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Geological Society, London, Special Publications; 1969; v. 3; p. 157-195;
DOI: 10.1144/GSL.SP.1969.003.01.09
© 1969 Geological Society of London

Historical Analysis of Orogenic Belts

A new approach to radio-isotopic dating in orogenic belts

F. J. Fitch, B.Sc. F.G.S., J. A. Miller, Ph.D. F.G.S. F.C.S. & J. G. Mitchell, Ph.D.

Birkbeck College, Malet Street, London W C I
Department of Geodesy and Geophysics, Madingley Road, Cambridge
Radiobiological Research Unit, Harwell, Berkshire

The theory of conventional K-Ar dating and the opposed ‘overprinting’ and ‘slow-cooling’ interpretations of radio metric age sequences in orogenic belts are examined briefly. A new K-Ar age-spectrum method is described which enables intermediate ages obtained from partially overprinted rocks and minerals to be unmixed. Under ideal conditions one or both of the component ages can be determined. Applications of the K-Ar age-spectrum method to a number of dating problems in the British Caledonides are reported as examples of the importance of the new method in orogenic studies. In particular, there is a discussion of the geochronology of the Moine and Dalradian Series in Scotland and the Tanygriseau microgranite in North Wales. Finally, there is a discussion of the possible implications of the new data for orogenic theory.