Rheological controls on slab delamination

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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.