HR: 1330h
AN: V12B-0592    [PDF]
TI: Crustal and Uppermost Mantle Structure Beneath Iceland From Local Earthquake Tomography
AU: * Yang, T
EM: ty@ponlai.gso.uri.edu
AF: Graduate School of Oceanography University of Rhode Island, South Ferry Road, Narragansett, RI 02882 United States
AU: Shen, Y
EM: yang@island.gso.uri.edu
AF: Graduate School of Oceanography University of Rhode Island, South Ferry Road, Narragansett, RI 02882 United States
AB: The Iceland hotspot has been a site of extensive seismological investigation. The recent shear-velocity crustal model constructed from surface waves shows a broad low velocity zone in the upper crust near 10-15 km depth along the Icelandic neovolcanic zones, and a low velocity anomaly confined to a circular region in the lower crust ($>$ 15 km) beneath central Iceland. These features are suggestive of broad regions of high temperature and perhaps the presence of partial melt in the crust, and lateral transport of magma along the volcanic zones from the presumed plume center. However, the extensive presence of partial melt in the crust contradicts several other lines of evidence suggesting that the entire Icelandic crust is subsolidus (except for small volumes beneath central volcanoes). Independent measurements of compressional and shear velocities in the crust and uppermost mantle would help to resolve this controversy, which is important for understanding the thermal structure of and mechanisms of magma transfer in the crust and uppermost mantle. We present a three-dimensional P-wave velocity model of the Icelandic crust and uppermost mantle from tomographic inversions of over 6000 first-arrival P waves from local earthquakes recorded by two broadband seismic arrays in Iceland. The model shows low-velocity regions in the upper crust beneath active volcanic regions and in the middle and lower crust beneath central Iceland, in general agreement with the S-wave model. In addition, P waves traversing below the crust provide constraints on the uppermost mantle structure. A pronounced P-wave velocity reduction, 5% or about 2 times that in the 100-400 km depth range imaged by teleseismic tomography, is found in the uppermost mantle beneath central Iceland. The large velocity reduction requires an elevated temperature of up to 500 degrees or, more likely, a combination of an excess temperature and partial melt. The result provides further support for the hypothesis of a relatively focused melt supply of the Iceland hotspot.
DE: 0935 Seismic methods (3025)
DE: 7203 Body wave propagation
DE: 7223 Seismic hazard assessment and prediction
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8180 Tomography
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting