eCite Digital Repository

Origin of high-Si dacite from rhyolitic melt: evidence from melt inclusions in mingled lavas of the 1.6 Ga Gawler Range Volcanics, South Australia


Kamenetsky, VS and Morrow, NA and McPhie, J, Origin of high-Si dacite from rhyolitic melt: evidence from melt inclusions in mingled lavas of the 1.6 Ga Gawler Range Volcanics, South Australia, Mineralogy and Petrology, 69, (3/4) pp. 183-195. ISSN 0930-0708 (2000) [Refereed Article]

DOI: doi:10.1007/s007100070020


Part of the Mesoproterozoic (1.6Ga) Gawler Range Volcanics in South Australia is composed of mingled feldspar- quartz- phyric dacite, rhyodacite and rhyolite lavas. Field relationships suggest that dacite erupted first, locally grading into rhyodacite, followed by mingled dacite and rhyolite or rhyodacite and rhyolite, and finally in some areas rhyolite, and imply that the three lithofacies co-existed in a compositionally stratified magma chamber. Data on the bulk rock, groundmass and melt inclusion compositions suggest that post-eruption alteration has had very little effect on the original rock compositions. Melt inclusions in quartz from rhyolite and rhyodacite-dacite, respectively, belong to two compositional populations. Inclusions in the rhyolitic quartz have less evolved compositions with lower SiO 2 (72-76.4 wt%) and higher Al 2 O 3 (13.2-15.6wt%) and Na 2 O (2.5-4.2wt%) abundances. In contrast, melt inclusions in quartz from the rhyodacite-dacite are more "evolved" (i.e., 75.5-78.3 wt% SiO 2 , 11.2-12.7 wt% Al 2 O 3 and 1.7-2.2 wt% Na 2 O). The two melt populations define a single compositional trend towards groundmass compositions, which are essentially similar in all three lithofacies (77.8-80.5 wt% SiO 2 , 9.9-11.1 wt% Al 2 O 3 and 2.2-2.4 wt% Na 2 O). This trend is consistent with the derivation of the groundmass melt from a single precursor melt of rhyolitic composition by means of crystallisation of dominant plagioclase, K-feldspar and minor quartz. Plagioclase-enriched dacite-rhyodacite magma comprises a mixture of the residual melt and plagioclase phenocrysts that accumulated in the upper part of the magma chamber and erupted first. Similar residual melt containing quartz and K-feldspar phenocrysts was present deeper in the magma chamber and erupted later to form quartz-, K-feldspar-phyric rhyolite.

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:Kamenetsky, VS (Professor Vadim Kamenetsky)
UTAS Author:Morrow, NA (Ms Nicole Morrow)
UTAS Author:McPhie, J (Professor Jocelyn McPhie)
ID Code:20530
Year Published:2000
Web of Science® Times Cited:11
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2000-08-01
Last Modified:2010-08-25

Repository Staff Only: item control page