Empirical grouping of kimberlite locations results in delineation of five elliptical clusters that encompass all but four kimberlite occurrences. Clusters within the western part of the craton are elongate to the north–northeast and align within a narrow zone (“Western Corridor”). Elsewhere, the clusters are elongate to the northwest or west–northwest and appear to be arranged en echelon within a poorly defined north–northwest trending zone (“Central Corridor”). Geometrical spatial analyses of kimberlite locations highlight the craton-scale pattern of emplacement within the two main corridors. At regional and local scales, individual intrusions are preferentially located towards the west–northwest (ca. 280°) and north–northeast (ca. 015°) of other intrusions, and these orientations are interpreted to reflect upper mantle trends in magma generation. At local scales (10–25 km), kimberlite of the central and southern craton tends to be located to the northeast (ca. 045°), and possibly weakly to the east–northeast (ca. 070°), of other intrusions, and these orientations correspond to major crustal fractures systems. It is proposed that kimberlite emplacement is controlled primarily by the interaction of elongate 280° and 015° source regions with near-surface deviations influenced by crustal fracture systems.
The 015° trend evident at craton, regional, and local scales is parallel to a swarm of alkaline diabase dykes that are concentrated in a ca. 30-km-wide corridor passing through Lac de Gras. A profound spatial association between significantly diamondiferous kimberlite and the margins of the dyke corridor suggests the corridor is the surface expression of a mantle-depth structure. It remains unclear whether the proposed mantle structure coincides with a diamond-rich zone near the base of the lithosphere, or delineates pathways favorable for diamond preservation during emplacement. The linear array of kimberlite within the western craton forms a parallel corridor that may be an analogous mantle structure, but which to date has failed to yield economic diamond concentrations. 相似文献