203 Old and the New, Long and the Short: Perspectives on Integration of Timescales of Magmatic Processes: Special Session Related to MGPV Awards to Madison Myers and Anita Grunder

We encourage papers that challenge and give insights into the interplay between timescales, methodologies, and processes to build a cohesive understanding of the lifespan, evolution, storage, and eruption of magma, from plutonic to volcanic systems.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 216AB

An Expanded Lava Creek Tuff Eruption

Paper number: 203-0
Program: Technical Sessions
Time: 1:30 PM – 1:45 PM

Authors

Abstract

Recent reassessment of the Lava Creek Tuff (LCT; 1000 km3, 0.63 Ma) has provided several new insights that significantly alter our current view of Yellowstone’s youngest supereruption. Starting in the eastern resurgent dome, remapping has uncovered four new, visually distinct ignimbrites units with 40Ar/39Ar ages analytically indistinguishable from the known eruption age. The most dominant unit contains scoria, a feature not observed in any mapped deposit of the LCT. Another new unit is found as a lag-breccia deposit beneath the scoria-bearing ignimbrite, likely formed during the latter’s eruption. The breccia contains angular LCT-age ignimbrite material, providing field evidence for a major time break within the eruption that is unresolvable by current geochronology methods; these angular clasts are geochemically linked to nearby mapped LCT member A, suggesting a significant pause in deposition between the two. This lag-breccia deposit, taken alongside observed welding intensity variations found in the southern part of the dome, provide evidence for eruptive vent(s) significantly west of the currently mapped caldera boundary. Mapped faults attributed to resurgent dome activity display no offset to those of younger faulting in the region, suggesting that the resurgent dome is not resurgent at all. Taken together, we instead argue that a major structural fault, potentially representing the true caldera boundary, lays inward of the current boundary. Based on the placement of the Yellowstone River and the high 3He/4He values found to the west of the resurgent dome, we postulate this region is a major fault zone associated with the eruption of these later LCT units. In our larger reassessment of the LCT eruption, we find also little evidence for phenocrystic amphibole, the main distinguishing feature established between mapped members A (amphibole-bearing) and B; on the contrary, we find that only 4 of 150 samples analyzed contain amphibole, and these are from both mapped members. Our work strongly suggests that the LCT eruption was not fed simply by two separate sheet flows from a single stratified chamber but instead consists of distinct lobes that were systematically tapped from separate magma bodies over an extended period.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412636

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.