Philippe Gillet | EPFL Graph Search

Philippe GILLET completed his undergraduate studies in Earth Science at Ecole normale supérieure de la rue dUlm (Paris). In 1983 he obtained a PhD in Geophysics at Université de Paris VII and joined Université de Rennes I as an assistant. Having obtained a State Doctorate in 1988, he became a Professor at this same university, which he left in 1992 to join Ecole normale supérieure de Lyon.

The first part of his research career was devoted to the formation of mountain ranges particularly of the Alps. In parallel, he developed experimental techniques (diamond anvil cells) to recreate the pressure and temperature prevailing deep inside planets in the lab. These experiments aim at understanding what materials make up the unreachable depths of planets in the solar system.

In 1997, Gillet started investigating extraterrestrial matter. He was involved in describing meteorites coming from Mars, the moon or planets which have disappeared today and explaining how these were expelled from their original plant by enormous shocks which propelled them to Earth. He also participated in the NASA Stardust program and contributed to identify comet grains collected from the tail of Comet Wild 2 and brought back to Earth. These grains represent the initial minerals in our solar system and were formed over 4.5 billion years ago. He has also worked on the following subjects:

Interactions between bacteria and minerals.

Solid to glass transition under pressure.

Experimental techniques: laser-heated diamond anvil cell, Raman spectroscopy, X-ray diffraction with synchrotron facilities, electron microscopy.

Philippe Gillet is also active in science and education management. He was the Director of the CNRS Institut National des Sciences de lUnivers (France), the President of the French synchrotron facility SOLEIL and of the French National Research Agency (2007), and the Director of Ecole normale supérieure de Lyon. Before joining EPFL he was the Chief of Staff of the French Minister of Higher Education and Research.

Selected publications:

Ferroir, T., L. Dubrovinsky, A. El Goresy, A. Simionovici, T. Nakamura, and P. Gillet (2010), Carbon polymorphism in shocked meteorites: Evidence for new natural ultrahard phases, Earth and Planetary Science Letters, 290(1-2), 150-154.

Barrat J.A., Bohn M., Gillet Ph., Yamaguchi A. (2009) Evidence for K-rich terranes on Vesta from impact spherules. Meteoritics & Planetary Science, 44, 359374.

Brownlee D, Tsou P, Aleon J, et al. (2006) Comet 81P/Wild 2 under a microscope. Science, 314, 1711-1716.

Beck P., Gillet Ph., El Goresy A., and Mostefaoui S. (2005) Timescales of shock processes in chondrites and Martian meteorites. Nature 435, 1071-1074.

Blase X., Gillet Ph., San Miguel A. and Mélinon P. (2004) Exceptional ideal strength of carbon clathrates. Phys. Rev. Lett. 92, 215505-215509.

Gillet Ph. (2002) Application of vibrational spectroscopy to geology. In Handbook of vibrational spectroscopy, Vol. 4 (ed. J. M. Chalmers and P. R. Griffiths), pp. 1-23. John Wiley & Sons.

Gillet Ph., Chen C., Dubrovinsky L., and El Goresy A. (2000) Natural NaAlSi3O8 -hollandite in the shocked Sixiangkou meteorite. Science 287, 1633-1636.

Composition and Pressure Effects on Partitioning of Ferrous Iron in Iron-Rich Lower Mantle Heterogeneities

James Badro, Charles-Edouard Boukaré, Marco Cantoni, Susannah McGregor Dorfman, Philippe Gillet, Farhang Nabiei

Both seismic observations of dense low shear velocity regions and models of magma ocean crystallization and mantle dynamics support enrichment of iron in Earth’s lowermost mantle. Physical properties of iron-rich lower mantle heterogeneities in the modern Earth depend on distribution of iron between coexisting lower mantle phases (Mg,Fe)O magnesiowüstite, (Mg,Fe)SiO3 bridgmanite, and (Mg,Fe)SiO3 post-perovskite. The partitioning of iron between these phases was investigated in synthetic ferrous-iron-rich olivine compositions (Mg0.55Fe0.45)2SiO4 and (Mg0.28Fe0.72)2SiO4 at lower mantle conditions ranging from 33–128 GPa and 1900–3000 K in the laser-heated diamond anvil cell. The resulting phase assemblages were characterized by a combination of in situ X-ray diffraction and ex situ transmission electron microscopy. The exchange coefficient between bridgmanite and magnesiowüstite decreases with pressure and bulk Fe# and increases with temperature. Thermodynamic modeling determines that incorporation and partitioning of iron in bridgmanite are explained well by excess volume associated with Mg-Fe exchange. Partitioning results are used to model compositions and densities of mantle phase assemblages as a function of pressure, FeO-content and SiO2-content. Unlike average mantle compositions, iron-rich compositions in the mantle exhibit negative dependence of density on SiO2-content at all mantle depths, an important finding for interpretation of deep lower mantle structures.

2021

Investigating Magma Ocean Solidification on Earth Through Laser‐Heated Diamond Anvil Cell Experiments

James Badro, Charles-Edouard Boukaré, Marco Cantoni, Philippe Gillet, Cécile Hébert, Farhang Nabiei

We carried out a series of silicate fractional crystallization experiments at lower mantle pressures using the laser-heated diamond anvil cell. Phase relations and the compositional evolution of the cotectic melt and equilibrium solids along the liquid line of descent were determined and used to assemble the melting phase diagram. In a pyrolitic magma ocean, the first mineral to crystallize in the deep mantle is iron-depleted calcium-bearing bridgmanite. From the phase diagram, we estimate that the initial 33%–36% of the magma ocean will crystallize to form such a buoyant bridgmanite. Substantial calcium solubility in bridgmanite is observed up to 129 GPa, and significantly delays the crystallization of the calcium silicate perovskite phase during magma ocean solidification. Residual melts are strongly iron-enriched as crystallization proceeds, making them denser than any of the coexisting solids at deep mantle conditions, thus supporting the terrestrial basal magma ocean hypothesis (Labrosse et al., 2007).

2021

Effects of composition and pressure on electronic states of iron in bridgmanite

Susannah McGregor Dorfman, Philippe Gillet, Arnaud Magrez

Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O-3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mossbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mossbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10-50% Fe/total cations, 0-25% Al/total cations, 12-100% Fe3+/total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe3+ provide a Mossbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at similar to 70 GPa. Thus center shift can easily distinguish Fe3+ from Fe2+ at high pressure, which exhibits two distinct Mossbauer sites with center shift similar to 1 mm/s and quadrupole splitting 2.4-3.1 and 3.9 mm/s at similar to 70 GPa. Correct quantification of Fe3+/total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. In Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to similar to 20% of the Fe may be a Fe2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.

MINERALOGICAL SOC AMER2020

Effects of composition and pressure on electronic states of iron in bridgmanite

Susannah McGregor Dorfman, Philippe Gillet, Arnaud Magrez

MINERALOGICAL SOC AMER2020