Upper mantle structure underlying the diamondiferous Slave craton from teleseismic body-wave tomography

Abstract

Cratons are, by definition, the most tectonically stable and oldest parts of the continental lithosphere on Earth. The Archean Slave craton is located in the northwestern part of the Canadian Shield. The propensity of diamondiferous kimberlite pipes in the Central Slave Craton raises many questions regarding their structural environment and source. Here, we provide the most robust teleseismic P and S body wave tomography models over the Slave craton region based on 20,547 P-wave delay times, 6140 direct S-wave delay times and 3381 SKS delay times. The P-wave model reveals an alternating pattern of relative positive and negative anomalies over a fine scale region within the Central Slave Craton. Furthermore, the P-wave model reveals two fine structures located in the lithosphere beneath the Lac de Gras kimberlite field, with relatively slow anomalies (B–C) that extend from 75 km to 350 km depths with an apparent dip to the north. These relatively slow P-wave anomalies are associated with metasomatised regions within the lithosphere. The most recent kimberlite pipes (75–45 Ma) in the Lac de Gras field are located on steep VP and VS gradients. The S-wave model displays a slow S-wave anomaly lying from 300 km depth to the transition zone beneath the Central Slave Craton. This anomaly is located beneath the Lac de Gras kimberlite field. We suggest that this anomaly is not the cause of the actual kimberlites at the surface since the last eruptions occurred 75–45 Ma ago but may be related to a potential kimberlite magma ascent in the asthenosphere.