Rheological controls on slab delamination

Lead Research Organisation: University College London
Department Name: Earth Sciences

Abstract

Subducted oceanic lithosphere displays a range of complex behaviours including penetration into the lower mantle, stagnation in the transition zone and ponding at, or just below, the 660 km seismic discontinuity, and intermediate behaviour between these end-members. At a finer scale, the MORB component is thought to mechanically decouple from the slab core to produce seismic scatterers in the lower mantle and potential reservoirs for enriched OIB material at the core-mantle boundary and the base of the transition zone. The exact behaviour of the slab and its different components will depend on their densities and strengths relative to each other and the surrounding mantle. While the densities of the various rocks and minerals in the mantle are well known our knowledge of their strengths is very poor; geodynamical simulations show a range of slab behaviours dependent on these properties. We will measure the relative strength of the main rocks which comprise the slab (mid-ocean-ridge basalt and depleted peridotite) under the range of pressure and temperature conditions of the subducting slab to ~1000 km depth. This will allow us to assess which phase assemblages of the two compositions along the slab geotherm show the main rheological contrasts and hence better understand the processes of slab deformation and delamination.

Planned Impact

This is curiosity-driven research with no direct relevance to industry or policy makers.
However, there is potential for technological spin offs:
1)The development of in-situ X-ray facilities for high-pressure research would be of interest to some UK industry, for example AWE who we are developing links with.

2)High-pressure mineralogy can be useful for informing novel crystallography at low pressure. Dobson is developing a new blue pigment based around the crystal structure of ringwoodite and a better understanding of its defect chemistry (as might be achieved through looking at the effects of deformation on ringwoodite's optical properties) might help this process. UK-based Colart is interested in commercialising this pigment when it reaches a sufficient level of development.

In addition, the Earth's interior catches the public imagination. Dobson has a strong collaboration with the Slade School of Art, having developed and pioneered their Scientist in Residence programme and we propose to continue this in the form of a public outreach symposium and high-quality publication based around the science and materiality of colour.

Publications

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