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Tidal tomography constrains Earth's deep-mantle buoyancy.

Harriet C P Lau¹, Jerry X Mitrovica¹, James L Davis²

¹Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA.

|November 17, 2017

Summary

Earth's solid Earth tide reveals that Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific are denser than previously thought. This suggests their buoyancy is dominated by high-density chemical components, impacting mantle dynamics.

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Reservoir Condition Pore-scale Imaging of Multiple Fluid Phases Using X-ray Microtomography

Reservoir Condition Pore-scale Imaging of Multiple Fluid Phases Using X-ray Microtomography

Published on: February 25, 2015

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.