Seismic structure of the Iceland mantle plume

Cecily J. Wolfe, Ph.D.
Woods Hole Oceanographic Institution

Wednesday, May 13, 1998
3:30 p.m.¾ Pacific Forum

Understanding the geometry of upwelling mantle flow and the characteristics of melting beneath hotspots and mid-ocean ridges is of fundamental importance for topics ranging from the formative processes for the crust and lithosphere to the large-scale dynamics and chemical makeup of the mantle. One of the most studied regions is Iceland, a hotspot centered on the Mid-Atlantic Ridge, yet previous seismological and geodynamic studies have been unable to constrain the width, temperature, and depth extent of the plume.

ICEMELT was a regional broadband seismometer array designed to resolve the detailed characteristics of the upper-mantle seismic structure beneath Iceland. We obtain the three-dimensional seismic velocity structure of the upper mantle using the relative travel times of body waves from teleseismic earthquakes recorded across the ICEMELT array. Inversion solutions show a cylindrical zone of low P-wave and S-wave velocities that persists from 100 km to at least 400 km depth beneath central Iceland, which can be interpreted as the locus of the active Iceland mantle plume. The radius of the low-velocity anomaly is about 150 kilometers, and the magnitude of the velocity anomaly is 2% for P waves and 4% for S waves. This high-resolution upper mantle image indicates that Iceland is underlain by a hot and narrow plume of upwelling mantle.

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