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Geometrically complex magmatic plumbing system revealed by high-silica rhyolite glasses from the Highland Range Volcanic Sequence (NV, USA)

Sarah Hickernell1 , Ayla Pamukcu1, Genna Chiaro2, Karrie Weaver1

  • Affiliations: 1Department of Earth & Planetary Sciences, Stanford University, Stanford, California, USA; 2Department of Earth & Environmental Sciences, Vanderbilt University, Nashville, Tennessee, USA.

  • Presentation type: Talk [Invited]

  • Presentation time: Monday 10:30 - 10:45, Room R280

  • Programme No: 1.7.1

  • Theme 1 > Session 7

Abstract

Monitoring and predicting eruptive behavior at silicic volcanoes requires an improved understanding of where rhyolites are stored prior eruption. In this study, we (1) estimate magma storage pressures from matrix and quartz-hosted melt inclusion glasses in four high-silica rhyolite units from the Highland Range Volcanic Sequence (HRVS; NV), and (2) utilize glass trace element compositions to evaluate the geometry of the HRVS plumbing system. Melt inclusion vapor saturation pressures suggest minimum pressures of ~100 MPa for magmas that produced rhyolitic tuffs and ~100-130 MPa for those that produced a block-and-ash and an obsidian flow. Matrix glasses from all samples give deeper average Rhyolite-MELTS quartz+2feldspar and quartz+2feldspar+oxides pressures (134 ± 39 MPa and 146 ± 28 MPa, respectively). Pressure estimates from a new machine-learning geobarometer, MagMaTaB, are highly sensitive to the choice of phase assemblage: results using a quartz+2feldspars+oxides assemblage are similar to quartz+2feldspar±oxides rhyolite-MELTS and melt inclusion vapor saturation pressures for all samples (109 ± 46 MPa), but a quartz+2feldspar-only MagMaTaB assemblage leads to significantly higher pressure estimates inconsistent with other results (238 ± 36 MPa). Regardless of the method used, pressure results suggest storage of the HRVS rhyolitic magmas at similar depths. However, variations in matrix glass Rb, Ba, Sr, and Eu through the HRVS stratigraphy cannot be explained by fractional crystallization, suggesting the eruptions were likely tapping separate magmas. The outcomes of this work indicate that the pre-eruptive storage of the HRVS magmas was geometrically complex, with several discrete eruptible melt lenses residing at 4-5 km depth.