Graduate Thesis Or Dissertation
 

On the Volcanic and Geodynamic Evolution of the Shatsky Rise and the Louisville Seamount

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m613n360w

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  • Large igneous provinces (LIPs) and intraplate seamounts reflect of anomalous mantle melting and illuminate interior processes of the Earth. These features are in all ocean basins and show the mantle’s evolution over time, then can provide information on plate tectonic processes, such as plate motion over time, spreading ridge formation, and continental breakup. This dissertation examines both of these features temporal and spatial evolution and interprets their geodynamic significance. Large igneous provinces are massive basaltic mountains thought to be formed from hot anomalies that ascend from the bottom of either the upper or lower mantle and impinge at the base of and then extrude upon the lithosphere. Alternatively, LIPs are thought to be derived from rapid adiabatic melting solely within the upper mantle. I present a study of the geochronology of Shatsky Rise, an oceanic plateau with an area the size of California or Japan, to help refine the origin of LIPs. Previous geochronology studies have limited age analyses and the overall age progression was limited to paleomagnetic reversals and interpretations. Previous studies also speculated that Tamu massif is the initial plume ‘head’ and the subsequent massifs, Ori and Shirshov, were a result of a plume tail and they represented age progressive volcanism. The samples presented here were collected from International Ocean Drilling Project (IODP) Expedition 324 and the Ocean Drilling Project Leg 198. The drill cores that penetrated up to 160 meters into the igneous basement of Tamu, Ori, and Shirshov Massifs. Based on the 70 new 40Ar/39Ar ages from these massifs, we find that the age difference between the uppermost lavas collected from the drill cores on Tamu massif are within 1 Ma of the age of the oceanic crust it overlays. The study concludes that Tamu and Ori massif were emplaced within 1 Ma of their underlying oceanic crust and that their formation is closely linked to crustal generation. Shatsky Rise does not represent age progressive volcanism but is linked to mid-ocean ridge processes. Our investigation into Shatsky Rise focused on the initial timing and duration of hotspot volcanism, whereas the following study investigates around the characteristics of a long-lived primary hotspot, the Louisville seamount trail, and how the seamounts within formed and reflect absolute plate motion and hotspot mobility. We analyzed 70 samples from IODP Expedition 330 for 40Ar/39Ar geochronology which covered an age range from ~74 Ma to 51 Ma. Louisville is the south Pacific analog to the Hawaiian-Emperor seamount trail and has been active from ~80 Ma to 1 Ma but has no known active hotspot. We broadly look at known seamount lifespans from Louisville and Hawaii to determine the duration of seamount volcanism. Hawaii has an overall lifespan of ~6-7 Ma whereas Louisville seamounts show an age range of ~4-5 Ma. The ages from samples do not accurately reflect the inception age of a given seamount but are representative of a later stage of volcanism. We conclude that past plate motion models do not accurately reflect the age progression of the Louisville seamount trail. The final study presented here collates the new age data from Louisville seamount trail and the seamount lifespans to better interpret the geography of seamounts over the past 80 Ma within the Pacific Plate. We built a plate motion model that searches for stage poles that fit the age progression and geometry of both Louisville and Hawaii seamount trails within a ‘fixed’ and ‘moving’ hotspot reference frame. Our results find that a fixed hotspot solution is viable for describing Louisville and Hawaiian-Emperor from 45 Ma to 0 Ma. Prior to 45 Ma, the Hawaiian hotspot and an average of ~4° of southward latitudinal movement while Louisville hotspot motion was limited to ~1°. These studies cover three major areas of oceanic volcanism research and provide crucial information on emplacement characteristics of Large Igneous Provinces and intraplate hotspot volcanoes and how their behavior can provide insights to mantle processes and the absolute plate motion of the Pacific plate. All the hotspot motion models confirmed that the Hawaiian hotspot has a latitudinal motion of ~4 degrees and that there is limited hotspot motion of ~1 degree for Louisville. The amount of west to east motion is very limited.
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  • Ongoing Research
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  • 2019-04-10 to 2021-05-13

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