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Understanding the D'' region
24 June 2013
Plate tectonic theory was the most significant
breakthrough in geophysics in the last half-century: it explained many of the
surface features of Earth and linked them to convection in the Earth’s silicate
interior, the mantle.
What was missing from plate tectonics, and has been the
focus of much subsequent investigation, was the way the bottom of the
convection system worked above the core-mantle boundary. Seismic observations
of texturing can be used to map out flow in the lowermost mantle but only if we
understand how the seismically observed texturing is created in terms of
mineral deformation and recrystallisation.
So far no mineralogical model has
been able to predict all of the texturing observed in the lowermost mantle. The
present paper addresses this shortcoming by including the effect of
recrystallization as one form of the most common lower-mantle mineral (MgSiO3) recrystallizes into
another, lower pressure form. This gives us, for the first time, the
possibility of understanding the flow at the base of the mantle and hence
closing the mantle convection loop.
Figure caption: Electron diffraction pattern showing strong crystallographic alignment between perovskite and post-perovskite. This texture inheritance can explain the switch of siesmic anisotropy observed between hot and cold regions of D'' above the core-mantle boundary.
Strong inheritance of texture between perovskite and post-perovskite in the D'' layer. D.P. Dobson, N. Miyajima, F.Nestols, M. Alvaro, N. Casati, C. Liebske, I.G. Wood and A.M. Walker. Nature Geoscience. DOI:10.1038/ngeo1844