1 Theory and Experience ........................................ 1
1.1 The Law of Rutherford-Soddy ............................. 2
1.2 Determination of Decay Constants ........................ 4
1.3 Mass Spectrometry ....................................... 4
1.4 Isotope Dilution ........................................ 5
1.5 Statistical Estimation of Results ....................... 8
1.6 Summary ................................................. 9
2 Geochronometric Models ...................................... 11
2.1 Isochron Model ......................................... 11
2.1.1 Isochron Plane .................................. 11
2.1.2 Common Rb-Sr Isochron ........................... 15
2.2 Pb-Pb Isochron ......................................... 17
2.3 Concordia-Discordia Model .............................. 19
2.4 Summary: Models for Open and Closed Parent-Daughter
Systems ................................................ 24
3 Principle Geochronometric Isotope Systems ................... 25
3.1 Th, U-Pb Isotope System ................................ 25
3.1.1 Decay Constants of 235U and 238U ................. 25
3.1.2 U-Pb Dating ..................................... 25
3.1.3 Pb-Pb Dating .................................... 26
3.2 K-Ar Isotope System .................................... 27
3.2.1 Constants of Radioactive Transformation ......... 28
3.2.2 Conventional K-Ar Method ........................ 28
3.2.3 40Ar/39Ar Method ................................. 30
3.3 Rb-Sr Isotope System ................................... 35
3.4 Sm-Nd Isotope System ................................... 35
3.5 Re-Os Isotope System ................................... 37
3.6 Isotope Systems of Extinct Nuclides .................... 38
3.7 Isotope System of 14C .................................. 39
3.8 Summary: Reliability of the Modern Isotopic Methods .... 42
4 Atmospheric Argon ........................................... 43
4.1 Origin of 40Ar ......................................... 43
4.2 Variations of 40Ar/36Ar and 36Ar/38Ar .................... 45
4.3 Summary: Isotopically Inhomogeneous Atmosphere ......... 48
5 Distribution of Radiogenic Argon Within a Mineral ........... 49
5.1 Closing Isotopic System: a-Factor ...................... 50
5.2 The a-Factor in the Conventional K-Ar Method ........... 51
5.3 Influence of Argon Distribution on Diffusion
Parameters ............................................. 53
5.4 Application for Dating of Imposed Geologic Processes ... 55
5.4.1 Rectangular Distribution of Argon (a = 0) ....... 56
5.4.2 Dominating Rectangular Argon Fraction\
(0 < α < 0.5) ................................... 56
5.4.3 Dominating Semi-Sinusoidal Argon Fraction\
(0.5 < α ≤ 1) ................................... 58
5.5 Summary: Low-Temperature Argon Losses .................. 59
6 Thermal Spectra of Argon Isotopes ........................... 61
6.1 Presentation of Argon-Argon Spectra on Diagrams ........ 61
6.2 Histograms of Argon Release ............................ 63
6.3 Deduction of an Algebraic Expression for an Isochron
Line in Inverse Ar-Ar Coordinates ...................... 66
6.4 Kinetics of Stepwise Heating ........................... 67
6.5 Separating Air and Radiogenic Argon .................... 68
6.6 Econt = Erad = E39 ....................................... 69
6.7 Econt < Јrad = E39 ....................................... 70
6.8 Econt < E39 < Erad ....................................... 71
6.9 Loss of Radiogenic Argon in the Geologic Past .......... 73
6.10 Excessive Argon-40 ..................................... 74
6.11 Argon of Poly-mineral Aggregates ....................... 74
6.12 Argon in Two-Component Crystal Structure ............... 76
6.13 Irreversible Processes of Argon Release from Mineral
Phases ................................................. 78
6.14 Summary: Peculiarities of Ar-Ar Spectra ................ 81
7 Radiogenic Argon in a Cooling Dike .......................... 85
7.1 Argon Kinetics ......................................... 85
7.2 K-Ar Isotopic Balance in a Cooling Dike ................ 88
7.3 Closure of K-Ar Isotope System ......................... 92
7.4 Geologic Application ................................... 94
7.5 Summary: Temporally Varying Diffusion .................. 95
8 Radiogenic Isotopes in an Exocontact Zone of a Magmatic
Body ........................................................ 97
8.1 Theoretical Consideration .............................. 99
8.1.1 Thermal Model ................................... 99
8.1.2 Radiogenic Argon Retention in a Mineral under
Varying Temperatures ........................... 102
8.2 Geochronological Application .......................... 104
8.3 Summary: Theory of Diffusion and Its Application
for Study of Exocontact Processes ..................... 106
8.4 Appendix: Two- and Three-Dimensional Cases ............ 107
9 Diffusion in a Laplace Regime .............................. 109
9.1 Deduction of the Laplace Age Equation ................. 109
9.2 Geologic Examples ..................................... 1ll
9.3 Summary: Estimation of the Diffusion Parameter
