Thomas Ferrand, promo 2013 vient de recevoir le prix OPSA meilleure présentation AGU
We show the first recording of acoustic emissions due to serpentine dehydration in slightly serpentinized sintered peridotites deformed at pressure and temperature conditions representative for earthquakes at intermediate depths. Experiments were conducted in a D-DIA apparatus using simultaneously X-ray diffraction and acoustic-emission monitoring, to estimate both stress-strain relationship and occurrence of micro-earthquakes. We use powders of San Carlos olivine and Corsica antigorite, the HT serpentine variety.
Around a confining pressure of 1.5 GPa a serpentine content of 5% results in a seismogenic potential of the synthetic peridotite aggregates while acoustic emissions are not detected in mixtures with larger serpentine content (20%). At higher pressure (3.5 GPa) acoustic emissions are observed for melanges with up to 50% of serpentine.
Presence of serpentine may favor initiation of mechanical failure of the olivine “load bearing” network for contents lower than a threshold value, at which connection of the weaker phase (serpentine) prevents the build-up of stress in the stronger matrix (olivine). This threshold seems to increase with pressure. Thus, mechanical instability of peridotites may originate from serpentine dehydration for some intermediate-depth earthquakes, in the lower Benioff zone.
Nice presentation of the importance of the distribution and abundance of antigorite for the mechanical behavior of mantle lithologies with implications for beniof zone brittle failure. Student had excellent command of the subject matter, the significance and limitations of the study, and overall, a logical understandable presentation.
Olivine jewelry nice touch. >> référence à l’olivine de san carlos que je me suis accrochée à l’oreille ! 🙂