| Summary: | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. Includes bibliographical references. Lavas 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). (cont.) I infer that this component was lower continental crust. At Hawaii there are systematic geochemical differences between the < ...
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