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Seismological support for the metastable superplume model, sharp features, and phase changes within the lower mantle
- Sun, Daoyuan, Tan, Eh, Helmberger, Don, Gurnis, Michael
- Proceedings of the National Academy of Sciences of the United States of America 2007 v.104 no.22 pp. 9151-9155
- geophysics, mixing, models, phase transition, temperature
- 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, PCP, and PKP) and S (S, SCS, 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.