Constraints from seismic anisotropy on the nature of the lowermost mantle

被引:203
作者
Kendall, JM [1 ]
Silver, PG [1 ]
机构
[1] CARNEGIE INST WASHINGTON,DEPT TERR MAGNETISM,WASHINGTON,DC 20015
关键词
D O I
10.1038/381409a0
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
THE D '' layer lies at the bottom of the Earth's rocky mantle, and separates it from the liquid metal-alloy core, This region, extending from the cure-mantle boundary to a few hundred kilometres above (Fig. 1), is geodynamically analogous to the more easily studied lithosphere, at the top of the mantle, The structure of D '' may reflect the style of lower-mantle convection, the nature of core-mantle interaction and perhaps even the fate of subducting lithosphere(1). Observations of lithospheric seismic anisotropy have provided valuable insight into the nature of the upper-mantle boundary layer, but discussion of lower-mantle seismic anisotropy has been somewhat contentious(2-5). Here we present evidence, from seismic waves that have traversed the lowermost mantle beneath the Caribbean region, for a zone of seismic anisotropy below the D '' discontinuity, which in this region lies 250 km above the core-mantle boundary. The anisotropy is most probably due to horizontal layering or aligned inclusions of a material with differing shear-wave velocity. If D '' is a graveyard for subducted lithosphere, a plausible explanation of the anisotropy may be the contrast between cold lithospheric mantle and material that formerly constituted the oceanic crust, which may have lower shear-wave velocity owing to the presence of melt.
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页码:409 / 412
页数:4
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