The outstanding goal of this project was to investigate two previously unexplored seamount chains in the Papahānaumokuākea Marine National Sanctuary.  The Naifeh and Plumeria seamount clusters, which consist of 10 submarine volcanoes located ~220km north of the Northwest Hawaiian Ridge, were mapped and sampled by the E/V Nautilus expedition NA101. The origin of these seamounts was unknown, but their unique orientation and location suggested several possible mechanisms of formation.  To investigate the origin of these seamount clusters we used geochemical analyses of lavas erupted at each seamount to better constrain the composition of the underlying mantle, as well as the depth and extent of melting required to generate these large volcanic structures and provide insight into the interaction between mantle plumes, the upper mantle, and surrounding lithosphere.

Major and trace element compositions of 28 samples from the five Naifeh seamounts and 22 samples from the five Plumeria seamounts were collected. Major element data indicate that all lavas are alkalic, ranging from trachybasalts to trachyandesites. Trace element patterns are relatively consistent throughout both chains, suggesting the lavas came from a similar mantle source and extent of melting. Naifeh and Plumeria both have enriched incompatible trace element compositions compared to mid ocean ridge basalts, suggesting their source is not typical depleted upper mantle, but more similar to a mixture of ocean island basalt and mid ocean ridge basalt. Thus, it is not likely these were formed from intraplate extension and deformation as has been suggested for the nearby Musician seamounts or from Cretaceous crust building. Further, the seamounts are distinct from North and South Arch lavas (that are associated with the Hawaiian Islands), suggesting that they were not created in the flexural bulge associated with plate loading.  Instead, Naifeh and Plumeria have compositions similar to lavas from the Line Islands and Rurutu, which have been explained by multiple hotspots stemming from the South Pacific Superswell or small scale sublithospheric convection. They also have compositional similarities with the Shatsky, Ojin, and Hess rise seamounts, which are hotspot derived seamounts erupted during the Cretaceous. Based on this, we suggest that the Naifeh and Plumeria seamounts originated from a hotspot source emanating from the South Pacific Superswell with the incorporation of recycled oceanic crust.

This project provided significant hands on training at both graduate and undergraduate level. Five undergraduate and one graduate student prepared and ran samples for geochemical analyses. Both graduate and undergraduate students collected geochemical data using an ICP-MS at Boise State. Undergraduates were trained to cut, crush and pick rocks for geochemical analyses.  The graduate student presented results of the project at AGU and the Idaho Mining Conference, which provided training in both written and oral communication. An undergraduate student presented results of her research at the Idaho Mining Conference. 

A major outcome of this project focused on developing new educational tools for an undergraduate Petrology course at Boise State.  During the spring of 2022, undergraduate students were trained to prepare samples for geochemical analyses (clean, sieve, and pick samples using a binocular microscope).  They then ran their own samples for major and trace element contents on the ICP-MS at Boise state.  Post data collection, the students learned to plot data in meaningful ways, compared data sets to other nearby seamounts (including the Enigmatic Seamounts) and hotspot chains, created maps with sample locations and ran petrologic models to determine degrees of fractional crystallization and extents of mantle melting.  They presented the results as a final project to the department at the end of the semester.  One student continued to work on this project over the summer and following fall and presented the results of the research at a local conference. Overall this the undergraduates loved this aspect of the course and they got to contribute to data collection for the MS student thesis.  This model for combining undergraduate course work with data collection and research will be used in future undergraduate courses. 

The graduate student wrote abstracts and presented results to the scientific community at the American Geophysical Union meeting in 2021 and 2022. These results were also incorporated into abstracts and presentations by Co-PIs (Goldschmidt, AGU, and GSA).  Major element data was incorporated into a manuscript (Sotomayor et al., 2023) and the data was published in a MS Thesis at Boise State. 

 The results of this work will have an impact beyond the geophysical/geochemical questions. Bathymetric data collected during this project will be used by OET and Papahānaumokuākea Marine National Sanctuary in their efforts to evaluate and map the Sanctuary.  Further, this project has provided training for undergraduates that will extend beyond science and technology.  Students were able to learn hands on laboratory and computer modelling skills that they can take into the workforce and they worked on presentation skills that will be valuable for a wide variety of post-graduation employment. 

Last Modified: 09/12/2023
Modified by: Virginia Dorsey Wanless