Deep mantle origin of large igneous provinces and komatiites.

Large igneous provinces (LIPs) resulted from intraplate magmatic events mobilizing volumes of magma up to several million cubic kilometers. LIPs and lavas with deep mantle sources have compositions ranging from komatiites found in Archean greenstone belts to basalts and picrites in Phanerozoic flood basalt and recent oceanic islands. In this study, we identify the mantle conditions appropriate to each type of lava based on an experimental study of the melting of pyrolite.

In situ characterization of liquids at high pressure combining X-ray tomography, X-ray diffraction and X-ray absorption using the white beam station at PSICHÉ.

A novel experimental setup dedicated to the study of liquid and amorphous materials, on the white beam station of the PSICHÉ beamline at SOLEIL, is described. The Beer-Lambert absorption method has been developed using a broad-spectrum (white) incident beam for in situ density measurements at extreme conditions of pressure and temperature. This technique has been combined with other existing X-ray techniques (radiographic imaging, tomography and combined angle energy dispersive X-ray diffraction).

A new high-pressure technique for the measurement of low frequency seismic attenuation using cyclic torsional loading.

We report a new technique for torsional testing of materials under giga-pascal pressures, which uses a shearing module in a large-volume Paris-Edinburgh press in combination with high-resolution fast radiographic x-ray imaging. The measurement of the relative amplitude and phase lag between the cyclic displacement in the sample and a standard material (AlO) provides the effective shear modulus and attenuation factor for the sample. The system can operate in the 0.

Quantitative 4D X-ray microtomography under extreme conditions: a case study on magma migration.

X-ray computed tomography (XCT) is a well known method for three-dimensional characterization of materials that is established as a powerful tool in high-pressure/high-temperature research. The optimization of synchrotron beamlines and the development of fast high-efficiency detectors now allow the addition of a temporal dimension to tomography studies under extreme conditions. Presented here is the experimental setup developed on the PSICHE beamline at SOLEIL to perform high-speed XCT in the Ultra-fast Tomography Paris-Edinburgh cell (UToPEc).

Stability and equation of state of face-centered cubic and hexagonal close packed phases of argon under pressure.

The compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Three samples conditioning are used: (1) single crystal sample directly compressed between the anvils, (2) powder sample directly compressed between the anvils, (3) single crystal sample compressed in a pressure medium. A partial transformation of the face-centered cubic (fcc) phase to a hexagonal close-packed (hcp) structure is observed above 4.

Melting Curve and Isostructural Solid Transition in Superionic Ice.

The phase diagram and melting curve of water ice is investigated up to 45 GPa and 1600 K by synchrotron x-ray diffraction in the resistively and laser heated diamond anvil cell. Our melting data evidence a triple point at 14.6 GPa, 850 K.

Boron-MgO composite as an X-ray transparent pressure medium in the multi-anvil apparatus.

X-ray transparent materials are very beneficial for in situ X-ray experiments in the multi-anvil apparatus. We sintered machinable blocks of boron-MgO composites at 800-1000 °C under atmospheric pressure from a mixture of amorphous boron and brucite or Mg(OH). The machinability of composite blocks improved with an increase in the brucite content in the starting material; a brucite content higher than 15 wt.

Formation of bridgmanite-enriched layer at the top lower-mantle during magma ocean solidification.

Thermochemical heterogeneities detected today in the Earth's mantle could arise from ongoing partial melting in different mantle regions. A major open question, however, is the level of chemical stratification inherited from an early magma-ocean (MO) solidification. Here we show that the MO crystallized homogeneously in the deep mantle, but with chemical fractionation at depths around 1000 km and in the upper mantle.

Argon-neon binary diagram and ArNe Laves phase.

Mixtures of argon and neon have been experimentally studied under high pressure. One stoichiometric compound, with ArNe composition, is observed in this system. It is a Laves phase with a hexagonal MgZn structure, stable up to at least 65 GPa, the highest pressure reached in the experiments.

High-speed tomography under extreme conditions at the PSICHE beamline of the SOLEIL Synchrotron.

In situ microtomography at high pressure and temperature has developed rapidly in the last decade, driven by the development of new high-pressure apparatus. It is now routinely possible to characterize material under high pressure with acquisition times for tomograms of the order of tens of minutes. Here, advantage was taken of the possibility to combine the use of a pink beam projected through a standard Paris-Edinburgh press in order to demonstrate the possibility to perform high-speed synchrotron X-ray tomography at high pressure and temperature allowing complete high-resolution tomograms to be acquired in about 10 s.

Development of synchrotron X-ray micro-tomography under extreme conditions of pressure and temperature.

X-ray tomography is a non-destructive three-dimensional imaging/microanalysis technique selective to a wide range of properties such as density, chemical composition, chemical states and crystallographic structure with extremely high sensitivity and spatial resolution. Here the development of in situ high-pressure high-temperature micro-tomography using a rotating module for the Paris-Edinburgh cell combined with synchrotron radiation is described. By rotating the sample chamber by 360°, the limited angular aperture of ordinary high-pressure cells is surmounted.

Tomography and imaging at the PSICHE beam line of the SOLEIL synchrotron.

PSICHE (Pressure, Structure and Imaging by Contrast at High Energy) is the high-energy beam line of the SOLEIL synchrotron. The beam line is designed to study samples at extreme pressures, using diffraction, and to perform imaging and tomography for materials science and other diverse applications. This paper presents the tomograph and the use of the beam line for imaging, with emphasis on developments made with respect to existing instruments.

Synthesis of β-Mg(2)C(3): a monoclinic high-pressure polymorph of magnesium sesquicarbide.

A new monoclinic variation of Mg2C3 was synthesized from the elements under high-pressure (HP), high-temperature (HT) conditions. Formation of the new compound, which can be recovered to ambient conditions, was observed in situ using X-ray diffraction with synchrotron radiation. The structural solution was achieved by utilizing accurate theoretical results obtained from ab initio evolutionary structure prediction algorithm USPEX.

High melting points of tantalum in a laser-heated diamond anvil cell.

In situ x-ray diffraction has been used to characterize the structural modifications of tantalum samples under intense laser irradiation, up to 135 GPa in a diamond anvil cell. Melting data points are obtained that do not confirm the previously reported anomalously low melting curve. Two effects are identified that might alter the melting determination of refractory metals such as Ta under high static pressures.

Dissociative melting of ice VII at high pressure.

We have used x-ray diffraction to determine the structure factor of water along its melting line to a static pressure of 57 GPa (570 kbar) and a temperature of more than 1500 K, conditions which correspond to the lower mantle of the Earth, and the interiors of Neptune and Uranus up to a depth of 7000 km. We have also performed corresponding first principles and classical molecular dynamics simulations. Above a pressure of 4 GPa the O-O structure factor is found to be very close to that of a simple soft sphere liquid, thus permitting us to determine the density of liquid water near the melting line.

Pressure-induced chemical decomposition and structural changes of boric acid.

A combined synchrotron X-ray diffraction, Raman scattering, and infrared spectroscopy study of the pressure-induced changes in H(3)BO(3) to 10 GPa revealed a new high-pressure phase transition between 1 and 2 GPa followed by chemical decomposition into cubic HBO(2), ice-VI, and ice- VII at approximately 2GPa. The layered triclinic structure of H(3)BO(3) exhibits a highly anisotropic compression with maximum compression along the c direction, accompanied by a strong reduction of the interlayer spacing. The large volume variation and structural changes accompanying the decomposition suggest high activation energy.