Delaney John R.

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Delaney
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John R.
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  • Article
    Focused fluid flow along the Nootka fault zone and continental slope, explorer-Juan de Fuca Plate Boundary
    (American Geophysical Union, 2020-08-07) Riedel, Michael ; Rohr, Kristin Marie Michener ; Spence, George D. ; Kelley, Deborah S. ; Delaney, John R. ; Lapham, Laura L. ; Pohlman, John W. ; Hyndman, Roy D. ; Willoughby, Ele C.
    Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from >20 years of investigations to demonstrate the nature of fluid‐flow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to near‐seafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100–300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show opposite‐to‐seafloor reflection polarity, and are associated with frequency reduction and velocity push‐down indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonconformable high‐amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottom‐video observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios <500 indicating a possible slight contribution from a deep source. We infer the reflective zones beneath the two mounds are basaltic intrusions that create hydrothermal circulation within the overlying sediments. Across the Nootka continental slope, gas hydrate‐related bottom‐simulating reflectors are widespread and occur at depths indicating heat flow values of 80–90 mW/m2.
  • Article
    Sulfide geochronology along the Endeavour Segment of the Juan de Fuca Ridge
    (John Wiley & Sons, 2013-07-08) Jamieson, John W. ; Hannington, Mark D. ; Clague, David A. ; Kelley, Deborah S. ; Delaney, John R. ; Holden, James F. ; Tivey, Margaret K. ; Kimpe, Linda E.
    Forty-nine hydrothermal sulfide-sulfate rock samples from the Endeavour Segment of the Juan de Fuca Ridge, northeastern Pacific Ocean, were dated by measuring the decay of 226Ra (half-life of 1600 years) in hydrothermal barite to provide a history of hydrothermal venting at the site over the past 6000 years. This dating method is effective for samples ranging in age from ∼200 to 20,000 years old and effectively bridges an age gap between shorter- and longer-lived U-series dating techniques for hydrothermal deposits. Results show that hydrothermal venting at the active High Rise, Sasquatch, and Main Endeavour fields began at least 850, 1450, and 2300 years ago, respectively. Barite ages of other inactive deposits on the axial valley floor are between ∼1200 and ∼2200 years old, indicating past widespread hydrothermal venting outside of the currently active vent fields. Samples from the half-graben on the eastern slope of the axial valley range in age from ∼1700 to ∼2925 years, and a single sample from outside the axial valley, near the westernmost valley fault scarp is ∼5850 ± 205 years old. The spatial relationship between hydrothermal venting and normal faulting suggests a temporal relationship, with progressive younging of sulfide deposits from the edges of the axial valley toward the center of the rift. These relationships are consistent with the inward migration of normal faulting toward the center of the valley over time and a minimum age of onset of hydrothermal activity in this region of 5850 years.