Seismological support for the metastable superplume model, sharp features, and phase changes within the lower mantle

doi:10.1073/pnas.0608160104

Seismological support for the metastable superplume model, sharp features, and phase changes within the lower mantle

Seismological Laboratory, 252-21, California Institute of Technology, Pasadena, CA 91125

Edited by Russell J. Hemley, Carnegie Institute of Washington, Washington, DC, and approved March 7, 2007 (received for review September 15, 2006)

Abstract

Recently, a metastable thermal-chemical convection model was proposed to explain the African Superplume. Its bulk tabular shape remains relatively stable while its interior undergoes significant stirring with low-velocity conduits along its edges and down-welling near the middle. Here, we perform a mapping of chemistry and temperature into P and S velocity variations and replace a seismically derived structure with this hybrid model. Synthetic seismogram sections generated for this 2D model are then compared directly with corresponding seismic observations of P (P, P_CP, and PKP) and S (S, S_CS, and SKS) phases. These results explain the anticorrelation between the bulk velocity and shear velocity and the sharpness and level of SKS travel time delays. In addition, we present evidence for the existence of a D” triplication (a putative phase change) beneath the down-welling structure.

Footnotes

^†To whom correspondence should be addressed. E-mail: helm{at}gps.caltech.edu
Author contributions: D.S. performed research; E.T., D.H., and M.G. contributed new reagents/analytic tools; and D.H. wrote the paper.
↵*Present address: Computational Infrastructure for Geodynamics, 220-12, California Institute of Technology, Pasadena, CA 91125.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
↵ ‡ Lee, K.K., Asimow, P.D., Tschauner, O. (2005) EOS Trans AGU 86:V42A-02 (abstr.).
This article contains supporting information online at www.pnas.org/cgi/content/full/0608160104/DC1.
Abbreviations:

LLVP,

large low velocity province;

PV,

perovskite;

PPV,

postperovskite;

CMB,

core-mantle boundary;

PREM,

Preliminary Reference Earth Model;

HBMS,

High Bulk Modulus Structure;

ALVS,

African Low Velocity Structure;

Pd,

P-wave diffraction;

Sd,

S-wave diffraction.