Regional prograde pumpellyite actinolite facies metamorphism (Ml) has affected the Gramscatho Group sediments and volcanics structurally underlying the Lizard Complex. Metamorphism took place synchronously with the main penetrative deformation (Dl). There is no evidence of any increase in the regional gradient towards the Lizard Complex or of any local thermal overprinting. It is concluded that the Lizard Complex was emplaced in a cooled thrust sheet during Dl deformation during a regional heat flow which produced very low grade metamorphism. Temperatures of 250–350°C and a pressure of several kilobars are estimated.