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
Related Links

Product Type/Sub Type

nonGeographicDataset

Constraints

Creative Commons Attribution 4.0 International Licence

IP Owner

Commonwealth of Australia (Geoscience Australia)

Author(s)

Date (publication)

1983-01-01T00:00:00

Product Type

nonGeographicDataset

Topic Category

geoscientificInformation

GA Catalogue Number

81132 Product http://www.ga.gov.au/metadata-gateway/metadata/record/81132/

Keywords

GA Publication
Journal
WA
Earth Sciences

Resource Language

English

Resource Character Set

utf8

Resource Security Classification

unclassified

Geographic Extent

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

Lineage

Unknown

Digital Transfer Options

onLine

Distributor

Role
distributor
Organisation Name
Commonwealth of Australia (Geoscience Australia)
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address

Source Description

Source data not available.

Metadata File Identifier

fae9173a-7049-71e4-e044-00144fdd4fa6

Metadata Standard Name

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

Metadata Standard Version

1.1

METADATA SECURITY CLASSIFICATION

unclassified

Metadata Contact

Role
pointOfContact
Organisation Name
Commonwealth of Australia (Geoscience Australia)
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address
Related Links