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

当像夏威夷群岛和海山这样的大型火山结构在海底形成时，它们的质量会在周围的海底造成巨大的弯曲凸起。在一些地方，沿着与这些弯曲隆起相关的裂缝可以观察到独特的火山特征。形成这些特征的火山过程还没有得到很好的研究或很好的理解。特别是，这些海底火山活动所产生的岩浆的深度和潜在性质一直备受争议。2018年秋天，一支海上探险队对几个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个古老部分相关的弯曲凸起形成的。一些海山的平顶表明，它们曾经大到足以突破海洋表面。通过对熔岩流样本的放射性测年和地球化学分析，该项目将揭示产生这些神秘海底山的潜在力量。该项目支持培养一名早期职业科学家和两名研究生。拱形火山作用目前是一个未被充分认识和理解的岩浆过程。此外，关于夏威夷拱形火山作用的年龄和组成的现有工作尚未导致对所涉及的源物质类型，过程的潜在动力学，甚至潜在规模的共识。最近的一次采样考察以一组神秘的海山为目标，并对其进行了采样，这些海山恰好位于夏威夷拱门（较古老的部分）上。它们的大小和位置邻近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融生产力之间的潜在关系，熔岩达到了意想不到的体积。该项目将对从两个以前未勘探过的海底山链中回收的玄武岩样品进行40Ar/39Ar年龄测定、主要元素和微量元素浓度以及Sr-Nd-Pb同位素分析。这些链不是夏威夷主要羽流轨迹的一部分，而是位于帕帕哈瑙莫库亚克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，沿着岛链有两个凹点，表明这两个特征都足够大，可以突破海面。这个项目的首要目标是确定产生如此大的火山特征的火山过程，到目前为止，远离主羽流的轨迹。需要验证的假设是：1)加德纳尖峰北部神秘的海山群是由拱形火山作用形成的；2)拱形火山作用可以产生块状海山；3)这些海山熔岩的地球化学亲和力与火山作用形成的岩石相似。该项目将用一套新的岩石学、地球化学和地质年代学约束来检验这些假设。如果结果表明这些海山是由拱形火山作用产生的，那么结果就意味着拱形火山作用可以产生比以前认为的更大的特征。更广泛地说，这项工作将直接讨论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。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.