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Amalgamation of multiple, discrete magma bodies fueled the tuff of Elevenmile Canyon

^^ Anna C. Ruefer1^^ , Ayla S. Pamukçu1, Genna R. Chiaro2, Madeline J. Lewis3, Michael P. Eddy4, Karrie L. Weaver1, Joel W. DesOrmeau5

  • Affiliations:  1Department of Earth and Planetary Sciences, Stanford University, Stanford, CA; 2 Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN; 3Department of Geology and Geophysics, University of Wyoming, Laramie, WY; 4Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN; 5Department of Geological Sciences and Engineering, University of Nevada, Reno, NV 

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 25

  • Programme No: 1.7.12

  • Theme 1 > Session 7

Abstract

The occurrence of super-sized eruptions (>1000 km3) implies that staggering quantities of eruptible magma must have existed in the crust over relatively short time periods. However, the architecture of these systems remains elusive, particularly for crystal-rich systems. One such eruption in western Nevada, the tuff of Elevenmile Canyon (25.1 Ma), is compositionally variable (~65-78 wt.% SiO2), crystal-rich (20-60%), and enormous (<5000 km3 total erupted volume). Here, we expand on the bulk rock geochemistry determined by previous workers with major and trace element analyses of glasses from individual fiamme and vitrophyres. Our samples span the bulk compositional and stratigraphic extent of Elevenmile. We identify multiple distinct glass populations in major and trace elements, and the span of major element compositions mimics the bulk tuff compositional range (e.g., 66-78 wt.% SiO2). Zircon saturation thermometry also reveals discrete temperature populations of ~800-850 oC associated with more evolved (75.5-78 wt.% SiO2) glasses and ~900-925 oC associated with less evolved (67-75 wt.% SiO2) glasses. Fractional crystallization alone cannot explain trace element differences between samples. Different fiamme populations display variable mixing and mingling textures in single hand samples, which supports magma mixing as an important process in the generation of the observed compositional variability. However, other samples contain compositionally homogenous fiamme populations, suggesting that open-system processes may have been localized. We conclude that the tuff of Elevenmile Canyon is more consistent with models describing giant eruptions as being sourced by the amalgamation of multiple, discrete bodies rather than the product of one zoned magma body.