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Sample records for fuca ridge northeast

  1. Efficacy of 230Th normalization in sediments from the Juan de Fuca Ridge, northeast Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Costa, Kassandra; McManus, Jerry

    2017-01-01

    230Th normalization is an indispensable method for reconstructing sedimentation rates and mass fluxes over time, but the validity of this approach has generated considerable debate in the paleoceanographic community. 230Th systematics have been challenged with regards to grain size bias, sediment composition (CaCO3), water column advection, and other processes. In this study, we investigate the consequences of these effects on 230Th normalization from a suite of six cores on the Juan de Fuca Ridge. The proximity of these cores (<30 km) suggests that they should receive the same particle rain rate of sediment, but the steep bathymetry of the ridge leads to substantial sediment redistribution and variable carbonate preservation, both of which may limit the usage of 230Th in this region. Despite anticipated complications, 230Th normalization effectively reconstructs nearly identical particle rain rates from all six cores, which are summarily unrelated to the total sedimentation rates as calculated from the age models. Instead the total sedimentation rates are controlled almost entirely by sediment focusing and winnowing, which are highly variable even over the short spatial scales investigated in this study. Furthermore, no feedbacks on 230Th systematics were detected as a consequence of sediment focusing, coarse fraction variability, or calcium carbonate content, supporting the robustness of the 230Th normalization technique.

  2. Hydrothermal fluid effects on sediment column in Middle Valley, Juan de Fuca Ridge (northeast Pacific)

    SciTech Connect

    Al-Aasm, I.S.; Blaise, B.

    1987-05-01

    Core PAR 85-34, located near a high heat flow area in Middle Valley, northern Juan de Fuca Ridge, contains carbonate nodules of various sizes (less than or equal to 1-5 cm in length). Sedimentological, geochemical, and isotopic results allow us to understand the origin of these concretions and the effects of hydrothermal activity from nearby sulfide vents on the sediment column. The mineralogy of the olive-gray surface sediment (0-15 cm) is identical to unaffected hemipelagic sediments in the region except for a concentration of barite crystals (up to 1 cm) at the water-sediment interface. In the clay, mud fraction, and bulk sediment, the FeO, S, Ba, Cu, Ni, Pb, Zn and As are more enriched than in normal hemipelagic sediment in the area due to hydrothermal activity. Petrographic and SEM analysis of the nodules reveal iron calcite and barite minerals in cracks and on the outside part of the nodules with mineralogical and textural variations downcore. Stable isotope curves of these nodules appear to demonstrate the effects of both bacterial sulfate reduction and microbiological methane generation, with consequent extreme /sup 13/C-depletion in the precipitated carbonate. The curves also demonstrate that the hydrothermal fluid entering the system may have caused the negative shift in oxygen isotopes downcore, although this effect may have been of cyclic or episodic nature.

  3. AUV Mapping of Axial Seamount, Juan de Fuca Ridge: The Northern Caldera Floor and Northeast Rim

    NASA Astrophysics Data System (ADS)

    Caress, D. W.; Clague, D. A.; Paduan, J. B.; Chadwick, W. A.; Butterfield, D.; Thomas, H.; Conlin, D.; Thompson, D.

    2007-12-01

    , then turned N and finally NE. The distal end of this flow has a peculiar mottled pattern in the bathymetric data; it consists of jumbled sheet flows with small ridges of broken crusts. A 150-m across pillow cone with a 32 m deep central crater is apparently the oldest volcanic feature in the north caldera floor. The southern flank of this cone is truncated by a 070° scarp. Along the northeast caldera wall there is a smooth lava pond with a jumbled sheet flow surface. The pond has a flat bottom (1580 m depth) and is bordered to the east and south by a 4 m high lava highstand (bath-tub ring). Inside the pond, we observe 12 mounds consisting of uptilted slabs of pond crust draped over large pillars. A second small region of flat pond surface, located just SE of the cone, is at the same depth and may have once been contiguous with the eastern pond. Adjacent to the small pond is a segmented ring of spatter levees with channels cut through in all directions.

  4. Constant Flux Proxies and Pleistocene Sediment Accumulation Rates on the Juan de Fuca Ridge in the Northeast Pacific

    NASA Astrophysics Data System (ADS)

    Middleton, J. L.; Mukhopadhyay, S.; Langmuir, C. H.; Costa, K.; McManus, J. F.; d'Almeida, M.; Huybers, P. J.; Winckler, G.

    2016-12-01

    Mass accumulation rates of marine sediments are often employed to constrain deposition rates of important proxies such as terrigenous dust, carbonate, and biogenic opal to quantitatively examine variations in continental aridity, atmospheric transport, and biologic productivity across changing climatic conditions. However, deposition rates that are estimated using traditional mass accumulation rates calculated from sediment core age models can be subject to bias from lateral sediment transport and limited age model resolution. Constant flux proxies, such as extraterrestrial helium-3 (3HeET) and excess thorium-230 (230ThXS), can be used to calculate vertical sediment accumulation rates that are independent of age model uncertainties and the effects of lateral sediment transport. While a short half-life limits analyses of 230ThXS to the past 500 ka, 3HeET is stable and could be used to constrain sedimentary fluxes during much of the Cenozoic. Despite the vast paleoceanographic potential of constant flux proxies, few studies have directly compared the behavior of 230ThXS and 3HeET using measurements from the same samples. Sediment grain size fractionation and local scavenging effects may differentially bias one or both proxy systems and complicate the interpretation of 230ThXS or 3HeET data. We will present a new record of vertical sediment accumulation rates spanning the past 600 ka in the Northeast Pacific constrained using analyses of both 3HeET and 230ThXS in two sediment cores from cruise AT26-19 on the Juan de Fuca Ridge. Such a record allows for intercomparison of both constant flux proxies in the mid-ocean ridge environment and examination of sedimentary behavior across multiple glacial cycles. The 230ThXS-derived accumulation rates typically range from 0.5 to 2 g cm-2 ka-1 over the past 450 ka, with periods of maximum deposition coinciding with glacial maxima. Preliminary results of samples analyzed with both 3HeET and 230ThXS indicate relative consistency

  5. Fin whale tracks recorded by a seismic network on the Juan de Fuca Ridge, Northeast Pacific Ocean.

    PubMed

    Soule, Dax C; Wilcock, William S D

    2013-03-01

    Fin whale calls recorded from 2003 to 2004 by a seafloor seismic network on the Endeavour segment of the Juan de Fuca Ridge were analyzed to determine tracks and calling patterns. Over 150 tracks were obtained with a total duration of ~800 h and swimming speeds from 1 to 12 km/h. The dominant inter-pulse interval (IPI) is 24 s and the IPI patterns define 4 categories: a 25 s single IPI and 24/30 s dual IPI produced by single calling whales, a 24/13 s dual IPI interpreted as two calling whales, and an irregular IPI interpreted as groups of calling whales. There are also tracks in which the IPI switches between categories. Call rates vary seasonally with all the tracks between August and April. From August to October tracks are dominated by the irregular IPI and are predominantly headed to the northwest, suggesting that a portion of the fin whale population does not migrate south in the fall. The other IPI categories occur primarily from November to March. These tracks have slower swimming speeds, tend to meander, and are predominantly to the south. The distribution of fin whales around the network is non-random with more calls near the network and to the east and north.

  6. Pb, Sr, and Nd isotopes in seamount basalts from the Juan de Fuca Ridge and Kodiak-Bowie seamount chain, northeast Pacific

    USGS Publications Warehouse

    Hegner, E.; Tatsumoto, M.

    1989-01-01

    Pb, Sr, and Nd isotopic ratios and their parent/daughter element concentrations for 28 basalts from 10 hotspot and nonhotspot seamounts are reported. Nd and Sr isotopic compositions (143Nd/144Nd = 0.51325-0.51304; 87Sr/86Sr = 0.70237-0.70275) plot in the envelope for Juan de Fuca-Gorda ridge basalts with tholeiitic basalts showing more depleted sources and a better negative correlation than transitional to alkalic basalts. Pb isotopic ratios in tholeiitic and alkalic basalts overlap (206Pb/204Pb = 18.29-19.44) and display a trend toward more radiogenic Pb in alkalic basalts. The isotopic data for hotspot and nonhotspot basalts are indistinguishable and correlate broadly with rock composition, implying that they are controlled by partial melting. The isotopic variation in the seamount basalts is about 60% (Nd-Sr) to 100% (Pb) of that in East Pacific Rise basalts and is interpreted as a lower limit for the magnitude of mantle heterogeneity in the northeast Pacific. The data indicate absence of a chemically distinct plume component in the linear seamount chains and strongly suggest an origin from mid-ocean ridge basalt-like east Pacific mantle. -Authors

  7. Ultrastructure and potential sub-seafloor evidence of bacteriogenic iron oxides from Axial Volcano, Juan de Fuca Ridge, north-east Pacific Ocean.

