Published August 2025 | Supplemental material
Journal Article Open

Edges of thermochemical structures in the lower mantle

  • 1. ROR icon California Institute of Technology

Abstract

Global seismic tomography consistently identifies two large low shear velocity provinces (LLSVPs) beneath Africa and the Pacific in the lower mantle. These structures are generally hypothesized to have a thermochemical origin with a higher bulk modulus (K) than ambient mantle. Regional high-resolution seismic studies have revealed that LLSVPs exhibit diverse edge morphologies, though the factors controlling these variations remain unclear. Here we quantitatively investigate the evolution of LLSVP boundary topographies through high-K thermochemical convection models. The calculations show that the boundary morphology of a thermochemical pile is primarily controlled by its density and viscosity. Comparison with observed boundary shapes suggests that the African LLSVP may be less dense and thus less stable than the Pacific LLSVP, potentially reflecting differences in their compositions and evolutions. Additionally, the observed boundary complexity indicates that the viscosity of LLSVPs is likely no more than an order of magnitude higher than that of the surrounding mantle.

Copyright and License

Acknowledgement

We are grateful to Co-Guest Editor Lauren Waszek for handling our manuscript and the three anonymous reviewers for their constructive comments, which significantly contributed to improving the manuscript. We also thank Wei Mao for valuable guidance on code modifications and for insightful discussions. Most figures in this paper were generated using GMT6 (Wessel et al., 2019). We acknowledge use of the Anvil computer at Purdue University, supported by the NSF, through ACCESS allocation EAR160027. This work was supported by NSF EAR-2303148.

Code Availability

The mantle convection code CitcomS is available at https://geodynamics.org/resources/citcoms. The input files is available at Caltech Data (https://doi.org/10.22002/3jqpw-3xp19).

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Additional Information

This article is part of a Special issue entitled: ‘SEDI 2024’ published in Physics of the Earth and Planetary Interiors.

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Additional details

Created:
June 2, 2025
Modified:
June 24, 2025