S-type ignimbrites with polybaric crystallisation histories: the Tolmie Igneous Complex, Central Victoria, Australia

The Late Devonian Tolmie Igneous Complex (in north-eastern Victoria, Australia) contains S-type, intracaldera, rhyolitic ignimbrites with multiple generations of phenocrysts of biotite, garnet, cordierite and orthopyroxene; one unit also contains fayalitic olivine. Geothermometry and calculated phas...

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Bibliographic Details
Published in:Contributions to mineralogy and petrology 2011-12, Vol.162 (6), p.1315-1337
Main Authors: Clemens, J. D., Birch, W. D., Dudley, R. A.
Format: Article
Language:English
Subjects:
Crystallization
Devonian
Earth and Environmental Science
Earth Sciences
Fractionation
Geochemistry
Geology
Magma
Mineral Resources
Mineralogy
Original Paper
Petrology
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Summary:The Late Devonian Tolmie Igneous Complex (in north-eastern Victoria, Australia) contains S-type, intracaldera, rhyolitic ignimbrites with multiple generations of phenocrysts of biotite, garnet, cordierite and orthopyroxene; one unit also contains fayalitic olivine. Geothermometry and calculated phase relations indicate high- T deep- to mid-crustal origins for the magmas, with crystallisation at several levels. At least four separate magma groups make up the complex. Compositional variations within and between ignimbrites are adequately modelled by selective entrainment of peritectic garnet, ilmenite, orthopyroxene and plagioclase into the magmas. Neither crystal fractionation nor mafic-felsic magma mixing played a role. Chemical and isotope data suggest that the magma sources were once variably Ba-enriched arc greywackes with different proportions of clay. The deep origin of some of the Tolmie Complex magmas means that supracrustal rocks underlie parts of north-eastern Victoria at depths of around 35 km. This has important implications for understanding the region’s tectonic development.
ISSN:0010-7999
1432-0967
DOI:10.1007/s00410-011-0652-1