    PubMed

    Kennedy, C B; Scott, S D; Ferris, F G

    2003-03-01

    Iron oxides from the caldera of Axial Volcano, a site of hydrothermal vent activity along the Juan de Fuca Ridge, were found to consist predominantly of microbial structures in hydrated whole mounts examined using an environmental scanning electron microscope. Novel observations were made of the iron oxides revealing the spatial relationships of the bacteria within to be more consistent with microbial mats than mineral precipitates. The bacterial structures are attributed to the sheaths of Leptothrix ochracea, the stalks of Gallionella ferruginea, and the filaments of a novel iron oxidizing PV-1 strain, based on the distinctive morphological characteristics of these three bacteria. Energy dispersive X-ray spectroscopy revealed the presence and distribution of Fe, Si, and Cl on the bacterial sheaths, stalks and filaments. The iron oxides were identified by X-ray diffraction to be two-line ferrihydrite, a poorly ordered iron oxyhydroxide. Adsorption of Si in particular to two-line ferrihydrite likely contributes to its stability on the seafloor, and might also be a preservation mechanism creating microfossils of the bacterial structures encrusted with ferrihydrite. Presumptive evidence of the sub-seafloor presence of L. ochracea, G. ferruginea and PV-1 at Axial Volcano was obtained from the presence of these bacteria on a trap that had been placed within an active vent, and also in a vent fluid sample. If indeed these bacteria are present in the sub-seafloor, it may be an indication that the surface expression of iron oxide deposits at Axial Volcano is minimal in comparison to what exists beneath the seafloor.

  8. Water column hydrothermal plumes on the Juan de Fuca Ridge

    SciTech Connect

    Lupton, J.E. )

    1990-08-10

    Hydrographic surveys on the Juan de Fuca Ridge (JdFR) carried out from 1980 to 1987 show a complex pattern of {sup 3}He and Mn-rich water column plumes produced by venting from several submarine hot spring areas. In the vicinity of Axial Volcano at latitude 46{degree}N, distinct plumes were detected in 1980, 1982, and 1983 with {sup 3}He signatures up to {delta}({sup 3}He) = 64% at {approximately} 1,500 m depth at distances of {approximately} 10 km from the seamount summit. However, the same plumes had no detectable thermal signature, a paradox which is attributed to the high {sup 3}He/heat ratios and low salinities of the fluids venting within the caldera of Axial Volcano. Profiles directly over the seamount show hydrothermal {sup 3}He in the water column up to 300 m above the caldera floor, with the {sup 3}He signal increasing with depth to very high and uniform ratios of {delta}({sup 3}He) = 108-150% below the {approximately} 1,500-m caldera sill depth. Another apparent locus of hydrothermal input is Helium Basin, a depression on the northeast flank of Axial Volcano which had {delta}({sup 3}He) = 51% when first sampled in 1980. However, subsequent hydrocasts into Helium Basin in 1982 and 1983 yielded lower helium enrichments, suggesting either a decrease in hydrothermal input or flushing of the basin via a mixing event. To the south of Axial Volcano, high {delta}({sup 3}He) values of {approximately} 40% observed over the ridge axis at 45{degree}18{prime}N and 45{degree}39{prime}N indicate venting on this previously unexplored section of the ridge. The water column plumes over the US Geological Survey vent site at {approximately} 44{degree}40{prime}N on the southern JdFR have very high Mn/{sup 3}He ratios of 4,600 mol/cm{sup 3}, an apparently unique characteristic which can be used to distinguish these plumes from those originating at other JdFR vent fields.

  9. Sr isotopic variations along the Juan de Fuca Ridge.

    USGS Publications Warehouse

    Eaby, J.; Clague, D.A.; Delaney, J.R.

    1984-01-01

    The Sr isotopic ratios of 39 glass and microcrystalline basalt samples along the Juan de Fuca Ridge and one glass sample from Brown Bear Seamount are at the lower end of the range for normal MORB; the average 87Sr/86Sr ratio is 0.70249 + or - 0.00014 (2sigma ). Although subtle variations exist along the strike of the ridge, the Sr isotopic data do not show systematic variation relative to the proposed Cobb hotspot. The isotopic data are inconsistent with an enriched mantle-plume origin for the Cobb-Eikelberg Seamount chain.-W.H.B.

  10. Distribution of hydrothermal manganese over the Juan de Fuca Ridge

    SciTech Connect

    Jones, C.J.; Johnson, H.P.; Delaney, J.R.

    1981-08-01

    Bottom waters from five hydrographic stations, spaced equally along a 400-km section of the Juan de Fuca Ridge north of the Blanco Fracture Zone, contain anomalously high concentrations of total dissolvable manganese (TDM). The two bottom-most bottles from each hydrocast (approx. 100 to 200 m above bottom) range from 8.3 to 108.9 nmol kg/sup -1/ with a median value of 12.0 nmol kg/sup -1/. This median is nearly a factor of 10 higher than similar near bottom samples obtained from two off-axis locations. Analogy to work on the East Pacific Rise implies that hydrothermal activity along the ridge axis is contributing substantially to the manganese content of the water column in this portion of the northeastern Pacific.

  11. Divergent Ridge Features on the Juan de Fuca and Gorda Ridges

    NASA Astrophysics Data System (ADS)

    Eaton, M. E.; Sautter, L.; Steele, M.

    2014-12-01

    Multibeam data collected using a Kongsberg EM122 sonar system on the NOAA ship R/V Marcus G. Langseth led by chief scientist Douglas Toomey (University of Oregon) in 2009 and with a Simrad EM302 sonar system on two NOAA ship Okeanos Explorer cruises led by chief scientists James Gardner (University of New Hampshire) and Catalina Martinez (University of Rhode Island) in 2009 show the morphology of the Juan de Fuca and Gorda Ridges, as well as the Blanco and Mendocino Fracture Zones. These ridges and fracture zones comprise the divergent plate boundary of the eastern edge of the Pacific Plate and the western edges of the Juan de Fuca and Gorda Plates. Both plates are being subducted beneath the western edge of the North American Plate. CARIS HIPS 8.1 software was used to process the multibeam data and create bathymetric images. The ridge axes, located off the coast of Washington and Oregon (USA) adjacent to the Cascadia Basin, indicate obvious signs of spreading, due to the series of faults and rocky ridges aligned parallel to the plate boundaries. Fault and ridge orientations are used to compare the direction of seafloor spreading, and indicate that both the Juan de Fuca Plate and Gorda Plate are spreading in a southeastern direction. Younger ridges from the Gorda Ridge system mapped in the study run parallel to the boundary, however older ridges do not show the same orientation, indicating a change in spreading direction. The presence of hydrothermal vents along the Juan de Fuca Ridge is also evidence of the active boundary, as the vent chimneys are composed of minerals and metals precipitated from the hot water heated by magma from beneath the spreading seafloor. In this study, the data are used to compare and contrast earthquake seismicity and ridge morphologies at a depth range of approximately 762 to 2134 meters. The diverging Pacific, Juan de Fuca, and Gorda Plates along with the San Andreas Fault have potential to increase seismic and volcanic activity around

  12. Basalt Geochemistry of the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Woodcock, J. P.; Gill, J.; Kela, J.; Michael, P.; Ramos, F.

    2006-12-01

    We present new trace element, volatile, isotope, and modeling data for mid-ocean ridge basalts (MORB) from the Endeavour Axial Ridge Volcano (EARV) segment of the Juan de Fuca Ridge. Endeavour MORB are categorized to a first order using K2O/TiO2, with T-MORB = 0.15-0.25, N-MORB lower, and E- MORB higher. Within these groups, there are 2 subgroups of N-MORB and 3 of T-MORB, distinguished by differences in Si8, Fe8, Ti8, and differentiation paths. Liquid lines of descent are best explained by crystallization within the crust at measured water contents (0.2-0.5 wt. %). EARV basalts exhibit spatial heterogeneities that far exceed what can be explained by these fractional crystallization models. Incompatible trace element ratios such as Zr/Nb, La/Yb, and K2O/TiO2 exhibit 3- to 4-fold variations, indicating heterogeneity of source or melting processes. The heterogeneity is observed along axis in samples only tens to hundreds of meters apart and is most prominent along the western wall of the axial valley, suggesting that axial magma chambers may be short-lived. Despite their heterogeneity, axial samples have nearly constant 87Sr/86Sr and ^{143}Nd/^{144}Nd ratios. Pb isotopes are more variable (206Pb/204Pb = 18.35-18.90). The heterogeneity seems unrelated to the chemical influence of a plume or the thermal perturbations of a transform fault.

