22-2 Project HOTSPOT, The Snake River Scientific Drilling Project: Looking Forward, Looking Back

Abstract:

Project Hotspot was an international collaboration focused on understanding interactions between the Yellowstone mantle plume and continental lithosphere. Our funded goal was to investigate innovative approaches to geothermal energy exploration, but we were able to address significant scientific issues as well: how do mantle plumes interact with continental lithosphere and how does this interaction affect the geochemical evolution of mantle-derived magmas and continental lithosphere?

Project Hotspot completed three holes in the eastern, central, and western SRP: Kimama, Kimberly, and Mountain Home. We acquired 5324m of continuous core that documents the volcanic and sedimentary record of the hotspot track. The Kimama hole is dominantly basalt, while the Kimberly hole encountered alternating basalt-sediment, underlain by >1550m of rhyolite. These holes overlap in age, providing a stratigraphic record spanning ~8Ma. The Mountain Home hole penetrated ~640m of lacustrine sediment overlain (215m) and underlain (960m) by basalt; this hole also intersected an ~150C hydrothermal resource at 1745m. The project included water chemistry and geophysical studies comprising gravity, magnetic surveys, active source seismic surveys, vertical seismic profiles, and wireline logging of all three holes. Paleomagnetic inclinations were determined every 1.5m, supplemented by Ar-Ar and zircon U-Pb age determinations.

Our work shows that continental lithosphere forms a reactive filter which affects mantle derived magmas. The Kimama core contains 432 basalt flow units that document fractionation and recharge of mid-crustal magma chambers over 5.6Ma. Recharge magmas mix with residual magma from the previous cycles so that subsequent melts are more enriched than their parents. Paleomagnetic inclination data further show that both fractionation and recharge occur on timescales of a few decades to centuries (20-200 years). Similar cycles are documented in iron-rich basalts from Mountain Home (2.2-5.4Ma), which are coeval with basalts from Kimama (0.5-5.6Ma). The Kimberly core sampled two rhyolite lavas and a 1350m ash flow, as well as younger basalt flows.

Project Hotspot has generated nineteen publications and many geothermal conference papers. A GSA Special Publication with further results is in preparation. The core is now stored at LacCore (lake sediment) or at the USGS CRC in Denver, where it continues to be studied.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.