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dc.contributor.advisorFrederick A. Frey.en_US
dc.contributor.authorXu, Guangpingen_US
dc.contributor.otherMassachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.en_US
dc.date.accessioned2008-09-03T15:09:39Z
dc.date.available2008-09-03T15:09:39Z
dc.date.copyright2007en_US
dc.date.issued2007en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/42275
dc.descriptionThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007.en_US
dc.descriptionIncludes bibliographical references.en_US
dc.description.abstractLavas derived from long-lived mantle plumes provide important information of mantle compositions and the processes that created the geochemical heterogeneity within the mantle. Kerguelen and Hawaii are two long-lived mantle plumes and lavas associated with them have very different geochemical characteristics. In this thesis I studied the geochemical compositions of the lavas associated with Kerguelen plume (Mt. Capitole in Kerguelen Archipelago) and Hawaiian plume (Mauna Kea, East Molokai and West Molokai volcanoes) to understand what processes contributed to the geochemical variations observed in Kerguelen and Hawaiian lavas and the geochemical structure of the mantle beneath them. Mt. Capitole is in the central part of the Kerguelen Archipelago and is attributed to Cenozoic volcanism arising from the Kerguelen hotspot. Based on the study of Mt. Capitole and previous isotopic data for the Kerguelen Plateau, Kerguelen Archipelago and Heard Island, I propose that two stages of mixing can explain the significant Sr, Nd, Hf and Pb isotopic heterogeneity. The first mixing process, best shown by the submarine lavas from Northern Kerguelen Plateau, is between a depleted component (i.e., relatively low 87Sr/86Sr with high 143Nd/144Nd and 176Hf/177Hf), probably related to Southeast Indian Ocean mid-ocean ridge basalt, but possibly intrinsic to the Kerguelen plume, and an enriched Kerguelen plume component. From -34 Ma to <1 Ma, on average the proportion of the depleted component decreased. Subsequently, a second mixing process involved addition of a component with relatively high 87Sr/86Sr (>0.7060) and low 143Nd/144Nd (<0.5125) and 176Hf/177Hf (<0.2827) and non-radiogenic Pb isotope ratios (<17.9 for 206Pb/204Pb).en_US
dc.description.abstract(cont.) I infer that this component was lower continental crust. At Hawaii there are systematic geochemical differences between the < 3 My Hawaiian shields forming the subparallel spatial trends, known as Loa and Kea. East Molokai (> 1.5 Ma), the oldest volcano on the Kea-trend, maintains the Kea-like geochemical characteristics. As East Molokai and other Kea-trend volcanoes (Mauna Kea, Kohala, Haleakala and West Maui) migrate away from the hotspot and evolve from the shield to postshield stage, isotopic ratios of 87Sr/86Sr decrease and 143Nd/144Nd and 176Hf/177Hf increase in postshield lavas; however, all Kea postshield lavas have similar ratios of Sr, Nd, Hf and Pb showing that the periphery of the hotspot sampled by Kea-trend postshield lavas had long-term geochemical homogeneity (>1.5 My). The temporal changes in Sr, Nd and Hf isotope ratios are attributed to incorporation of a depleted component that dominantly sampled by rejuvenated stage lavas. This depleted component has Kea-trend Pb isotopic characteristics, relatively low 208Pb/204pb at a given 206Pb/204Pb, and it is probably not related to oceanic lithosphere or the source of mid-ocean ridge basalt. The Loa-Kea spatial geochemical differences end at West Molokai shield (- 1.9 Ma) which is the oldest Loa-trend volcano on the double parallel chains. West Molokai shield includes lavas with Loa- and Kea-like geochemical characteristics; a mixed Loa- Kea source is required. In contrast, West Molokai postshield lavas are exclusively Kea-like. This change in source geochemistry can be explained by the observed change in strike of the Pacific plate near Molokai Island so that as West Molokai volcano moved away from a mixed Loa-Kea source it sampled only the Kea side of a bilaterally zoned plume (Abouchami et al., Nature, v434, 2005).en_US
dc.description.statementofresponsibilityby Guangping Xu.en_US
dc.format.extent338 p.en_US
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582en_US
dc.subjectEarth, Atmospheric, and Planetary Sciences.en_US
dc.titleOrigin of geochemical heterogeneity in the mantle : constraints from volcanism associated with Hawaiian and Kerguelen mantle plumesen_US
dc.typeThesisen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
dc.identifier.oclc231846778en_US


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