Rayleigh wave tomography beneath intraplate volcanic ridges in the South Pacific

Dayanthei S. Weeraratne*, Donald W. Forsyth, Yingjie Yang, Spahr C. Webb

*Corresponding author for this work

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Abstract

We test models for the origin of intraplate volcanic ridges and gravity lineations on young seafloor west of the East Pacific Rise using Rayleigh wave dispersion measured in the Gravity Lineations and Intraplate Melting Petrology and Seismic Expedition (GLIMPSE) seismic experiment. The excellent azimuthal distribution of teleseismic sources recorded over a 12-month period provides resolution of phase velocities at periods up to 100 s. The average phase velocities for the study area reveal a pronounced low-velocity zone reaching a minimum shear velocity of ∼3.95 km/s. The negative velocity gradient defining the base of the lithosphere, observed at 40 ± 15 km, abruptly reverses at 70 km depth. The underlying positive gradient changes slope at ∼125 kin. We attribute these changes in gradient to the onset of incipient partial melting of upwelling mantle in the presence ofwater at 125 km, followed by increased melt production at 70 km that leads to dehydration of the residual matrix and migration of melt to the surface spreading center. Rayleigh wave tomography shows that there are anomalously low shear velocities extending to at least 50 km depth beneath the Sojourn Ridge and the Hotu Matua volcanic complex, with relatively high velocities between these volcanic chains. These observations are not consistent with passive models for the origin of the volcanic ridges involving lithospheric extension or thermoelastic cracking. Dynamic models invoking flow in the asthenosphore in the form of small-scale convection or viscous fingering instabilities may explain the observed pattern of seismic velocity anomalies.

Original languageEnglish
Article numberB06303
Pages (from-to)1-18
Number of pages18
JournalJournal of Geophysical Research
Volume112
Issue numberB6
DOIs
Publication statusPublished - 4 Jun 2007
Externally publishedYes

Bibliographical note

Copyright 2007 by the American Geophysical Union. Originally published as Weeraratne, D. S., D. W. Forsyth, Y. Yang, and S. C. Webb (2007), Rayleigh wave tomography beneath intraplate volcanic ridges in the South Pacific, J. Geophys. Res., 112, B06303. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

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