Geochemical constraints on the structure of the Earth’s deep mantle and the origin of the LLSVPs

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1029/2021GC009932. This is version 3 of this Preprint.

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Authors

Matthew Lloyd Morgan Gleeson , Caroline Soderman, Simon Matthews , Sanne Cottaar , Sally Gibson 

Abstract

Geophysical analysis of the Earth’s lower mantle has revealed the presence of two superstructures characterized by low shear wave velocities on the core-mantle boundary. These Large Low Shear Velocity Provinces (LLSVPs) play a crucial role in the dynamics of the lower mantle and act as the source region for deep-seated mantle plumes. However, their origin, and the characteristics of the surrounding deep mantle, remain enigmatic. Mantle plumes located above the margins of the LLSVPs display evidence for the presence of this deep-seated, thermally and/or chemically heterogeneous mantle material ascending into the melting region. As a result, analysis of the spatial geochemical heterogeneity in OIBs provides constraints on the structure of the Earth’s lower mantle and the origin of the LLSVPs. In this study, we focus on the Galápagos Archipelago in the eastern Pacific, where bilateral asymmetry in the radiogenic isotopic composition of erupted basalts has been linked to the presence of LLSVP material in the underlying plume. We show, using spatial variations in the major element contents of high-MgO basalts, that the isotopically enriched south-western region of the Galápagos mantle – assigned to melting of LLSVP material – displays no evidence for lithological heterogeneity in the mantle source. As such, it is unlikely that the Pacific LLSVP represents a pile of subducted oceanic crust. Clear evidence for a lithologically heterogeneous mantle source is, however, found in the north-central Galápagos, indicating that a recycled crustal component is present near the eastern margin of the Pacific LLSVP, consistent with seismic observations.

DOI

https://doi.org/10.31223/X5JS7Z

Subjects

Physical Sciences and Mathematics

Keywords

Galapagos, Pyroxenite, LLSVP

Dates

Published: 2021-08-03 12:53

Last Updated: 2021-09-10 13:31

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License

CC BY Attribution 4.0 International

Additional Metadata

Conflict of interest statement:
None

Data Availability (Reason not available):
The data used in this study, and the python scripts used for data plotting, are available via https://zenodo.org/badge/latestdoi/384184976

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