Abstract
Three ring-complexes are considered as possible sources for the volcanic sequences of the Lamington Group and Main Range Volcanics, all of Lower Miocene age. The Lamington Group lavas comprise transitional tholeiitic basalts and rhyolites with alkali basalts at the base; the Main Range Volcanics are an alkali olivine basalt - trachyte - soda rhyolite association. The Mt. Warning intrusive complex is thought to be the source of most of the lavas of the Lamington Group. It consists largely of plutonic rocks which have probably moved upwards by ring-faulting determining the initiation of erosion of the wide caldera in which the complex lies. Most of the members of the Mt. Barney complex preceded the Lamington Group lavas; the Mt. Alford complex was synchronous with the Main Range lavas, but is unlikely, from structural considerations, to have contributed to them. The two major volcanic groups are compared with each other and with the intrusive rocks of Mt. Warning and Mt. Alford by an alkali-silica diagram and 0 values.
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