Effects of heat‐producing elements on the stability of deep mantle thermochemical piles

Citron, R. I., Lourenço, D. L., Wilson, A. J., Grima, A. G. , Wipperfurth, S. A., Rudolph, M. L., Cottaar, S. and Montési, L. G. J. (2020) Effects of heat‐producing elements on the stability of deep mantle thermochemical piles. Geochemistry, Geophysics, Geosystems, 21(4), e2019GC008. (doi: 10.1029/2019GC008895)

Abstract

Geochemical observations of ocean island and mid-ocean ridge basalts suggest that abundances of heat-producing elements (HPEs: U, Th, and K) vary within the mantle. Combined with bulk silicate Earth models and constraints on the Earth's heat budget, these observations suggest the presence of a more enriched (potentially deep and undepleted) reservoir in the mantle. Such a reservoir may be related to seismically observed deep mantle structures known as large low shear velocity provinces (LLSVPs). LLSVPs might represent thermochemical piles of an intrinsically denser composition, and many studies have shown such piles to remain stable over hundreds of Myr or longer. However, few studies have examined if thermochemical piles can remain stable if they are enriched in HPEs, a necessary condition for them to constitute an enriched HPE reservoir. We conduct a suite of mantle convection simulations to examine the effect of HPE enrichment up to 25× the ambient mantle on pile stability. Model results are evaluated against present-day pile morphology and tested for resulting seismic signatures using self-consistent potential pile compositions. We find that stable piles can form from an initial basal layer of dense material even if the layer is enriched in HPEs, depending on the density of the layer and degree of HPE enrichment, with denser basal layers requiring increased HPE enrichment to form pile-like morphology instead of a stable layer. Thermochemical piles or LLSVPs may therefore constitute an enriched reservoir in the deep mantle.

• Item Type: Articles
• Additional Information: We thank the Computational Infrastructure for Geodynamics (geodynamics.org), which is funded by the NSF under Awards EAR-0949446 and EAR-1550901 for supporting the development of ASPECT. S. C. and a meeting for this project have been funded by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement 804071—ZoomDeep). Support for D. Lourenco was provided through NSF EAR-1622464.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Grima, Dr Antoniette
• Authors: Citron, R. I., Lourenço, D. L., Wilson, A. J., Grima, A. G., Wipperfurth, S. A., Rudolph, M. L., Cottaar, S., and Montési, L. G. J.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Geochemistry, Geophysics, Geosystems
• Publisher: American Geophysical Union
• ISSN: 1525-2027
• ISSN (Online): 1525-2027
• Published Online: 27 March 2020