Program > Browse abstracts by speaker > Ledoux Estelle

Stishovite, a high-pressure polymorph of SiO2, is expected to be present in the deep Earth, in particular in the crustal part of subducted slabs. It has also been proposed that SiO2 can exsolve from Earth's core as it crystallizes, and/or that silica-rich regions have remained in the lower mantle after crystallization of the magma ocean. Determining stishovite properties at high pressures is hence crucial to interpret seismic signals from the mantle and understand geodynamic processes. Previous studies have determined the elastic properties of stishovite at high pressure and high temperature, but its response to an imposed oscillating pressure has not been investigated. In nature, however, seismic waves induce stress oscillations, imposing a cyclic stress loading to the rocks they pass through.

Here, we employed the dynamic diamond anvil cell (dDAC) to mimic in the laboratory the stress oscillations that a seismic wave can produce in a rock. A sintered polycrystalline stishovite sample was first pressured manually up to 40 GPa. Using the dDAC setup available at the P02.2 beamline at PETRA III (DESY), we then applied loadings by sending a cyclic signal to the piezoactuator controlling the compression of the dDAC. Every second during the loading, an X-ray diffraction pattern of the sample was acquired in radial scattering geometry to monitor in-situ the symmetry, shape, and volume of the unit cell as well as lattice strains and preferred orientation in the sample. We will discuss the relevance of our results for the interpretation of seismic data and geodynamic modelling.