Evolution of Large Volume Silicic Magmas of the Yellowstone Hotspot: The Record of the Bruneau-Jarbidge Eruptive Center

University Of Utah, Salt Lake City UT

Investigators

Abstract

The study examines the long-term evolution of silicic magmas at a major explosive volcanic center of the Yellowstone hotspot track. The Bruneau-Jarbidge eruptive center provides a singular opportunity to evaluate modern concepts regarding the dynamics of large silicic magma reservoirs, including magma generation, storage, differentiation, the timescales thereof, as well as the ancestral lineage of contemporaneously erupted magmas. The Cougar Point Tuff (CPT) and associated lavas of the Bruneau-Jarbidge center, erupted from 12.7 to ~8 Ma, are ideal for the study of large silicic systems because the estimated volume rate of production for the CPT is unrivaled by even the present day Yellowstone system. The average recurrence interval for eruption of large volume ash flow tuffs is 250 ka, which allows a more intimate inspection than in modern systems of the details of large-volume magma production through examination of successively erupted individual units. Specific aspects of the study include: 1) major and trace element composition of phenocryst phases and airfall glass through electron probe and laser ablation ICP mass spectrometry to assess differentiation mechanisms; 2) determination of eruption ages by Ar chronology to precisely quantify the intervals between eruptions; 3) determination of zircon crystallization ages by single crystal U/Pb chronology to establish magma longevities and identify potential source materials; and 4) Oxygen isotope analyses of quartz, feldspar, glass and zircon to test the published hypothesis of a hydrothermally altered protolith. The broader impacts of this study include an enhanced understanding of the life cycle of an eruptive center of the Yellowstone hotspot with applications to assessing possible hazards associated with future eruptive activity at Yellowstone National Park.