High-pressure dehydration experiments of antigorite-olivine samples to explain seismicity in the lower Benioff plane

Abstract:

Here we show the first recording of acoustic emissions due to serpentine dehydration in partially serpentinized sintered peridotites deformed in pressure and temperature conditions representative for intermediate depths earthquakes. 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 sintered powders of San Carlos olivine and Corsica antigorite, which is the HT serpentine polymorph. Our results demonstrate that around 2 GPa, serpentinized peridotite with serpentine content of 5% has a seismogenic potential. In the same conditions, no acoustic emission is detected in melanges with larger serpentine content (20%). At higher pressure (3.5 GPa) acoustic emissions are observed for melanges with up to 20% serpentine.

Serpentine contents may favor initiation of mechanical failure of the olivine “load bearing” network for contents lower than a threshold value, at which connection of the weak phase (serpentine) prevents from stress rise in the stronger matrix (olivine). This threshold seems to increase with pressure. Thus mechanical instability may originate in serpentine dehydration for part of the intermediate-depth earthquakes, and hence at least part of the lower Benioff zone seismicity. Serpentine dehydration would act as a triggering mechanism for earthquakes nucleating and propagating in the olivine network.