Yellowstone plume - continental lithosphere interaction beneath Snake River Plain

The widespread Miocene to recent volcanism in the Pacific Northwest associated with the Columbia Plateau, Oregon High Lava Plains, Snake River Plain, Northern Nevada Rift, and Yellowstone Plateau may represent a single magmatic system related to a hotspot, where a plume of material from the deep mantle rises and melts to form lavas along the plain. The mantle plume is spatially fixed, and the Snake River Plain formed as the westward migrating North American continental plate rode over it. Hanan et al. discuss one problem with this interpretation—the radiogenic isotopic composition of the basaltic lavas is the same as that of the relatively shallow mantle attached to the overriding westward-migrating continent, instead of deep mantle sources as predicted. New mass-balance mixing models show that deep mantle plume melts inherit the radiogenic isotope composition of the sub-continental mantle as they passed through it on their way to erupt on the Snake River Plain. This happens because the concentration of radiogenic elements in the sub-continental mantle beneath the Snake River Plain is one to two orders of magnitude higher than in the mantle plume melts. A small amount of pollution (less than 4%) of the plume magmas by melt from sub-continental mantle is all that is required to wipe out the radiogenic isotope signature of the mantle plume source. The results support the idea that the Snake River Plain lavas and associated widespread Miocene to recent volcanism in the Pacific Northwest is likely related to a magmatic system controlled by a mantle plume. -Geological Society of America