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Geological Society, London, Special Publications; 1964; v. 1; p. 43-54;
DOI: 10.1144/GSL.SP.1964.001.01.07
© 1964 Geological Society of London

Part 1: Introduction

The relationship between radiometric ages obtained from plutonic complexes and stratigraphical time

R. St J. Lambert, M.A., PH.D., F.G.S.

Department of Geology and Mineralogy, Parks Road, Oxford

For most of Phanerozoic time errors in radio- metric ages are usually approximately 3 per cent. except for Rb-Sr results from Mesozoic and Tertiary minerals, which must have high Rb/Sr ratios to give such low errors. Rates of uplift appear to be of the order of 10 cm/100 years for sustained movement; in consequence, uplift will normally take place within the error of an age except for post-Jurassic examples. The age obtained for a plutonic complex marks the time of closure of radiogenic systems: the available data indicate that this effectively takes place at about 200°C for the most retentive minerals, but this figure is subject to considerable uncer- tainty. Closure of systems at low temperatures poses several problems, which are discussed. It is concluded that there is much uncertainty about the stratigraphical meaning of ages obtained from minerals from large plutonic complexes.