Mantle Wedge Water Contents Estimated From Ultrasonic Laboratory Measurements of Olivine-Antigorite Aggregates

While it is known that serpentinized peridotite acts as a water reservoir in the mantle wedge of a subduction zone, the spatial distribution and quantity of the water stored in these reservoirs, as well as the acoustic velocity of the olivine-antigorite aggregates, are not well constrained. Here, we report the propagation of seismic waves through synthetic olivine-antigorite aggregates, which are used as proxies for various mantle wedge lithologies, by varying the amount of antigorite at pressures up to 8 GPa. Our results indicate that the acoustic velocity is strongly dependent on the proportion of antigorite in the sample and somewhat dependent on pressure. We empirically explore the relationship between the acoustic velocity and the degree of serpentinization as well as pressure to map the water content in the mantle wedge. Our estimations show that the water content among the subducting slabs around the Pacific Ocean is between 0.5 and 5.0 wt%.