Geochronology and Thermochronology by the 40ar/39ar Method

by McDougall, Ian; Harrison, T. Mark

• ISBN13: 9780195109207
• ISBN10: 0195109201
• Edition: 2nd
• Format: Hardcover
• Copyright: 1999-08-05
• Publisher: Oxford University Press

Summary

Argon isotopic dating is one of the most important techniques for estimating the ages of rocks and can be used on very small samples. It has been used to assign reliable ages to the Earth and numerous meteorites. This second edition covers the standard principles and methods and incorporates many of new developments from the last decade. It covers the basis of the method, technical aspects, data presentation, diffusion theory, thermochronology, and many applications and case studies.

Table of Contents

Historical Introduction	3	(6)
General comments	3	(1)
Historical outline	4	(5)
Basis of the 40Ar/39Ar Dating Method	9	(35)
Potassium-argon dating	9	(3)
40Ar/39Ar dating	12	(2)
Potassium and its isotopes	14	(1)
The 40K decay scheme and constants	15	(1)
Derivation of age equations	16	(3)
Atmospheric argon	19	(1)
Materials suitable for dating	20	(19)
Range of applicability	39	(5)
Technical Aspects	44	(65)
Introduction	44	(1)
Sample preparation	44	(1)
Monitor minerals	45	(5)
Nuclear reactions	50	(1)
Nuclear reactors as a neutron source	51	(3)
The 39K(n,p)39 Ar reaction	54	(3)
Interfering nuclear reactions and correction factors	57	(8)
Optimization of irradiation parameters	65	(5)
Neutron flux gradients	70	(4)
Self-shielding	74	(1)
Temperature effects	74	(1)
Lattice damage	74	(1)
Decay factors	75	(1)
Total sample activity	75	(1)
Safety aspects	76	(1)
Argon extraction systems	76	(6)
Mass spectrometry	82	(11)
Laser microprobes	93	(16)
40Ar/39Ar Data Presentation and Interpretation	109	(28)
Introduction	109	(1)
Simple behavior (closed system)	109	(6)
Complex behavior (open sytem)	115	(5)
Mixed phases	120	(3)
Excess argon	123	(7)
Nuclear recoil	130	(1)
Grain size and distribution	131	(1)
Phase changes in vacuum	132	(1)
Resolution within the age spectrum	133	(4)
Appendix 4.A.1 Isochron analysis	134	(3)
Diffusion Theory and Measurements	137	(28)
Introduction	137	(1)
The process of diffusion	137	(1)
The phenomenological basis of diffusion theory	138	(1)
Methods of solution for constant D	139	(1)
Episodic 40Ar loss	140	(3)
Diffusion mechanisms	143	(2)
Measurement of argon diffusion in silicates	145	(20)
Appendix 5.A.1 Derivation of the diffusion equation	159	(2)
Appendix 5.A.2 Separation-of-variables solution for a plane sheet	161	(2)
Appendix 5.A.3 Translation to spherical coordinates	163	(1)
Appendix 5.A.4 Sample diffusion calculation	164	(1)
40Ar/39Ar Thermochronology	165	(26)
Introduction	165	(1)
The closure temperature concept	165	(8)
Models for complex argon diffusion behavior of silicates	173	(7)
Evaluation of the multidiffusion domain and multipath models	180	(5)
Nonmonotonic thermal histories	185	(6)
Appendix 6.A.1 Closure temperature for first-order loss	185	(2)
Appendix 6.A.2 Closure temperature for volume diffusion	187	(1)
Appendix 6.A.3 Closure profiles	188	(1)