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

智力价值：这项研究解决了大洋地壳构造中的一个首要问题：即从浅地幔上升的岩浆如何影响地幔融化过程。这项工作确定并描述了假想的扩散-反应过程，这些过程发生在为海洋中脊扩张中心附近的海山火山提供燃料的熔融管道周围。样本分别来自拉蒙特和万斯海山链，分别位于东太平洋隆起北部和胡安德富卡海脊南部附近。这两个不同的背景使海洋科学界目前高度感兴趣的两个经过充分研究的领域得以比较。这项工作测试了沿着绝对板块运动方向排列的海山链是否反映了上升地幔中富含橄榄石(即纯橄榄石)的岩浆管道的影响，这些管道的焦点融化到接近山脊的位置。如果是真的，那么沿着绝对板块运动方向排列的海山链将与沿着相对板块运动方向排列的海山链具有不同的岩石成因和喷发历史。这项研究还将检查一旦建立了纯橄榄岩熔体通道，是否会发生围绕管道的地幔的扩散熔剂熔化。模型的检验将通过测量海山熔岩样品中的U-Th-Ra-Pa不平衡、锶-钕-铅同位素、硅和钙同位素以及选定的微量元素来进行。为了确定温度梯度是否在岩浆成分中起着重要作用，将对231Pa值的过剩和硅、钙的轻同位素组成进行研究。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目前尚未得到很好解释的矿物学和成分特征中发挥作用。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各机构之间的合作。本科生将融入到研究中，并参与整个实验室体验。扩展到伊利诺伊州厄巴纳大学实验室高中的地球科学课程将为学生提供学习海底地质学和使用水深地图和地球化学数据的机会。这项研究将极大地扩展目前的全球数据库，以获取海山链样本的一些地球化学特征。

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.