Dismantling the Deep Earth: Geochemical Constraints from Hotspot Lavas for the Origin and Lengthscales of Mantle Heterogeneity
WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
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Chapter 1 presents the first published measurements of Sr-isotope variability in olivine-hosted melt inclusions. Melt inclusions in just two Samoan basalt hand samples exhibit most of the total Sr-isotope variability observed in Samoan lavas. Chapter 3 deals with the largest possible scales of mantle heterogeneity, and presents the highest magmatic 3He4He 33.8 times atmospheric discovered in Samoa and the southern hemisphere. Along with Samoa, the highest 3He4He sample from each southern hemisphere high 3He4He hotspot exhibits lower 43Nd44Nd ratios than their counterparts in the northern hemisphere. Chapter 2 presents geochemical data for a suite of unusually enriched Samoan lavas. These highly enriched Samoan lavas have the highest 87Sr86Sr values 0.72163 measured in oceanic hotspot lavas to date, and along with trace element ratios low CePb and NbU ratios, provide a strong case for ancient recycled sediment in the Samoan mantle. Chapter 4 explores whether the eclogitic and peridotitic portions of ancient subducted oceanic plates can explain the anomalous titanium, tantalum and niobium TITAN enrichment in high 3He4He ocean island basalts OIBs. The peridotitic portion of ancient subducted plates can contribute high 3He4He and, after processing in subduction zones, a refractory, rutile-bearing eclogite may contribute the positive TITAN anomalies.
- Geology, Geochemistry and Mineralogy