Authors / CoAuthors
Drummond, B.J.
Abstract
Two Archaean cratons are exposed in the Precambrian shield of Western Australia: the Pilbara in the north and the Yilgarn in the south. They are separated by the Capricorn Orogen. Seismic recordings of quarry blasts in the north of the West Australian shield indicate that the upper crustal rocks have seismic velocities of 6.0 km s^-1, and are probably of acid to intermediate chemical composition. They overlie a lower crust, presumed to be granulitic, which has a seismic velocity of 6.4 km s^-1 at 13 km depth in the north of the Pilbara Craton and 16 km in the north of the Yilgarn Craton. The northern Yilgarn has a third layer, with a seismic velocity of about 7.0 km s^-1, at the base of the crust. This may represent a higher grade (eclogite?) phase, or it may indicate injection of basic material into the base of the crust. The crust-mantle boundary at the base of the Pilbara Craton and Capricorn Orogen appears to be transitional - it shows velocity gradients rather than a first-order velocity discontinuity. Within the Pilbara Craton, the crust is about 28 km thick in the north and 33 km in the south. South of the Pilbara Craton, the crust thickens under the Capricorn Orogenic Belt, and again under the northern Yilgarn Craton where it is 52 km thick. The form of the structures in the zone of thickening cannot be determined uniquely from the present data. Three models incorporating faults or monoclines and a wedge of 7.0 km s^-1 material at the base of the crust have been derived. The different crustal thicknesses of the cratons suggest that they formed separately and were then tilted towards the Orogenic Belt.
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document
eCat Id
81000
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
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Keywords
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- GA PublicationJournal
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- WA
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_External
Publication Date
1979-01-01T00:00:00
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geoscientificInformation
Series Information
BMR Journal of Australian Geology and Geophysics 4:3:171-180
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Unknown
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Extents
[-27.0, -20.0, 115.0, 121.0]
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