Sulfide geochronology along the Endeavour Segment of the Juan de Fuca Ridge

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

Anisotropy in seafloor flange, slab, and crust samples from measurements of permeability and porosity : implications for fluid flow and deposit evolution

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): Q03018, doi:10.1029/2011GC003840.Seafloor hydrothermal vents accommodate the convective transfer of fluids from subsurface environments to the oceans. In addition to black smoker chimneys, a variety of other deposit-types form. Flanges protrude from the sides of edifices as horizontal ledges, below which vent fluids pool. Slabs are hydrothermally silicified layered volcaniclastic deposits. Crusts are deposits composed of previously deposited material underlain by hot fluids. Permeability and porosity measurements were conducted on flanges from Guaymas Basin and the Main Endeavour Vent Field, slabs from the Lucky Strike Vent Field, and a crust sample from the Trans-Atlantic Geotraverse (TAG) active mound. Cores taken parallel to textural layers have high permeabilities (≈10−12 m2) and porosities (30–40%) that follow a power law relationship with exponent α ≈ 1 to 2. Cores taken perpendicular to layering have permeabilities from 10−16 to 10−12 m2 and porosities from 20 to 45%, with α ≈ 5 to 8. The two distinct trends result from the heterogeneity of textural layers within these deposits. Microstructural observations show large variations in grain packing and pore distributions between layers, consistent with flow perpendicular to layering being more susceptible to changes in permeability that result from mineral precipitation than flow parallel to layering. These results imply that the primary flow direction in these deposits is parallel to layering, whereas flow perpendicular to layering is more restricted. Quantification of anisotropic permeability provides important constraints for determination of fluid flux from these layered deposits, and temperatures, chemistry, and availability of nutrients to organisms living in and at exteriors of deposits.This work was supported by the National Science Foundation under grants EAR-0741339 and OCE-0648337. Partial support for JG and WZ from DOE # DEFG0207ER15916 is also acknowledged.2012-09-2

Permeability-porosity relationships in seafloor vent deposits : dependence on pore evolution processes

Author Posting. © American Geophysical Union, 2007. 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 112 (2007): B05208, doi:10.1029/2006JB004716.Systematic laboratory measurements of permeability and porosity were conducted on three large vent structures from the Mothra Hydrothermal vent field on the Endeavor segment of the Juan de Fuca Ridge. Geometric means of permeability values obtained from a probe permeameter are 5.9 × 10−15 m2 for Phang, a tall sulfide-dominated spire that was not actively venting when sampled; 1.4 × 10−14 m2 for Roane, a lower-temperature spire with dense macrofaunal communities growing on its sides that was venting diffuse fluid of <300°C; and 1.6 × 10−14 m2 for Finn, an active black smoker with a well-defined inner conduit that was venting 302°C fluids prior to recovery. Twenty-three cylindrical cores were then taken from these vent structures. Permeability and porosity of the drill cores were determined on the basis of Darcy's law and Boyle's law, respectively. Permeability values range from ∼10−15 to 10−13 m2 for core samples from Phang, from ∼10−15 to 10−12 m2 for cores from Roane, and from ∼10−15 to 3 × 10−13 m2 for cores from Finn, in good agreement with the probe permeability measurements. Permeability and porosity relationships are best described by two different power law relationships with exponents of ∼9 (group I) and ∼3 (group II). Microstructural analyses reveal that the difference in the two permeability-porosity relationships reflects different mineral precipitation processes as pore space evolves within different parts of the vent structures, either with angular sulfide grains depositing as aggregates that block fluid paths very efficiently (group I), or by late stage amorphous silica that coats existing grains and reduces fluid paths more gradually (group II). The results suggest that quantification of permeability and porosity relationships leads to a better understanding of pore evolution processes. Correctly identifying permeability and porosity relationships is an important first step toward accurately estimating fluid distribution, flow rate, and environmental conditions within seafloor vent deposits, which has important consequences for chimney growth and biological communities that reside within and on vent structures.Support from the National Science Foundation under grants NSF OCE-9986456 (W.Z. and M.K.T.) and NSF OCE-0327488 (P.R.C.) is gratefully acknowledged. We also thank the WHOI summer student fellowship for providing support to H.G

Seismic structure of the Endeavour Segment, Juan de Fuca Ridge : correlations with seismicity and hydrothermal activity

