Catherine Armstrong

I am interested in how the isotopic and trace element composition of rocks and minerals can reveal clues about their origin and evolution. The aim of my M.Sc. project is to model the source of the enriched geochemical signature at Hawai'i by obtaining high-precision compositional analyses of the 'Makapu'u-stage' basalts from Ko'olau Volcano on O'ahu. The Hawaiian Islands extend along two geographical trends, Loa and Kea. They are volcanic islands formed by the upwelling of hot lower mantle material, so their isotopic composition reflects that of their mantle source and allows for extensive insight into mantle plume structure and geodynamics. With respect to the range of geochemical compositions displayed by Hawaiian basalts, the Makapu'u-stage basalts represent an extreme, enriched end-member, which might also be responsible for the geochemical variability observed among Loa-trend volcanoes.

Presently, there are diverging hypotheses for the origin of this enriched mantle component. To proceed, a careful modern, systematic analysis of the Makapu'u-stage basalts is necessary, as past interpretations are restricted by both instrumental limitations and inconsistent sample sets. To this end, I will sample the Makapu'u section basalts and conduct high-precision geochemical analyses of their trace element and Sr-Nd-Pb-Hf isotopic compositions, on the same sample powders and after careful leaching. With a more complete and precise dataset for this compositional end-member, I will model its contribution to the genesis of Loa-trend geochemical variability. The Loa-trend volcanoes represent a prominent feature of modern Hawaiian volcanism, so resolving their origin is fundamental to understanding the nature and variability of the Hawaiian mantle source. On a larger scale, this study could have implications for the processes governing the formation of other dual-chain oceanic islands and associated mantle geodynamics worldwide.