  13. Seafloor Uplift in Middle Valley, Juan de Fuca Ridge: New High-Resolution Pressure Data

    NASA Astrophysics Data System (ADS)

    Inderbitzen, K. E.; Becker, K.; Davis, E. E.

    2011-12-01

    Currently, in-situ seafloor and basement pressures are continuously monitored and recorded by an ODP subseafloor hydrogeological observatory (CORK) located in Middle Valley, Juan de Fuca Ridge. Hole 857D was drilled in 1991 in thickly sedimented crust to a depth of 936 mbsf and instrumented with an original CORK that was replaced in 1996. A large hydrothermal field (Dead Dog) lies roughly 1.7 km north of the hole, and two isolated chimneys and several diffuse flow sites are located ~800 meters northeast. The borehole and the vent fields have been visited periodically by submersible/ROV since 1999. Recent results from the CORK at 857D have shown apparent seafloor uplift, supported by depth records from the submersible Alvin. A constant rate of pressure change of ~6 kPa/yr, from its initiation in 2005 to the visit in 2010, has reduced mean seafloor pressure by ~28 kPa, equivalent to nearly 3 meters of head. This uplift rate is several times the typical pre-eruption inflation rates observed at Axial Seamount further south along the Juan de Fuca Ridge. Initially, the apparent uplift at 857D did not seem to have any effect on local high-temperature hydrothermal venting, however recent operations in Middle Valley revealed distinct changes at not only the hydrothermal field to the northeast, but also a shutdown of high-temperature venting to the north of 857D. We will present new data from Middle Valley, including the first year of data collected by a high-resolution pressure data logger deployed at 857D in June, 2010.

  14. Distribution of geothermal fields on the Juan De Fuca ridge

    SciTech Connect

    Crane, K.; Aikman F. III; Embley, R.; Hammond, S.; Malahoff, A.; Lupton, J.

    1985-01-10

    Near bottom water temperatures were mapped along 400 km of the strike of the Juan de Fuca Ridge as part of a combined Sea MARC/Seabeam experiment to image the variability of morphology and structure along a spreading center segment. The water temperature data collected by a continuously towed thermistor chain, in addition to salinity data, indicate that there are four geothermal areas spaced at distances of 100 km from each other south of the Cobb propagator and one field just to the north of the propagator on the Endeavor Ridge segment. Each thermal region is located above a morphological dome on the spreading center. These domes are an average of 100--200 m shallower than the rest of the axis. The structure of bottom water suggests that the geothermal regions are on average 20 km long and that the heat from these fields raises the temperature in the water column by a minimum of 0.06/sup 0/C up to 300 m above the bottom. Two simple models are used to estimate the heat flux associated with these features.

  15. Investigating the Relationship between Fin and Blue Whale Locations, Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge

    DTIC Science & Technology

    2011-09-30

    Whale Locations, Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge William S. D. Wilcock School of Oceanography...OBJECTIVES We are continuing a study of seismic and bio-acoustical data sets from the Juan de Fuca Ridge with the following three objectives for FY2011...Whale Locations, Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM

  16. Investigating the Relationship Between Fin and Blue Whale Locations, Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge

    DTIC Science & Technology

    2009-09-30

    Locations, Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge William S. D. Wilcock School of Oceanography University...We are conducting a retrospective study using existing seismic and bio-acoustical data sets from the Juan de Fuca Ridge with the following four...Investigating The Relationship Between Fin And Blue Whale Locations, Zooplankton Concentrations And Hydrothermal Venting On The Juan de Fuca Ridge 5a. CONTRACT

  17. Investigating the Relationship Between Fin and Blue Whale Locations, Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge

    DTIC Science & Technology

    2008-01-01

    Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge William S. D. Wilcock School of Oceanography University of Washington Box...between whale tracks, enhanced zooplankton concentrations and hydrothermal vents above the Juan de Fuca Ridge with the long-term goal of understanding...conducting a retrospective study using existing seismic and bio-acoustical data sets from the Juan de Fuca Ridge with the following four objectives

  18. Magma storage beneath Axial volcano on the Juan de Fuca mid-ocean ridge.

    PubMed

    West, M; Menke, W; Tolstoy, M; Webb, S; Sohn, R

    2001-10-25

    Axial volcano, which is located near the intersection of the Juan de Fuca ridge and the Cobb-Eickelberg seamount chain beneath the northeast Pacific Ocean, is a locus of volcanic activity thought to be associated with the Cobb hotspot. The volcano rises 700 metres above the ridge, has substantial rift zones extending about 50 kilometres to the north and south, and has erupted as recently as 1998 (ref. 2). Here we present seismological data that constrain the three-dimensional velocity structure beneath the volcano. We image a large low-velocity zone in the crust, consisting of a shallow magma chamber and a more diffuse reservoir in the lower crust, and estimate the total magma volume in the system to be between 5 and 21 km3. This volume is two orders of magnitude larger than the amount of melt emplaced during the most recent eruption (0.1-0.2 km3). We therefore infer that such volcanic events remove only a small portion of the reservoir that they tap, which must accordingly be long-lived compared to the eruption cycle. On the basis of magma flux estimates, we estimate the crustal residence time of melt in the volcanic system to be a few hundred to a few thousand years.

  19. Continuing Investigations of the Relationship Between Fin Whales, Zooplankton Concentrations and Hydrothermal Venting on the Juan De Fuca Ridge

    DTIC Science & Technology

    2013-09-30

    Fin Whales , Zooplankton Concentrations and Hydrothermal Venting on the Juan De Fuca Ridge William S. D. Wilcock School of Oceanography...are investigating the potential correlation between fin whale tracks, enhanced zooplankton concentrations and hydrothermal vents above the Juan de...Fuca Ridge. Our goal is to understand the influences of globally distributed hydrothermal plumes on the trophic ecology of the deep ocean

  20. Geology, structure, and volcanic processes of southern Juan de Fuca Ridge

    SciTech Connect

    Morton, J.L.; Normark, W.R.; Holcomb, R.T.

    1986-07-01

    The southern Juan de Fuca Ridge is a medium-rate spreading center (total opening rate = 6 cm/year) in the northeast Pacific Ocean, 500 km west of central Oregon. A 25-km segment of the ridge has been the focus of a 6-year study by the US Geological Survey. The ridge crest displays well-developed cross-axis symmetry with 80 to 100-m high ridges formed by predominantly inward-facing fault scarps and a relatively smooth 1-km wide axial valley floor. Multichannel seismic reflection profiles across the axis indicate the presence of a crustal magma chamber roof, 1-2 km wide and 2.3 km beneath the valley floor. The seismic reflection data are insufficient to determine the along-axis continuity of the magma chamber. Sea MARC II side-scan imagery, extensive photographic surveys, and observations from the Alvin submersible reveal a continuous linear depression 30-50 m wide and 10-30 m deep that bisects the axial valley floor through the study area. The depression is offset in places and may locally have short overlapping strands. The depression is characterized by sharp rims, steep walls, and a floor of mostly rough-surfaced lava and lineated sheet flow. It is flanked by a region of subsided, fresh lava flows. These flows, in turn, are surrounded by sheet flows containing numerous small collapse pits. Unpitted sheet flows occupy the marginal part of the axial valley floor. The depression appears to be the site of voluminous fissure eruptions that fed the lavas on the surrounding valley floor. Active hydrothermal vents are present within the axial depression, but have not been observed elsewhere on the axial valley floor. This axial depression appears to be a unique feature among medium-rate spreading centers that have been studied to date.

  1. Seismic imaging of water column structure across the Juan de Fuca ridge system

    NASA Astrophysics Data System (ADS)

    Newman, K. R.; Nedimovic, M. R.; Carbotte, S. M.; Diebold, J. B.

