Abstract

T. C. Pharaoh & W. J. Barclay write: Strachan et al. 1996 are to be congratulated for providing further details on the tectonothermal evolution of the Malverns Complex, and for constraining the provenance of detrital grains in the basal Cambrian sequence. The new data add substance to the evolution outlined by Barclay et al. in press in the forthcoming BGS memoir, the manuscript of which was supplied to the authors during their study.

As the authors have demonstrated, the >600 Ma ductile deformation of the plutonic igneous rocks of the Malverns Complex predates, and is unrelated to, the development of the latest Proterozoic (<565 Ma) terrane boundary invoked by Pharaoh et al. 1987. The ductile fabrics of the complex are not only discordant to the brittle structures of the Malvern Lineament, as recognized by Baker (1971), but are cross-cut by mafic dykes testifying to late brittle extension of the complex at about 566 Ma (Barclay et al. in press).

Contrary to the authors' inference, Pharaoh et al. 1987 did not invoke ductile deformation of the Malverns Complex during the accretion of the 566 Ma Warren House Formation marginal-basin lithosphere and somewhat older Charnwood Terrane (Pharaoh & Gibbons 1994). The latter event occurred in a more brittle tectonic regime subsequent to 566 Ma. The cause of the tectonism between 650 and 600 Ma is not clear at present, but presumably reflects compressional or transpressional deformation of the cooling Malverns calc-alkaline magmatic arc and is manifestly not related to the accretion of

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