HR: 0800h
AN: V31B-1430    [Abstracts]
TI: Short-Period Surface Wave Study of the Upper Mantle Beneath the Reykjanes Ridge: Investigation of the Effect of the Icelandic Hotspot on Sub-Ridge Mantle Flow and Melting
AU: * Delorey, A A
EM: delorey@hawaii.edu
AF: SOEST/University of Hawaii, School of Ocean and Earth Science and Technology University of Hawaii 1680 East-West Road, Honolulu, HI 96822 United States
AU: Dunn, R A
EM: dunnr@hawaii.edu
AF: SOEST/University of Hawaii, School of Ocean and Earth Science and Technology University of Hawaii 1680 East-West Road, Honolulu, HI 96822 United States
AU: Gaherty, J B
EM: gaherty@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, Columbia University 61 Rt 9W, Palisades, NY 10964 United States
AB: Although it is a slow-spreading mid-ocean ridge, the Reykjanes Ridge exhibits some characteristics typical of faster-spreading ridges, presumably due to far reaching effects of the Icelandic hotspot. Two end-member models exist to describe the hotspot's influence. In one model, plume material spreads out in a radial manner under the lithosphere; in the other model, plume material is preferentially channeled down the ridge axis. We analyze short-period Love and Rayleigh wave records for waves that propagated along the Reykjanes Ridge. These waves were generated by regional earthquakes occurring in the North Atlantic to the south of Iceland, and were recorded by the HOTSPOT and ICEMELT arrays and the GSN station BORG, located on Iceland. We show that surface waves traveling along the ridge are focused into a wide low-velocity channel beneath the ridge, at least 125km across, where the low-velocity channel is consistent with high temperatures and a small amount of melt. The waveforms are sensitive to the magnitude and width of this channel. We extract the phase, group, and amplitude information of narrow-pass filtered waveforms over the period range of ~14-80s. Over ~12000 such measurements are included in an inversion for mantle and crustal shear velocity structure; in addition the joint inversion of horizontally polarized Love and vertically polarized Rayleigh wave data provides a measure of mantle anisotropy. We will present tomographic images of the shear velocity structure of the upper mantle and crust and discuss constraints that our results place on thermal structure, the distribution of melt, and mantle flow beneath the Reykjanes Ridge in association with hotspot influence.
DE: 8180 Tomography
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 7218 Lithosphere and upper mantle
DE: 3035 Midocean ridge processes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting