Computer Science
Scientific paper
Mar 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005natur.434..371d&link_type=abstract
Nature, Volume 434, Issue 7031, pp. 371-374 (2005).
Computer Science
26
Scientific paper
Ultralow-velocity zones (ULVZs) are regions of the Earth's core-mantle boundary about 1-10kilometres thick exhibiting seismic velocities that are lower than radial-Earth reference models by about 10-20per cent for compressional waves and 10-30per cent for shear waves. It is also thought that such regions have an increased density of about 0-20per cent (ref. 1). A number of origins for ULVZs have been proposed, such as ponding of dense silicate melt, core-mantle reaction zones or underside sedimentation from the core. Here we suggest that ULVZs might instead be relics of banded iron formations subducted to the core-mantle boundary between 2.8 and 1.8billion years ago. Consisting mainly of interbedded iron oxides and silica, such banded iron formations were deposited in the world's oceans during the late Archaean and early Proterozoic eras. We argue that these layers, as part of the ocean floor, would be recycled into the Earth's interior by subduction, sink to the bottom of the mantle and may explain all of the observed features of ULVZs.
Brodholt John P.
Dobson David P.
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