    2006-12-01

    We have processed a series of long (150-300 km) multi-channel seismic reflection lines, collected in the northeast Pacific for studies of structure of the Juan de Fuca Ridge, for water column reflections. Our initial results reveal the first reflection images of water column structure across a spreading center. Reflections within the water column are well imaged in the upper 750 to 1000 m. The strong, low frequency direct water wave, which obscures the higher frequency reflections in the upper 200 m, was removed using bandpass filtering and CMP mutes. In our first finalized section, the ~130 km-long profile across the Endeavour ridge, we image an entire eddy and find evidence that the presence of the ridge affects the water column structure. The thermocline beneath the eddy extends down to a maximum depth of about 750 m and the eddy is bounded on top by a concave down reflector. This geometry suggests that the eddy could be an intrathermocline feature, formed around a lens of water that has intruded along the thermocline. No CTD or XBT data were collected along this line, so the thermal structure through the eddy is unknown. However, inspection of historic CTD data often shows a temperature excursion around 150 m. This is in agreement with the depth of ~150 m for the center of the imaged water lens. We will finalize processing of the other two long profiles crossing Northern Symmetric and Gorda ridges to determine if similar features exist in these areas further south, and to examine what effect the topography of this spreading center has on circulation in the upper water column.

  2. Hydrothermal sulfide accumulation along the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Jamieson, J. W.; Clague, D. A.; Hannington, M. D.

    2014-06-01

    Hydrothermal sulfide deposits that form on the seafloor are often located by the detection of hydrothermal plumes in the water column, followed by exploration with deep-towed cameras, side-scan sonar imaging, and finally by visual surveys using remotely-operated vehicle or occupied submersible. Hydrothermal plume detection, however, is ineffective for finding hydrothermally-inactive sulfide deposits, which may represent a significant amount of the total sulfide accumulation on the seafloor, even in hydrothermally active settings. Here, we present results from recent high-resolution, autonomous underwater vehicle-based mapping of the hydrothermally-active Endeavour Segment of the Juan de Fuca Ridge, in the Northeast Pacific Ocean. Analysis of the ridge bathymetry resulted in the location of 581 individual sulfide deposits along 24 km of ridge length. Hydrothermal deposits were distinguished from volcanic and tectonic features based on the characteristics of their surface morphology, such as shape and slope angles. Volume calculations for each deposit results in a total volume of 372,500 m3 of hydrothermal sulfide-sulfate-silica material, for an equivalent mass of ∼1.2 Mt of hydrothermal material on the seafloor within the ridge's axial valley, assuming a density of 3.1 g/cm3. Much of this total volume is from previously undocumented inactive deposits outside the main active vent fields. Based on minimum ages of sulfide deposition, the deposits accumulated at a maximum rate of ∼400 t/yr, with a depositional efficiency (proportion of hydrothermal material that accumulates on the seafloor to the total amount hydrothermally mobilized and transported to the seafloor) of ∼5%. The calculated sulfide tonnage represents a four-fold increase over previous sulfide estimates for the Endeavour Segment that were based largely on accumulations from within the active fields. These results suggest that recent global seafloor sulfide resource estimates, which were based mostly

  3. Petrological Constraints on Magma Plumbing Systems along the Reykjanes and Juan de Fuca Ridges

    NASA Astrophysics Data System (ADS)

    Scott, J. L.; Kelley, D. F.; Barton, M.

    2012-12-01

    Plate spreading at mid-ocean ridges is accompanied by intrusion of dikes and eruption of lava along the ridge axis. It has been suggested that the depth of magma chambers that feed the dikes and flows is related to the heat flux - the higher the heat flux the shallower the depth of the magma chamber. As a preliminary test of this hypothesis, we have determined the depths of magma chambers beneath the slow spreading Reykjanes Ridge (RR) in the north Atlantic and the intermediate spreading Juan de Fuca Ridge (JdF) in the northeast Pacific. Pressures of partial crystallization were determined by quantitatively comparing the compositions of natural liquids (glasses) with those of experimental liquids in equilibrium with olivine, plagioclase, and augite at different pressures and temperatures using the method described by Yang and co-workers (1996). Published analyses of mid-ocean ridge basalt glasses sampled from along the RR and JdF were used as liquid compositions. Samples with anomalous chemical compositions and samples that yielded pressures associated with unrealistically large uncertainties were filtered out of the database. The calculated pressures for the remaining 519 samples for the RR and 479 samples for the JdF were used to calculate the depths of partial crystallization and to identify the likely location of magma chambers. The RR results indicate that the pressure of partial crystallization decreases from 102 ± 33 MPa at the Charlie Gibbs Fracture Zone to 21 ± 12 MPa at 56°N, then increases to 367 ± 68 MPa as Iceland is approached. Four magma lenses were identified at depths of 2.5±0.8km, 5.2±0.8km, 5.9±1km, and 6.7±1. The magma lens at 2.46±.83 km agrees very well with seismically imaged sill at 2.5 km. The JDF results indicate that the pressure of partial crystallization decreases from 200 to100±50 MPa from the Blanco fracture zone to the north along the Cleft segment of the ridge. Calculated pressures remain approximately constant at 87±.53

  4. Nontronite from a low-temperature hydrothermal system on the Juan de Fuca Ridge

    USGS Publications Warehouse

    Murnane, R.; Clague, D.A.

    1983-01-01

    A deposit of Fe-rich, Al-poor, hydrothermal nontronite was recovered from the Juan de Fuca Ridge. Analyses show the deposit to be mineralogically and chemically similar to nontronite described at other oceanic localities. The deposit is located near the tip of a propagating segment of the Juan de Fuca Ridge. Rare earth elements and Sr isotopes indicate that the nontronite precipitated from seawater. A formation temperature of 57??C is suggested by oxygen isotopic composition. The low-temperature nontronite deposits apparently form from newly established hydrothermal systems associated with the propagating rift segment. More mature hydrothermal systems that deposit sulfide on the seafloor may develop from these low-temperature systems. ?? 1983.

  5. Effects of hydrostatic pressure on growth of hyperthermophilic archaebacteria from the juan de fuca ridge.

    PubMed

    Reysenbach, A L; Deming, J W

    1991-04-01

    Two new strains (AL1 and AL2) of hyperthermophilic, sulfur-reducing, heterotrophic archaebacteria from high-temperature (350 degrees C) vents on the Juan de Fuca Ridge were highly barotolerant at their optimal growth temperatures (90 and 100 degrees C, respectively). A trend towards barophily at pressures greater than those encountered in situ at the sea floor was demonstrated for the more extremely thermophilic strain (AL2), implying an ability to thrive in (unexplored) habitats well below accessible vent formations.

  6. Hydrothermal venting on the Juan de Fuca Ridge over the last 600,000 years

    NASA Astrophysics Data System (ADS)

    Costa, K.; McManus, J. F.; Winckler, G.; Huybers, P. J.; Langmuir, C. H.; Giosan, L.; Middleton, J. L.; Mukhopadhyay, S.

    2015-12-01

    Mid-ocean ridges provide a unique chemical, physical, and biological environment on the seafloor. They are a significant source of dissolved Fe, a critical micronutrient in the ocean, and they are a primary source of CO2 from the mantle, Earth's largest carbon reservoir. Although more than a hundred modern hydrothermal systems have been discovered, few records of their variation through geological time have been obtained. Sediments near ocean ridges hold the potential to provide such records, and here we investigate sediments near the Juan de Fuca Ridge through continuous XRF scans coupled with oxygen isotope temporal constraints to explore hydrothermal activity over the past 600,000 years. These are the first records over multiple glacial-interglacial cycles and permit investigation of potential feedbacks between glacial-interglacial climate change and hydrothermal activity. Today, hydrothermal activity on the Juan de Fuca Ridge is characterized by hydrothermal particles with high concentrations of Fe, Cu, and Zn (Feely et. al., 1987). Over longer time scales, Fe concentrations are positively correlated with Ti (r2≥0.75), so that the dominant variability in Fe is due to the input of lithogenic material. Additional Fe inputs from hydrothermal activity increase the Fe/Ti ratio above the lithogenic value of 11.7 wt%/wt%. Intense hydrothermal activity (Fe/Ti > 25 wt%/wt%) is observed on the Juan de Fuca Ridge from ~375-430ka, and less intense but still elevated hydrothermal activity (Fe/Ti > 17 wt%/wt%) recurs at near 100kyr cyclicity, from 80-120ka, 180-220ka, 290-330ka, and 470-520ka. These time periods correspond to times of sea level fall owing to expanding ice volume, supporting a link between sea level changes and ridge crest activity

  7. Earthquake-induced changes in a hydrothermal system on the Juan de Fuca mid-ocean ridge

    PubMed

    Johnson; Hutnak; Dziak; Fox; Urcuyo; Cowen; Nabelek; Fisher

    2000-09-14

    Hydrothermal vents on mid-ocean ridges of the northeast Pacific Ocean are known to respond to seismic disturbances, with observed changes in vent temperature. But these disturbances resulted from submarine volcanic activity; until now, there have been no observations of the response of a vent system to non-magmatic, tectonic events. Here we report measurements of hydrothermal vent temperature from several vents on the Juan de Fuca ridge in June 1999, before, during and after an earthquake swarm of apparent tectonic origin. Vent fluid temperatures began to rise 4-11 days after the first earthquake. Following this initial increase, the vent temperatures oscillated for about a month before settling down to higher values. We also observed a tenfold increase in fluid output from the hydrothermal system over a period of at least 80 days, extending along the entire ridge segment. Such a large, segment-wide thermal response to relatively modest tectonic activity is surprising, and raises questions about the sources of excess heat and fluid, and the possible effect on vent biological communities.

