Earth Sciences

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.

Reference:

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