Tidal tomography constrains Earth's deep-mantle buoyancy

Area of Science:

• Geophysics
• Earth Science
• Seismology

Background:

• The body tide, or solid Earth tide, is the displacement of Earth's surface due to lunar and solar gravity.
• Large Low Shear Velocity Provinces (LLSVPs) are massive structures at the core-mantle boundary, whose buoyancy is debated.
• Understanding LLSVP density is crucial for mantle dynamics and Earth's evolution.

Purpose of the Study:

• To constrain the deep-mantle buoyancy of LLSVPs using body tide deformation.
• To investigate the density anomalies within the African and Pacific LLSVPs.

Main Methods:

• Utilized tidal tomography, analyzing semi-diurnal body tide deformation.
• Employed Global Positioning System (GPS) measurements for precise surface displacement data.
• Applied a probabilistic approach to analyze density variations.

Main Results:

• Showed that the lower two-thirds of LLSVPs have a mean density approximately 0.5% higher than the surrounding mantle.
• Indicated that this density anomaly might be concentrated at the very base of the mantle.
• Constrained the mean buoyancy of the LLSVPs to approximately -0.5%.

Conclusions:

• LLSVPs' buoyancy is primarily driven by enrichment of high-density chemical components.
• Subducted oceanic plates or primordial material are likely sources for these dense components.
• The density structure of LLSVPs has significant implications for mantle convection, LLSVP stability, and long-term Earth system evolution.