Argon methods

A popular method used to date rocks is the potassium-argon method. Potassium is abundant in rocks such as feldspars, hornblendes, and micas. The K-Ar method has been used to date the Earth and its geologic formations. It has also been applied to determine magnetic reversals that have taken place throughout the Earth s history. Another method used in geologic dating is the rubidium-strontium, Rb-Sr, method. Some of the oldest rocks on Earth have been dated with this method, providing evidence that the Earth is approximately 5 billion years old. The method has also been used to date moon rocks and meteorites. 

Evernden, J.F., Curtis, G.H., Obradovich, J. and Kistler, R., 1961. On the evaluation of glauconite and illite for dating sedimentary rocks by the potassium-argon method. Geochim. Cosmochim. Acta, 23 78-99. 

Sigurgeirsson, Th. (1962) Dating recent basalt by the potassium argon method. Report of Physical Laboratory of the University of Iceland. (In Icelandic.)... 

Potassium-argon method of geochronology. Bull. geol. Soc. Amer. 

Fritze, K., u. F. Strassmann Zur geologischen Altersbestimmung nach der Kalium-Argon-Methode. Naturwissenschaften 39, 522 (1952). 

McDougall, I. Potassium-argon ages from lavas of the Hawaiian islands. Geol. Soc. Amer. Bull. 75, 107 (1964) Determination of the age of basic igneous intrusion by the potassium-argon method. Nature [London] 190, 1184 (1961). 

Mussett AE (1969) Diffusion measurements and the Potassium-Argon method of dating. Geophys J Roy Astron Soc 18 257-303... 

McDougall I (1961) Determination of the age of a basic igneous intrusion by the potassium argon method. Nature 190 1184-1186... 

For a better understanding of the argon/argon method, it is recommended that Sect. 17.15 on potassium/argon dating be read first. The method presented below can be considered as a special variant of the K/Ar method in which the potassium content is monitored by an argon isotope that is readily formed by the neutron irradiation of potassium. 

The argon/argon method is partly based on the formation of argon-39 by irradiation of potassium-bearing samples using both thermal and fast neutrons in a nuclear reactor. The relevant reaction is... 

The system must be closed so that no parent or daughter isotopes are added or subtracted by any process other than radioactive decay. The potassium-argon method is especially risky as argon is a gas that can disappear. 

Mirkina, S. L., Gerling, E. K., Shukolyukov, Y. A. Determination of the absolute age of the alkaline complexes of the Middle Urals with the aid of the lead-isotopic and the potassium-argon methods. Geokhimiya, no. 8, 643—648 (1962). 

---