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Difficulties in Seismically Imaging the Icelandic Hotspot



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Difficulties in Seismically Imaging the Icelandic Hotspot William R Keller Don L Anderson Robert W Clayton Department of Geological and Planetary Sciences California Institute of Technology Submitted to Science 02 28 00 Correspond with William R Keller Seismological Laboratory Caltech MC 252 21 Pasadena CA 91125 Ph 626 395 6932 Fax 626 564 0715 e mail keller gps caltech edu Keller et al IMAGING ICELAND HOTSPOT 03 08 00 page 1 of 12 Abstract The locations of volcanic islands may be controlled by thin or extending parts of the lithosphere over a partially molten asthenosphere 1 2 by edge effects near the boundaries of thick cratonic lithosphere 3 or by narrow jets of hot mantle rising from deep within the mantle 4 6 Many hotspots are found on or near ridges at lithospheric discontinuities or in extensional environments so high resolution seismic images are required to determine whether it is lithospheric structure stresses in the lithosphere or the deep mantle that is the controlling factor for the location of active volcanoes In this study we perform a simple experiment in which we use basic geometrical arguments and idealized experimental parameters in order to understand the resolution of tomographic images of the upper 400 km of the mantle under Iceland Our results indicate that a narrow deep seated mantle plume is not required in order to explain the observed travel time delays Results of tomographic inversions are often viewed as unique however recent seismic studies of the Icelandic Hotspot have illustrated the non unique nature of these models The geometry of plumes in laboratory and computer simulations is a narrow cylinder capped by a bulbous head that flattens beneath the lithosphere giving an overall mushroom shape to the upwelling 7 9 Deep mantle upwellings are also expected to broaden beneath the 650 km endothermic phase change On the other hand the geometry of upwellings driven by Keller et al IMAGING ICELAND HOTSPOT 03 08 00 page 2 of 12 plate



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