Helium, Sr, Nd, and Pb Isotope Geochemistry of Intraplate Mafic Igneous Rocks in Eastern Pacific: Implications for the Origin of Linear Volcanic Chains

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ABSTRACT Castillo (0550237)Intellectual merit: The origin of the high 3He/4He signature of some intraplate lavas is one of the most controversial topics in Earth Science today. In general, the origin of the signature boils down to two competing models: the perisphere model, which states that high 3He/4He lavas originate from the shallow part of the mantle that contains recycled extraterrestrial materials and/or experienced (U + Th)/ 3He depletion processes, and the plume model, which claims that high 3He/4He lavas originate from a more primitive, relatively undegassed portion of the lower mantle. This research tries to determine which of the two models better explains the origin of high 3He/4He signature of intraplate lavas by testing which model makes valid predictions. The perisphere model predicts: (1) all intraplate lavas exhibit similar compositional characteristics, (2) some intraplate lavas have high whereas others have low 3He/4He ratios and (3) there is no correlation between He and radiogenic isotopic signatures. The plume model predicts: (1) lavas from localized intraplate volcanoes have a helium source signature different from those of lavas that form major linear volcanic chains and (2) these localized intraplate volcanoes do not have high 3He/4He ratios. This research uses He-Sr-Nd-Pb isotopic compositions of mafic igneous rocks from fossil spreading centers and fissure ridges in the eastern Pacific, as well as their corresponding major and trace element chemistry to test the models to see which is supported by the data. Broader Impacts: This project supports investigators in the state of California and form part of a Ph.D. dissertation of a student who will be responsible for much of the chemical and isotopic analyses and interpretation of the analytical results. All the analyses will support use of existing analytical infrastructure at the Scripps Institution of Oceanography. The research also supports work with the California Center for Ocean Sciences Education Excellence (COSEE-CA) to share key aspects of the research with the public, particularly science educators and students. It involves working with the creators of Earthguide (http://earthguide.ucsd.edu/), an online science educational resource to produce an interactive online animation feature focusing on the formation of magmas and lavas that comprise the oceanic crust. Also covered are the driving forces of plate tectonics, the nature of the Earths hidden interior, planetary rheology, and the geophysical and petrological evidence on which our current understanding is based.