  8. Mantle flow geometry from ridge to trench beneath the Gorda-Juan de Fuca plate system

    NASA Astrophysics Data System (ADS)

    Martin-Short, Robert; Allen, Richard M.; Bastow, Ian D.; Totten, Eoghan; Richards, Mark A.

    2015-12-01

    Tectonic plates are underlain by a low-viscosity mantle layer, the asthenosphere. Asthenospheric flow may be induced by the overriding plate or by deeper mantle convection. Shear strain due to this flow can be inferred using the directional dependence of seismic wave speeds--seismic anisotropy. However, isolation of asthenospheric signals is challenging; most seismometers are located on continents, whose complex structure influences the seismic waves en route to the surface. The Cascadia Initiative, an offshore seismometer deployment in the US Pacific Northwest, offers the opportunity to analyse seismic data recorded on simpler oceanic lithosphere. Here we use measurements of seismic anisotropy across the Juan de Fuca and Gorda plates to reconstruct patterns of asthenospheric mantle shear flow from the Juan de Fuca mid-ocean ridge to the Cascadia subduction zone trench. We find that the direction of fastest seismic wave motion rotates with increasing distance from the mid-ocean ridge to become aligned with the direction of motion of the Juan de Fuca Plate, implying that this plate influences mantle flow. In contrast, asthenospheric mantle flow beneath the Gorda Plate does not align with Gorda Plate motion and instead aligns with the neighbouring Pacific Plate motion. These results show that asthenospheric flow beneath the small, slow-moving Gorda Plate is controlled largely by advection due to the much larger, faster-moving Pacific Plate.

  9. Pb, Sr, and Nd isotopes in basalts and sulfides from the Juan de Fuca Ridge

    SciTech Connect

    Hegner, E.; Tatsumoto, M.

    1987-10-10

    Pb, Sr, Nd isotopes of seven basalt glasses collected by the submersible Alvin from the southern Juan de Fuca Ridge (SJFR) are almost identical (/sup 206/Pb//sup 204/Pbapprox.18.45, /sup 207/Pb//sup 204/Pbapprox.15.47, /sup 208/Pb//sup 204/Pbapprox.37.81, /sup 87/Sr//sup 86/Srapprox.0.70249, /sup 143/Nd//sup 144/Ndapprox.0.51315). Whereas all basalts appear cogenetic, four of the samples have uniform abundances of U, Th, Rb, Nd, Sm, Pb, and Sr, indicating that they are also comagmatic. Two basalt glasses dredged previously at the SJFR have similar isotopic compositions but higher concentrations of U, Th, and Pb. The /sup 206/Pb//sup 204/Pb ratios are intermediate between generally less radiogenic ridge basalts from south of the Juan de Fuca Ridge (JFR) and often more radiogenic basalts from the northern JFR and NE Pacific seamounts. Sr and Nd isotopic compositions closely resemble data of other ridge basalts from the northernmost East Pacific Rise and are intermediate between isotopically more diverse seamount basalts produced nearby.

  10. Warm springs discovered on 3.5 Ma oceanic crust, eastern flank of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Mottl, M. J.; Wheat, G.; Baker, E.; Becker, N.; Davis, E.; Feely, R.; Grehan, A.; Kadko, D.; Lilley, M.; Massoth, G.; Moyer, C.; Sansone, F.

    1998-01-01

    We have located warm springs on an isolated basement outcrop on 3.5 Ma crust on the eastern flank of the Juan de Fuca Ridge in the northeast Pacific Ocean. These are the first ridge-flank hydrothermal springs discovered on crust older than 1 Ma. The springs are venting altered seawater at 25.0 °C along a fault near the summit of Baby Bare outcrop, a high point along a ridge-axis-parallel basement ridge that is otherwise buried by turbidite sediment. Baby Bare is a small volcano that probably erupted off-axis ca. 1.7 Ma; it is thermally extinct, but acts as a high-permeability conduit for venting of basement fluids. The springs have been sampled from the manned submersible Alvin. Compared with the ambient ocean bottom water, they are heavily depleted in Mg, alkalinity, CO2, sulfate, K, Li, U, O2, nitrate, and phosphate, and enriched in Ca, chlorinity, ammonia, Fe, Mn, H2S, H2, CH4, 222Rn, and 226Ra. The springs appear to support a community of thysirid clams. Although we saw no obvious bacterial mats, the surficial sediments contain the highest biomass concentrations ever measured in the deep sea, based on their phospholipid phosphate content. Areal integration of Alvin heat-flow and pore-water velocity data yields flux estimates of 4 13 L/s and 2 3 MW for the total (diffuse and focused) hydrothermal output from Baby Bare, comparable to that from a black smoker vent on the ridge axis. Warm springs such as those on Baby Bare may be important for global geochemical fluxes.

  11. No spreading across the southern Juan de Fuca ridge axial cleft during 1994-1996

    USGS Publications Warehouse

    Chadwell, C.D.; Hildebrand, J.A.; Spiess, Fred N.; Morton, J.L.; Normark, W.R.; Reiss, C.A.

    1999-01-01

    Direct-path acoustic measurements between seafloor transponders observed no significant extension (-10 ?? 14 mm/yr) from August 1994 to September 1996 at the southern Juan de Fuca Ridge (44??40' N and 130??20' W). The acoustic path for the measurement is a 691-m baseline straddling the axial cleft, which bounds the Pacific and Juan de Fuca plates. Given an expected full-spreading rate of 56 mm/yr, these data suggest that extension across this plate boundary occurs episodically within the narrow (~1 km) region of the axial valley floor, and that active deformation is occurring between the axial cleft and the plate interior. A cleft-parallel 714-m baseline located 300 m to the west of the cleft on the Pacific plate monitored system performance and, as expected, observed no motion (+5??7 mm/yr) between the 1994 and 1996 surveys.Direct-path acoustic measurements between seafloor transponders observed no significant extension (-10 ?? 14 mm/yr) from August 1994 to September 1996 at the southern Juan de Fuca Ridge (44??40 minutes N and 130??20 minutes W). The acoustic path for the measurement is a 691-m baseline straddling the axial cleft, which bounds the Pacific and Juan de Fuca plates. Given an expected full-spreading rate of 56 mm/yr, these data suggest that extension across this plate boundary occurs episodically within the narrow (approx. 1 km) region of the axial valley floor, and that active deformation is occurring between the axial cleft and the plate interior. A cleft-parallel 714-m baseline located 300 m to the west of the cleft on the Pacific plate monitored system performance and, as expected, observed no motion (+5 ?? 7 mm/yr) between the 1994 and 1996 surveys.

  12. Regional acoustic imagery and detailed geophysical studies of northern Juan de Fuca Ridge

    SciTech Connect

    Davis, E.E.; Currie, R.G.; Villinger, H.; Goodfellow, W.D.; Hussong, D.M.; Ryan, W.B.F.; Hammond, S.R.

    1986-07-01

    Acoustic image and high-resolution swath mapping studies have been conducted over the northern Juan de Fuca Ridge system from the central Juan de Fuca Ridge at lat. 46/sup 0/N to the triple junction of the ridge with the Queen Charlotte Islands continental margin at lat. 52/sup 0/N. Results of the surveys have been published as 1:250,000 compilations and 1:50,000 detailed sheets of acoustic image mosaics and 10-m contour bathymetric maps. Of particular interest is the information that influences processes of hydrothermal mineralization. In general, little direct information is present in the imagery; only the exact location and nature of the currently active rift axis are seen. However, this information is important, since the along-strike variations in crestal morphology, the recency and level of volcanic activity, and the degree of post-volcanic extension must be known in order to understand any hydrothermal system observed along the axis. An exceptional case has been studied in detail at the northern Juan de Fuca Ridge, lat. 49/sup 0/30'N, where Pleistocene turbidite sediments bury the axial valley, and structures suspected to be of hydrothermal origin were observed in the acoustic imagery over faults that bound the valley. Subsequent higher resolution acoustic imagery, seismic reflection profiling, and heat-flow studies indicated that the features were of hydrothermal origin. A 2.5-m piston core sample of massive sulfides from one of the structures confirmed this speculation. The setting in which these relatively large (500-m diameter, 60-m surficial relief, 350-m relief above basement) structures occur is remarkably similar to that where large sediment-hosted sulfide deposits are found on land, although they do not know what the bulk composition of the structures is, and thus whether the analogy is complete.