Author Posting. © American Geophysical Union, 2007. 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 112 (2007): B02401, doi:10.1029/2005JB004210.Multichannel seismic reflection data collected in July 2002 at the Endeavour Segment, Juan de Fuca Ridge, show a midcrustal reflector underlying all of the known high-temperature hydrothermal vent fields in this area. On the basis of the character and geometry of this reflection, its similarity to events at other spreading centers, and its polarity, we identify this as a reflection from one or more crustal magma bodies rather than from a hydrothermal cracking front interface. The Endeavour magma chamber reflector is found under the central, topographically shallow section of the segment at two-way traveltime (TWTT) values of 0.9–1.4 s (∼2.1–3.3 km) below the seafloor. It extends approximately 24 km along axis and is shallowest beneath the center of the segment and deepens toward the segment ends. On cross-axis lines the axial magma chamber (AMC) reflector is only 0.4–1.2 km wide and appears to dip 8–36° to the east. While a magma chamber underlies all known Endeavour high-temperature hydrothermal vent fields, AMC depth is not a dominant factor in determining vent fluid properties. The stacked and migrated seismic lines also show a strong layer 2a event at TWTT values of 0.30 ± 0.09 s (380 ± 120 m) below the seafloor on the along-axis line and 0.38 ± 0.09 s (500 ± 110 m) on the cross-axis lines. A weak Moho reflection is observed in a few locations at TWTT values of 1.9–2.4 s below the seafloor. By projecting hypocenters of well-located microseismicity in this region onto the seismic sections, we find that most axial earthquakes are concentrated just above the magma chamber and distributed diffusely within this zone, indicating thermal-related cracking. The presence of a partially molten crustal magma chamber argues against prior hypotheses that hydrothermal heat extraction at this intermediate spreading ridge is primarily driven by propagation of a cracking front down into a frozen magma chamber and indicates that magmatic heat plays a significant role in the hydrothermal system. Morphological and hydrothermal differences between the intermediate spreading Endeavour and fast spreading ridges are attributable to the greater depth of the Endeavour AMC and the corresponding possibility of axial faulting.E.V.A. was supported by a National Science Foundation Graduate Research Fellowship, the WHOI-MIT Joint Program, and the WHOI Deep Ocean Exploration Institute. This work was also supported by OCE-0002551 to the Woods Hole Oceanographic Institution, OCE-0002488 to Lamont-Doherty Earth Observatory, and OCE-0002600 to Scripps Institution of Oceanography

Bringing Mid-Ocean Ridge Discoveries to Audiences Far and Wide: Emerging Trends for the Next Generation

The "Ridge" community has pioneered not only scientific exploration of and research on the global mid-ocean ridge system but also innovative and attractive ways of reaching out to the public with fascinating stories of scientific discovery and cutting-edge deep-sea technology. This article summarizes 30 years of education and public outreach (EPO) projects conducted by scientists and outreach professionals in the Ridge community to highlight the key principles of effective EPO, such as the importance of targeting specific audiences' needs and expectations. Other elements discussed include collaboration with professionals outside of the scientific community, increased participation of individuals from underrepresented groups in science, and rigorous evaluation to strengthen the impact of future programs. The article also explores how cyber technology and observatory science offer new opportunities for sharing discoveries as they occur and involving the public in the research endeavor. By reaching audiences on a more direct and personal level, these novel approaches may hold the most promise for increasing public appreciation for the marine environment. Scientists' perspectives on EPO programs, lessons, learned, and personal benefits address the question "Why should I do outreach?" Ridge EPO programs highlighted include (1) "Research and Education: Volcanoes, Exploration and Life" (REVEL)—a seagoing, research-focused professional development program for K–12 teachers; (2) "Why is Earth Habitable?"—an iconic American Museum of Natural History exhibit; (3) "Volcanoes of the Deep Sea" and "Aliens of the Deep," two popular IMAX films; (4) "Dive & Discover," an online resource and expedition archive; (5) Extreme 2000, Student Experiments at Sea (SEAS), and From Local to Extreme Environments (FLEXE), three innovative education projects for K–12 students; (6) the Ridge 2000 Distinguished Lecturer Series targeting institutions without marine science programs; and (7) "Beyond the Edge of the Sea," a traveling exhibit of vent-ecosystem illustrations

Biological and geological dynamics over four years on a high-temperature sulfide structure at the Juan de Fuca Ridge hydrothermal observatory

An extensive v~deoscopics tudy of a h~gh- temperatures ulfide structure on the Juan d e Fuca Rldge (northeast Pacific) examined temporal variation in vent community distnbution and l~nks between faunal and environmental changes V~ d e oim agery was acquired d u l ~ n ga total of 5 manned submersible and ROV (remotely-operated vehicle) dive programs between 1991 and 1995 The structure was systemat~callym apped for each year of the study and a serles of analytical tools was developed to quantify changes in biological and geological features and observable flow patterns Results shoiv (l) heterogeneous faunal distnbution, characterized by decimeter-scale patchiness and general absence of vertical gladients, (2) apparent links between commun~tyd ~s tnbut iona, nd environmental features such as fluid flow patterns, substratum and temperature/chemicdl conditions, (3) a significant influence of perturbations on community dynamics, (4) dbsence of d ~ r e c t ~ o nbailo logical succession at the time scale examlned (years) Overall, these observations strongly suggest that many hydrothermal community changes are initiated by gradual and ablupt flow mod~fications Results are compiled in a dynamic succession model for sulfide edifices where community transitions are dnven by flow vanatlons, and by biolog~calp rocesses operating at sub-annual t ~ m esc ales CVe conclude by stressing the need for extended momtonng of short-term dynamics in order to understand the relationslup between hydrothermal communities and their environment.Thls work would not have been posslble wthout the field support by the pdots of ROPOS, Alvln and Jason and the crews of the CSS 'John P. Tully' and the RV 'Atlantis 11'. This research was sponsored by NSERC-Canada, Fisheries and Oceans Canada and the National Science Foundation J S was supported by post-graduate fellowships from NSERC (Canada) FCAR (Quebec) and CEOTOP (UQAM) We are particuldrly grateful to Dr Pierre Legendre for h ~ hse lp with canonical analyses and to Drs Verena Tunnicllffe and Margaret Tlvey for the11 suggestions and comments on the manuscnpt Dr Mark Hannington klndly provided drawlngs of S&M from 1991 Jason and Alvin Imagery, and Enriette Gagnon aided in drafting of Fig 3 The UQAM Decanat des Etudes Avancees, provlded support for pubhcatlon of color figures Four anonymous reviewers are thanked for their constructlve inputFacultyReviewe