Understanding the deep Earth

The structure of the deep Earth and the D'' region

The structure of the deep Earth and the D'' region between lower mantle and core. Post-perovskite MgSiO3 in D’’ consists of layers of octahedra and hendecahedra. In the lower mantle, MgSiO3 is made up of corner-linked octahedra.
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Studies at ISIS reveal important information about the behaviour of a post-perovskite.

At the bottom of the Earth’s lower mantle and just above the liquid outer core, there is a ~300 km thick region termed the D''-zone. Although thin, this zone plays a crucial role in Earth’s evolution as it regulates heat exchange from the metallic core to the silicate mantle and is the source of plume-style mantle convection.

 D'' is associated with a change in crystal structure of MgSiO3 perovskite – the major mineral in the lower mantle – to a denser ‘post-perovskite’ form. Post-perovskite MgSiO3 is stable only at million-atmosphere pressures and so it is impossible to measure directly many of its physical properties. Instead, measurements must be made on other materials with the same structure and combined with computer simulations to estimate values for the D'' MgSiO3 structure. Our experiments at ISIS on CaPtO3, one of very few post-perovskites stable at atmospheric pressure, show that its structure responds to temperature differently from MgSiO3 and so it may not be a suitable substitute. The search for good post-perovskite analogues must, therefore, continue.

A Lindsay-Scott, IG Wood, DP Dobson, L Voc˘adlo, JP Brodholt (University College London), T Taniguchi (National Institute for Materials Science, Japan), KS Knight, MG Tucker (ISIS)

Research date: August 2011

Further Information

Contact: Dr I Wood, ian.wood@ucl.ac.uk

Further reading: Lindsay-Scott et al., Phys. Earth. Plan. Int. 182 (2010) 113

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