  13. Spreading Dynamics of an Intermediate Ridge: Endeavour Segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Scott, S. R.; Ramos, F. C.; Gill, J. B.

    2011-12-01

    U/Th disequilibria analyses of 36 on- and off-axis MORB samples from the Endeavour segment of the Juan de Fuca Ridge, an intermediate spreading ridge off the Pacific Northwest coast of the USA, reflect recent spreading and time-integrated geochemical variability. Previous major and trace element and isotopic data from Endeavour samples exhibit a wide range of geochemical characteristics for samples within close spatial proximity, including EMORB, TMORB and NMORB. Morphology of Endeavour constrains lavas erupted on-axis to flow within the current axial valley, preventing axial lavas from flowing off-axis. This relationship can be used to date any MORB found outside of the axial valley, assuming all types lie on a single zero-age line from the most depleted to most enriched lavas. U-Th data indicate that all EMORB and the majority of TMORB are zero-age (<10 ka) within error and lie on a single zero-age line. EMORB with equivalent (within error) young ages on both sides of the axial valley and that span across the entire eastern flank of the ridge erupted prior to the formation of the current axial valley and within a short time interval (<10 ky). If the axial valley formed within the last 10 ky, the minimum full spreading rate falls around 8 cm/yr. If the majority of EMORB are <8 ka, the axial valley may have formed at a full spreading rate of 10 cm/yr or greater. These U-Th age constraints on EMORB yield a spreading rate faster than the time-integrated spreading rate (5 cm/yr). An EMORB sample located furthest east of the axis is at least 70 ky younger than expected based on the time-integrated spreading rate (5 cm/yr). One on-axis TMORB is not within error of the E-T zero-age line, and may be as old as 17 ka. U-Th ages of TMORB from the western flank fall between 25 and ~100 ka, older than all EMORB. NMORB generally have higher Th isotope ratios than E- or TMORB for a given U/Th ratio and lie on a second zero-age line. One NMORB, on the far western flank, is ~40 ky

  14. Biogenic iron oxyhydroxide formation at mid-ocean ridge hydrothermal vents: Juan de Fuca Ridge

    SciTech Connect

    Toner, Brandy M.; Santelli, Cara M.; Marcus, Matthew A.; Wirth, Richard; Chan, Clara S.; McCollom, Thomas; Bach, Wolfgang; Edwards, Katrina J.

    2008-05-22

    Here we examine Fe speciation within Fe-encrusted biofilms formed during 2-month seafloor incubations of sulfide mineral assemblages at the Main Endeavor Segment of the Juan de Fuca Ridge. The biofilms were distributed heterogeneously across the surface of the incubated sulfide and composed primarily of particles with a twisted stalk morphology resembling those produced by some aerobic Fe-oxidizing microorganisms. Our objectives were to determine the form of biofilm-associated Fe, and identify the sulfide minerals associated with microbial growth. We used micro-focused synchrotron-radiation X-ray fluorescence mapping (mu XRF), X-ray absorption spectroscopy (mu EXAFS), and X-ray diffraction (mu XRD) in conjunction with focused ion beam (FIB) sectioning, and highresolution transmission electron microscopy (HRTEM). The chemical and mineralogical composition of an Fe-encrusted biofilm was queried at different spatial scales, and the spatial relationship between primary sulfide and secondary oxyhydroxide minerals was resolved. The Fe-encrusted biofilms formed preferentially at pyrrhotite-rich (Fe1-xS, 0<_ x<_ 0.2) regions of the incubated chimney sulfide. At the nanometer spatial scale, particles within the biofilm exhibiting lattice fringing and diffraction patterns consistent with 2-line ferrihydrite were identified infrequently. At the micron spatial scale, Fe mu EXAFS spectroscopy and mu XRD measurements indicate that the dominant form of biofilm Fe is a short-range ordered Fe oxyhydroxide characterized by pervasive edge-sharing Fe-O6 octahedral linkages. Double corner-sharing Fe-O6 linkages, which are common to Fe oxyhydroxide mineral structures of 2-line ferrihydrite, 6-line ferrihydrite, and goethite, were not detected in the biogenic iron oxyhydroxide (BIO). The suspended development of the BIO mineral structure is consistent with Fe(III) hydrolysis and polymerization in the presence of high concentrations of Fe-complexing ligands. We hypothesize that

  15. Biogenic iron oxyhydroxide formation at mid-ocean ridge hydrothermal vents: Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Toner, Brandy M.; Santelli, Cara M.; Marcus, Matthew A.; Wirth, Richard; Chan, Clara S.; McCollom, Thomas; Bach, Wolfgang; Edwards, Katrina J.

    2009-01-01

    Here we examine Fe speciation within Fe-encrusted biofilms formed during 2-month seafloor incubations of sulfide mineral assemblages at the Main Endeavor Segment of the Juan de Fuca Ridge. The biofilms were distributed heterogeneously across the surface of the incubated sulfide and composed primarily of particles with a twisted stalk morphology resembling those produced by some aerobic Fe-oxidizing microorganisms. Our objectives were to determine the form of biofilm-associated Fe, and identify the sulfide minerals associated with microbial growth. We used micro-focused synchrotron-radiation X-ray fluorescence mapping (μXRF), X-ray absorption spectroscopy (μΕXAFS), and X-ray diffraction (μXRD) in conjunction with focused ion beam (FIB) sectioning, and high resolution transmission electron microscopy (HRTEM). The chemical and mineralogical composition of an Fe-encrusted biofilm was queried at different spatial scales, and the spatial relationship between primary sulfide and secondary oxyhydroxide minerals was resolved. The Fe-encrusted biofilms formed preferentially at pyrrhotite-rich (Fe 1-xS, 0 ⩽ x ⩽ 0.2) regions of the incubated chimney sulfide. At the nanometer spatial scale, particles within the biofilm exhibiting lattice fringing and diffraction patterns consistent with 2-line ferrihydrite were identified infrequently. At the micron spatial scale, Fe μEXAFS spectroscopy and μXRD measurements indicate that the dominant form of biofilm Fe is a short-range ordered Fe oxyhydroxide characterized by pervasive edge-sharing Fe-O 6 octahedral linkages. Double corner-sharing Fe-O 6 linkages, which are common to Fe oxyhydroxide mineral structures of 2-line ferrihydrite, 6-line ferrihydrite, and goethite, were not detected in the biogenic iron oxyhydroxide (BIO). The suspended development of the BIO mineral structure is consistent with Fe(III) hydrolysis and polymerization in the presence of high concentrations of Fe-complexing ligands. We hypothesize that

  16. Seismic anisotropy of the shallow crust at the Juan de Fuca Ridge

    USGS Publications Warehouse

    Almendros, J.; Barclay, A.H.; Wilcock, W.S.D.; Purdy, G.M.

    2000-01-01

    Microearthquake data recorded on four ocean bottom seismometers are used to study shear-wave splitting on the Endeavour Segment of the Juan de Fuca Ridge. The covariance matrix decomposition method is used to determine the sensor orientation from explosive shot data and to estimate the anisotropy parameters for 238 earthquake records. At three of the four sites, the results show a remarkably consistent fast direction parallel to the ridge axis. The time delays between the fast and the slow waves range from 40 to 200 ms, with an average of 90 ms. They are not clearly related to earthquake range, focal depth or source-receiver azimuth. The splitting of the shear waves is interpreted as an effect of structural anisotropy due to the presence of ridge-parallel cracks in the shallow crust. If we assume that anisotropy is concentrated in the upper 1-2 km, the splitting times require a high crack density of ~0.1.

  17. Propagation as a mechanism of reorientation of the Juan de Fuca ridge

    NASA Technical Reports Server (NTRS)

    Wilson, D. S.; Hey, R. N.; Nishimura, C.

