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Evidence for a Large-Scale Remnant of Subducted Lithosphere Beneath Fiji

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Science  29 Jun 2001:
Vol. 292, Issue 5526, pp. 2475-2479
DOI: 10.1126/science.292.5526.2475

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Abstract

We combine spatial variations of P- andS-wave speeds, 1000 fault plane solutions, and 6600 well-determined hypocenters to investigate the nature of subducted lithosphere and deep earthquakes beneath the Tonga back-arc. We show that perplexing patterns in seismicity and fault plane solutions can be accounted for by the juxtaposition of a steep-dipping Wadati-Benioff zone and a subhorizontal remnant of slab that is no longer attached to the actively subducting lithosphere. The detached slab may be from a previous episode of subduction along the fossil Vitiaz trench about 5 to 8 million years ago. The juxtaposition of slabs retains a large amount of subducted material in the transition zone of the mantle. Such a configuration, if common in the past, would allow the preservation of a primordial component in the lower mantle.

  • * To whom correspondence should be addressed. E-mail: w-chen{at}uiuc.edu

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