A reconnaissance teleseismic study of the upper mantle and transition zone beneath the Archean Slave craton in NW Canada

Abstract

The objective of this study is to investigate 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 craton formation and kimberlite genesis. To this aim, a temporary array, consisting of 13 sites equipped with broadband seismometers, recorded teleseisms between November 1996 and May 1998. This data set has been augmented with recordings from the Yellowknife seismic array. Our three most robust observations and their interpretation are: (1) P-wave travel-time tomography reveals the oldest part of the craton, the Central Slave Basement Complex, to be underlain by the fastest seismic velocities, indicating that this block remains distinct well into mantle depths; (2) receiver function analysis requires only the Moho as major S-wave velocity discontinuity and points to a fairly constant crustal thickness throughout the Slave province; and (3) SKS splitting analysis shows little variation in delay times and fast polarization directions across the array, leading us to conclude that the present-day plate motion of North America is the primary cause for mantle fabric beneath the entire array. Furthermore, the data let us rule out the possibility that the Mackenzie plume had any seismologically detectable effect on the Slave lithosphere. More speculative results of our investigation, namely a possible genetic link between a low seismic velocity anomaly at depth with the overlying Lac de Gras kimberlite field, and a possible Archean origin of two shallow low-velocity anomalies, will require further investigation.