Mantle Plume Reconstruction by Three-Dimensional Electromagnetic Induction

The Earth's interior consists of multi-scale structures that range from micrometer-scale mineral assemblages to thousand-kilometer-scale heterogeneities. Mantle plumes are one such mega-scale structure that connect the core-mantle boundary with Earth's surface. Reconstructing these structures can provide insights into mantle material and energy convection, as well as Earth's long-term evolution. However, mantle plume has not yet been convincingly reconstructed by electromagnetic induction, even they have significantly high electrical conductivity compared with the surrounding mantle. Here we numerically reconstruct mantle plumes by employing a deep Earth electromagnetic induction method - geomagnetic depth sounding (GDS). We build the electrical structure of mantle plumes and conduct inversion tests to investigate how different station coverage areas, station spacings, noise levels, and response period ranges influence the construction. The test results indicate that the reconstruction of a broad 10°-diameter plume head near the mantle transition zone requires a station coverage area of at least 10° × 10° and a 2° station spacing; the station spacing can be increased to 5° for a 20° × 20° coverage area. A continuous two-year record with ~5% noise is sufficient to recover the electrical structure of the plume head. Plumes with different types and roots can be distinguished by images near the mantle transition zone while reconstruction of the narrow tail in the deep lower mantle seems to be difficult due to the limited resolution of GDS. A mantle plume beneath South China is discovered by GDS from the field geomagnetic data. GDS is expected to be used for reconstructing the mantle plume beneath important locations and contributing to the study in Earth's dynamics.