Collaborative Research: Probing mantle plumbing beneath Pacific ridges thriugh study of the Lamont and Vance Seamount chains

智力优势：这项研究解决了海洋地壳构造中的一个一级问题：即，岩浆上升通过浅地幔如何影响地幔熔融过程。这项工作确定和特点的假设扩散反应过程中发生的熔融管道，饲料海山火山附近的洋中脊扩张中心。样本来自拉蒙和万斯海山链，这两个海山链分别位于东太平洋海隆北方附近和胡安·德富卡海脊南部附近。这两个不同的背景使人们能够对海洋科学界目前高度关注的两个经过充分研究的领域进行比较。这项工作的测试是否海山链，对齐沿着绝对板块运动方向，反映了富橄榄石（即纯橄榄岩）岩浆导管的影响，在上涌地幔集中熔融到近脊的位置。如果是这样，那么沿沿着绝对板块运动方向排列的海山链与沿沿着相对板块运动方向排列的海山链将具有不同的岩石成因和喷发历史。这项研究还将探讨是否扩散通量熔化的地幔周围的管道发生一旦纯橄榄岩熔体通道建立。将通过测量U-Th-Ra-Pa不平衡、Sr-Nd-Pb同位素、Si和Ca同位素以及海山熔岩样品中的某些微量元素来检验这些模型。231 Pa过剩和轻同位素组成的Si和Ca将被检查，以确定温度梯度是否发挥重要作用的岩浆成分。这些数据还将有助于确定不同地幔来源在岩浆成因中的作用，并测试温度梯度是否在矿物学和成分特征中发挥作用，目前还没有得到很好的解释。更广泛的影响：这项工作的更广泛的影响包括培训两名研究生和机构之间的合作。本科生将融入研究，并参与整个实验室的经验。伊利诺伊州厄巴纳大学实验高中的高中地球科学课程将为学生提供机会，让他们了解海底地质学，并使用测深图和地球化学数据。这项研究将大大扩大目前关于海山链样品若干地球化学特征的全球数据库。

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.