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Thistlethwaite, Elly

The mantle represents 84% of Earth’s volume and drives large-scale geological processes, including forming and recycling the continental crust. Mantle plumes rise from the deep mantle to melt at the base of the crust, generating volcanic chains at the surface as tectonic plates move over them. These erupted lavas contain geochemical signatures that are proxies for the deep mantle compositions, offering a unique opportunity to learn about its structure and composition. The Hawaiian mantle plume has been active in the Pacific Ocean for over 85 million years, creating the Hawaiian Islands over the last 5 million years. The Hawai’i volcanoes form two subparallel geographic and geochemical trends: the southwestern side is the Loa trend, and the northeastern side is the Kea trend. The volcanoes’ distinct geochemical compositions reflect the sampling of distinct mantle heterogeneities by the Hawaiian plume at the core-mantle boundary, with the Loa trend volcanoes sampling the Pacific large-low shear velocity province (LLSVP), and the Kea trend volcanoes sampling the ambient Pacific mantle. Using high-precision isotopic data, the two trends have been refined further into six distinct geochemical groups, the Average Loa, Enriched Loa, and Lō’ihi groups (Loa trend), and the Kea, Transitional Kea, and Kohala groups (Kea trend). Combined with isotopes, trace element ratios are a powerful tool for distinguishing the mantle source composition of the Hawaiian lavas. However, up to now, previous studies on Hawai’i’s trace element data were lacking. In this thesis, a large-scale compilation of Hawai’i’s trace element data was conducted to further characterize the Hawai’i geochemical groups, shedding light on the composition of the deep mantle heterogeneities feeding the Hawaiian plume. The results indicate that the Loa trend is much more heterogeneous than the Kea trend. Trace element concentrations and ratios indicate the presence of recycled continental crust material within the deep mantle heterogeneities sourcing the Average Loa and Enriched Loa groups. The Enriched Loa group shows unique differences in its geochemical data compared to any other group, suggesting a separate mantle heterogeneity within the Pacific LLSVP. This thesis critically characterizes the trace element compositions of the six Hawai’i geochemical groups. It contributes to understanding the composition and source of the deep mantle heterogeneities sourcing the Hawaiian mantle plume and shows the Pacific LLSVP to contain a variety of recycled continental material. The geochemical data used for the systematic analysis carried out came from the EarthChem database. The next steps will consist of reanalyzing key lavas with better sampling constraints and higher-precision instruments.

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University of British Columbia. EOSC 449

Vancouver : University of British Columbia Library

10.14288/1.0447397

Science, Faculty of; Earth, Ocean and Atmospheric Sciences, Department of

Undergraduate

DSpace