Dr Annette Kleppe


Visiting Senior Research Fellow

Email: annettek@earth.ox.ac.uk
TEL: +44 (1865) 272065
FAX: +44 (1865) 272072

Research Profile

The majority of minerals in the Earth are hidden at great depths under high-pressures and high-temperatures. The behaviour of these minerals controls the large-scale processes of our planet, which are manifested at the surface by volcanism, earthquakes, and plate tectonics. I explore the physical properties and crystal structures of geological materials under extreme pressures and temperatures in order to understand the structure as well as composition and the formation and evolution of the Earth’s mantle and core.

In the laboratory I create the conditions that prevail within the Earth’s deep interior in a diamond-anvil cell: Two brilliant-cut diamonds under a load of several tonnes compress a sample, a few micrometer in size, up to pressures of the Earth’s core (360 GPa or 3.6 million atm). Simultaneous high-temperatures (up to 4000 K) are achieved by focusing high-power infra-red laser beams through the diamond-windows on the sample. I study changes in structure and bonding, and phase transformations including amorphization of materials in-situ under high-pressures and/or temperatures with synchrotron X-ray diffraction techniques (Diamond,ESRF) and Micro-Raman spectroscopy (Oxford).

My research interests cover many fields of high-pressure and high- or low-temperature Earth and Physical Sciences. Currently I am working on

  • Pressure and/or temperature induced phase transitions in high-pressure silicates and their implications for the structure and dynamics of the Earth’s mantle.
  • Volatiles, in particular H, in the Earth’s mantle. I would like to understand the significance and properties of hydrogen bonding in minerals at deep-Earth conditions and the influence of protonation on phase transformation behaviour.
  • Metal-hydride systems. The Earth's core is known to be less dense than pure iron and one candidate for the alloying component is hydrogen making it of fundamental interest to understand properties of metal-hydrogen systems.
  • The Earth's core. I am investigating the melting line of iron and iron-alloys at high-pressures and -temperatures.
  • Development of synchrotron and spectroscopic techniques for in-situ measurements at high-pressures and -temperatures.

Selected Publications

  • A.K. Kleppe and A.P. Jephcoat, Raman spectroscopic studies of hydrous and nominally anhydrous deep mantle phases, AGU Monograph"Earth’s Deep Water Cycle", 2006.
  • A.K. Kleppe, A.P. Jephcoat, and J.R. Smyth, High-pressure Raman spectroscopic studies of hydrous wadsleyite II, American Mineralogist, 91 (7), 1102-1109, 2006.
  • A.K. Kleppe, A.P. Jephcoat, and J.R. Smyth, High-pressure Raman spectroscopic study of Fo 90hydrous wadsleyite, Physics and Chemistry of Minerals, 32, 700-709, 2006.
  • A.K. Kleppe and A.P. Jephcoat, High-pressure Raman spectroscopic studies of FeS 2pyrite, Mineralogical Magazine,68 (3), 433-441, 2004.
  • M.D. Welch, A.K. Kleppe and A.P. Jephcoat, Novel high-pressure behaviour in chlorite: A synchrotron XRD study of clinochlore to 27 GPa, American Mineralogist, 89, 1337-1340, 2004.
  • A.K. Kleppe, A.P. Jephcoat, and M.D. Welch, The effect of pressure upon hydrogen bonding in chlorite: A Raman spectroscopic study of clinochlore to 26.5 GPa, American Mineralogist, 88, 567-573,  2003.
  • A.K. Kleppe, A.P. Jephcoat, J.R. Smyth and D.J. Frost, On protons, and the High-Pressure Behavior of Ringwoodite, Geophysical Research Letters, 29 (21), 17-1-17-4, 2002.
  • A.K. Klepp e, A.P. Jephcoat, J.R. Smyth, Raman Spectroscopic Study of hydrous g -Mg 2SiO 4to 56.5 GPa, Physics and Chemistry of Minerals, 29 (7), 473-476, 2002.
  • M.D. Brasier, O.R. Green, A.P. Jephcoat, A.K. Kleppe, M.J. van Kranendonk, J.F. Lindsay, A. Steele and N.V. Grassineau, Questioning the evidence for Earth's oldest fossils, Nature, 416, 76-81, 2002.
  • A.K. Kleppe, A.P. Jephcoat and N.L. Ross, Raman Spectroscopic Studies of Phase E to 19 GPa, American Mineralogist, 85, 1275-1281, 2001.
  • A.K. Kleppe, A.P. Jephcoat, H. Olijnyk, A.E. Slesinger, S.C. Kohn and B.J. Wood, Raman Spectroscopic Study of Hydrous Wadsleyite (ß-Mg 2SiO 4) to 50 GPa, Physics and Chemistry of Minerals, 28, 232-241, 2001.