EVIDENCE FROM MAGNETIC FABRIC FOR THE FLOW PATTERN OF MAGMA IN THE MACKENZIE GIANT RADIATING DYKE SWARM

CONTINENTAL flood basalts, and their associated swarms of mafic dykes, are thought to result from melting in mantle plumes 1-3 , but the processes by which the resulting magma makes its way from mantle to crust remain obscure. Here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the Proterozoic Mackenzie dyke swarm. Our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm, and then travelled horizontally at all further distances out to at least 2,100 km. The sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the Mackenzie igneous events.