Authors / CoAuthors
Champion, D.C. | Cassidy, K.F. | Smithies, R.H.
Abstract
The timing and mechanisms of crustal growth, the role (if any) of modern-style plate tectonics and potential secular changes, during the Archaean are poorly understood. To provide constraints on these questions, we present isotopic and geochemical data for the well exposed, classic, Paleoarchean to Mesoarchean Pilbara Craton (>3.5 to <2.8 Ga), and the large, but poorly outcropping, largely Neoarchean Yilgarn Craton (>3.0 to 2.6 Ga), both in Western Australia. Both are dominated by typical Archaean granite-greenstone geology. Regional Sm-Nd data from felsic magmatism indicates both cratons are comprised of large proto-cratonic cores with relatively uniform Nd TDM model ages - c. 3.5-3.6 Ga for the eastern Pilbara, c. 3.1-3.3 Ga for the western Yilgarn. Distinct isotopic breaks separate these proto cratons from marginal terranes with both significantly younger, but also more domainally-variable, TDM model ages. The cratonic nucleii are characterised by episodic felsic magmatism spanning 650 Ma (from >3.47 Ga to 2.85 Ga) for the Pilbara Craton and 350 Ma years (3.0 Ga to 2.63 Ga) for the Yilgarn Craton. In both, this magmatism was dominated by transitional TTG-type compositions, and shows secular variations to more potassic, siliceous compositions, consistent with an increasing component of crustal reworking. Definitive arc-related magmatism, e.g., boninites, calc-alkaline andesites, sanukitoids, are largely absent. The surrounding marginal terranes are characterised by isotopically younger domains that broadly correspond to geological domains. Importantly, these domains are either characterised by primitive isotopic signatures (i.e., Nd TDM ages close to crystallisation ages), and/or contain evidence for arc-related magmatism, i.e., boninites, sanukitoids (Pilbara), calc-alkaline andesites (Yilgarn). The Pilbara cratonic nucleus is best interpreted to have formed as a result of vertical crustal growth in an episodic plume-environment. The Yilgarn cratonic nucleii possibly formed in a similar manner, though the evidence is not as clear. Subsequent marginal arc-related magmatism affected both cratons and the marginal terranes in both are best interpreted as representing lateral crustal growth and terrane accretion, not dissimilar to modern day plate tectonics. Best indications are that such accretion commenced at least by 3.2 Ga.
Product Type
nonGeographicDataset
eCat Id
64193
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
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2601
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Keywords
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- External PublicationAbstract
- ( Theme )
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- geochemistry
- ( Theme )
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- geology
- ( Theme )
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- plate tectonics
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- AU-WA
- 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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[-35.0, -20.0, 115.0, 125.0]
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