The Petrology of the Warren House Series, Malvern

Extract

THE Warren House Series consists of lavas which belong to a sodic suite, being rhyolites, keratophyres, and spilites. The rhyolites have a fine-grained micrographic groundmass, and some contain phenocrysts of quartz, orthoclase, anorthoclase, and plagioclase felspar. Epidotization of the rocks has occurred, but it is the felspathic and femic constituents of the groundmass which have suffered alteration and not the felspar phenocrysts, the action not being intense enough to affect the latter. The keratophyres consist essentially of small lath-shaped albite crystals which give a trachytic texture to the rock. The spilites are more basic, vesicular, and variolitic or sub-ophitic in texture, while some of them show pillowstructure in the field. The keratophyres and the spilites also exhibit varying degrees of epidotization. Pyroclastic rocks are not very common, but a few interesting varieties have been noted. Intrusions of dolerite occur within the lavas. One type is an ophitic dolerite, which when fresh probably contained olivine. Another type is now an epidiorite. Both these types have been epidotized, the epidiorite to such an extent that it passes into an epidote-uralite rock in places.