Olivine is the most important phase in the Earth’s upper mantle, where the bulk rock composition varies on average from lherzolitic to harzburgitic, where the olivine fractions are normally >60 %. Olivine is of major importance for Earth’s mantle dynamics and the presence of grain boundaries in olivine and their type might partially be responsible for attenuation phenomena as well as thermal an...

Hot–spots are anomalous regions of magmatism that cannot be directly associated with plate tectonic processes. They are widely regarded as the surface expression of hot, columnar plumes, upwelling from deep within Earth’s 2900–km thick mantle. Hot–spots have variable life–spans, magmatic productivity and fixity. This suggests that a wide– range of upwelling structures co–exist within Earth’s ma...

We present an overview of the present knowledge of the Earth’s lower mantle 3D structure, as currently obtained owing to progress, in the last ten years, in seismic tomography as well as forward modelling of seismic travel times and waveforms. We discuss constraints that seismic modelling brings to the debate concerning major geodynamical questions, in particular the issue of global ‘1 layer’ o...

A decade of observations in geodetic mode with the VLBA network gave valuable results. Approximately 1/5 of all geodetic observations are recorded in VLBA mode and processed at the Socorro correlator. Ten years of observations allowed us to reliably measure slow intra-plate motion of the VLBA stations located on the North-American plate. It also helped us to achieve scientific objectives of geo...

In order to examine the potential of seismology to determine the interior structure and properties of Europa, it is essential to calculate seismic velocities and attenuation for the range of plausible interiors. We calculate a range of models for the physical structure of Europa, as constrained by the satellite’s composition, mass, and moment of inertia. We assume a water-ice shell, a pyrolitic...

Natural olivine with 12 mol % Fe(2)SiO(4) and synthetic orthopyroxenes with 20% and 40% FeSiO(3) were studied beyond the pressure-temperature conditions of the core-mantle boundary. All samples were found to convert entirely or partially into the CaIrO(3) postperovskite structure, which was recently reported for pure MgSiO(3). The incorporation of Fe greatly reduces the pressure needed for the ...

In situ x-ray diffraction measurements of MgSiO3 were performed at high pressure and temperature similar to the conditions at Earth's core-mantle boundary. Results demonstrate that MgSiO3 perovskite transforms to a new high-pressure form with stacked SiO6-octahedral sheet structure above 125 gigapascals and 2500 kelvin (2700-kilometer depth near the base of the mantle) with an increase in densi...

We simulate the effects of an intrinsically dense boundary layer at the base of the mantle on the thermal structure of D and the dynamics of the lower mantle. Using a finite element model of thermo-chemical convection in 2-D with a Rayleigh number of 10, we investigate the dynamic consequences of varying the density and of increasing thermal diffusivity in the basal layer to simulate enrichment...