Collaborative Research: Early Evolution of the Hawaiian Plume from the Geochemistry and Geochronology of Basalts Spanning the Entire Emperor Seamount Chain

The Hawaiian-Emperor Chain is one of the longest (>6,000 km), largest (>6 million cubic km), and most persistently active (>100 volcanoes over ~80 million years) hotspot provinces on Earth. The extensive volcanism of the Hawaiian-Emperor Chain is caused by the Hawaiian mantle plume, which rises buoyantly from the core-mantle boundary and produces some of the hottest and most primitive basalt lavas in recent geological time.

Studies of the Hawaiian-Emperor Chain have led to major discoveries and concepts of critical importance to the Earth Sciences, including plate tectonics and the nature of compositional heterogeneity in the deep mantle. The Emperor Seamounts are the oldest, least studied, and most enigmatic portion of the Hawaiian-Emperor Chain. This project is a detailed geochemical (lava chemistry) and geochronological (age determination) study that will resolve the temporal progression of the Emperor Seamounts and the origin of their unusual basalt compositions compared to the Hawaiian Islands.

The results of this study will facilitate testing of controversial models on the early dynamics of the Hawaiian mantle plume and its relationship to the history of Pacific plate tectonics. An integrated summer program for local high school and community college students will be initiated as part of this project. The long-term goal of this summer program is to increase the number and diversity of local (especially Native Hawaiian and Pacific Islander) college students in STEM by exposing them to the (1) exciting range of careers in the Geosciences and (2) the profound impact that Earth processes have on the Hawaiian Islands and people (e.g., volcanic eruptions, earthquakes, landslides, and seasonal flooding).

This project will examine the temporal-compositional evolution of the oldest (~80-50 Ma) and most enigmatic volcanoes of the Hawaiian-Emperor Chain using the geochemistry (major and trace elements, and Pb-Sr-Nd-Hf isotope ratios) and geochronology (40Ar/39Ar incremental heating) of Emperor Seamount basalts. The major goals are 1) to delineate the transition of the Hawaiian mantle plume from a near-ridge environment to the recent style of upwelling that is far from plate boundaries and 2) improve understanding of Pacific mantle dynamics.

The research will answer six key questions: (1) Why are basalts from Detroit Seamount so depleted? Basalts from Detroit, the second oldest Emperor Seamount (~81-76 Ma), are compositionally depleted; some are identical to Pacific mid-ocean ridge basalts (MORB). Two models for Detroit basalts will be tested: (a) entrainment of the ambient depleted Pacific upper mantle into the Hawaiian plume or (b) melting of a depleted lower mantle component—intrinsic to the Hawaiian plume—to an unusually high degree and shallow depth.

These depleted mantle models are each consistent with Pacific plate reconstructions that suggest Detroit formed on young, thin oceanic lithosphere near the axis of a mid-ocean ridge. (2) How old is Meiji Seamount? Tholeiitic basalts from Meiji, the oldest Emperor Seamount, will be used to constrain a major tectonic shakeup in the Pacific basin and the earliest known influence of the depleted Detroit mantle component on the composition of Hawaiian-Emperor Chain basalts. (3) Has the age progression of the Emperor Seamounts varied?

Geodynamic models suggest that the Hawaiian-Emperor bend was caused by the rapid southward motion of the Hawaiian plume rather than an abrupt change in Pacific plate motion. New dating of basalts from the Emperor Seamounts will be used to nail down the migration rate and provide context for future geodynamic models. (4) What is the distribution of the depleted Kea- and Detroit-types of mantle heterogeneities along the Emperor Seamounts?

A detailed temporal-spatial map of basalt chemistry will help to constrain models for the early dynamics of the Hawaiian plume. Does a top-down (5) or bottom-up (6) geodynamic model best explain these temporal-spatial-compositional trends? The trace element and isotopic map will be used to distinguish an upper vs. lower mantle origin for the Detroit component.

A top-down model (e.g., plume-ridge interaction or plume capture by a mid-ocean ridge) would be supported by an upper mantle origin, whereas a bottom-up model (e.g., mantle wind) would be supported by a lower mantle (i.e., plume) origin.

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.