Authors / CoAuthors
Budd, A.R.
Abstract
Felsic units of the Hiltaba Association Granites and the comagmatic Gawler Range Volcanics (together the GRHVP) can be divided into four supersuites: the I-type Malbooma and Jenners Supersuites; and the A-type Roxby and Venus Supersuites. All units are aged between ~1595 - 1575 Ma. Major and trace element modelling of granites of both the strongly fractionated and evolved Malbooma and moderately fractionated and evolved Jenners Supersuites suggests derivation by crystal fractionation from granodiorite compositions. Neodymium isotopes of the granites and volcanics indicate a more primitive Nd input than available from the known Archaean and Palaeoproterozoic crust alone. However, these felsic rocks are thought to be derived by partial melting of granodiorite compositions, rather than being the result of extensive fractionation from basalts. Mafic rocks of the GRHVP have variable isotopic and chemical signatures. The Lady Jane Diorite at Tarcoola has Nd ~0.2, and a composition incompatible with OIB derivation, but compatible with partial melting of a crustally-contaminated MORB. Some of the alkaline mafic/ultramafic rocks have Nd values as high as +4 [1]. Maximum zircon saturation temperatures of ~800C and ~900C for the I- and A-type supersuites respectively, are significantly lower than those of ~1000C measured by other geothermometers [2] for the Yardea Dacite (Roxby Supersuite), but show that the A-type supersuites were higher temperature than the I-type supersuites. The distribution of high temperature A-type granites shows some correlation with areas of coeval iron oxide copper-gold mineralisation. The coincidence of very high temperature granites with crustal Nd signatures, and mafic rocks with primitive to weakly evolved signatures indicates an extensional environment with very elevated geotherm and mantle upwelling. However, the felsic rocks are dissimilar to those associated with mantle plumes, and therefore a back arc distal to a continental-oceanic subduction zone setting is suggested, perhaps analagous to the present Altiplano Puna region of the Central Andes.
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nonGeographicDataset
eCat Id
64151
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
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Keywords
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- External PublicationAbstract
- ( Theme )
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- economic geology
- ( Theme )
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- geochemistry
- ( Theme )
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- metallogenesis
- ( Theme )
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- plate tectonics
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- AU-SA
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2006-01-01T00:00:00
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geoscientificInformation
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[-35.0, -28.0, 132.0, 138.0]
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