Citation

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Drummond, B.J., 1983. Detailed seismic velocity/depth models of the Upper lithosphere of the Pilbara Craton, Northwest Australia. BMR Journal of Australian Geology and Geophysics  8:1:35-51. Bureau of Mineral Resources, Geology and Geophysics, Canberra.

Abstract

Detailed velocity/depth models of the crust of the Pilbara Craton have been produced from amplitude studies of refracted and reflected seismic waves and their travel-times. On three profiles, a near-surface high-velocity layer, in which the velocity sometimes reaches 6.65 km s-1, is interpreted as Hamersley Basin strata overlying the crystalline basement. The seismic velocity in the near-surface crystalline basement is about 6.0 km s-1, and increases with depth through the crust, reaching 6.1-6.2 km s-1 at 11-14 km depth. Below this , at about 15 km depth, a steeper gradient to 6.35-6.45 km s-1 defines an intracrustal seismic boundary. In the lower part of the crust, velocity gradients increase the velocity to 6.6-7.2 km s-1 . In some models, second-order velocity increases with depth are used to explain bright cusps in the data. although these could also be caused by topography on the crust/mantle boundary. The crust/mantle boundary is transitional over 4-5 km, and upper mantle (Pn) velocities range from 7.5 to 8.5 km s-1 . On one profile, a sub-Moho boundary at which the velocity increases from 8.2 to 8.35 km s-1 was recognised 14 km below the crust/mantle boundary. Previously published seismic models of the region show lateral inhomogeneity in the crust of the Capricorn Orogenic Belt, and this complicates a quantitative analysis of the amplitudes of seismic signals recorded in the orogen. However, a qualitative analysis based on the observed amplitudes, the positions of the ray-critical cusps of the previously published models , and the gravity field suggests that , while the intracrustal boundary at about 15 km depth may be sharp, the lower crust in the orogen must have high seismic velocities (and densities) and the crustal thickness in the previous models is probably not an overestimate. Increasing metamorphic grade with depth in the Yilgarn Craton probably ensures positive velocity gradients in the crust in the craton , so that the crustal thickness in the previously published models is considered reasonable. Thus, the interpreted large difference in crustal thickness between the Pilbara Craton (approximately 30 km) and the Yilgarn Craton ( 50 km) is substantiated.
Google map showing geographic bounding box with values North bound -19.37 East bound 121.89 West bound 115.21 South bound -27.7
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license
Creative Commons Attribution 4.0 International Licence

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Commonwealth of Australia (Geoscience Australia)

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Date (publication)

1983

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geoscientificInformation

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GA Publication
Journal
Earth Sciences

Resource Language

English

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utf8

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unclassified

Geographic Extent

North bound
-19.37
East bound
121.89
West bound
115.21
South bound
-27.7

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Unknown

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pdf

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ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata

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1.1

Metadata Date Stamp

2015-05-19

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unclassified

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pointOfContact
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
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2601
Country
Australia
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Downloads
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