Asymmetric Electrical Structure in the Mantle Beneath the East Pacific Rise at 17°S
R. L. Evans,
1*
P. Tarits,
2
A. D. Chave,
1
A. White,
3
G. Heinson,
3
J. H. Filloux,
4
H. Toh,
5
N. Seama,
6
H. Utada,
7
J. R. Booker,
8
M. J. Unsworth
8
The magnetotelluric component of the Mantle
Electromagnetic and Tomography (MELT) Experiment measured the
electrical resistivity structure of the mantle beneath the
fast-spreading southern East Pacific Rise (EPR). The data reveal an
asymmetric resistivity structure, with lower resistivity to the west of
the ridge. The uppermost 100 kilometers of mantle immediately to the
east of the ridge is consistent with a dry olivine resistivity
structure indicating a mantle depleted of melt and volatiles. Mantle
resistivities to the west of the ridge are consistent with a low-melt
fraction (about 1 to 2 percent interconnected melt) distributed over a broad region and extending to depths of about 150 kilometers. The
asymmetry in resistivity structure may be the result of asymmetric spreading rates and a westward migration of the ridge axis and suggests
distinct styles of melt formation and delivery in the mantle beneath
the two plates.
1 Woods Hole Oceanographic Institution, Woods
Hole, MA 02543, USA.
2 UMR CNRS 6538, Universite
Bretagne Occidentale, Brest, France.
3 Flinders
University, Adelaide, South Australia 5042, Australia.
4 Scripps Institution of Oceanography, La Jolla, CA
92093, USA.
5 Toyama University, Toyama 930-8555, Japan.
6 Chiba University, Chiba, Japan.
7 Earthquake Research Institute, University of
Tokyo, Tokyo 113, Japan.
8 Geophysics Program AK-50,
University of Washington, Seattle, WA 98195, USA.
*
To whom correspondence should be addressed. E-mail:
revans{at}whoi.edu
