Age Determinations of Rocks in the Lizard (Cornwall) Area

Abstract

A PREVIOUS attempt to date the major geological events in the Lizard area¹ using the potassium–argon total volume method on biotites and muscovites gave a Caledonian age of 391 million years for the youngest intrusivos, the Kennack Gneiss, but gave an anomalously younger age of 356 million years for the regionally metamorphosed Old Lizard Head Series. A series of independent measurements by Dodson² using the isotope dilution method gave a similar pattern with the younger age (350 million years) from muscovite from the Old Lizard Head Series and the older age (368 million years) from the Kennack Gneiss and also from biotite from the Landewednack Hornblende Schist, co-metamorphic with the Old Lizard Series. The differences between our results and those of Dodson are of the same magnitude evident in comparative measurements previously described³.