Document Type
Article
Date of Original Version
2014
Department
Oceanography
Abstract
Melt generation and volcanism at subduction zones may result from several possible processes: hydration of the mantle wedge by fluid released from the slab, subduction-induced mantle upwelling beneath the back-arc, and heating of downgoing sediments/oceanic crust atop the slab. Each process predicts a distinctly different spatial pattern of melt generation and can thus be distinguished with high-resolution seismic imaging. Here we construct an upper mantle model of the Pacific Northwest using a full-wave ambient noise tomographic method. Normalized vertical components of continuous seismic records at station pairs are cross-correlated to extract empirical Green's functions at periods of 7–200 s. We simulate wave propagation within the 3D Earth structure using a finite-difference method and calculate sensitivity kernels of Rayleigh waves to perturbations of VpVp and VsVs based on the Strain Green's Tensor database. Phase delays are extracted by cross-correlating the observed and synthetic waveforms at multiple frequency bands.
Our tomographic result reveals three separate low shear-wave velocity anomalies along the back-arc in the upper mantle ∼200 km east of the Cascade volcanic arc, with the central one being the largest in size and lowest in velocity. These back-arc low-velocity anomalies are spatially correlated with the three arc-volcano clusters. The geometry of the low-velocity volumes relative to the slab and arc is consistent with the pattern of subduction-induced decompressional melting in the back-arc. Their along-strike variation suggests that the large-scale plate-motion-induced flow in the back-arc mantle wedge is modulated by small-scale convection, resulting in a highly 3D process that defines the segmentation of volcanism along the Cascade arc.
Citation/Publisher Attribution
Gao, H. & Shen, Y. (2014). Upper mantle structure of the Cascades from full-wave ambient noise tomography: Evidence for 3D mantle upwelling in the back-arc. Earth and Planetary Science Letters, 390(15), 222-233. http://dx.doi.org/10.1016/j.epsl.2014.01.012
Available at: http://dx.doi.org/10.1016/j.epsl.2014.01.012
Author Manuscript
This is a pre-publication author manuscript of the final, published article.
Terms of Use
This article is made available under the terms and conditions applicable
towards Open Access Policy Articles, as set forth in our Terms of Use.
