An expanded lava creek tuff eruption: re-mapping the Sour Creek Dome, Yellowstone National Park

Abstract

The ~1000 km 3, ~630 ka Lava Creek Tuff is the product of the younger major caldera- forming eruption of the Yellowstone Volcanic Field. It is currently mapped as two ignimbrite units, hot dense flows of ash, gas, and molten material, termed members A and B, with accompanying widespread ashfalls over the western U.S. This view of the Lava Creek Tuff, and its eruption, was complicated when two, visually distinct, ignimbrites were recognized on the Sour Creek dome in Yellowstone National park (Wilson et al., 2018). These visually distinct ignimbrites on the Sour Creek dome were initially mapped as the older (2.08 Ma) Huckleberry Ridge Tuff, however, when dated by U - Pb on zircon and 40Ar/39Ar on sanidine the ignimbrites returned ages analytically indistinguishable from the Lava Creek Tuff (0.631 Ma). In the newly dated ignimbrites, one unit is found as clasts of dense welded tuff withing a lag deposit which is conformably overlain by a second, cliff-forming, densely welded ignimbrite that contains scoria. This study further complicate matters due to the discovery of two additional, previously unrecognized, ignimbrites while mapping on the Sour Creek dome, bringing the total to four ignimbrites. Physical and chemical evidence suggests there were multiple magma bodies tapped during the eruptions. This project broadens our understanding of the four ignimbrites documenting their spatial distribution and source area(s) and determine how they relate geochemically to the established members A and B. This was done through field mapping, thin section examination, and whole-rock and single crystal geochemistry. This resulted in a revised understanding of the Lava Creek Tuff stratigraphy and holds implications for reevaluating the eastern boundary of the Yellowstone Caldera.