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Geological Society, London, Special Publications; 1964; v. 1; p. 101-117;
DOI: 10.1144/GSL.SP.1964.001.01.11
© 1964 Geological Society of London

Part 2: Radiometric Methods with Respect to the Time-Scale

Potassium—argon methods with special reference to basic igneous rocks

John Alfred Miller, M.SC., PH.D., F.G.S.

Department of Geodesy and Geophysics, Madingley Rise, Madingley Road, Cambridge

Frank John Fitch, B.SC., F.G.S.

Department of Geology, Birkbeck College, Malet Street, London, W.C.1.

The theory, analytical method, and experimental errors of potassium–argon radiometric age-determination are briefly reviewed. The choice of suitable material for analysis and the application of the method to basic igneous and other rocks using whole-rock samples are described. ‘Discrepancy’ in potassium-argon age-determination is defined; geological factors that control the accuracy of potassium-argon ages, and must be taken into consideration in their interpretation, are discussed. It is asserted that, in favourable circumstances, potassium-argon age studies can provide a wide variety of alternative information of geological significance as well as, or instead of, indicating the initial age of consolidation of a rock: in particular, that it is possible to define the dates of subsequent cleavage, metasomatism, or metamorphism from a consideration of the discrepantly low ages obtained from older rocks.