Receiver Functions of the Transition Zone Below Yellowstone: Searching for Water

Abstract:

Earth’s mantle transition zone (MTZ) is a possible global water reservoir and may be responsible for long-term (~100 Ma) ocean-mass regulation, driven by plate-tectonics and mantle convection. Estimates of MTZ mineral water capacity are ~1 wt %, far greater than that of mantle rocks of the either the upper or lower mantle. When water-rich material from the transition zone penetrates the upper or lower mantle, partial melting occurs due to the decrease in water capacity after phase transition, generating a reduction in seismic velocities. This process can add an additional interface that can be imaged above(below) the 410(660)-km discontinuities, if melt is present. Previously, high frequency (~0.6 Hz) multitaper-correlation Ps receiver functions detected velocity reductions both above and below the mantle transition zone, interpreted to be partial melting induced by high water content, under the Alpine orogeny and in the deep Japan-slab subduction zone. The Yellowstone hotspot provides an ideal location to test this hypothesis. If the hotspot source is the relict Farallon Plate, partial melting and a corresponding low-velocity zone (LVZ) are expected above the transition zone. A velocity reduction below the 660 km discontinuity would not be anticipated as the plate material should be upwelling as part of the plume. A deep mantle source below the Yellowstone hotspot could also explain these observations as plume will entrain the MTZ. We conduct high frequency multitaper-correlation receiver Ps analysis with common conversion point stacking for binning depths of 410- and 660-km to investigate the presence of LVZs above and below the transition zone in the vicinity of Yellowstone. Approximately 50,000 waveforms from 200-500 seismic stations can be obtained via IRIS for RF analysis. Potential vertical resolution is ~10 km, allowing for interpretation of possible layering in the transition zone due to the presence of the Farallon Plate.