Evidence for a Large-Scale Remnant of Subducted Lithosphere Beneath Fiji
Wang-Ping Chen,12*
Michael R. Brudzinski1
We combine spatial variations of P- and
S-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.
1 Department of Geology, University of
Illinois, Urbana, IL 61801, USA.
2 Mid-America
Earthquake (MAE) Center, University of Illinois, Urbana, IL 61801, USA.
*
To whom correspondence should be addressed. E-mail:
w-chen{at}uiuc.edu
