Elasticity of Earth Materials

Elasticity of Earth Materials Elastic properties determine the response of materials to stress within the elastic limit. They reflect the nature of atomic bonding (strength) and carry crucial information about materials’ physical behavior. This motivates the strong interest in elasticity of several scientific disciplines, including materials sciences, solid state physics, geosciences and chemistry. Elastic properties also govern the propagation speed of elastic waves (and seismic waves). A quantitative understanding of elastic properties and elastic wave velocities in the minerals that likely compose the deep Earth is of central importance for geosciences as it facilitates the interpretation of seismological observations in terms of composition, evolution, dynamics and thermal state of the Earth’s interior.

The elastic properties of spinels at high pressure

Spinel oxides, with the general formula (AB2O4), are among the most abundant non-silicate minerals of the Earth’s crust and upper mantle. A special characteristic of spinels is their ability to host a wide range of cations.

Silicate minerals can also have spinel structure. In fact, ringwoodite (Mg,Fe)2SiO4 is one of the most abundant minerals of the Earth's transition zone (the region between 410 and 660 km depth).

In this project we conduct studies of the effects of cations substitution, degree of inversion and cations disorder in spinel oxides in a wide range of pressure conditions. The methods we use are Brillouin scattering, Raman scattering, synchrotron X-ray diffraction and first principles computations.

Fig.: The elastic moduli Cij of spinel-galaxite (MgAl2O4-MnAl2O4) as a function of Mg-Mn substitution

Contact

Dr. Sergio Speziale

Dr. Hans Josef Reichmann

Dr. Ilias Efthimiopoulos

Partner

Dr. Enrico Bruschini / Prof. Giovanni B. Andreozzi / Prof. F. Bosi - Sapienza Universität Rom, Italien

The effect of chemical substitutions on the elastic properties of silicate garnets

Silicate garnets (A3B2Si3O12) are a large family of silicates very well represented in the Earth’s crust, and they are among the major components of the upper mantle and transition zone rocks. Silicate garnets have been the subject of more than 30 studies dedicated to the determination of their full elastic tensor. However, due to the very rich range of chemical substitutions, our understanding of the systematic effect of chemical substitutions on the elastic tensor is far from being complete.

We conduct Brillouin scattering studies of series of natural and syntehtic silicate garnets single crystals selected to span almost ideal binary cations substitutions. In addition we investigate the effect of OH incorporation in natural spessartine (Mn3Al2Si3O12) and andradite (Ca3Fe2Si3O12).

Fig.: The elastic moduli Cij of a natural hydrospessartine (∼Mn3Al2(SiO4)2.5(H4O4)0.5) compared with the anhydrous endmember (Mn3Al2Si3O12). The line is a model linear dependence based on the behavior of the system grossular (Ca3Al2Si3O12) – hibschite (Ca3Al2(SiO4)1.74(O4H4)1.28).

Contact

Dr. Sergio Speziale

Partner

Prof. Charles A. Geiger, Universität Salzburg, Österreich

Prof. F. Bellatreccia / S. Grita, University Roma Tre, Rom, Italien

Prof. F. Bosi, Sapienza University, Rom, Italien

N. Satta, Bayerisches Geoinstitut, Universität Bayreuth

The elastic properties of portlandite at high pressures

The elastic properties of portlandite, which is an important compound of cement and a prototype of strongly anisotropic layered materials. We investigate stress-induced amorphization, the effects of experimental geometries and possible strategies to optimize the approach to analyze volume and axial strains for equation of state studies of anisotropic materials. We perform elasticity and equation of state measurements at high pressure in the diamond anvil cell and multi anvil apparatus measurement.

Fig.: The ambient temperature isothermal compression curve of portlandite (Ca(OH)2) based on volume measurements in different compression devices (LVP: large volume press, DAC: diamond anvil cell). The colored symbols are our measurements, the curves our model compression curves based on the LVP and the DAC datasets. They are largely different due to the sensitivity of portlandite to non-hydrostatic stress in different compression devices.

Contact

Dr. Sergio Speziale

Dr. Hans Josef Reichmann

Partner

Prof. Dr. Frank Schilling, Karlsruher Institut für Technologie (KIT)

Silicate glasses at high pressures

Structural and elastic properties of silicate glasses with compositions of the most important components of the Earth mantle are investigated at the relevant deep Earth pressures. Sound velocity measurements are used to determine in situ high-pressure density.

Fig.: The pressure effect on the acoustic velocity of MgSiO3 glass compressed to 25 GPa at ambient temperature. The plot shows anomalous change of pressure dependence at about 7 GPa and a large hysteresis in decompression. This is a typical indication of important changes in the compression behavior of this amorphous silicate.

Contact

Dr. Sergio Speziale

Partner

Zachary Geballe, Geophysical Laboratory, Carnegie Institution of Washington, USA

Raymond Jeanloz, University of California, Berkeley ,USA

Sang-Heon (Dan) Shim, Arizona State University, USA