Isotopic age-determinations of rocks from the British Isles, 1955–64

Abstract

Over 475 individual age-determinations of British rocks, recorded in some sixty papers, have appeared during 1955–64, the decade in which isotopic dating reached practical maturity and began to have great effect in establishing the scale of events in historical geology, including that of the Pre-Cambrian. The willing co-operation of all the British laboratories in which isotopic ages are determined has enabled abstracts of these papers to be prepared for publication; the emphasis of the abstracts lies in the geological implications. In an introductory section (by P. A. Sabine& J. Watson), the number of determinations of British rocks is plotted against apparent ages. The resulting histograms are broadly similar to those derived from world-wide sources and from other countries, showing that they record not only the incidence of laboratory determinations but fundamentally significant geological events. Major peaks of activity are indicated, the implications of which are reviewed. Periods of plutonic activity are shown in the Lewisian at 2600 to 2200m.y. (Scourian) and 1600 to 1450m.y. (Laxfordian). Metamorphic rocks, migmatites, and granites from the Caledonian Belt are spread from about 750 to 360 m.y. with a weak maximum at 750 to 650 m.y. and a stronger one at 450 to 360 m.y. In south-west England metamorphic activity yields dates from 400 to 350m.y., and Hercynian granites dates from 300 to 250 m.y. Tertiary granites and allied rocks are mainly 65 to 50 m.y. old. In each abstract an attempt is made to include geographical locality, character and geological relationships of specimens investigated, method employed, and constants used, ages obtained, and conclusions drawn. Full indexes are provided.