The Whitsunday Volcanic Province, Central Queensland, Australia: lithological and stratigraphic investigations of a silicic-dominated large igneous province

被引:89
作者
Bryan, SE [1 ]
Ewart, A
Stephens, CJ
Parianos, J
Downes, PJ
机构
[1] Univ Queensland, Dept Earth Sci, St Lucia, Qld 4072, Australia
[2] Cent Norseman Gold Corp Ltd, Norseman, WA 6443, Australia
[3] QNI Ltd, Brisbane, Qld 4001, Australia
[4] Western Australian Museum Nat Sci, Dept Earth & Planetary Sci, Perth, WA 6000, Australia
基金
美国国家科学基金会;
关键词
Early Cretaceous; large igneous province; Eastern Australia; ignimbrite; volcanic evolution;
D O I
10.1016/S0377-0273(00)00157-8
中图分类号
P [天文学、地球科学];
学科分类号
07 ;
摘要
Contrary to general belief, not all large igneous provinces (LIPs) are characterised by rocks of basaltic composition. Silicic-dominated LIPs, such as the Whitsunday Volcanic Province of NE Australia, are being increasingly recognised in the rock record. These silicic LIPs are consistent in being: (1) volumetrically dominated by ignimbrite; (2) active over prolonged periods (40-50 m.y.), based on available age data; and (3) spatially and temporally associated with plate break-up. This silicic dominated LIP, related to the break-up of eastern continental Gondwana, is also significant for being the source of > 1.4 x 10(6) km(3) of coeval volcanogenic sediment preserved in adjacent sedimentary basins of eastern Australia. The Whitsunday Volcanic Province is volumetrically dominated by medium- to high-grade, dacitic to rhyolitic lithic ignimbrites. Individual ignimbrite units are commonly between 10 and 100 m thick, and the ignimbrite-dominated sequences exceed 1 km in thickness. Coarse lithic lag breccias containing clasts up to 6 m diameter are associated with the ignimbrites in proximal sections. Pyroclastic surge and fallout deposits, subordinate basaltic to rhyolitic lavas, phreatomagmatic deposits, and locally significant thicknesses of coarse-grained volcanogenic conglomerate and sandstone are interbedded with the ignimbrites. The volcanic sequences are intruded by gabbro/dolerite to rhyolite dykes (up to 50 m in width), sills and comagmatic granite. Dyke orientations are primarily from NW to NNE. The volcanic sequences are characterised by the interstratification of proximal/near-vent lithofacies such as rhyolite domes and lavas, and basaltic agglomerate, with medial to distal facies of ignimbrite. The burial of these near-vent lithofacies by ignimbrites, coupled with the paucity of mass wastage products such as debris-flow deposits indicates a low-relief depositional environment. Furthermore, the volcanic succession records a temporal change in: (1) eruptive styles; (2) the nature of source vents; and (3) erupted compositions. An early explosive dacitic pyroclastic phase was succeeded by a later mixed pyroclastic-effusive phase producing an essentially bimodal suite of lavas and rhyolitic ignimbrite. From the nature and distribution of volcanic lithofacies. the volcanic sequences are interpreted to record the evolution of a multiple vent, low-relief volcanic region, dominated by several large caldera centres. (C) 2000 Elsevier Science B.V. All rights reserved.
引用
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页码:55 / 78
页数:24
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