23-8 It's Tuff getting recognized: Ignimbrites of the Sour Creek dome, Yellowstone

Session: Distributed volcanic fields of the southwestern U.S. (Posters)

Poster Booth No.: 15

Presenting Author:

Raymond Salazar

Authors:

Salazar, Raymond¹, Myers, Madison², Wilson, Colin James Ness³, Finch, Hailey⁴, Henderson, Stacy⁵, Ketel, Jess⁶

(1) New Mexico Bureau of Geology and Mineral Resources, Socorro, NM, USA, (2) Montana State University, Bozeman, MT, , (3) Victoria University of Wellington, Wellington, , (4) Central Washington University, Ellensburg, WA, , (5) Montana State University, Bozeman, MT, , (6) ,

Abstract:

Field observations, plus sanidine compositional and 40Ar/39Ar age data collected on rocks from the Sour Creek dome (SCD) area of Yellowstone, serve to identify five new ignimbrite packages with ages (average 631.5 ± 0.9 ka) that are analytically indistinguishable from those of the Lava Creek Tuff (LCT), challenging its current framework of two eruptive members. Newly recognized unit 1 occurs as LCT-aged recycled clasts within a proximal lag breccia, reflecting a major time break in the LCT eruption sequence. Conformably above, the scoria-bearing ignimbrite of unit 2 is extensively found in the dome, having been previously mis-mapped as Huckleberry Ridge Tuff and Lava Creek Tuff member A. To the south, unit 3 is a crystal-rich, densely welded ignimbrite (inferred to be younger than unit 2) that is conformably overlain by unit 4, a fine-grained ignimbrite that contains abundant clasts of recycled tuff. Lastly, the topographically highest parts of the dome are made up of unit 5, a multi-component ignimbrite 2 containing scoria, recycled clasts and pumices, potentially correlative with unit 2 and/or unit 4. Cathodoluminescence imaging and zoning assessment was integrated with sanidine geochemistry from all five packages, including their recycled clasts. Four of the five packages were sourced from separate magmatic bodies within a larger plumbing system, each defined by their sanidine Ba distributions and componentry. The abundance of recycled materials (and absence of Absaroka country rocks) in the SCD ignimbrites imply that vent locations were well inboard of the mapped caldera boundary, with some potentially along the line of the Yellowstone River and possibly requiring a revision of the currently accepted LCT caldera outline. The Lava Creek Tuff eruptive events were thus far more complex than currently recognized, with multiple deposits fed from multiple magma bodies over a timescale that cannot be resolved by radiometric dating.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4, 2026

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