DISENTANGLING THE LAVA CREEK TUFF ERUPTION THROUGH RE-MAPPING OF SOUR CREEK DOME, YELLOWSTONE NATIONAL PARK

The ~1000 km³, ~630 ka Lava Creek Tuff (LCT) is the youngest major caldera-forming eruption of the Yellowstone volcanic system. It generated two ignimbrite units, A and B, separated by a reversal in welding profiles and the presence of phenocrystic amphibole in member A [1], with an accompanying exceptionally widespread fall deposit distributed over the western US. Recent age dating on ignimbrite units in the Sour Creek Dome area, originally mapped as older (2.08 Ma) Huckleberry Ridge Tuff, yielded age estimates (~658 ka from U-Pb dating of zircons and 634 ka from ⁴⁰Ar/³⁹Ar dating on sanidine) identical within error to those of the nominally younger LCT ignimbrites [2]. These results imply the overall "LCT eruption” is more complex than currently thought. In the newly dated deposits, one unit is found as welded clasts within a lag deposit which is conformably overlain by a cliff-forming, densely welded ignimbrite. Both newly dated units are petrographically distinct from the Lava Creek A and B units cropping out elsewhere and are inferred to represent separate outbursts. This project seeks to resolve the nature of the newly dated ignimbrite units, which were produced by an expanded LCT eruption, document their spatial distribution and source area(s), estimate their volumes, and determine how they relate, geochemically, to members A and B. To accomplish these questions, we have begun remapping and documenting the newly recognized LCT units in and around Sour Creek Dome in order to compare them against the previously documented LCT A and B units. This work will have significant impacts on how we currently understand the dynamics of the Lava Creek supereruption and the formation of the Yellowstone caldera.

[1] Christiansen, R.L., 2001, The Quaternary and Pliocene Yellowstone Plateau volcanic field of Wyoming, Idaho, and Montana: U.S. Geological Survey Professional Paper 729 G, 144 p.

[2] Wilson, C.J.N., Stelten, M.E., and Lowenstern, J.B., 2018, Contrasting perspectives on the Lava Creek Tuff eruption, Yellowstone, from new U-Pb and 40Ar/39Ar age determination: Bulletin of Volcanology, v. 80, 53 p., doi:10.1007/s00445-018-x.