Solving the mystery of Bermuda: Implications for intraplate magmatism

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The island of Bermuda, which sits on one of the largest non-mid-ocean ridge volcanic platforms in the Atlantic Ocean, is not far from the East Coast of the United States. The origin of this platform, the source and composition of the lavas that make it up, and the melting mechanisms that caused its formation are still unknown. This research will analyze the geochemistry of the volcanic and intrusive igneous rocks of a drill core, presently stored at Dalhousie University in Canada, that was drilled through the Bermuda platform back in the 1970's and never analyzed. The research will explore various hypotheses as to the platform's source and origin And it may also have implications for volcanic hazard work and atmospheric CO2 concentrations. Various theories have been proposed for the origin of the Bermuda platform. One is that it was formed by a mantle plume, which is a hot, long-lived, stationary jet of magma that comes from deep in the mantle and erupts lava onto the seafloor, similar to how Hawaii, Iceland, and the Galapagos islands formed. Another hypothesis is that the platform was formed by the upwelling of magma as convection in the mantle bumped up against the roots of the North American continent and overturned, causing sustained melting and volcanism that formed the Bermuda Platform. This research is focused on understanding the source of the Bermuda volcanic activity and other similar seafloor volcanic sites around the world that share its characteristics. The work will also provide new clues as to the role this kind of volcanic activity has in the global carbon cycle because some of the samples in the Bermuda drill core appear to have come from a strongly carbonated mantle source. Broader impacts of the research include support of early career scientist from a minority group under-represented in the sciences who has a strong track record of engaging and mentoring both undergraduate and graduate students and providing them with full-bodied research experiences in state-of-the-art analytical techniques. Results of the project will be incorporated into college level courses in addition to being used for public outreach activities and teacher professional development workshops through the Geosciences Museum at Virginia Tech. The project will also foster international collaboration with a Swiss scientist and will rescue an important drill core by moving it to a US core repository where it will be curated and samples will be made accessible to the public and to other scientists wishing to study the Bermuda volcanic platform. The mantle plume model has generally been accepted as a plausible mechanism behind intraplate volcanism. However, not all locations that are considered hotspots have the seismic and geochemical signatures to support a deep-rooted mantle plume. Small-scale convection (e.g., edge-driven convection, shear-driven convection) has been proposed as an alternative to the mantle plume model, especially to describe the Bermuda swell. This volcanic platform is near a continent, but away from mid-ocean ridges, making it an ideal location to test alternative models for intraplate magma generation. To date, no geochemical, volatile, or petrological data have been published for Bermuda; and this is crucial data to elucidate melting mechanisms and magmatic processes. In 1972, the Bermuda Deep Drill Core was collected and then forgotten. Preliminary geochemical results of samples from this core suggest that some of the Bermuda volcanic units are derived from a carbonated source, indicating the presence of a deep carbon reservoir linked to a highly radiogenic mantle end-member. This research will address fundamental questions of mantle geochemistry and dynamics, such as: (1) how mantle plume and small-scale convection-derived magmas differ from one another geochemically and petrologically; (2) the mantle source composition of Bermuda volcanics; and (3) what the link is between a deep carbonated mantle reservoir and the generation of silica under-saturated magmas and, thus, the role of intraplate magmatism in the global carbon cycle. Geochemical analyses that indicate the temperature of the magma source, the volatile composition of melt inclusions and depth of their formation, and the full suite of major and trace element geochemical analyses of the lavas and their radiogenic isotope compositions will be used to determine the origin and source of the Bermuda volcanics and evaluate the validity of the various proposed hypotheses.