SEISMIC CONSTRAINTS ON THE CHEMICAL COMPOSITION OF THE CRUST OF THE PILBARA CRATON, NORTHWEST AUSTRALIA
SEISMIC CONSTRAINTS ON THE CHEMICAL COMPOSITION OF THE CRUST OF THE PILBARA CRATON, NORTHWEST AUSTRALIA
| dc.contributor | en-US | |
| dc.contributor | pt-BR | |
| dc.creator | DRUMMOND, B. J. | |
| dc.date | 2018-08-10 | |
| dc.date.accessioned | 2023-06-19T15:34:54Z | |
| dc.date.available | 2023-06-19T15:34:54Z | |
| dc.identifier | https://ppegeo.igc.usp.br/index.php/rbg/article/view/12198 | |
| dc.identifier.uri | https://repositorioslatinoamericanos.uchile.cl/handle/2250/6693043 | |
| dc.description | Modelling of seismic travel-times and amplitudes has shown that the crust of the Archaean Pilbara Craton of northwest Australia is two-layered. The boundary between the layers and the crust/mantle boundary are both transitional over several (2.5) kilometres. The velocity increases steadily with depth through the layers, from 6.0 km.-1 at the surface to about 6.2 km.s-1 at 10 to 12 km depth in the upper layer, and from 6.35 km.-1 at about 15 km depth in the upper parts of the lower layer to 6.6 to 6.9 km.-1 at the base of the crust at 28 to 35 km depth. Only in the deepest parts of lhe thickest crust does the crustal velocity reach 7.2 km.-1. Throughout the Pilbara Craton the velocity at any particular depth within the crust is very uniform. The crustal velocities suggest that the upper crust is of average granitic composition, and is metamorphosed to granulite facies at about 10 to 15 km depth. The proportion of garnet would increase below this depth as the metamorphic grade increases, but a slight increase in the mafic content to dioritic composition is required to increase the velocity to about 6.8 km -1. The velocities in the lower crust are too low to be caused by rocks of basaltic composition. Thus, the traditional classification of a two-layered crust into an upper, granitic, sialic layer and a lower , basaltic, simatic layer does not hold in the Pilbara Craton. The velocity contrast across the crust/mantte boundary and the sharpness of the boundary suggest that the crust/mantle boundary is a chemical discontinuity, and not a phase change to eclogite facies. The crust of the Pilbara craton is much thinner and the crust/mantle boundary much sharper than in younger Precambrian and Palaeozoic provinces in Australia, North America and Europe. Perhaps the tectonism in the Archaean was somehow different from that in younger eras and could not penetrate the velocity contrast at the base of the crust. | en-US |
| dc.description | Modelling of seismic travel-times and amplitudes has shown that the crust of the Archaean Pilbara Craton of northwest Australia is two-layered. The boundary between the layers and the crust/mantle boundary are both transitional over several (2.5) kilometres. The velocity increases steadily with depth through the layers, from 6.0 km.-1 at the surface to about 6.2 km.s-1 at 10 to 12 km depth in the upper layer, and from 6.35 km.-1 at about 15 km depth in the upper parts of the lower layer to 6.6 to 6.9 km.-1 at the base of the crust at 28 to 35 km depth. Only in the deepest parts of lhe thickest crust does the crustal velocity reach 7.2 km.-1. Throughout the Pilbara Craton the velocity at any particular depth within the crust is very uniform. The crustal velocities suggest that the upper crust is of average granitic composition, and is metamorphosed to granulite facies at about 10 to 15 km depth. The proportion of garnet would increase below this depth as the metamorphic grade increases, but a slight increase in the mafic content to dioritic composition is required to increase the velocity to about 6.8 km -1. The velocities in the lower crust are too low to be caused by rocks of basaltic composition. Thus, the traditional classification of a two-layered crust into an upper, granitic, sialic layer and a lower , basaltic, simatic layer does not hold in the Pilbara Craton. The velocity contrast across the crust/mantte boundary and the sharpness of the boundary suggest that the crust/mantle boundary is a chemical discontinuity, and not a phase change to eclogite facies. The crust of the Pilbara craton is much thinner and the crust/mantle boundary much sharper than in younger Precambrian and Palaeozoic provinces in Australia, North America and Europe. Perhaps the tectonism in the Archaean was somehow different from that in younger eras and could not penetrate the velocity contrast at the base of the crust. | pt-BR |
| dc.format | application/pdf | |
| dc.language | eng | |
| dc.publisher | Sociedade Brasileira de Geologia | pt-BR |
| dc.relation | https://ppegeo.igc.usp.br/index.php/rbg/article/view/12198/11745 | |
| dc.rights | Direitos autorais 2018 Revista Brasileira de Geociências | pt-BR |
| dc.source | Revista Brasileira de Geociências; v. 12, n. 1-3 (1982): Anais do ISAP "International Symposium on Archean and Early Proterozoic Geologic Evolution and Metallogenesis", Salvador, Bahia, Brasil - 3 a 11 setembro, 1982; 113-120 | en-US |
| dc.source | Revista Brasileira de Geociências; v. 12, n. 1-3 (1982): Anais do ISAP "International Symposium on Archean and Early Proterozoic Geologic Evolution and Metallogenesis", Salvador, Bahia, Brasil - 3 a 11 setembro, 1982; 113-120 | es-ES |
| dc.source | Revista Brasileira de Geociências; v. 12, n. 1-3 (1982): Anais do ISAP "International Symposium on Archean and Early Proterozoic Geologic Evolution and Metallogenesis", Salvador, Bahia, Brasil - 3 a 11 setembro, 1982; 113-120 | pt-BR |
| dc.source | 0375-7536 | |
| dc.subject | en-US | |
| dc.subject | pt-BR | |
| dc.title | SEISMIC CONSTRAINTS ON THE CHEMICAL COMPOSITION OF THE CRUST OF THE PILBARA CRATON, NORTHWEST AUSTRALIA | en-US |
| dc.title | SEISMIC CONSTRAINTS ON THE CHEMICAL COMPOSITION OF THE CRUST OF THE PILBARA CRATON, NORTHWEST AUSTRALIA | pt-BR |
| dc.type | info:eu-repo/semantics/article | |
| dc.type | info:eu-repo/semantics/publishedVersion | |
| dc.type | pt-BR |