Abstract

Dr J. R. Vearncombe writes: Hailwood et al. 1984 present a number of palaeomagnetic pole determinations for the Lizard Complex (SW England). Although the data presented are coincident with the Permian geomagnetic field direction for SW England, they reject the concept of the 370Ma Lizard Complex being remagnetized in the early Permian and prefer to apply a 90° tilt correction to their data, which leaves their geomagnetic field direction in close coincidence with the mean U.K. pole direction for the Silurian-Devonian interval. It is the applicability of the 90° rotation which I wish to discuss here

Hailwood et al. 1984 state that 'convincing arguments have been put forward by Kirby (1979) that the uppermost sheet of the Lizard Complex was turned on its side during emplacement'. In fact this theory was rejected by Bromley (1979), who shows that if such a mechanism had operated it would imply that either the overlying dykes were originally emplaced as a series of inclined sheets, fortuitously re-oriented into a vertical position, or that the dykes were intruded after the gabbro had been rotated. This second possibility must be rejected because of the coincidence of the geomagnetic pole directions for both the dykes and gabbro. The other possibility of a fortuitous re-orientation must also be rejected because the orientation of igneous layering cannot be used to denote palaeohorizontal. Campbell (1978) recognized nearly vertical primary layering in the Jimberlana intrusion (Australia), and Casey & Karson (1981) and Rothery (1983) have shown that magma chambers from both

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