Imaging the mantle beneath Iceland using integrated seismological techniques
Richard M. Allen (1),
Guust Nolet (1),
W. Jason Morgan (1),
Kristin Vogfjord (2),
Bergur H. Bergsson (2),
Palmi Erlendsson (2),
Gillian R. Foulger (3),
Steinunn Jakobsdottir (2),
Bruce R. Julian (4),
Matt Pritchard (3),
Sturla Ragnarsson (2),
Ragnar Stefansson (2).
(1) Dept. Geosciences, Princeton University, USA.
(2) Vedurstofa Islands, Reykjavik, Iceland.
(3) Dept. Geological Sciences, University of Durham, UK.
(4) U.S. Geological Survey, Menlo Park, CA, USA.
J. Geophys. Res. 107 (B12), 2325, doi: 10.1029/2001JB000595, 2002.
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Using a combination of body wave and surface wave datasets to reveal the
mantle plume and plume head, this study presents a tomographic image of
the mantle structure beneath Iceland to 400 km depth.
Data comes primarily from the PASSCAL-HOTSPOT deployment of 30 broadband instruments
over a period of two years, and is supplemented by data from the SIL and ICEMELT networks.
Three sets of relative teleseismic body wave arrival times are generated through cross-correlation:
S and SKS arrivals at 0.03-0.1 Hz, and P and PKIKP arrivals at 0.03-0.1 and 0.8-2.0 Hz.
Prior to inversion the crustal portion of the travel-time anomalies is removed using the
crustal model ICECRTb. This step has a significant effect on the mantle velocity variations imaged
down to a depth of ~250 km.
Inversion of relative arrival times only provides information on lateral velocity
variations. Surface waves are therefore used to provide absolute velocity information
for the uppermost mantle beneath Iceland.
The average wavenumber for the Love wave fundamental mode at 0.020 and 0.024 Hz
is measured and used to invert for the average S-velocity.
Combination of the body wave and surface wave information reveals a predominantly horizontal
low velocity anomaly extending from the Moho down to ~250 km depth,
interpreted as a plume head.
Below the plume head a near-cylindrical low velocity anomaly with a radius of ~100 km
and peak Vp and Vs anomalies of -2% and -4% respectively
extends down to the maximum depth of resolution at 400 km.
Within the plume head, in the uppermost mantle above the core of the plume, there is a relatively
high velocity with a maximum Vp and Vs anomaly of +2%.
This high velocity anomaly may be the result of the extreme degree of melt extraction necessary
to generate the thick (46 km) crust in central Iceland.
Comparison of the plume volumetric flux implied by our images, the crustal generation rate,
and the degree of melting suggested by Rare Earth Element inversions, suggests that (1) mantle material
must be flowing horizontally away from the plume core faster than the overlying
lithosphere, and (2)
the bulk of the plume material does not participate in melting beneath Iceland.
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© Richard M Allen