Collaborative Research: Testing for large scale Hawaiian arch volcanism and associated magma sources

当夏威夷群岛和海山等大型火山结构建造在海底时，它们的质量会在其周围的海底造成巨大的挠性隆起。在一些地方，沿着与这些挠性隆起相关的裂缝观察到了独特的火山特征。形成这些特征的火山过程没有得到很好的研究或很好的理解。特别是，为这些海底火山事件提供动力的岩浆的深度和潜在性质引起了激烈的争论。2018年秋天，一支海洋探险队对几座火山海山进行了采样，这些火山海山是沿着与夏威夷海山链的一段古老部分相关的挠性隆起形成的。一些被采样的海山的平顶表明，它们曾经足够大，足以冲破海洋表面。通过对熔岩流样本的放射性测年和地球化学分析，该项目将揭开产生这些神秘海山的潜在力量。该项目支持对一名早期职业科学家和两名研究生的培训。拱形火山作用目前是一种被低估和缺乏了解的岩浆过程。此外，关于夏威夷拱形火山活动的年代和组成的现有工作尚未导致就所涉及的来源物质的类型、该过程的潜在动态、甚至潜在规模达成共识。最近的一次采样考察瞄准并采样了一组神秘的海山，这些海山恰好位于夏威夷拱门(较老的部分)上。它们的大小和位置毗邻夏威夷最大的火山复合体之一(加德纳尖峰)，暗示了弯曲幅度和拱形熔体生产力之间的潜在关系，熔岩达到了意想不到的数量。该项目将对从两个以前未勘探的海山链中回收的玄武岩样品进行40Ar/39Ar年龄测定、常量元素和微量元素浓度以及锶-钕-铅同位素分析。这些链条不是主要夏威夷羽流轨道的一部分，而是位于帕帕哈瑙莫库卡海洋国家纪念碑内巨大的加德纳海山以北的弯曲凸起上。最近的地图显示，沿着铁链有两个土卫二，表明这两个地物都足够大，足以冲破海面。该项目的首要目标是确定在距离主柱轨迹很远的地方产生如此大的火山特征的火山过程。要检验的假设是：1)加德纳尖峰以北神秘的海山团是由与拱形火山作用有关的过程形成的；2)拱形火山作用可以产生巨大的海山；3)这些海山熔岩的地球化学亲和力类似于年轻火山作用形成的岩石。这个项目将用一套新的岩石学、地球化学学和地质年代学的约束来检验这些假说。如果结果表明这些海山是拱形火山活动产生的，那么这一结果将意味着拱形火山活动可以产生比之前认为的更大的地貌。更广泛地说，这项工作将直接涉及热点火山活动的浅层和深层控制以及源物质的类型和位置的讨论。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

When large volcanic structures such as the Hawaiian islands and seamounts are constructed on the seafloor their mass can cause large flexural bulges in the seafloor surrounding them. In some places, unique volcanic features have been observed along the fractures that form in association with these flexural bulges. The volcanic processes that form these features are not well studied or well understood. In particular, the depth and underlying properties of the magma that feed these submarine volcanic events are heavily debated. In the fall of 2018, a seagoing expedition sampled several volcanic seamounts that formed along the flexural bulge associated with an ancient section of the Hawaiian seamount chain. The flat tops of some of the seamounts that were sampled indicate they were once large enough to breach the surface of the ocean. Through radiometric dating and geochemical analyses of the lava flow samples, this project will unravel the underlying forces that generated these enigmatic seamounts. The project supports the training of an early career scientist and two graduate students.Arch volcanism is currently an underappreciated and poorly understood magmatic process. Moreover, available work on the ages and compositions of Hawaiian Arch volcanism has not yet led to a consensus of the type of source material involved, the potential dynamics of the process, or even the potential scale. A recent sampling expedition targeted and sampled a set of enigmatic seamounts located exactly on (an older part of) the Hawaiian Arch. Their size and location adjacent to one of the largest Hawaiian volcanic complexes (Gardner Pinnacles) hints at the potential relationship between flexural amplitude and arch melt productivity, with lavas reaching unexpected volumes. This project will conduct 40Ar/39Ar age determinations, major and trace element concentrations and Sr-Nd-Pb isotopic analyses on basaltic rock samples recovered from two previously unexplored seamounts chains. These chains are not part of the primary Hawaiian plume track but reside on the flexural bulge, north of the massive Gardner Seamount within the Papahanaumokuakea Marine National Monument. Recent mapping revealed two guyots along the chains, indicating both features were large enough to breach the sea surface. The overarching goal of this project is to determine the volcanic processes that produced such large volcanic features so far from the track of the main plume. The hypothesizes to be tested are 1) The enigmatic seamount clusters north of Gardner Pinnacles were formed by processes associated with arch volcanism, 2) Arch volcanism can produce massive seamounts, and 3) The geochemical affinities of lavas from these seamounts are similar to rocks formed by rejuvenated volcanism. This project will test these hypotheses with a new suite of petrological, geochemical and geochronological constraints. If the results show that arch volcanism produced these seamounts, the results would imply that arch volcanism can produce features much larger than previously thought. More broadly, this work will speak directly to the discussion of shallow versus deep controls for hot spot volcanism and the types and locations of source materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.