmosphere
D. Porcelli, C.J. Ballentine
INTRODUCTION ....................................................................................................................... 411
RADIOGENIC COMPONENTS IN THE BULK EARTH AND ATMOSPHERE ................... 412
Radiogenic He and nucleogenic Ne ...................................................................................... 412
Radiogenic Ar ....................................................................................................................... 414
Radiogenic and fissiogenic Xe.............................................................................................. 415
MANTLE NOBLE GAS CHARACTERISTICS ........................................................................ 419
Helium isotopic compositions in the mantle ......................................................................... 419
Neon isotopic compositions in the mantle ............................................................................ 420
Argon isotopic compositions in the mantle........................................................................... 423
Xe isotopes and a nonresidual upper mantle ......................................................................... 427
Mantle noble gas relative abundances .................................................................................. 428
Noble gas fluxes and mantle concentrations ......................................................................... 430
Undepleted mantle ................................................................................................................ 434
Coupled degassing of noble gases ........................................................................................ 435
TRACE ELEMENT ISOTOPE CONSTRAINTS ON MANTLE RESERVOIRS ..................... 436
Relationship between noble gases and radiogenic isotopes .................................................. 436
Mass and character of the depleted mantle ........................................................................... 436
Timing of mantle depletion and recycling ............................................................................ 438
PHYSICAL CONSTRAINTS ON MANTLE MODELS ........................................................... 438
Mantle reservoirs .................................................................................................................. 438
Geophysical evidence for the scale of mantle convection .................................................... 439
Early Earth history ................................................................................................................ 443
NOBLE GAS MANTLE MODELS ............................................................................................ 446
Single reservoir degassing .................................................................................................... 446
Limited Interaction Box models ........................................................................................... 448
Steady state box models ........................................................................................................ 452
Break-up of a previously layered mantle .............................................................................. 457
The lower boundary layer reservoir ...................................................................................... 457
The upper boundary layer reservoir ...................................................................................... 459
Deeper or ‘abyssal’ layering ................................................................................................. 459
Heterogeneities preserved within the convecting mantle...................................................... 460
Depleted, high He/U mantle ................................................................................................. 462
Storage of noble gases in the core......................................................................................... 463
Subduction of meteoritic He ................................................................................................. 465
CONCLUSIONS ......................................................................................................................... 466
Overall assessment of the models ......................................................................................... 466
Some persistent misconceptions ........................................................................................... 467
Important parameters that are still unknown......................................................................... 468
ACKNOWLEDGMENTS ........................................................................................................... 469
REFERENCES ............................................................................................................................ 469
12
Production, Release and Transport of
Noble Gases in the Continental Crust
Chris J. Ballentine, Pete G. Burnard
INTRODUCTION ....................................................................................................................... 481
RADIOGENIC, NUCLEOGENIC, AND FISSIOGENIC NOBLE GASES .............................. 482
The subsurface neutron flux and reaction probability .......................................................... 482
Helium .................................................................................................................................. 487
Neon ...................................................................................................................................... 490
Argon .................................................................................................................................... 495
Krypton and xenon................................................................................................................ 498
Cosmogenic noble gas production ........................................................................................ 501
Interplanetary dust accumulation .......................................................................................... 503
Production rates in continental crust today and over the history of the Earth ...................... 504
RELEASE OF NOBLE GASES FROM MINERALS IN THE CRUST .................................... 506
Recoil loss ............................................................................................................................. 506
Diffusive loss from minerals ................................................................................................. 509
Mineral breakdown/diagenesis/metamorphism/alteration .................................................... 512
TRANSPORT OF NOBLE GASES FROM THE DEEP CRUST
TO SHALLOW-LEVEL SYSTEMS ....................................................................................... 514
Diffusion: A viable transport mechanism to degas the continental Crust? ........................... 515
Differential release and transport of helium and argon ......................................................... 517
Accumulation and release: Fluid flow in the Crust............................................................... 519
HEAT AND HELIUM ................................................................................................................ 521
The relationship between 4He and heat ................................................................................. 521
Transport of mantle heat and helium through the crust ........................................................ 521
Transport of crustal heat and 4He .......................................................................................... 524
MAGMATIC NOBLE GASES IN THE CRUST ....................................................................... 525
Tectonic control on magmatic fluid location ........................................................................ 525
Fossil magmatic gases........................................................................................................... 529
ACKNOWLEDGMENTS ........................................................................................................... 529
REFERENCES ............................................................................................................................ 529
Tracing Fluid Origin, Transport and Interaction in the Crust
13
615
Tracing Fluid Origin, Transport and Interaction in the Crust
Chris J. Ballentine, Ray Burgess, Bernard Marty
INTRODUCTION ....................................................................................................................... 539
PHYSICAL CHEMISTRY OF NOBLE GASES IN CRUSTAL FLUIDS ................................ 540
Henry’s law and the assumption of ideality ........................................................................... 540
Non-ideality in the gas phase ................................................................................................. 541
