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

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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.