Events Calendar

"Investigating <10 Ma off-axis magmatism in northwest Wyoming and southwest Montana: Yellowstone hotspot - lithosphere interactions at the leading edge of the Snake River"

Abstract: Hot spot identification centers on the identification of clear, time-transgressive, linear chains of magmatic products across the crust. These age-progressions are ambiguous when volcanism along a hot spot “track” does not temporally fit in the age progression and is therefore, out-of-sequence and at times off-axis. Complicating Earth’s record of hot spot volcanism is the paucity of continental hot spots that have been identified in the geological record and the relationship between upwelling mantle and upper-plate processes, such as lithospheric extension. The Snake River plain-Yellowstone (SRPY) volcanic province is the archetypal example of a continental hot spot, where the postulated mantle plume is now under the >2.1 Ma Yellowstone Plateau volcanic field. South-southeast of Yellowstone and the SRPY axis, are primarily monogenetic, ~9 to 0.5 Ma volcanoes (e.g., Upper Wind River Basin volcanic field and Jackson Hole volcanics; UWRB-JH) that are distinct from YSRP volcanism. UWRB-JH magmatism is spatially coincident with a migrating ~100-200-km-wide topographically high region of active continental extension (e.g., Yellowstone Crescent of High Terrain, YCHT) defining the leading edge of SRPY. These off-axis and out-of-sequence SRPY rocks define two chemical groups, a K-rich, alkaline to transitional group, and a calc-alkaline group. Rocks from both groups, however, have large ion lithophile element enrichments, high field strength element depletions, and other geochemical characteristics associated with subduction zone magmatism, though they formed in an intraplate setting. New whole rock Sr-Nd-Pb-Os isotope data, including results from the least evolved rocks, show that these magmas were likely sourced from Archean, metasomatized lithospheric mantle. Similar small volume off-axis volcanism has been identified adjacent to other locations where voluminous mantle upwelling occurs regardless of cause (e.g., oceanic hot spots and continental/oceanic rifts). Thus, UWRB-JH magmatism represents an example of this phenomena, where continental hot spot-related off-axis magmatism occurs due to mantle melting and associated YCHT lithosphere extension, which facilitates small volume melt production and eruption.