    1984-01-01

    A revised model is presented of the tectonic evolution of the Juan de Fuca ridge by propagating rifting. The new model has three different relative rotation poles, covering the time intervals 17.0-8.5 Ma, 8.5-5.0 Ma, and 5.0 Ma to the present. The rotation pole shifts at 8.5 and 5.0 Ma imply clockwise shifts in the direction of relative motion of 10 deg to 15 deg. At each of these shifts, the pattern of propagation reorganizes, and the new ridges formed by propagation are at an orientation closer to orthogonal to the new direction of motion than the orientation of the preexisting ridges. The model, containing a total of seven propagation sequences, shows excellent agreement with the isochrons inferred from the magnetic anomaly data, except in areas complicated by the separate Explorer and Gorda plates. The agreement between model and data near the Explorer plate breaks down abruptly at an age of about 5 Ma, indicating that the probable cause of the rotation pole shift at that time was the separation of the Explorer plate from the Juan de Fuca plate.

  18. Propagation as a mechanism of reorientation of the Juan de Fuca ridge

    NASA Technical Reports Server (NTRS)

    Wilson, D. S.; Hey, R. N.; Nishimura, C.

    1984-01-01

    A revised model is presented of the tectonic evolution of the Juan de Fuca ridge by propagating rifting. The new model has three different relative rotation poles, covering the time intervals 17.0-8.5 Ma, 8.5-5.0 Ma, and 5.0 Ma to the present. The rotation pole shifts at 8.5 and 5.0 Ma imply clockwise shifts in the direction of relative motion of 10 deg to 15 deg. At each of these shifts, the pattern of propagation reorganizes, and the new ridges formed by propagation are at an orientation closer to orthogonal to the new direction of motion than the orientation of the preexisting ridges. The model, containing a total of seven propagation sequences, shows excellent agreement with the isochrons inferred from the magnetic anomaly data, except in areas complicated by the separate Explorer and Gorda plates. The agreement between model and data near the Explorer plate breaks down abruptly at an age of about 5 Ma, indicating that the probable cause of the rotation pole shift at that time was the separation of the Explorer plate from the Juan de Fuca plate.

  19. Effects of Hydrostatic Pressure on Growth of Hyperthermophilic Archaebacteria from the Juan de Fuca Ridge

    PubMed Central

    Reysenbach, Anna-Louise; Deming, Jody W.

    1991-01-01

    Two new strains (AL1 and AL2) of hyperthermophilic, sulfur-reducing, heterotrophic archaebacteria from high-temperature (350°C) vents on the Juan de Fuca Ridge were highly barotolerant at their optimal growth temperatures (90 and 100°C, respectively). A trend towards barophily at pressures greater than those encountered in situ at the sea floor was demonstrated for the more extremely thermophilic strain (AL2), implying an ability to thrive in (unexplored) habitats well below accessible vent formations. PMID:16348469

  20. Ascending and descending particle flux from hydrothermal plumes at Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Cowen, James P.; Bertram, Miriam A.; Wakeham, Stuart G.; Thomson, Richard E.; William Lavelle, J.; Baker, Edward T.; Feely, Richard A.

    2001-04-01

    Bio-acoustic surveys and associated zooplankton net tows have documented anomalously high concentrations of zooplankton within a 100 m layer above the hydrothermal plumes at Endeavour Segment, Juan de Fuca Ridge. These and other data suggest that congregating epi-plume zooplankton are exploiting a food substrate associated with the hydrothermal plume. Ascending, organic-rich particles could provide a connection. Consequently, two paired sequentially sampling ascending and descending particle flux traps and a current meter were deployed on each of three moorings from July 1994 to May 1995. Mooring sites included an on-axis site (OAS; 47°57.0'N, 129°05.7'W) near the main Endeavour vent field, a "down-current" site 3 km west of the main vent field (WS), and a third background station 43 km northeast of the vent field (ES). Significant ascending and descending particle fluxes were measured at all sites and depths. Lipid analyses indicated that ascending POC was derived from mid-depth and deep zooplankton whereas descending POC also contained a component of photosynthetically derived products from the sea surface. Highest ascending POC fluxes were found at the hydrothermal plume-swept sites (OAS and WS). The limited data available, however, precludes an unequivocal conclusion that hydrothermal processes contribute to the ascending flux of organic carbon at each site. Highest ascending to descending POC flux ratios were also found at WS. Observed trends in POC, PMn/PTi, and PFe/PTi clearly support a hydrothermal component to the descending flux at the plume-swept WS site (no descending data was recovered at OAS) but not at the background ES site. Alternative explanations for ascending particle data are discussed. First-order calculations for the organic carbon input (5-22 mg C m -2 d -1) required to sustain observed epi-plume zooplankton anomalies at Endeavour are comparable both to measured total POC flux to epi-plume depths (2-5 mg C m -2 d -1: combined hydrothermal

  1. Magmagenesis at Axial Seamount, Juan de Fuca Ridge: Insights from Uranium-series systematics

    NASA Astrophysics Data System (ADS)

    Dreyer, B.; Clague, D. A.; Gill, J. B.

    2009-12-01

    Uranium-series data from the Juan de Fuca ridge indicate source composition, melting, transport, accumulation, and/or eruption processes vary on the ridge segment-scale over a few decades [1]. Axial Seamount is the most volcanically robust portion of the Juan de Fuca ridge. Sparse existing data indicate short magma residence times beneath Axial Seamount [1,2], and (210Pb)-excesses in the 1998 eruption may imply 222Rn gas or plagioclase accumulation in the magma chamber; this contrasts with (210Pb)-deficits in the historic sheet flow at adjacent North Cleft and MORB in general [1]. We have conducted a systematic U-series study of Axial Seamount caldera and rim flanks to investigate petrogenetic processes and timescales and to clarify relationships within the Juan de Fuca ridge and global MORB. Axial Seamount offers a unique opportunity to address these questions because it has an atypically large, stable magma chamber [3,1], and variations in the magma source composition are minimal [4]. Multibeam and sidescan surveys and ROV ground-truth observations were used to create high-resolution (sub-meter) bathymetric and geologic maps; individual lava flows were indentified and sampled during multiple ROV dives. New analyses of glasses from Axial Seamount have the lowest 230Th/232Th on the Juan de Fuca ridge. Maximum 230Th-excesses of ~15% are greater than reported previously; the range in 230Th-excesses are similar to adjacent segments of the Juan de Fuca ridge but lower than Endeavour ridge [5]. Preliminary U-Th data used to estimate the age of U-Th fractionation (i.e., partial melting) indicate that flows on the flanks of the volcano range in age from ~5 to <30 ka but cluster ~ 15 ka. Multiple flows from the caldera floor range in age from zero-age to <15 ka, which may be used to constrain the age of caldera formation. Negative correlations between (230Th)/(238U) and depth are likely related to the dynamics of mantle melting. A return cruise by MBARI in August 2009

  2. Magmatic effects of the Cobb hot spot on the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Chadwick, John; Perfit, Michael; Ridley, Ian; Jonasson, Ian; Kamenov, George; Chadwick, William; Embley, Robert; Le Roux, Petrus; Smith, Matthew

    2005-03-01

    The interaction of the Juan de Fuca Ridge with the Cobb hot spot has had a considerable influence on the magmatism of the Axial Segment of the ridge, the second-order segment that overlies the hot spot. In addition to the construction of the large volcanic edifice of Axial Seamount, the Axial Segment has shallow bathymetry and a prevalence of constructional volcanic features along its 100-km length, suggesting that hot spot-derived magmas supplement and oversupply the ridge. Lavas are generally more primitive at Axial Seamount and more evolved in the Axial Segment rift zones, suggesting that fractional crystallization is enhanced with increasing distance from the hot spot because of a reduced magma supply and more rapid cooling. Although the Cobb hot spot is not an isotopically enriched plume, it produces lavas with some distinct geochemical characteristics relative to normal mid-ocean ridge basalt, such as enrichments in alkalis and highly incompatible trace elements, that can be used as tracers to identify the presence and prevalence of the hot spot influence along the ridge. These characteristics are most prominent at Axial Seamount and decline in gradients along the Axial Segment. The physical model that can best explain the geochemical observations is a scenario in which hot spot and mid-ocean ridge basalt (MORB) magmas mix to varying degrees, with the proportions controlled by the depth to the MORB source. Modeling of two-component mixing suggests that MORB is the dominant component in most Axial Segment basalts.

  3. Variability of low temperature hydrothermal alteration in upper ocean crust: Juan de Fuca Ridge and North Pond, Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Rutter, J.; Harris, M.; Coggon, R. M.; Alt, J.; Teagle, D. A. H.

