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

知识价值：本研究解决了海洋地壳构造中的一级问题：即岩浆如何通过浅层地幔上升影响地幔融化过程。这项工作确定并描述了假设的扩散-反应过程，这些过程发生在海洋中脊扩张中心附近为海山火山提供补给的熔体导管周围。样品分别来自拉蒙特和万斯海山链，它们位于东太平洋隆起的北部，毗邻胡安·德·富卡山脊的南部。这两种不同的环境可以比较目前海洋科学界高度关注的两个研究充分的领域。这项工作测试了沿绝对板块运动方向排列的海山链是否反映了上升流地幔中富含橄榄石（即白云岩）的岩浆通道的影响，这些岩浆通道集中融化到靠近山脊的位置。如果是这样，那么沿绝对板块运动方向排列的海山链与沿相对板块运动方向排列的海山链具有不同的成岩成因和喷发历史。该研究还将检验一旦建立了一个泥质熔体通道，管道周围的地幔是否会发生弥漫性通量熔化。该模型将通过测量海山熔岩样品中的U-Th-Ra-Pa不平衡、Sr-Nd-Pb同位素、Si和Ca同位素以及选定的微量元素来进行测试。231Pa过量和Si和Ca的轻同位素组成将被检查，以确定温度梯度是否在岩浆组成中起重要作用。这些数据还将有助于确定不同地幔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起作用。更广泛的影响：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体验。伊利诺斯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图和地球化学数据的机会。该研究将极大地扩展目前海山链样品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.