Abstract

Zircon and rutile in two garnet-bearing mafic granulite xenoliths from a kimberlite in the Archean Slave province record Proterozoic ages similar to the 1.27 Ga Mackenzie dike swarm or similar to the ca. 2.23–2.21 Ga Malley-McKay diabase dike swarms. The xenolith sample site currently overlies thick lithosphere, more than 700 km to the southeast of the proposed Mackenzie plume center. Because lower crust was effectively shielded from the thermal effects of an upwelling plume by thick lithospheric mantle, heat was most likely advected into the lower crust by lateral intrusion of mafic sills over distances of hundreds of kilometres from magma generation zones nearer the plume center.

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