Graduate Thesis Or Dissertation
 

Revisiting Lōʻihi: Geochemistry of Kamaʻehuakanaloa Lavas Reveals Complexities in the Pre-Shield to Shield Transition and Hawaiian Mantle Plume Source

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rn301883z

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  • Studies of Hawaiian volcanoes contribute valuable insights about Earth processes and mantle evolution, and are fundamental for understanding the construction of the largest volcanoes on terrestrial planets. The pre-shield stage exists in every Hawaiian volcano, but is usually blanketed by high volume tholeiitic lava flows during the main shield stage. Submarine Kamaʻehuakanaloa (formerly Lōʻihii) Seamount represents the elusive pre-shield stage, but shows a transition to early shield-type tholeiitic eruptions. In this dissertation, the evolutionary history of Kamaʻehuakanaloa lavas in Hawaii was revisited to understand the lesser understood transition occurring between pre-shield and shield phases of intraplate volcanoes. Broad trends on the volcano indicate that different processes affect observed compositions. Helium isotopes, which are central to geochemical assessment of deep mantle plume origin, show coherence with major elements and trace elements. Spatial variation can be examined with the highly constrained location metadata of this sample suite. South Rift suite shows consistent evolution within suite, similar to variation observed in East Flank stratigraphic section. Volatile and Helium isotopes of major rock groups shows evidence of increasing 3He/4He of with higher volumes of melting, but not towards increased mid-ocean ridge source contribution with volcano age, as predicted by most Hawaiian evolution models. Evidence for a distinct mantle source for North Rift tholeiites suggests the North and South rift zones sample different mantle sources. This has not been previously proposed at Kamaʻehuakanaloa. Radiogenic Pb isotopes provide additional support for the origin of two rift zones from different mantle sources, and suggest derivation from the Loa component in a bilaterally zoned plume. The combination of radiogenic isotopes with Helium is central to geochemical assessment of deep mantles plume origin, as this shows evidence of gases with lithophile elements. Overall, variation in the mantle source can be confirmed by close studies of well-constrained samples on a single volcano.
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