OCE-PRF: Determining the depth of fluid infiltration in slow and ultra-slow spread oceanic crust

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

Dr. Benjamin Urann has been granted an NSF OCE PRF to work alongside Drs. Barbara John and J.

Michael Cheadle in the Dept of Geology & Geophysics at the University of Wyoming. The goal of this project is to evaluate the depth to which seawater penetrates ocean crust, and whether seawater penetration depth varies with tectonic plate spreading rates across different ocean basins. Research products will promote a deeper understanding of earth system processes including subduction and the interaction between the hydrosphere and deep Earth.

In addition, this work will help to constrain the habitability of deep ocean crust for microbial life, which relies on delivery of organic and inorganic carbon by circulating hydrothermal fluids. Science outreach and education will be a central tenet of the project and involve: (1) outreach with UWyoming Office of Diversity, Equity and Inclusion to promote STEM and geoscience for underrepresented groups (2) community lectures, both online and in person, including at the Wind River Indian Reservation (3) creation of a UWyoming Geological Museum exhibit on the generation of ocean crust, hydrothermal vents and the biological diversity of the seafloor.

Deep-seated faults expose mantle peridotite and lower crust across broad expanses of seafloor (more than one third of all spreading ridges globally) at slow and ultra-slow spreading ridges. Abundant mylonites suggest that these faults must root below regions of earthquake activity, however the depth at which these shear zones initiate remains unknown.

These faults act as fluid conduits, yet little is known about the depth to which seawater infiltrates the mantle lithosphere. The PI will investigate the geochemical and textural characteristics of a suite of rock samples from several mid-ocean ridge localities (Mid-Atlantic, Southwest Indian, Mid-Cayman and Gakkel Ridges) to understand: (1) the depth to which seawater penetrates exposed mantle peridotite along faults, (2) if seawater penetration depth varies with plate spreading rate, (3) the effect of seawater intrusion on global volatile (H2O, F, Cl, C) cycles and (4) the implications of deep seawater intrusion on the habitability of deep ocean crust.

The PI will measure volatile abundances and B isotopes by secondary ion mass spectrometry, in conjunction with petrologic and geochemical thermobarometers and phase equilibria modeling to constrain seawater penetration depths. Taken together, this project will provide novel insights into lithosphere-hydrosphere interaction and place some lower bounds on the habitability of the deep lithosphere.

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.