Abstract
Early Cretaceous volcanic and hypabyssal rocks and Early-Mid Jurassic sedimentary units outcrop in the vicinity of Mts Bauple and Kanigan in the southern part of the Maryborough Basin.The previously undivided hypabyssal intrusions are defined as separate units on the basis of detailed mapping. Mineral assemblages and geochemistry have revealed that mineralogically and geochemically, the Mt. Bauple Syenite is in fact a granite and similarly the diorite in the Mt. Bauple area is a monzodiorite. The Rossendale Beta Rhyolite and the microgranite around Mt. Bauple are shown to be a single intrusive unit, referred to as a quartz porphyry. The volcanic units in the Mt. Bauple area are not as extensive as previously inferred. Volcanic sequences are more extensive in the Mt. Kanigan area further to the south, however, and include andesite lavas and crystal and lithic ignimbrites.All but the quartz porphyry igneous units are related by fractional crystallisation. The volcanic rocks in both regions are part of the Graham's Creek Volcanics with the monzodiorite and hornblende porphyry intrusions representing the magma chamber from which they were derived. The quartz porphyry is shown to be unrelated to the other igneous units. The Maryborough Basin formed in response to rifting of the eastern Australian margin and the volcanic and hypabyssal units represent the igneous activity associated with this rifting. These igneous units are analogous to those in the Whitsunday and Proserpine regions and represent the re-melting of older calc-alkaline material.
Published Version
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