THE SNAKE RIVER PLAIN SCIENTIFIC DRILLING PROJECT (SRP-SDP): TRACKING THE YELLOWSTONE HOTSPOT THROUGH SPACE AND TIME

Basaltic volcanism of the Snake River Plain volcanic province has long been associated with the concept of a migrating hotspot that now underlies the Yellowstone plateau. Most researchers believe that Yellowstone is the world's best example of a plume beneath continental crust, making it a unique place to test the plume hypothesis. This model has been questioned in recent years, but new mantle tomographic studies have shown that a plume-like thermal anomaly extending to at least 400 km dips to the NW beneath Yellowstone. In detail, the story is more complex, as basaltic volcanism spans a significant range in time and the youngest basalts may post-date the hotspot in a given location by millions of years. In addition, basaltic volcanism in the western SRP (which formed in two distinct episodes separated by some 5 million years) lies well off the hotspot track and cannot be related directly to the hotspot in any simple way.

We propose a series of 4-6 intermediate depth (1-2 km) drill holes taken along the axis of the SRP that will specifically target the origin and evolution of alleged plume-related volcanism in both space and time. Samples from each hole will allow us to examine the geochemical and isotopic characteristics of rhyolites and basalts through time at each site, while the series of holes will allow comparison of coeval lavas erupted at different locations, and estimation of the eruptive volume thru time. Holes drilled in the WSRP graben will help define the relationship between this structure and the ESRP plume track. These drill holes will complement geophysical studies of continental dynamics, as well as current studies centered on Yellowstone. Additional components of a targeted drilling program include paleoclimate studies of North America during the Pliocene—Pleistocene through sampling of lacustrine sediments, hydrology of the SRP aquifer, fluid flow at deeper crustal levels, and the impact of heat flow and the chemical reequilibration of rocks and fluids at depth. This project will be an ideal test of plume hypothesis. If a plume origin is supported, it may be generalized to plume processes and plume-lithosphere interactions globally. Alternatively, it may validate recent proposals that eschew a plume origin for these features.