Caroline Bollinger

Low-temperature plasticity of olivine revisited with in situ TEM nanomechanical testing

The flow properties of the mineral olivine under lithospheric conditions, as seen in the transmission electron microscope (TEM). The rheology of the lithospheric mantle is fundamental to understanding how mantle convection couples with plate tectonics. However, olivine rheology at lithospheric conditions is still poorly understood because experiments are difficult in this temperature range where rocks and mineral become very brittle. We combine techniques of quantitative in situ tensile testing in a transmission electron microscope and numerical modeling of dislocation dynamics to constrain the low-temperature rheology of olivine. We find that the intrinsic ductility of olivine at low temperature is significantly lower than previously reported values, which were obtained under strain-hardened conditions. Using this method, we can anchor rheological laws determined at higher temperature and can provide a better constraint on intermediate temperatures relevant for the lithosphere. More generally, we demonstrate the possibility of characterizing the mechanical properties of specimens, which can be available in the form of submillimeter-sized particles only.

In Situ Quantitative Analysis of Stress and Texture Development in Forsterite Aggregates Deformed at 6 GPa and 1373 K

The investigation of materials plastic properties at high pressure is a fast-growing field, owing to the coupling of high-pressure deformation apparatuses with X-ray synchrotron radiation. In such devices, materials strain and strain rate are measured by time-resolved radiography, while differential stress is deduced from the elastic response of the d spacing of the crystallographic planes as measured by X-ray diffraction. Here a new protocol is presented, which allows the in situ measurement of stress and texture development in aggregates deformed at high pressure for experiments carried out with the recently installed ten-element energy-dispersive detector at the X17B2 beamline of the National Synchrotron Light Source (Brookhaven National Laboratory, Upton, NY, USA). Cycling deformation of a forsterite specimen was carried out at a pressure of ∼6 GPa and a temperature of ∼1373 K, using a deformation-DIA apparatus. Diffraction peak energies are analysed in terms of differential stress and principal stress direction, while the intensities of peaks obtained at different azimuths are analysed in terms of lattice preferred orientation (LPO). The development and evolution of a marked LPO, with the (010) plane perpendicular to the compression axis, is observed in situ during the run and is confirmed by electron backscatter diffraction measurements on the run product.