HR: 1330h
AN: V12B-0593    [PDF]
TI: Structure of Crust and Upper Mantle Beneath Iceland from Rayleigh Wave Tomography
AU: * Li, A
EM: ali2@mail.uh.edu
AF: University of Houston, 4800 Calhoun Rd, Houston, TX 77204 United States
AU: Detrick, R S
EM: rdetrick@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd, Woods Hole, MA 02543 United States
AB: We have imaged the 3-D velocity structure in the crust and upper mantle beneath Iceland using Rayleigh waves recorded at the HOTSPOT and ICEMELT broadband seismic stations. The two-plane-wave inversion technique was adopted to obtain 2-D phase velocities at eleven frequencies from 0.01 to 0.05 Hz. These phase velocities were subsequently inverted for shear wave structure. A 1-D velocity model of Iceland was constructed using the average phase velocities. Crustal thickness was fixed at 29 km in this model. The velocity is significantly lower ($>$ 4%) than that in the global model of AK135 to at least 200 km depth. A strong low velocity layer with a shear velocity of 3.9-4.0 km/s appears at depths of 50 to 110 km. Both crustal thickness and velocity are solved in obtaining the 3-D structure of Iceland. The crust is generally thick in eastern Iceland and thin in western Iceland, while the thickest crust of $\sim$38 km is found in central Iceland rather than beneath the current hotspot in southeastern Iceland. Low velocity anomalies in the crust follow the trend of Icelandic rift zones in the south and appear slightly west off the rift zones in the north. In the shallow upper mantle ($<$90 km), low velocity anomalies are generally observed under the Icelandic rift zones and high velocities beneath western and eastern Iceland, reflecting the variation of lithosphere thickness across Iceland. The slowest area is imaged from the northern part of the hotspot to the northern rift zones, which is probably associated with the presence of partial melt. At depths of 100 to 200 km, velocity images are dominated by two distinctive anomalies, a low velocity area in southwestern Iceland and a high velocity region in southeastern Iceland. Surprisingly, this high velocity anomaly is under the location of the current hotspot, which may reflect a strong radial anisotropy associated with the upwelling flow in the plume conduit and/or a more-depleted mantle due to the extensive melt extraction under the hotspot.
DE: 7218 Lithosphere and upper mantle
DE: 7255 Surface waves and free oscillations
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8145 Physics of magma and magma bodies
DE: 8180 Tomography
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting