Upper mantle seismic anisotropy and lithospheric decoupling

Abstract

The lithosphere underlying stable continental shield regions is thought to extend to a depth of ∼200 km. Compressional wave velocity models derived from a recent approximately NS refraction profile in northern Australia include a pronounced high-velocity zone at a depth of around 200-250 km. Conventional petrological interpretations in terms of mineralogical or compositional changes cannot readily explain this feature. Calculated velocities for the garnet pyrolite model (using a derived geotherm), fit the velocities above and below this high-velocity zone, but cannot account for the high-velocity (∼8.6 km s-1) zone itself. This feature is explained in terms of velocity anisotropy, which might reflect mechanical decoupling of the continental lithosphere from the underlying mantle. Show more