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TitleStacked uppermost mantle layers within the Slave craton of NW Canada as defined by anisotropic seismic discontinuities
AuthorSnyder, D B
SourceTectonics vol. 27, TC4006, 2008 p. 1-20,
Alt SeriesEarth Sciences Sector, Contribution Series 20060656
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formathtml; pdf
ProvinceNorthwest Territories; Nunavut
NTS75; 76; 85; 86
AreaMacKay Lake
Lat/Long WENS-120.0000 -104.0000 68.0000 60.0000
Lat/Long WENS-120.0000 -104.0000 68.0000 60.0000
Subjectstectonics; geophysics; structural geology; tectonic history; mantle; discontinuities; Mohorovicic discontinuity; anisotropy; lithosphere; seismic arrays; geophysical interpretations; seismic interpretations; earthquakes; modelling; models; structural analyses; structural features; subduction zones; rifts; tectonic interpretations; tectonic elements; tectonic models; tectonic setting; tectonic stages; stockworks; igneous rocks; intrusive rocks; intrusions; plutons; dykes; kimberlites; diamond; harzburgites; eclogites; carbon; garnet; geochemical analyses; igneous petrology; crustal studies; crustal thickness; crustal evolution; crustal structure; sutures; plate tectonics; plate boundaries; plate margins; geochronometry; radiometric dating; Archean; Slave Craton; Wopmay Orogen; Central Slave Basement Complex; POLARIS Slave Array; Lac de Gras kimberlite field; Diavik diamond mine; Ekati diamond mine; Gahcho Kué diamond mine; Jericho diamond mine; Snap Lake diamond mine; Great Slave Lake Shear Zone; Wopmay Fault Zone; Great Bear Arc; Taltson Magmatic Zone; Thelon Magmatic Zone; Thelon Front; Bathurst Fault Zone; Coronation Supergroup; wehrlite; cratonization; Paleoproterozoic; Precambrian; Proterozoic
Illustrationssketch maps; cross-sections; models; tables; spectra; profiles; graphs
ProgramNorthern Resources Development Program
LinksPOLARIS Consortium
AbstractA 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.