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The Eucarro Rhyolite, Gawler Range Volcanics, South Australia: A > 675 km3, compositionally zoned lava of Mesoproterozoic age


Allen, SR and McPhie, J, The Eucarro Rhyolite, Gawler Range Volcanics, South Australia: A > 675 km3, compositionally zoned lava of Mesoproterozoic age, Bulletin of Geological Society of America, 114, (12) pp. 1592-1609. ISSN 0016-7606 (2002) [Refereed Article]

DOI: doi:10.1130/0016-7606(2002)114<1592:TERGRV>2.0.CO;2


The Eucarro Rhyolite is remarkable in being far more voluminous (>675 km3) and extensive than most felsic lavas (<1 km3). Its dimensions are comparable to the largest known volcanic units (felsic ignimbrites and flood basalts). It is one of several voluminous felsic units within the Mesoproterozoic (ca. 1592 Ma), Gawler Range Volcanics, an intracontinental, intraplate volcanic province in South Australia and is typical of the voluminous felsic magmatism associated with Laurentia (cf. Belt Super-group, Midcontinent United States). The lava is ∼300 m thick, with ground-mass textures and lithofacies characteristics consistent with cooling and degassing as a single unit. There are gradational compositional and textural variations throughout its highly elongate distribution (∼225 km east-west, <15 km north-south). Although predominantly rhyolitic (71-72 wt% SiO2), the base is more silica rich (72-74 wt% SiO2), and compositional flow banding along the northern margin involves higher SiO2 rhyolite (>74 wt% SiO2). Pyroxene is the dominant ferromagnesian phase, but at the base in the west, primary amphibole and olivine are present. Granitic and mafic clasts are ubiquitous but most abundant (∼5 vol%) in western and eastern parts of the unit. The main Eucarro magma was compositionally zoned, and several smaller batches of compositionally distinct magma were tapped during the eruption. Concentrations of granitic clasts coincide with changes in bulk composition and may record the rupture of wall rock between nearby but separate magmas. The distribution, subtle lateral variations in composition and texture, and local presence of compositional flow banding along the northern margins suggest that the Eucarro Rhyolite was derived from several source vents located along an east-trending fissure(?) system. Although very widespread, outflow of the Eucarro lava was probably no more than a few tens of kilometers from source vents.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geology
Research Field:Volcanology
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the earth sciences
UTAS Author:Allen, SR (Dr Sharon Allen)
UTAS Author:McPhie, J (Professor Jocelyn McPhie)
ID Code:24715
Year Published:2002
Web of Science® Times Cited:43
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2002-08-01
Last Modified:2007-10-12

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