Collaborative Research: Investigating the Detachment Fault Cycle at the Mid-Cayman Spreading Center

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Continuous paving of new seafloor at the center of the oceans is one the fundamental processes that shape Earth’s surface. Where plates spread apart relatively quickly, new crust is formed as molten rock rises to the surface, and cools to form solid crust. Where the plates move apart more slowly less molten rock fills the gap, and instead, plate separation is taken up by motion on long-lived faults called detachments. Creation of new oceanic seafloor by slip on these kilometer-scale faults is poorly understood, and is associated with hydrothermal vent systems that provide metal-rich fluids, which create ore deposits and support thriving deep-sea ecosystems. One of the best ways to understand the behavior of these faults is to study the earthquakes that they generate. This project will use earthquake data recorded by a network of seafloor seismometers, deployed on a detachment fault system where two plates are spreading apart in the Caribbean Sea, at the Mid-Cayman Spreading Center. The results will help us understand the final stages of the ‘life cycle’ of an oceanic detachment fault, by monitoring the faulting, magmatism, and hydrothermal fluid flow in the subsurface. This project supports the training of a graduate student at the University of California San Diego, and a postdoctoral investigator at Woods Hole Oceanographic Institution. It also supports the training of undergraduate students, through participation in a sea-going research expedition and summer programs.The overarching goal of this project is to understand the processes that govern the late stages of the detachment faulting life cycle, and the processes by which the fault system is abandoned, in particular. Oceanic detachments undergo a life cycle of slip and abandonment that lasts millions of years, and commonly expose upper mantle rocks on the seafloor in kilometer-scale domes called oceanic core complexes. Although they form in magma-poor settings, detachments often host high-temperature hydrothermal systems, and interactions between hydrothermal vents and ultramafic rocks generate fluids with distinct compositions. Detachment faults are associated with a delicate interplay between tectonic, magmatic, and hydrothermal processes, but how such interactions evolve over the ~2 Myr life cycle are controversial. This project will use a local microearthquake survey of the Mt. Dent massif on the Mid-Cayman Spreading Center, to constrain the tectono-magmatic processes associated with the late stage of the life cycle. A network of ocean bottom seismographs will be deployed for 6–12 months to detect microearthquake arrivals, which will be used to generate hypocenter and focal mechanism catalogs, and also to test new full-waveform methods for detecting and locating hypocenters.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.