Mantle Dynamics Beneath the Discrete and Diffuse Plate Boundaries of the Juan de Fuca Plate: Results from Cascadia Initiative Body Wave Tomography

Authors

Joseph S. Byrnes, University of Oregon
Douglas R. Toomey, University of Oregon
Emilie E. E. Hooft, University of Oregon
John Nábělek, Oregon State University
Jochen Braunmiller, University of South FloridaFollow

Document Type

Article

Publication Date

8-2017

Keywords

mid‐ocean ridges, dynamic upwelling, tomography, Juan de Fuca, Gorda, asthenosphere

Digital Object Identifier (DOI)

https://doi.org/10.1002/2017GC006980

Abstract

We use the delay times of teleseismic S phases recorded by ocean bottom seismometers during the plate‐scale Cascadia Initiative community experiment to constrain the heterogeneity of seismic velocity structure beneath young oceanic lithosphere. Our study area covers the entire Juan de Fuca (JdF) and Gorda plates, from their creation at the JdF and Gorda Ridges to their subduction beneath the North American continent, and the entire length of the Blanco transform fault. The range of the observed Vs anomalies requires variations in the melt fraction of the asthenosphere. The data require that low Vsanomalies extend to depths of at least 200 km, which is within the carbonatite melting regime. In the upper 200 km of the mantle, Vs increases rapidly to the east of the JdF Ridge, while there is no clear relationship with the age of the lithosphere in the Gorda region. The distribution of melt is asymmetric about both the JdF and Gorda Ridges. Dynamic upwelling – due to the buoyancy of the mantle – and accompanying downwelling can explain the rapid decrease in melt fraction to the east of the JdF Ridge, the asymmetry about the JdF Ridge, and the sinuous pattern of upwelling near the Blanco transform fault. Finally, mantle flow beneath the diffuse Gorda and Explorer plate boundaries is distinct from that beneath the discrete plate boundary of the JdF Ridge. In particular, shear between the Pacific and JdF plates appears to dominate mantle deformation over seafloor spreading beneath the Gorda Ridge.

Rights Information

Terms of use for work posted in Scholar Commons.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Geochemistry, Geophysics, Geosystems, v. 18, issue 8, p. 2906-2929

© 2017. American Geophysical Union. All Rights Reserved.

Scholar Commons Citation

Byrnes, Joseph S.; Toomey, Douglas R.; Hooft, Emilie E. E.; Nábělek, John; and Braunmiller, Jochen, "Mantle Dynamics Beneath the Discrete and Diffuse Plate Boundaries of the Juan de Fuca Plate: Results from Cascadia Initiative Body Wave Tomography" (2017). School of Geosciences Faculty and Staff Publications. 1328.
https://digitalcommons.usf.edu/geo_facpub/1328