High mantle seismic P-wave speeds as a signature for gravitational spreading of superplumes
T. A. Stern, Simon Lamb, James D. Moore, D. A. Okaya, Katharina Hochmuth
Abstract
phases of ~8.8 ± 0.2 km/s are resolved with negligible azimuthal seismic anisotropy, but with strong radial anisotropy (~10%), characteristic of aggregates of olivine with an AG crystallographic fabric. These seismic results are the first in situ evidence for this fabric in the upper mantle. We show that its presence can be explained by isotropic horizontal dilation and vertical flattening due to late-stage gravitational collapse and spreading in the top 10 to 20 km of a depleted, mushroom-shaped, superplume head on a horizontal length scale of 1000 km or more. This way, it provides a seismic tool to track plumes long after the thermal effects have ceased.
Topics & Concepts
GeologyMantle (geology)FlatteningSeismic anisotropySeismologyAnisotropyGeophysicsIsotropySeismic arraySeismic wavePhysicsAstronomyQuantum mechanicsHigh-pressure geophysics and materialsearthquake and tectonic studiesGeological and Geochemical Analysis