Authors / CoAuthors
Gibson, G.M. | Nutman, A.
Abstract
Abstract: The multiply-deformed (D1-D3) Palaeoproterozoic Willyama Supergroup in south-central Australia incorporates upper and lower ca. 1700 Ma metasedimentary sequences with contrasting early tectonothermal histories that invite comparisons with the metamorphic core complexes and younger extensional orogens of western North America and Europe. A detachment surface of D1 age separating these two sequences has the deduced geometry of an extensional shear zone, juxtaposing rocks subjected to bimodal magmatism, sillimanite to granulite grade migmatisation, and Na-Fe metasomatism against a less intensely metamorphosed upper plate lacking both migmatites and bimodal magmatism. Syn-extensional metamorphism took place under low pressure-high temperature conditions, producing regionally extensive andalusite- and sillimanite-bearing mineral assemblages before further high grade metamorphism accompanying D2 recumbent folding and crustal thickening. D2 folding locally inverted the original D1 thermal structure so that sillimanite-grade lower plate rocks now lie structurally above andalusite-grade rocks of the upper plate, rendering recognition of the original detachment surface and associated thermal structure difficult. U/Pb dating of synextensional metabasites intruded into lower plate rocks just below the detachment surface indicate that extension and related bimodal magmatism peaked around 1690-1670 Ma. This is 70-90 m.y. earlier than some previously published 1600-1590 Ma ages for the onset of regional deformation and related low P-high T metamorphism and which we equate with events that overprinted the first phase of deformation and metamorphism at 1690-1670 Ma. A regionally extensive redox boundary associated with the detachment surface served as the locus for fluid flow and Pb-Zn mineralisation.
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nonGeographicDataset
eCat Id
42076
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
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Australia
Keywords
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- External PublicationArticle
- ( Theme )
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- structural geology
- ( Theme )
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- geochronology
- ( Theme )
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- metamorphism
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2002-12-16T00:00:00
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