Non-ideality in the fluid phase...............................................................................................544
Noble gas solubility in water and oil ..................................................................................... 546
PHASE EQUILIBRIUM AND FRACTIONATION OF NOBLE GASES ................................ 548
Liquid-gas phase partitioning of noble gases......................................................................... 548
Liquid-liquid phase partitioning of noble gases.................................................................... 549
Relative fractionation ............................................................................................................. 550
Rayleigh fractionation............................................................................................................ 551
Re-solution and effervescence ............................................................................................... 555
Multiple subsurface fluid phases ........................................................................................... 558
Diffusion or kinetic fractionation...........................................................................................559
RESOLVING DIFFERENT NOBLE GAS COMPONENTS IN CRUSTAL FLUIDS ............. 562
NOBLE GASES IN HYDROCARBON GAS AND OIL RESERVOIRS.................................. 565
Identifying and quantifying groundwater/gas/oil interaction ................................................ 567
Case studies............................................................................................................................ 569
NOBLE GASES IN ANCIENT GROUNDWATERS AND CRUSTAL DEGASSING ............ 581
Sources of He isotopes in groundwaters ................................................................................ 582
Deep aquifers and the crustal He flux .................................................................................... 584
Advective versus diffusive transfer of noble gases in basins ................................................. 590
Tentative synthesis ................................................................................................................. 592
MAGMATIC FLUIDS IN THE CRUST .................................................................................... 595
Mantle degassing in the continental crust: The noble gas imprint ......................................... 595
NOBLE GASES IN MINERAL DEPOSITS AND HYDROTHERMAL FLUIDS ................... 598
Post-entrapment modification of He and Ar isotopes ............................................................ 600
Noble gas mixtures in mineralizing fluids ............................................................................. 601
Description and analysis of multi-component noble gas mixtures in ore fluids .................... 601
Further developments............................................................................................................. 605
ACKNOWLEDGMENTS ........................................................................................................... 608
REFERENCES ............................................................................................................................ 608
14
Noble Gases in Lakes and Ground Waters
R. Kipfer, W. Aeschbach-Hertig, F. Peeters, M. Stute
INTRODUCTION ....................................................................................................................... 615
ANALYTICAL TECHNIQUES ................................................................................................. 617
NOBLE GAS COMPONENTS IN WATER .............................................................................. 619
Atmospheric noble gases 1: Solubility equilibrium ............................................................... 619
Atmospheric noble gases 2: Excess Air ................................................................................. 624
Radiogenic He (and Ar) ......................................................................................................... 629
Terrigenic He ......................................................................................................................... 629
Radioactive noble gas isotopes .............................................................................................. 630
Man made pseudo-conservative trace gases .......................................................................... 633
Data evaluation and interpretation ......................................................................................... 633
Conceptual models for noble gases in water .......................................................................... 634
Separation of the components ................................................................................................ 641
Interpretation .......................................................................................................................... 647
APPLICATIONS IN LAKES...................................................................................................... 650
Mixing and the distribution of dissolved substances in lakes ................................................ 651
Distribution of noble gases in lakes ....................................................................................... 653
Application of 3H-3He dating in lakes.................................................................................... 654
Quantification of vertical exchange rates and vertical turbulent diffusivities ....................... 658
He flux from the continental crust and oxygen depletion ...................................................... 661
Noble gases from the Earth’s mantle ..................................................................................... 664
Applications in ground water ................................................................................................. 666
Dating of young ground waters.............................................................................................. 667
Dating of old ground waters .................................................................................................. 676
Noble gas recharge temperatures ........................................................................................... 679
Excess air ............................................................................................................................... 684
NOBLE GASES IN ICE ............................................................................................................. 687
Gravitational separation ......................................................................................................... 687
Thermal diffusion .................................................................................................................. 687
Helium isotopes ..................................................................................................................... 689
REFERENCES ............................................................................................................................ 690
15
Noble Gases in Ocean Waters and Sediments
Peter Schlosser, Gisela Winckler
INTRODUCTION ....................................................................................................................... 701
TRACING OCEAN CIRCULATION USING 3HE AND TRITIUM ........................................ 702
Tritium/3He method .............................................................................................................. 702
Exemplary results from tritium/3He studies .......................................................................... 706
MANTLE 3HE ............................................................................................................................. 709
General background .............................................................................................................. 709
Geochemical background...................................................................................................... 709
3
He plumes in the ocean ........................................................................................................ 710
THE FLUX OF 3HE AND 4HE FROM THE SEAFLOOR ......................................................... 711
4
He ........................................................................................................................................ 711
3
He ........................................................................................................................................ 713
EXTRATERRESTRIAL 3HE IN DEEP-SEA SEDIMENTS ...................................................... 715
Delivery of extraterrestrial 3He to the ocean sediments ........................................................ 715
Applications of the IDP-derived 3He method ....................................................................... 717
