Controls on Global Mantle Convective Structures and Their Comparison With Seismic Models

Abstract

AbstractSeismic observations suggest (1) significant accumulation of subducted slabs above the 670‐km discontinuity in many subduction zones, (2) possible structure change at ~1,000‐km depth, and (3) the large low shear wave velocity provinces above the core‐mantle boundary in the African and Pacific lower mantle be associated with chemical heterogeneity. Global mantle convection models with realistic plate motion history reproduce most of these structures. However, it remains unclear how the convection models compare with seismic models at different spatial wavelengths and depths. By conducting quantitative analysis between mantle convection and seismic models, we found that mantle convective structures show significant correlations with seismic structures in the upper mantle and mantle transition zone for wavelengths up to spherical harmonic degree 20. However, the global correlation is weak at intermediate to short wavelengths (for degrees 4 and higher) in the lower mantle below ~1,000‐km depth. A weak layer beneath the spinel‐to‐postspinel phase change help consistently reproduce stagnant slabs in the western Pacific, while having insignificant effects elsewhere, that is, the large low shear wave velocity province structures. The cold slab structures and their correlations with the seismically fast anomalies are nearly identical for our convection models with and without the plumes, indicating that seismically fast anomalies in the mantle mainly result from the subducted slabs. Models with viscosity increase at 1,000‐km depth and the 670‐km depth phase change may reproduce seismic slab structures including the stagnant slabs in the mantle transition zone equally well as models with a thin weak layer below the 670‐km phase boundary.