Crustal inheritance and a top-down control on arc magmatism at Mount St. Helens

Public Deposited

Downloadable Content

Download PDF


Attribute NameValues
  • In a subduction zone, the volcanic arc marks the location where magma, generated via flux melting in the mantle wedge, migrates through the crust and erupts. While the location of deep magma broadly defines the arc position, here we argue that crustal structures, identified in geophysical data from the Washington Cascades magmatic arc, are equally important in controlling magma ascent and defining the spatial distribution and compositional variability of erupted material. As imaged by a three-dimensional resistivity model, a broad lower-crustal mush zone containing 3-10% interconnected melt underlies this segment of the arc, interpreted to episodically feed upper-crustal magmatic systems and drive eruptions. Mount St. Helens is fed by melt channeled around a mid-Tertiary batholith also imaged in the resistivity model and supported by potential-field data. Regionally, volcanism and seismicity are almost exclusive of the batholith, while at Mount St. Helens, along its margin, the ascent of viscous felsic melt is enabled by deep-seated metasedimentary rocks. Both the anomalous forearc location and composition of St. Helens magmas are products of this zone of localized extension along the batholith margin. This work is a compelling example of inherited structural control on local stress state and magmatism.
Resource Type
Date Issued
  • Bedrosian, P.A., J.R. Peacock, E. Bowles-Martinez, A. Schultz, G.J. Hill, Crustal inheritance and a top-down control on arc magmatism at Mount St Helens, Nature Geoscience, (2018).
Journal Title
Journal Volume
  • 11
Journal Issue/Number
  • 11
Academic Affiliation
Rights Statement
Related Items
Embargo date range
  • 2018-11-07 to 2019-06-08



This work has no parents.