GEOSCAN, résultats de la recherche


TitreCharacterization of the upper mantle beneath the Archean Slave Craton using teleseismic methods
AuteurBank, C -G; Bostock, M G; Ellis, R M; Cassidy, J F
SourceSeismological Research Letters vol. 70, 1999, 1 pages
Séries alt.Secteur des sciences de la Terre, Contribution externe 20090166
RéunionSeismological Society Of America Annual Meeting; US; 1999
Documentpublication en série
Mediapapier; en ligne; numérique
ProvinceTerritoires du Nord-Ouest
SujetsArchéen; structure de la croûte; croûte continentale; études de la croûte; lithosphère; évolution tectonique; milieux tectoniques; interprétations tectoniques; interpretations sismiques; levés sismiques; Craton de Slave ; tectonique; géophysique; Précambrien
Résumé(disponible en anglais seulement)
A temporary array, consisting of 13 broadband seismic stations, recorded teleseisms between November 1996 and May 1998. This data set has been augmented by recordings from the Yellowknife seismic array. The objective of our study is to determine upper mantle structure below the Archean Slave craton, site of the oldest known rocks on Earth and numerous diamondiferous kimberlites, and thence to gain an understanding of early crust formation and kimberlite genesis. Tomographic travel-time inversion indicates variations in P-wave velocity of up to 3%. A high velocity anomaly underlies much of the oldest portion of the Slave craton (the Anton terrane), and extends to near 250 km depth. We interpret this to represent the approximate thickness of the cool subcratonic lithosphere, in agreement with results from magnetotelluric and petrological studies. Low velocities occur along an E-W trending corridor near 65N, and may be associated with kimberlite magmatism in the Lac de Gras area. SKS-splitting analysis yields moderate delay times (~1s), and fast directions at all stations that are approximately parallel to the plate motion of North America. This direction is oblique to the Bathurst Fault and MacKenzie dike swarms, suggesting that neither continental collision to the east nor plume interaction to the north has had major effect on the bulk lithospheric fabric beneath the Slave province. A scatter in splitting direction of 30 degrees for events from varying azimuths may be due to complex anisotropic stratification known to occur in the mantle beneath Yellowknife. Simultaneous deconvolution of P-coda for receiver functions reveals a Moho depth ranging from 36 to 42km within the Slave craton. P-to-S conversions from the 410 km and 660 km discontinuities can be identified at several stations and where present are $\sim$1s faster than predicted by IASP91. This is in accordance with high absolute velocities generally observed for upper mantle beneath cratons.