Geophysical and Geochemical Constraints on Magma Storage Depths along the Cascade Arc: Knowns and Unknowns

Abstract

The iconic volcanoes of the Cascade arc stretch from Lassen Volcanic Center in northern California, through Oregon and Washington, to the Garibaldi Volcanic Belt in British Columbia. Recent studies have reviewed differences in the distribution and eruptive volumes of vents, as well as variations in geochemical compositions and heat flux along strike (amongst other characteristics). We investigate whether these along-arc variations manifest as variations in magma storage conditions. We compile available constraints on magma storage depths from InSAR, geodetics, seismic inversions, and magnotellurics for each major edifice, and compare these to melt inclusion saturation pressures, pressures calculated using mineral-only barometers, and constraints from experimental petrology. The availability of magma storage depth estimates varies greatly along the arc, with abundant geochemical and geophysical data available for some systems (e.g. Lassen Volcanic Center, Mt. St. Helens), and very limited data available for other volcanoes, including many which are classified as “very high threat” by the USGS (e.g., Glacier Peak, Mt. Baker, Mt. Hood, Three Sisters). Acknowledging the limitations of data availability and the large uncertainties associated with certain methods, available data is indicative of magma storage within the upper 15 km of the crust (~2 ± 2 kbar). These findings are consistent with previous work recognising barometric estimates cluster within the upper crust in many arcs worldwide. There are no clear offsets in magma storage between arc segments that are in extension, transtension or compression, although substantially more petrological work is needed for fine scale evaluation of storage pressures.

Monogenetic volcanoes as windows into transcrustal mush: A case study of Slamet and Loyang volcanoes, Central Java

“…Given the lack of H 2 O in S303B, its vapor bubble likely formed by H + diffusive loss during heating, as has bene seen in other melt-inclusion hosted vapor bubbles e.g., Mt. Shasta (USA) (Gaetani et al 2012;Wieser, Kent, et al 2023).…”