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  • 1
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    Temporal variability and tidal modulation of hydrothermal exit-fluid temperatures at the Lucky Strike deep-sea vent field, Mid-Atlantic Ridge (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 119 (2014): 2543–2566, doi:10.1002/2013JB010478.
    Description: We deployed autonomous temperature sensors at black smoker chimneys, cracks, and diffuse flow areas at the Lucky Strike hydrothermal field (Mid-Atlantic Ridge, ~37°17'N) between summer 2009 and summer 2012 and contemporaneously measured tidal pressures and currents as part of the long-term MoMAR experiment to monitor hydrothermal activity. We classify the temperature data according to the hydrogeologic setting of the measurement sites: a high-temperature regime (〉190°C) representing discharge of essentially unmixed, primary hydrothermal fluids through chimneys, an intermediate-temperature regime (10–100°C) associated with mixing of primary fluids with cold pore fluids discharging through cracks, and a low-temperature regime (〈10°C) associated with a thermal boundary layer forming over bacterial mats associated with diffuse outflow of warm fluids. Temperature records from all the regimes exhibit variations at semi-diurnal tidal periods, and cross-spectral analyses reveal that high-temperature discharge correlates to tidal pressure while low-temperature discharge correlates to tidal currents. Intermediate-temperature discharge exhibits a transitional behavior correlating to both tidal pressure and currents. Episodic perturbations, with transient temperature drops of up to ~150°C, which occur in the high-temperature and intermediate-temperature records, are not observed on multiple probes (including nearby probes at the same site), and they are not correlated with microearthquake activity, indicating that the perturbation mechanism is highly localized at the measurement sites within the hydrothermal structures. The average temperature at a given site may increase or decrease at annual time scales, but the average temperature of the hydrothermal field, as a whole, appears to be stable over our 3 year observation period.
    Description: This project was funded by CNRS/IFREMER through the 2009, 2010, 2011, and 2012 cruises within the MoMAR program (France) and by ANR (France) Mothseim Project NT05-3 42213, led by J. Escartín. T. Barreyre was supported by University Paris Diderot (Paris 7—France) and Institut de Physique du Globe de Paris (IPGP, France).
    Description: 2014-10-02
    Keywords: Hydrothermal activity ; Time-series ; Spectral analysis ; Tidal forcing ; Temperature variations ; Mid-ocean ridge
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Three-dimensional seismic structure of a Mid-Atlantic Ridge segment characterized by active detachment faulting (Trans-Atlantic Geotraverse, 25°55′N-26°20′N) (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q0AG13, doi:10.1029/2012GC004454.
    Description: We use air gun shots recorded by ocean bottom seismometers (OBSs) to generate a three-dimensional (3D) P-wave tomographic velocity model of the Trans-Atlantic Geotraverse (TAG) segment of the Mid-Atlantic Ridge, and to search for evidence of reflections from a shallow crustal fault interface. Near-vertical reflections were observed in some of the seismic records from OBSs deployed within the active seismicity zone defined by microearthquake hypocenters. Forward modeling of synthetic seismograms indicates that these reflections are consistent with a fault interface dipping at a low angle toward the ridge axis. Our observations suggest that the fault zone may extend beneath the volcanic blocks forming the eastern valley wall. Our 3D tomographic results show that the across-axis structural asymmetry associated with detachment faulting extends at least 15 km to the east of the ridge axis, indicating that detachment faulting and uplifting of deep lithologies has been occurring at the TAG segment for at least the last ∼1.35 Myr. The velocity model contains a 5 km by 8 km velocity anomaly within the detachment footwall. This anomaly, which is present beneath the active TAG hydrothermal mound, is characterized by a velocity inversion at 1.5–2.0 km below seafloor underlain by reduced P-wave velocities (∼6.2–6.5 km/s compared to surrounding areas ∼7.0–7.2 km/s) extending down to 3.5 km below seafloor. The velocity anomaly likely results from some combination of thermal and/or hydrothermal processes, and in either case our results suggest that hydrothermal fluids circulate within the upper section of the detachment footwall beneath the active mound.
    Description: This research was supported by grants from the Chinese National Natural Science Foundation (41076029, 41176053, 91028002) and the U.S.-NSF (OCE-0137329). M.Z. was supported by China Scholarship Council for 6 months of cooperative research at WHOI. J.P.C. acknowledges support from The Andrew W. Mellon Foundation Endowed Fund for Innovative Research.
    Description: 2013-05-02
    Keywords: 3D seismic structure ; Mid-Atlantic Ridge ; TAG hydrothermal field ; Active detachment fault
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Poroelastic response of mid-ocean ridge hydrothermal systems to ocean tidal loading : implications for shallow permeability structure (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 43 (2016): 1660–1668, doi:10.1002/2015GL066479.
    Description: We use the time delay between tidal loading and exit-fluid temperature response for hydrothermal vents to model the poroelastic behavior and shallow upflow zone (SUZ) effective permeability structure of three mid-ocean ridge (MOR) sites with different spreading rates. Hydrothermal vents at Lucky Strike field exhibit relatively small phase lags corresponding to high SUZ effective permeabilities of ≥ ~10−10 m2, with variations that we interpret as resulting from differences in the extrusive layer thickness. By contrast, vents at East Pacific Rise site exhibit relatively large phase lags corresponding to low SUZ effective permeabilities of ≤ ~10−13 m2. Vents at Main Endeavour field exhibit both high and low phase lags, suggestive of a transitional behavior. Our results demonstrate that tidal forcing perturbs hydrothermal flow across the global MOR system, even in places where the tidal amplitude is very low, and that the flow response can be used to constrain variations in SUZ permeability structure beneath individual vent fields.
    Description: This research was funded by Woods Hole Oceanographic Institution (USA). Thibaut Barreyre was supported by WHOI's Deep Ocean Exploration Institute (DOEI) postdoctoral scholarship.
    Description: 2016-08-26
    Keywords: Poroelasticity ; Tidal forcing ; Permeability ; Hydrothermalism ; Time-series ; Spectral analysis
    Repository Name: Woods Hole Open Access Server
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