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Originally published in Science Express on 12 April 2007
Science 11 May 2007:
Vol. 316. no. 5826, pp. 855 - 859
DOI: 10.1126/science.1138074
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Research Articles

Pervasive Seismic Wave Reflectivity and Metasomatism of the Tonga Mantle Wedge

Yingcai Zheng,1 Thorne Lay,1* Megan P. Flanagan,2 Quentin Williams1

Subduction zones play critical roles in the recycling of oceanic lithosphere and the generation of continental crust. Seismic imaging can reveal structures associated with key dynamic processes occurring in the upper-mantle wedge above the sinking oceanic slab. Three-dimensional images of reflecting interfaces throughout the upper-mantle wedge above the subducting Tonga slab were obtained by migration of teleseismic recordings of underside P- and S-wave reflections. Laterally continuous weak reflectors with tens of kilometers of topography were detected at depths near 90, 125, 200, 250, 300, 330, 390, 410, and 450 kilometers. P- and S-wave impedances decreased at the 330-kilometer and 450-kilometer reflectors, and S-wave impedance decreased near 200 kilometers in the vicinity of the slab and near 390 kilometers, just above the global 410-kilometer increase. The pervasive seismic reflectivity results from phase transitions and compositional zonation associated with extensive metasomatism involving slab-derived fluids rising through the wedge.

1 Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA.
2 Energy and Environment Directorate, Institute of Geophysics and Planetary Physics (IGPP), Lawrence Livermore National Laboratory (LLNL), Livermore, CA 94551, USA.

* To whom correspondence should be addressed. E-mail: thorne{at}pmc.ucsc.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Upper Mantle Discontinuity Topography from Thermal and Chemical Heterogeneity.
N. Schmerr and E. J. Garnero (2007)
Science 318, 623-626
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