A XENOLITH-BASED LITHOSPHERIC TRANSECT OF THE SLAVE CRATON, N.W.T., CANADA

Abstract

During the last decade, the Canadian Slave craton has emerged as an important global diamond resource. Recent work on the sub-continental lithospheric mantle (SCLM) beneath this craton has yielded tantalising suggestions about its structure and composition that are of interest to the diamond mining effort. Geochemical studies of xenoliths, sulphides, diamond inclusions and mineral separates, together with teleseismic and magnetotelluric interpretations have indicated that the Slave SCLM has a unique stratified structure. This consists of a highly depleted mantle layer above ~110 km, most pronounced in the central Slave region, with a relatively ‘fertile’ layer of mantle beneath that extends to the base of the lithosphere. As diamond mining and exploration in the Slave craton matures, more samples are available for study, allowing testing of earlier models and refinements on existing geotherm estimates.
This PhD provides new silicate major and trace element compositions, thermobarometry and rhenium-osmium (Re-Os) isotope data for two new suites of peridotite xenoliths from Slave craton kimberlites (Artemisia and Diavik), as well as new Re-Os data for existing suites from Gahcho Kué (Kopylova and Caro, 2004). Major element data from all localities are used to calculate new geotherms for the Slave Craton, using the method outlined by McKenzie et al (2005) and expanded by Mather et al. (2011). The average mineral compositions, rare-earth elements, Mg#, and Rhenium-depletion ages (TRD) for individual xenoliths from all localities are plotted on these new geotherms. The resulting patterns of TRD with depth are used to evaluate the suggestion that the Slave lithosphere is stratified in age as well as composition.
Finally, all kimberlite localities studied are used as ‘pseudo-boreholes’ to create a 2-dimensional linear transect from NNW-SSE through the Slave SCLM. The lithospheric stratigraphy illustrated by this transect is used to comment on the apparent layered nature of the continental lithosphere beneath the Slave province and explore which, if either, of the two main craton formation hypotheses were operating during its genesis.