Underwater volcanos on the seafloor are referred to as seamounts. Over 30,000 seamounts exist on the Pacific plate and less than 1% have been explored. Thus, the volcanic processes that generate these unexplored seamounts are also unknown. This project sought to understand the formation processes of several seamounts that reside within US waters, just north of the well-known Northwest Hawaiian Ridge seamount track. The target seamounts comprise the Naifeh and Plumeria clusters. Rock samples were previously collected from these seamounts using the ROV Hercules deployed from the research vessel E/V Nautilus (Ocean Exploration Trust). We used radiometric geochronological analyses (⁴⁰Ar/³⁹Ar incremental heating method) of these rock samples to determine the age of their formation. The lava flows ranged in age from 85 to 88 million years, disproving the original hypothesis that the seamounts were caused by arch volcanism generated from the emplacement of the massive Gardner Seamount that is a volcano within the Hawaiian Ridge that formed approximately 13 to 15 million years ago. These ancient Cretaceous formation ages indicate that the seamounts in our project were not related to processes that formed the younger Hawaiian Ridge. Next, we coupled the age determinations with geomorphologic observations of the seamounts to generate new hypotheses about how they formed. The coupled age determinations and geometry of the seamount tracks eliminated the possibility that a mantle plume was responsible for their formation. Therefore, two alternative hypotheses were proposed. First, the seamounts may have formed from an extensional tectonic process that thinned the crust. The thinned lithosphere allows for decompression melting of the mantle, thus forming the seamounts. This potential lithosphere extension regime could have formed during the Pacific basin plate reorganization during the late-Cretaceous, where in both the Osborn Trough (South Pacific) and Chinook Trough (North Pacific) ceased spreading. This cessation of spreading potentially allow for diffuse deformation of the Pacific lithosphere – generating volcanism. Alternatively, the seamounts represent a near-ridge age progressive chain with melt derived from small-scale convective currents in the mantle generating shear-driven upwelling.

To further test the shear-driven upwelling hypothesis, a additional previously collected lava flow samples from the Musician Seamount Province, which resides north of the Hawaiian Islands, were analyzed. These rocks allowed for tests on what role mantle plume – mid-ocean ridge interactions play in generating complex seamount provinces. The new ages confirmed that the seamount chain composing the western extent of the Musician Seamount Province were generated by a mantle plume while the east-west trending volcanic ridges formed contemporaneously from channelization of plume melt towards the ancient spreading center. These age constraints were then used to generate a tectonic evolution of the region, providing additional constraints that can be used to calibrate plate motion models. Part of the southern extent of the Musician Seamount Province likely represents the continuation of the Naifeh-Plumeria chain, extending the eastward age progression to 80 million years ago. These studies highlighted the wide and complex range of processes that can generate seamounts.

This grant supported the training of two graduate students at California State University Long Beach. Both students completed their Masters Degrees in Geology and are now gainfully employed. Both of their theses were published in peer-reviewed journals. The grant also supported four undergraduate student researchers that all completed their Bachelor's degrees in Geology. Two of these students are now gainfully employed and two others are in graduate school.

Last Modified: 12/02/2024
Modified by: Andrea M Balbas