Laboratory Manager: Prof David Dobson
The rheological properties of the Earth’s mantle exert a fundamental control on mantle convection. Many of the surface features of the Earth including mountain belts, subduction zones, hot spots and seismic zones are therefore significantly affected by mantle rheology. Unfortunately, field-based estimates of mantle rheology con only be determined for exceptional circumstances (such as isostatic rebound of the Canadian Shield) and many of the important parameters and regions are not sampled.
One approach uses an independently movable anvil to deform the sample at high pressure in a manner analogous to the Griggs solid-media apparatus. With this we can study the relative strength of materials and deform samples to very high strains, but the differential stress is poorly constrained.
Alternatively we can diffraction methods to measure the elastic strain of a sample as a proxy for stress while deforming a sample. We are developing a neutron-diffraction based uniaxial cell for use on ENGIN-X beamline at ISIS. This will allow rheological measurements at very low strain-rates (~10-9/s) approaching those of the Earth.
Within subducting oceanic crust the seismogenic zone can persist to ~700 km depth, 10 times deeper than in other tectonic settings. We have an active programme, using multi-anvil-based acoustic location techniques, to investigate the causes of seismicity under the extremes of pressure and temperature which exist within the subducting slab.