Archaean granites of the Yilgarn and Pilbara cratons, Western Australia  

Authors / CoAuthors

Champion, D.C. | Smithies, R.H.

Abstract

The current perception is that rocks of the tonalite-trondhjemite-granodiorite (TTG) suite are the dominant Archaean granite type, that only become less important towards the end of the Archaean with the onset of significant reworking of older continental crust and the production of more potassic granites. This broadly established sequence is, however, oversimplified. Clearly different granites, including high-Mg varieties, alkaline/sub-alkaline granites, and granites with A-type affinities, are also important in the Archaean. More importantly, the increasing recognition of granites with evidence for an enriched-mantle component is providing constraints on both crustal growth mechanisms and on possible tectonic environments. Archaean granites in Australia are best known from the Pilbara and Yilgarn Cratons, Western Australia. Both are examples of Archaean granite-greenstone terrains dominated (>65%) by granites (and orthogneisses). This paper compares and contrasts granites from the central and eastern parts of the Pilbara Craton (CEP) with those from the Eastern part of the Yilgarn Craton (EY). Geological data combined with a compilation of >1200 geochemical analyses are utilised to identify both broad regional granite groups and secular changes within the both regions. Although the cratons exhibit different pre-histories it is notable that they share a somewhat similar pattern of granite evolution. It is clear that the granite types in both the CEP and EY exhibit an overall tendency to become more potassic (higher LILE contents), but also more variable in composition with time. This reflects initial continental crustal growth, and subsequent reworking, to produce an increasingly mature and heterogeneous crust, occurring over a long period (eastern CEP), or very rapidly (EY, western CEP). There is also increasing evidence for enriched-mantle components in post 3.0 Ga magma production, in both the CEP and EY, that probably reflect subduction-environment processes. Finally, it is evident that TTG magmatism, often regarded as a voluminous characteristic of Archaean terrains, is, at the present exposure level, relatively poorly represented in both the Pilbara and Yilgarn cratons, and particularly the latter. Volumetrically, more important in these regions, are granites with a high pressure signature, that fall into a more felsic more potassic (LILE-richer) group, best thought of as transitional TTGs. The presence of such granites can be taken as indicative of the involvement of pre-existing felsic crust at the time of their genesis, unlike more typical TTGs.

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nonGeographicDataset

eCat Id

37303

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Keywords

• GA PublicationConference Paper

( Theme )

• geochemistry

( Theme )

• geology

( Theme )

• geochronology

• AU-WA

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

Publication Date

2001-01-01T00:00:00

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Australian Government Security ClassificationSystem    

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Creative Commons Attribution 4.0 International Licence    

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unknown

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geoscientificInformation

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[-34.0, -20.0, 116.0, 124.0]

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