Dating of adularia and the relationship of hydrothermal events in the Lizard Complex, Cornwall

A new total degassing argon-40/argon-39 age determination is given for crystals of fresh adularia from hydrothermal veins within the amphibolites near Porthkerris Point, the Lizard, Cornwall. The apparent age of 211±2 Ma obtained is regarded as a close minimum age for crystallization of the adularia. There appears to have been only one phase of crystallization of primary hydrothermal adularia, about 210–220 Ma, in the granulites and amphibolites in the vicinity of Porthkerris Point and in the gabbro of Dean quarry. Another hydrothermal event occurred c. 160–170 Ma. Younger apparent ages have been attributed to hydrothermal activity at one or more subsequent periods.