Geodynamic, geodetic, and seismic constraints favour deflated and dense-cored LLVPs
File(s)
Working paper
Author(s)
Richards, Frederick
Hoggard, Mark
Ghelichkhan, Siavash
Koelemeijer, Paula
Lau, Harriet
Type
Working Paper
Abstract
Two continent-sized features in the deep mantle, the large low-velocity provinces (LLVPs), influence Earth's supercontinent cycles, mantle plume generation, and its geochemical budget. Seismological advances have steadily improved LLVP imaging, but several fundamental questions remain unanswered, including: What is their vertical extent? And, are they purely thermal anomalies, or are they also compositionally distinct? Here, we investigate these questions using a wide range of observations. The relationship between measured geoid anomalies and long-wavelength dynamic surface topography places an important upper limit on LLVP vertical extent of ~900 km above the core-mantle boundary (CMB). Our mantle flow modelling suggests that anomalously dense material must exist at their base to simultaneously reproduce geoid, dynamic topography, and CMB ellipticity observations. We demonstrate that models incorporating this dense basal layer are consistent with independent measurements of semi-diurnal Earth tides and Stoneley modes. Our thermodynamic calculations indicate that a ~100 km-thick layer of early-formed, chondrite-enriched basalt is the chemical configuration most compatible with these geodynamic, geodetic and seismological constraints. By reconciling these disparate datasets for the first time, our results demonstrate that, although dominantly thermal structures, basal sections of LLVPs represent a primitive chemical reservoir that is periodically tapped by upwelling mantle plumes.
Date Issued
2021-06-18
Citation
2021
Publisher
EarthArXiv
Copyright Statement
© 2021 The Author(s). This work is published with CC BY Attribution 4.0 International.
License URL
Sponsor
Imperial College London
Schmidt Science Fellows
Identifier
https://eartharxiv.org/repository/view/2465/
Publication Status
Published