Heat and Fluid Flow at Pythia's Oasis, Cascadia Margin

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There is intense interest in understanding the nature, magnitude, and conditions of fluid flow deep within active continental margins due to the impact that fluids and mineral alteration processes have on seismicity and earthquakes in subduction zone environments. This is particularly true for the continental margin off Oregon and Washington State and Southern Canada, which is called the Cascadia Margin. This ~1000 kilometer-long subduction zone fault last ruptured in 1700 which produced a magnitude 9 earthquake that resulted in a large tsunami that impacted the Pacific Northwest and Japan and triggered significant underwater landslides. Gaining access to deep subduction zone fluids, however, is challenging because they are largely inaccessible, occurring at great depth below the seafloor. In 2015, a seep site was discovered off the Oregon coast where a jet of warm, hydrocarbon-enriched, low-salinity fluid was found venting from the seafloor. This site, called Pythia's Oasis, is unlike any seep site yet discovered, providing possible access to fluids formed deep within the Cascadia Subduction Zone. A second adjacent site includes an extensive collapse zone hosting multiple seeps that issue diffuse flows of warm and/or low salinity, methane-rich fluids that support dense microbial and macrofaunal communities. The goal of this research project is to better understand the heat flow around the sites in order to test hypotheses about the origin of these fluids and their effect on the environment. This will be done using a remotely operated vehicle from the National Deep Submergence Facility at the Woods Hole Oceanographic Institution and heat-flow probes from the Oregon State University, U.S. Academic Heat Flow Capability system. If these fluids come from deep in the subduction zone, this site will provide an opportunity to study high-temperature fluid sources and reactions in the only segment of the Cascadia Subduction Zone that is inferred to be seismically active. Results of the work have implications for understanding deep-seated fluid and seismogenic processes acting in other subduction zones as well. Broader impacts include an at-sea student training program in which at least 10 undergraduate and graduate students will participate on the 13-day sea-going field expedition to the site where they will learn about and participate in seagoing activities and the discovery processes. The students will work alongside experienced scientists and ship and deep submergence vehicle crews to conducting their own research using data collected on the cruise and by later onshore analyses. Public outreach will be carried out via students who will communicate their experiences and findings through a cruise website and formal and informal presentations, with messaging focused on K-20 opportunities in integrated oceanography-engineering programs. This research will involve collecting heat flow data in and around Pythia's Oasis, a submarine seep on the convergent Cascadia margin, thereby providing a process-based understanding for the thermal and hydrologic regime of the shallow Cascadia subduction zone (CSZ). Pythia's Oasis is located ~80 km offshore Oregon and approximately 19 km landward of the deformation front. This seafloor seep has been discharging an enormous flux of warm (11.8 degree C), low salinity (-0.6 PSU), hydrocarbon bearing fluid over a multi-year time scale. Fluids being discharged there are hypothesized to result from high temperature ( 250 degree C) dehydration reactions that provide a view of deep-seated fluids. The principal goals of this experiment are to: 1) measure heat flow in the region of Pythia's Oasis, on the incoming plate, across the deformation front, and the accretionary prism, using a violin-bow style marine heat flow probe; 2) link these observations with previously collected values of heat flow (seafloor probe, BSR estimates and continental measurements), along strike and across the forearc; and 3) develop models to better understand the thermal regime of Pythia's Oasis and the Cascadia subduction zone. The proposed work will address fundamental and long-standing questions about the links between thermal, hydrologic and geodynamic processes and will advance discovery and understanding of this unique seep.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.