D/h2λ ................................................. 113
10 Early Earth ................................................ 115
10.1 Initial Processes in the Solar System (4.57-4.54
Ga) ................................................... 115
10.1.1 Classification of Meteorites ................... 115
10.1.2 Dating of Meteorites ........................... 117
10.1.3 Significance of Short-Lived Radionuclides ...... 118
10.1.4 Evolution of Asteroids ......................... 121
10.2 Priscoan Crust (4.4-3.8 Ga) ........................... 122
10.3 Archean Crust (3.8-2.5 Ga) ............................ 123
10.4 Oldest Crust in Asia .................................. 125
10.5 Summary: Geologic Processes of the Early Earth ........ 126
11 Important Phanerozoic Boundaries ........................... 129
11.1 Vendian-Cambrian ..................................... 129
11.1.1 Stratotype Sections ............................ 129
11.1.2 Radiogenic Isotope Ages ........................ 130
11.1.3 Events and Hypotheses .......................... 131
11.1.4 Alkaline Ultramafic Magmatism with
Carbonatites in Cissayan, Siberia .............. 132
11.2 Permian-Triassic ..................................... 135
11.2.1 Stratotype Sections ........................... 135
11.2.2 Radiogenic Isotope Ages ....................... 137
11.2.3 Events ........................................ 137
11.2.4 Hypotheses .................................... 138
11.2.5 Siberian Traps ................................ 138
11.3 Cretaceous-Tertiary .................................. 145
11.3.1 Definition of the Boundary .................... 145
11.3.2 Radiogenic Isotope Ages ....................... 146
11.3.3 Events and Hypotheses ......................... 146
11.3.4 Deccan Traps .................................. 147
11.4 Summary: Specifications of the Important
Phanerozoic Boundaries ................................ 147
12 Late Phanerozoic Magmatic Evolution of Asia ................ 149
12.1 Hierarchy and Periodicity of Magmatic Events ......... 152
12.2 Middle-Late Cretaceous: First-Order Processes ........ 158
12.2.1 Dating ........................................ 159
12.2.2 Geologic Background ........................... 160
12.3 Early Tertiary: First-Order Processes ................ 162
12.3.1 Thanetian Magmatic Events ..................... 162
12.3.2 Spatial Connections Between the Thanetian
and Lutetian Magmatic Events .................. 163
12.3.3 Geologic Background ........................... 164
12.4 Middle-Late Tertiary through Quaternary Transition
from the First-, through the Second- to the Third-
Order Processes ....................................... 166
12.4.1 Central Mongolia and Adjacent Regions ......... 167
12.4.2 South Primorye and Adjacent East Asia ......... 190
12.5 Summary: Magmatic Geodynamics in Asia ................ 205
13 Late Phanerozoic Magmatic Evolution of North America
and Northeast Africa: Comparisons with Asia ................ 209
13.1 North America ........................................ 209
13.1.1 Magmatic Migration of 120-37 Ma ................ 211
13.1.2 Transition from Intermediate-Silicic to
Basaltic Magmatism of 37-18 Ma ................. 211
13.1.3 Predominating Basaltic Magmatism of the Past
17-15 Ma ................................................... 213
13.1.4 Geodynamic Models .............................. 214
13.2 Northeast Africa ...................................... 215
13.2.1 Earliest Volcanic Events in the Western Rift ... 216
13.2.2 Hypotheses ..................................... 218
13.2.3 Bilateral along-Axis Propagation of Rift-
Related Magmatism .............................. 219
13.2.4 Geodynamics of the East African Plateau ........ 221
13.3 Comparisons: Africa—Eurasia—North America ............. 222
13.4 Summary: Two Geodynamic Patterns of Rift-Related
Magmatic Evolution in Continents ...................... 229
14 Separated Lead Isotopes .................................... 231
14.1 Dating Problems of Ore Mineralization ................. 231
14.2 Definition of Separated Leads ......................... 232
14.3 Diffusion Discordia ................................... 233
14.4 Electrical Charge of Pb Separated from U-Pb System .... 236
14.5 Connected Points of Concordia and Discordia ........... 236
14.6 Leads Released by Continuous Diffusion ................ 238
14.7 Instant Release of Leads .............................. 239
14.8 Tuning of T, t and μ .................................. 240
14.9 Interpreting Separated Leads from Ore Deposits in
Asia .................................................. 242
14.9.1 The Southern Part of the Siberian Craton ....... 242
14.9.2 The Gargan Block ............................... 244
14.9.3 Geologic Implication ........................... 246
14.10 Summary: Application of Separated Leads for
Understanding Timing of Ore-Forming Processes ........ 247
References .................................................... 249
Index ......................................................... 291
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