PAPERS Department of Geology
PAPERS Department of Geology University of Queensland Volume 11 Number 3 PAPERS Department of Geology • University of Queensland VOLUME 11 NUMBER 3 Cainezoic volcanic centres in southeastern Queensland, with special reference to the Main Range, Bunya Mountains, and the volcanic centres of the northern Brisbane coastal region. A. EWART and A. GRENFELL P. 1 - 57 Upper Mantle xenoliths and megacrysts and the origin of the Brigooda basalt and breccia, near Proston, Queensland. A.D. ROBERTSON, F.L. SUTHERLAND and J.D. HOLLIS P. 58 - 71 Cainozoic volcanic rocks in the Bundaberg-Gin Gin-Pialba area, Queensland P. 72 — 92 A.D. ROBERTSON 1 CAINOZOIC VOLCANIC CENTRES OF SOUTHEASTERN QUEENSLAND WITH SPECIAL REFERENCE TO THE MAIN RANGE, BUNYA MOUNTAINS AND THE VOLCANIC CENTRES OF THE NORTHERN BRISBANE COASTAL REGION by A. Ewart and A. Grenfell ABSTRACT Remnants of the Miocene-Oligocene volcanism occur as large eroded shield volcanoes, complex lava fields, ring complexes, and as localised domes, plugs, laccoliths, sills, and dykes. Descriptions are presented of the field and age relations, mineralogy, and chemistry of three major occurrences. The Main Range volcanic province extends approximately 120 km NNW-SSE, averaging 35 km in width, with a maximum thickness of 900 m. Two formations are recognised, the lower formation ranging between 24.0 — 25.6 Ma, and the upper formation between 18.1 — 24.0 Ma. The former consists of a mildly alkaline basalt-comendite association, and includes hawaiites, mugearites, benmoreites, and trachytes. The upper formation consists of hawaiites, alkali olivine basalts, mugearites, and rarer undersaturated lavas; the latter eruptives contain megacryst and xenolith suites dominated by spinel lherzolites , but including various clino pyroxenite types, some amphibole-bearing.
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