NOBLE GASES IN DEEP-SEA BRINES .................................................................................. 720
The Red Sea .......................................................................................................................... 720
The Eastern Mediterranean ................................................................................................... 721
AIR/SEA GAS EXCHANGE STUDIED BY DUAL TRACER RELEASE EXPERIMENTS 721
Background ........................................................................................................................... 721
SF6/3He Method .................................................................................................................... 723
Results from oceanic dual gas tracer releases ....................................................................... 723
PERSPECTIVES ......................................................................................................................... 723
REFERENCES ............................................................................................................................ 725
Noble Gases as Dating Tools for Surficial Processes
16
785
Cosmic-Ray-Produced Noble Gases in
Terrestrial Rocks: Dating Tools for Surface Processes
Samuel Niedermann
INTRODUCTION ....................................................................................................................... 731
THE FUNDAMENTALS OF SURFACE EXPOSURE DATING ............................................. 732
Production mechanisms of cosmogenic nuclides in terrestrial rocks.................................... 732
Temporal variation of cosmogenic nuclide production ........................................................ 740
Cosmogenic nuclide production at depth and on eroding surfaces ....................................... 748
Derivation of exposure ages and erosion rates...................................................................... 750
Error considerations .............................................................................................................. 754
PRODUCTION RATES OF COSMOGENIC NUCLIDES ....................................................... 755
Experimental determinations of production rates ................................................................. 755
Production rates obtained by model calculations .................................................................. 761
EXPERIMENTAL ISSUES ........................................................................................................ 762
Retentivity of minerals for cosmogenic He and Ne .............................................................. 762
Discrimination of cosmogenic against trapped, radiogenic, and nucleogenic components .. 763
Cosmogenic noble gases as a nuisance ................................................................................. 769
Cosmogenic noble gases versus radionuclides ..................................................................... 770
APPLICATION EXAMPLES ..................................................................................................... 771
Dating of lava flows .............................................................................................................. 771
Glacier movement and ice sheet evolution ........................................................................... 772
Rates of erosion and soil accumulation................................................................................. 773
Rates of tectonic uplift .......................................................................................................... 775
Earthquakes and landslides ................................................................................................... 775
Further applications .............................................................................................................. 776
Future prospects .................................................................................................................... 776
ACKNOWLEDGMENTS ........................................................................................................... 777
REFERENCES ............................................................................................................................ 777
17
K-Ar and Ar-Ar Dating
Simon Kelley
INTRODUCTION — A BIT OF HISTORY .............................................................................. 785
THE K-AR AND AR-AR DATING METHODS ........................................................................ 786
Introduction ........................................................................................................................... 786
Assumptions.......................................................................................................................... 787
CALCULATING K-AR AND AR-AR AGES ............................................................................. 788
The values of constants and estimation of errors .................................................................. 792
ARGON DIFFUSION AND SOLUBILITY ............................................................................... 795
Argon diffusion (and its use to determine thermal histories) ................................................ 795
Argon solubility (and the causes of extraneous argon) ......................................................... 798
APPLICATIONS......................................................................................................................... 806
Thermochronology................................................................................................................ 806
Dating young volcanic eruptions .......................................................................................... 809
High-precision ages on altered basalts .................................................................................. 809
Dating low-temperature processes ........................................................................................ 809
Unique samples ..................................................................................................................... 810
Acknowledgments ....................................................................................................................... 810
REFERENCES ............................................................................................................................ 810
18
(U-Th)/He Dating: Techniques, Calibrations, and Applications
Kenneth A. Farley
INTRODUCTION ....................................................................................................................... 819
Rationale ............................................................................................................................... 819
TECHNICAL ASPECTS ............................................................................................................ 820
He ingrowth .......................................................................................................................... 820
DIFFUSION BEHAVIOR........................................................................................................... 821
Apatite ................................................................................................................................... 822
Hematite ................................................................................................................................ 825
Titanite .................................................................................................................................. 825
Zircon .................................................................................................................................... 826
Garnet.................................................................................................................................... 827
α-emission correction ............................................................................................... 827
Analytical procedures, accuracy, precision and mineral standards....................................... 832
INTERPRETATION OF HE AGES AND EXAMPLES ............................................................ 835
He cooling ages ..................................................................................................................... 835
Some case studies ................................................................................................................. 837
FUTURE PROSPECTS............................................................................................................... 839
ACKNOWLEDGMENTS ........................................................................................................... 840
REFERENCES ............................................................................................................................ 841
APPENDIX: ANALYTICAL TECHNIQUES........................................................................... 844