| The ocean basins contain thousands of submarine volcanoes known as seamounts, of which a large number are oceanic intraplate volcanoes (OIVs) that often form prominent age-progressive chains. A small fraction of these seamounts breach the sea surface and form ocean islands, making them accessible for direct geological observation. This accessibility has provided us with a detailed, though biased, understanding of OIVs. Much of our knowledge of these volcanic systems comes from seismic monitoring and lava geochemistry. The resulting datasets yield insight in both the short-term construction of these volcanoes, and the long-term evolution of their mantle sources. This dissertation builds on the knowledge obtained from ocean islands. It explores both seismic and geochemical data and reveals that existing models for volcanic structure and evolution, as well as mantle melting are suitable for more average sized OIVs: seamounts.; Chapter 2 presents a seismic monitoring study, using hydrophones, of Vailulu'u seamount (Samoan volcanic chain) that demonstrates strong structural and dynamic similarities to larger active oceanic intraplate volcanoes, such as Kilauea (Hawaii). Most earthquakes occur under Vailulu'u's central crater, defining a plane that lines up with the Southeastern rift zone of the volcano, successfully predicting the location of hydrothermal vents that were discovered after publication of this paper.; Chapter 3 focuses on the geochemical evolution of a single volcano, Jasper Seamount, and shows its geochemical evolution is very similar to large ocean islands in volcanic chains with simple age progressions. The isotope and trace element compositions indicate a similar step-wise evolution and suggest similar melting processes in different sized OIVs.; Chapter 4 is a comprehensive geochemical survey of Western Pacific Seamounts and demonstrates that the Cook-Austral Islands display persistent geochemical signatures for at least 70 Myrs in three distinct, but closely spaced, hotspots. This observation supports an origin of these volcanoes by deep mantle plumes even though they do not show simple along-chain age progressions. |
