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

Abstract

Contrary to general belief, not all large igneous provinces (LIPs) are characterised by rocks of basaltic composition. Silicicdominated 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 silicicdominated LIP, related to the break-up of eastern continental Gondwana, is also significant for being the source of Ͼ 1:4 × 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 pyroclasticeffusive phase producing an essentially bimodal suite of lavas and rhyolitic ignimbrite. 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. ᭧

Rhyolitic ignimbrites in the Rogerson Graben, southern Snake River Plain volcanic province: volcanic stratigraphy, eruption history and basin evolution

“…This is consistent with conclusions from studies of other ignimbrites in the Snake River Plain volcanic province (Ekren et al 1984;Honjo et al 1992;Cathey and Nash 2004) and some large igneous provinces, such as Etendeka-Parana (Bellieni et al 1984;Milner et al 1992;Kirstein et al 2001), the Whitsunday volcanic province, Australia (Bryan et al 2000), the Keweenawan rift, Minnesota (Green and Fitz 1993), and Trans-Pecos, Texas (Henry et al 1988). …”

Depositional Environment of the Lower Cretaceous (Upper Albian) Winton Formation At Isisford, Central-West Queensland, Australia, Inferred From Sandstone Concretions

“…The formation consists of volcanolithic sandstones interbedded with mudstone and siltstone, with interstitial calcite cement, minor intraformational conglomerate, lignite, and coal, that is chemically altered in part (kaolinized and ferruginized) (Geological Survey of Queensland 1970;Watson 1973;Gray 1975;Campbell and Haig 1999). The volcanolithic component of the Winton Formation sandstones most likely originated from rift-related volcanoes in the Whitsunday Volcanic Province to the east that was carried west as sediment loads by rivers (Bryan et al 1997(Bryan et al , 2000(Bryan et al , 2012Tucker et al 2013). The Winton Formation conformably overlies the shallow marine Mackunda Formation and unconformably underlies poorly consolidated Quaternary sands, silty sandstones, and Cenozoic smectitic alluvium consisting of black cracking clays known locally as "blacksoil" (Geological Survey of Queensland 1970;Gray et al 2002;Jell 2013).…”

An Early Permian (ca. 280Ma) silicic igneous province in the Alxa Block, NW China: A magmatic flare-up triggered by a mantle-plume?

“…During the last two decades, a significant number of SLIPs have been recognized including the Tertiary Sierra Madre Occidental of Mexico (Bryan et al, 2002), the Early Cretaceous Whitsunday igneous province (Bryan, 2007;Bryan et al, 1997Bryan et al, , 2000, the Jurassic Chon Aike Province (Pankhurst et al, 1998(Pankhurst et al, , 2000, the Paleozoic KennedyConnors-Auburn province, northeast Australia (Bryan et al, 2003) and the Mesoproterozoic Gawler SLIP, southern Australia (Allen et al, 2008;Pankhurst et al, 2011b). These SLIPs are characterized by large volumes (N10 5 km 3 ), of predominantly rhyodacite-rhyolite compositions, long periods of magmatic evolution (b40 myr) and were located along paleo-or active continental margins (Bryan, 2007;Bryan et al, 2002).…”