Intellectual Merit: This research addresses a first-order problem in ocean crustal construction: i.e., how magmas rising through the shallow mantle affect mantle melting processes. This work identifies and characterizes hypothesized diffusion-reaction processes that occur around melt conduits that feed seamount volcanoes near mid-ocean ridge spreading centers. Samples come from the Lamont and Vance Seamount chains located just off the northern East Pacific Rise and adjacent to the southern Juan de Fuca ridge, respectively. These two different settings allow comparison between two well-studied areas of high present interest in the ocean science community. This work tests whether seamount chains, aligned along absolute plate motion directions, reflect the effects of olivine-rich (i.e. dunite) magma conduits in the upwelling mantle that focus melts to near-ridge locations. If true, then seamount chains aligned along absolute plate motion directions will have different petrogenetic origins and eruption histories from those aligned along relative plate motion directions. The research will also examine whether diffusive flux-melting of the mantle surrounding a conduit occurs once a dunite melt channel is established. Tests of the models will be carried out by measuring U-Th-Ra-Pa disequilibria, Sr-Nd-Pb isotopes, Si and Ca isotopes and selected trace elements in seamount lava samples. 231Pa excesses and light isotopic compositions of Si and Ca will be examined to determine if temperature gradients play a significant role in magma composition. These data will also help ascertain the role of different mantle sources in magma genesis and test whether temperature gradients play a role in mineralogical and compositional traits that currently are not well explained.
Broader Impacts: Broader impacts of the work include training of two graduate students and collaboration between institutions. Undergraduates will be integrated into the research and engaged in the whole laboratory experience. Outreach to high school earth science classes at University Laboratory High School in Urbana Illinois will provide opportunities for students to learn about ocean floor geology and work with bathymetric maps and geochemical data. The study will greatly expand the current global database for a number of geochemical traits for seamount chain samples.
