GEOSCAN, résultats de la recherche


TitreStacked uppermost mantle layers within the Slave craton of NW Canada as defined by anisotropic seismic discontinuities
AuteurSnyder, D B
SourceTectonics vol. 27, TC4006, 2008 p. 1-20,
LiensPOLARIS Consortium
Séries alt.Secteur des sciences de la Terre, Contribution externe 20060656
ÉditeurAmerican Geophysical Union
Documentpublication en série
Mediapapier; en ligne; numérique
Formatshtml; pdf
ProvinceTerritoires du Nord-Ouest; Nunavut
SNRC75; 76; 85; 86
Lat/Long OENS-120.0000 -104.0000 68.0000 60.0000
Lat/Long OENS-120.0000 -104.0000 68.0000 60.0000
Sujetsantécédents tectoniques; manteau terrestre; discontinuités; discontinuité de Mohorovicic; anisotropie; lithosphère; rangées sismiques; interprétations géophysiques; interpretations sismiques; secousses séismiques; établissement de modèles; modèles; analyses structurales; caractéristiques structurales; zones de subduction; crevasses; interprétations tectoniques; éléments tectoniques; modèles tectoniques; cadre tectonique; stades tectoniques; eprentes; roches ignées; roches intrusives; intrusions; plutons; filons rocheux; kimberlites; diamant; harzburgites; éclogîtes; carbone; grenat; analyses géochimiques; pétrologie ignée; études de la croûte; épaisseur de la croûte; evolution de la croûte; structure de la croûte; sutures; tectonique de plaques; frontières de plaques; marges plaques; géochronométrie; datation radiométrique; Archéen; Craton de Slave ; Orogène de Wopmay ; Complexe de Central Slave Basement ; Champ de kimberlite de Lac de Gras; Mine de diamants Diavik; Mine de diamants Ekati; Mine de diamants Gahcho Kue; Mine de diamants Jericho; Mine de diamants Snap Lake; Zone de cisaillement de Great Slave Lake ; Zone de faille de Wopmay ; Arc de Great Bear ; Zone de Taltson Magmatic ; Zone de Thelon Magmatic ; Front Thelon; Zone de faille de Bathurst ; Supergroupe de Coronation ; tectonique; géophysique; géologie structurale; Précambrien; Protérozoïque
Illustrationssketch maps; cross-sections; models; tables; spectra; profiles; graphs
ProgrammeLa mise en valeur des ressources du Nord
Diffusé2008 07 23
Résumé(disponible en anglais seulement)
A 20-station seismic array in NW Canada recorded 336 teleseismic events with distribution in back azimuth and epicentral distance sufficient to characterize uppermost mantle discontinuities between depths typical of the Mohorovicic and Lehman discontinuities. Following wavefield decomposition, groups of seismograms were source-normalized through simultaneous deconvolution to estimate the
near-receiver impulse response and thus detect major discontinuities beneath each seismic station. Stations within the Lac de Gras kimberlite field display an unusually strong negative impulse on the radial component within the NW quadrant and two moderate impulses on the transverse component. Forward modeling of these impulses suggests a mantle layer dipping at 22° to the southeast with a mildly anisotropic (2%) upper discontinuity at 120-135 km depth and another mildly anisotropic (2%) discontinuity at about 170 km depth. Superimposed on these layers is another, stronger anisotropic (4%) layer between 110 and 180 km depths that dips to the west. Stations outside of the Lac de Gras field, but within the southeastern Slave craton, display more numerous, but weaker, impulses. The most prominent of these occurs at about 150 km depth on the transverse component and has opposite polarity to that observed farther north. The prominent negative impulse observed on the radial component is interpreted to arise from structural-preferred orientation in the form
of a stockwork of wehrlite dykes beneath the Lac de Gras field. Interpretation of the other layers in the context of known surface geology as well as xenolith petrology and garnet geochemistry of diamondiferous kimberlites favors previous suggestions that they represent 4000-2900 Ma depleted harzburgite and eclogite layers underthrust from the northwest at 2600 or 1880 Ma. The layer beneath the SE Slave craton has a similar, but distinct, tectonic history of NW-verging underthrusting associated with the 2635-2615 Ma Defeat Suite of plutonism. Taken together, these interpretations indicate that the Slave craton was assembled from at least four lithospheric blocks prior to its cratonization about 2580 Ma: each block is 90-120 km thick, and all four blocks abut across a steep suture boundary beneath MacKay Lake in the central Slave craton. Significant amounts of carbon and eclogites could have become incorporated into the central Slave mantle within the diamond stability field during the proposed underthrusting of lithosphere to explain their relatively common occurrence in
kimberlite eruptions within the Slave craton.