Research Interests
Along
with colleagues at UCL and the Bayerisches
Geoinstitut, I perform high-pressure experiments on
deep Earth minerals and rocks.
We have several high-pressure devices, including
multi-anvil presses, Diamond cells and a modified Paris-Edinburgh
cell for neutron diffraction.
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Internal view of a multi anvil press at UCL
which can generate pressures to 25 GPa.
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Diamond cell which can be used to 100 GPa or
more, but has far smaller sample volumes.
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Earth’s Core Materials
The
core of the Earth is among the most inaccessible and least
understood regions of Earth. The solid inner core and liquid outer core consist
of iron plus several percent of a light element. Together with Drs Ian Wood and
Lidunka Vocadlo, I have been investigating the iron-alloys which
are stable at high pressures.
We have discovered a new high-pressure phase of FeSi
which is a prime core candidate material.
The
outer core is responsible for the Earth’s magnetic
field. Geodynamo
models require a knowledge of the
viscosity and diffusivity of the outer core liquid.
We have an active programme to measure these properties
at high pressure.
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Stacked diffraction patterns from high-pressure
CsCl-structured FeSi.
These patterns were collected from a sample
in a Diamond-cell using synchrotron radiation at the
European Synchrotron Research Facility.
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Transport Properties of Mantle Materials
Subtle
variations in the Earth’s magnetic field can be used
to probe the electrical conductivity of the mantle.
This, in turn, is a powerful tool for investigating
variations in temperature and chemistry within the deep
Earth. Dr
John Brodholt and I been investigating the electrical conductivity
of mantle minerals olivine, wadsleyite,
magnesiowustite and perovskite. We have used these results to test whether the
mantle convects in a layered or
whole-mantle fashion.
The
viscosity of the mantle is very poorly constrained.
In the Laboratory for Mineral
Ice and Rock Physics , we have a programme to develop new rheological
testing apparatus for ultra-high-pressure experiments. These include the Gigapascal Deformation Cell
and the modified Paris-Edinburgh-Belt cell.
We will use Neutron diffraction to measure deviatoric
stresses and strains in situ at the new ENGIN-X
beamline at Rutherford Appleton Laboratory.
Along
with Prof. Phil Meredith and Steve
Boon we are developing new techniques to investigate
the origins of deep earthquakes.
Our recent work on serpentine dehydration was published
in Science and featured in the international press.
See what the BBC has to say about our
research ….and Science NOW
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True colour images of partially
dehydrated serpentine recovered from 6 GPa (top) and
8 GPa (bottom).
The strikingly different colours
are due to the different dehydration reactions at
the two pressures:
serpentine = olivine + enstatite + water (6 GPa)
and:
serpentine = phase A + enatatite + water (8GPa).
Both samples showed seismic
signals during dehydration, but the type of signal
was significantly different.
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Recent Publications
Dobson, D.P., Oxygen ionic conduction in MgSiO3 perovskite. Sub judice Phys. Earth Planet. Inter., 2002.
L.
Dubrovinsky, N. Dubrovinskaia, F.
Langenhorst, D. Dobson,
D. Rubie, C. Geßmann,
I. Abrikosov, B. Johansson, V.
I. Baykov, L. Vitos,
T. Le Bihan, Wilson A.
Crichton, Iron-silica interaction at extreme conditions
and the nature of the electrically conducting layer at the
base of Earth’s mantle.
Sub judice Nature, 2002.
Dobson, D.P., Crichton, W.A., Bouvier, P., Vocadlo,
L. and Wood, I.G., The equation of state of CsCl-structured
FeSi to 40 GPa;
implications for silicon in the Earth’s core. Geophys. Res. Lett., in press, 2002.
Dobson,
D.P., Meredith, P.G. and Boon, S.A., Simulation of Subduction zone seismicity by dehydration
of serpentine. Science,
298, 1407-1410, 2002.
Dobson, D.P. and Wiedenbeck, M., Fe- and C-self-diffusion
in liquid Fe3C to 15 GPa. Geophys. Res. Lett., 29, in press, 2002.
Vocadlo, L., Brodholt, J., Dobson, D.P.,
Knight, K.S., Marshall, W.G., Price, G.D. and Wood, I.G., The effect of ferromagnetism on
the equation of state of Fe3C studied by first-principles
calculations. Earth Planet. Sci. Lett., 203, 567-575, 2002.
Dobson,
D.P., Self-diffusion in liquid
Fe at high pressure. Phys. Earth Planet.
Inter., 130, 271-284, 2002.
Dobson, D.P., Vocadlo, L. and Wood, I., A new high-pressure
phase of FeSi. Am. Mineral, 87,
784-787, 2002.
Vocadlo, L. and Dobson, D.P. The Earth's deep interior. in Visions of the Future: Astronomy and Earth Science ed. J.M.M. Thompson, Cambridge University Press.
2001.
Dobson, D.P.,
Brodholt, J.P., Vocadlo, L. and Crichton, W.A., Experimental
verification of the Stokes-Einstein relation in liquid Fe-FeS
at 5 GPa. Molecular Physics, 99, 773-777
2001.
Dobson, D.P.,
Crichton, W.A., Vocadlo, L., Jones,
A.P., Wang, Y., Uchida, T., Rivers, M., Sutton, S. and Brodholt,
J.P., In situ measurement of viscosity of liquids in the
Fe-FeS system at high pressures
and temperatures. Amer. Mineral. 85, 1843-1847,
2000.
Dobson,
D.P & Brodholt, J.P. The electrical conductivity
and thermal profile of the Earth's mid-mantle.
Geophys. Res. Lett. 27 , 2325-2328, 2000.
Dobson, D.P. 57Fe and Co tracer diffusion in liquid Fe-FeS
at 2 and 5 GPa.
Phys. Earth.
Planet. Inter.
120, 137-144, 2000.
Dobson, D.P.
and Brodholt, J.P., The electrical conductivity of the lower mantle phase magnesiowüstite at high temperatures and pressures. J. Geophys. Res., 105, 531-538, 2000
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