title: Seismic evidence for a cold serpentinized mantle wedge beneath Mount St Helens.
abstract: Mount St Helens is the most active volcano within the Cascade arc; however, its location is unusual because it lies 50 km west of the main axis of arc volcanism. Subduction zone thermal models indicate that the down-going slab is decoupled from the overriding mantle wedge beneath the forearc, resulting in a cold mantle wedge that is unlikely to generate melt. Consequently, the forearc location of Mount St Helens raises questions regarding the extent of the cold mantle wedge and the source region of melts that are responsible for volcanism. Here using, high-resolution active-source seismic data, we show that Mount St Helens sits atop a sharp lateral boundary in Moho reflectivity. Weak-to-absent PmP reflections to the west are attributed to serpentinite in the mantle-wedge, which requires a cold hydrated mantle wedge beneath Mount St Helens (<∼700 °C). These results suggest that the melt source region lies east towards Mount Adams.
authors: Department of Earth and Planetary Sciences, MSCO3-2040, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA.
authors: S M
authors: SM
authors: Hansen
authors: Department of Earth and Planetary Sciences, MSCO3-2040, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA.
authors: B
authors: B
authors: Schmandt
authors: Department of Earth Science, MS-126 Rice University, 6100 Main Street, Houston, Texas 77005, USA.
authors: A
authors: A
authors: Levander
authors: Department of Earth Science, MS-126 Rice University, 6100 Main Street, Houston, Texas 77005, USA.
authors: E
authors: E
authors: Kiser
authors: Department of Earth and Space Sciences, University of Washington, Johnson Hall Rm-070, Box 351310, 4000 15th Avenue NE, Seattle, Washington 98195-1310, USA.
authors: J E
authors: 0000-0002-3658-818X
authors: JE
authors: Vidale
authors: Department of Earth and Atmospheric Sciences, Cornell University, 1103 Bradfield Hall, Ithaca, New York 14853-1901, USA.
authors: G A
authors: GA
authors: Abers
authors: Department of Earth and Space Sciences, University of Washington, Johnson Hall Rm-070, Box 351310, 4000 15th Avenue NE, Seattle, Washington 98195-1310, USA.
authors: K C
authors: 0000-0003-4501-7415
authors: KC
authors: Creager