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Type of Document Dissertation Author Shafer, John Travis Author's Email Address jshafer@nd.edu URN etd-12182006-104436 Title Major Element, Trace Element, and Isotopic Composition of Emperor Seamount Chain and Ontong Java Plateau Basalts Degree Doctor of Philosophy Department Civil Engineering and Geological Sciences Advisory Committee
Advisor Name Title Dr. Clive R. Neal Committee Chair Keywords
- petrology
- isotopes
- Hawaii
- Ontong Java Plateau
- geochemistry
- PGE
- platinum group elements
Date of Defense 2006-12-01 Availability unrestricted Abstract The Ontong Java Plateau (OJP) and the Hawaiian Ridge-Emperor Seamount Chain (HR-ESC) are two of the largest volcanic structures on Earth. As the OJP covers an area of more than 2 x 10^6, the plateau represents the largest known magmatic event in Earth's history. Equally impressive, the HR-ESC stretches for more than 6,000 km through the north-central Pacific Ocean. Despite the magnitude of these events, the chemistry of significant portions of the OJP and the HR-ESC are poorly known to completely unknown. A full understanding of the chemistry of the OJP and the HR-ESC is necessary to make realistic models of their formation.
Major element, trace element, platinum group element (PGE), and isotopic ratio analyses have been conducted on samples collected from several locations on both the OJP and the HR-ESC using inductively coupled plasma-optical emission spectroscopy (ICP-OES), ICP-mass spectrometry (ICP-MS), and negative thermal ionization mass spectrometry (NTIMS).
Using a combination of the aforementioned analytical techniques, it was discovered the OJP has more geochemical variation than previously recognized, especially at the margins of the plateau. The discovery of a previously unknown lava type from the volcaniclastic succession at Site 1184 on the eastern salient of the OJP and more primitive lava types from basaltic crustal xenoliths suggests that further sampling via deep sea drilling is necessary to better understand the complex origins of the worlds largest igneous province.
ESC seamounts have been assumed to undergo similar stages of development as their younger Hawaiian counterparts despite the paucity of non-dredge samples. The investigation of a greater than 300 km thick sequence of basement from Nintoku Seamount confirms that a typical ESC volcano develops in a similar manner to modern Hawaiian volcanoes. PGE and Re/Os isotopic work on three ESC seamounts suggests that both recycled oceanic crust and outer core material contribute to the overall PGE budget in the Hawaiian plume but that it requires unusual melting conditions for both sources to manifest themselves.
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