Title:
Superplumes from the CMB to the base of the
lithosphere: evidence from global tomography

Abstract

Many questions remain as to
the origin of hotspots, the active or passive character of upwellings 
under ridges and the role of the two large "superplumes" imaged by seismic tomography at the base of the mantle. We present a degree 8 three-dimensional Q model (QRLW8) of
the upper-mantle, derived from three component surface waveform
data in the period range 60-400 sec. The inversion procedure involves two
steps. In the first step, 3D whole-mantle velocity models are derived separately
for elastic SH (transverse component) and SV (vertical and longitudinal
component) velocity models, using both surface and body waveforms and the
NACT approach (Non-linear asymptotic coupling theory). In the second
step, the surface waveforms thus aligned in phase are inverted to obtain
a 3-D Q model in the depth range 80-670 km. Various resolution and stability
tests are preformed to assess the quality of the resulting Q models.

Combined with lower mantle elastic velocity tomography and upper mantle anisotropy results, this model shows that the upwellings associated with the two superplumes persist through the upper-mantle transition zone and may play a major and stable role in supplying heat and horizontal flow to the low viscosity asthenosphere, lubricating plate motions. We suggest that more heat may be carried through the core-mantle boundary than is accounted for by hot-spot fluxes alone. Ridges are shallow features in both velocity and Q models.