 Analysis of the chemical composition of the lavas gives important clues about the origin and dynamics of the flood basalt volcanism.The lowermost lavas were produced by melting in the garnet stability field below the surface at a depth of more than in a mantle plume environment beneath the North American lithosphere.As the mantle plume intruded rocks of the Canadian Shield, it created an upwelling zone of molten rock known as the Mackenzie hotspot.