    2014-12-01

    Over 2/3 of the global hydrothermal heat flux occurs at low temperatures (< 150°) on the ridge flanks carried by fluid volumes comparable to riverine discharge. Understanding ridge flank hydrothermal exchange is important to quantify global geochemical cycles. Hydrothermal chemical pathways are complex and the effects of water-rock reactions remain poorly constrained. Factors controlling fluid flow include volcanic structure, sediment thickness, and basement topography. This study compares the effects of low temperature alteration in two locations with contrasting hydrogeological regimes. The intermediate spreading Juan de Fuca ridge flank (JdF) in the northeast Pacific sports a thick sediment blanket. Rare basement outcrops are sites of fluid recharge and discharge. The average alteration extent (~10% secondary minerals), oxidation ratio (Fe3+/FeTOT=34%), and alteration character (orange, green, grey halos) of basement is constant with crustal age and depth along a 0.97-3.6 m.yr transect of ODP basement holes. However, vesicle fills record an increasingly complex history of successive alteration with age. In contrast, North Pond, a ~8 m.yr-old sediment-filled basin at 22N on the slow spreading Mid Atlantic Ridge, hosts rapid, relatively cool SE to NW basinal fluid flow. Average alteration extent (~10%) and oxidation ratio (33%) of Hole 395A basalts are similar to JdF. However, 395A cores are dominated by orange alteration halos, lack celadonite, but have abundant zeolite. Vesicle fill combinations are highly variable, but the most common fill progression is from oxidising to less oxidising secondary assemblages. The comparable extent of alteration between these two sites and the absence of an age relationship on the JdF suggests that the alteration extent of the upper crust is uniform and mostly established by 1 Myr. However, the variable alteration character reflects the influence of regional hydrology on hydrothermal alteration.

  4. Preeruptive flow focussing in dikes feeding historical pillow ridges on the Juan de Fuca and Gorda Ridges

    NASA Astrophysics Data System (ADS)

    Yeo, I. A.; Clague, D. A.; Martin, J. F.; Paduan, J. B.; Caress, D. W.

    2013-09-01

    Linear, hummocky pillow mound volcanism dominates at slow and intermediate spreading rate mid-ocean ridges. Volcanic hummocks are thought to be formed by low effusion rates or as a result of flow focussing during effusive fissure style eruptions in which the initial dike intercepts the seafloor and erupts along its entire length. In this study, high-resolution autonomous underwater vehicle (AUV) bathymetry is used to accurately map the extents of four historical fissure eruptions of the Juan de Fuca and Gorda ridges: on the North Gorda, North Cleft, and CoAxial ridge segments. The four mapped eruptions take the form of pillow mounds, which are similar in both lithology and dimension to hummocks on the Mid-Atlantic Ridge. Pillow mounds may be isolated, or coalesce to form composite mounds, aligned as ridges or as clustered groups. In three of the four mapped sites, the eruptions were discontinuous along their lengths, with pillow mounds and composite mounds commonly separated by areas of older seafloor. This style of discontinuous eruption is inconsistent with typical en echelon fissure eruptions and is probably due to a mildly overpressured, fingering dike intersecting the seafloor along parts of its length.

  5. Pb, Sr, and Nd isotopes in basalts and sulfides from the Juan de Fuca Ridge

    NASA Technical Reports Server (NTRS)

    Hegner, E.; Tatsumoto, M.

    1987-01-01

    Isotopic Pb, Sr, and Nd data were collected by the Alvin submersible from seven basalt glasses in the southern Juan de Fuca Ridge (JFR), giving similar ratios for Pb-206/Pb-204 of about 18.45, for Pb-207/Pb-204 of about 15.47, for Pb-208/Pb-204 of about 37.81, for Sr-87/Sr-86 of about 0.70249, and for Nd-143/Nd-144 of about 0.51315. Data suggest that the basalts are all cogenetic, and that four of the samples are also comagmatic. It is concluded that isotopic data for the JFR and seamount basalts provide additional support for the mantle blob cluster model (Allegre et al., 1984), suggesting the involvement of multiple components in the genesis of ridge basalts, and including an unusual end-member that has nonradiogenic Sr and variable Pb-206/Pb-204 isotopic compositions.

  6. U, Th, and Pb isotopes in hot springs on the Juan de Fuca Ridge

    NASA Technical Reports Server (NTRS)

    Chen, J. H.

    1987-01-01

    Concentrations and isotopic compositions of U, Th, and Pb in three hydrothermal fluids from the Juan de Fuca Ridge were determined from samples obtained by the Alvin submersible. The samples were enriched in Pb and Th relative to deep-sea water, and were deficient in U. No clear relationship with Mg was found, suggesting nonideal mixing between the hot hydrothermal fluids and the cold ambient seawater. Values for U-234/U-238 have a seawater signature, and show a U-234 enrichment relative to the equilibrium value. The Pb isotopic composition has a uniform midocean ridge basalt signature, and it is suggested that Pb in these fluids may represent the best average value of the local oceanic crust.

  7. U, Th, and Pb isotopes in hot springs on the Juan de Fuca Ridge

    NASA Technical Reports Server (NTRS)

    Chen, J. H.

    1987-01-01

    Concentrations and isotopic compositions of U, Th, and Pb in three hydrothermal fluids from the Juan de Fuca Ridge were determined from samples obtained by the Alvin submersible. The samples were enriched in Pb and Th relative to deep-sea water, and were deficient in U. No clear relationship with Mg was found, suggesting nonideal mixing between the hot hydrothermal fluids and the cold ambient seawater. Values for U-234/U-238 have a seawater signature, and show a U-234 enrichment relative to the equilibrium value. The Pb isotopic composition has a uniform midocean ridge basalt signature, and it is suggested that Pb in these fluids may represent the best average value of the local oceanic crust.

  8. Seismic and Acoustic Studies from a Seafloor Array on the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    McDonald, Mark Armstrong

    This dissertation consists of two related but separate studies, one a refraction seismic study of the oceanic crust and the other an acoustic study of whale behavior in the presence of noise, both using seafloor array data. The goal of the first study was to measure the lateral thickness variability in the extrusive volcanic layer on the Juan de Fuca Ridge. The Juan de Fuca Ridge is a medium rate (6 cm per year full rate), active spreading center, separating the Juan de Fuca and Pacific plates. It is a site of volcanic eruptions, associated with creation of new oceanic crust, and hydrothermal vents which are important in the chemical balance of the oceans. To better understand the mechanisms controlling hydrothermal venting and the creation of new crust, a seismic refraction survey was conducted over a 20 km by 30 km area of the ridge. This survey, conducted in August of 1990, used airguns as energy sources and ocean bottom seismometers as recorders. A 3-dimensional traveltime inversion was used to interpret extrusive volcanic layer thickness changes of 300 m, occurring over less than several kilometers laterally. These thickness changes are interpreted as lava accumulations on the low side of listric faults in an episodic spreading system. The traveltime inversion also reveals a large horizontal seismic velocity anisotropy which is confined to the upper 500 m of crust. Compressional velocities are 3.35 km/s in the ridge strike direction and 2.25 km/s across strike. This anisotropy is believed to be caused by oriented fractures within the extrusive layer. The second study involved the tracking and analysis of whale vocalizations which were recorded on the array 10 percent of the time. The goal was to determine if noises such as generated by the airguns, shipping or earthquakes affected the behavior of these fin and blue whales. The vocalization patterns allow analysis of swimming speed, direction, respiration cycle and call interaction. While no clear noise

  9. Diversity and abundance of ammonia-oxidizing archaea in hydrothermal vent chimneys of the juan de fuca ridge.

    PubMed

    Wang, Shufang; Xiao, Xiang; Jiang, Lijing; Peng, Xiaotong; Zhou, Huaiyang; Meng, Jun; Wang, Fengping

    2009-06-01

    The abundance and diversity of archaeal ammonia monooxygenase subunit A (amoA) genes from hydrothermal vent chimneys at the Juan de Fuca Ridge were investigated. The majority of the retrieved archaeal amoA sequences exhibited identities of less than 95% to those in the GenBank database. Novel ammonia-oxidizing archaea may exist in the hydrothermal vent environments.

  10. Continuing Investigations of the Relationship between Fin Whales, Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge

    DTIC Science & Technology

    2012-09-30

    detect fin whale calls along the tracks, and analyzed the results for call characteristics, calling patterns, swimming patterns, net seasonal migration ... Whales , Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge William S. D. Wilcock School of Oceanography...We are investigating the potential correlation between fin whale tracks, enhanced zooplankton concentrations and hydrothermal vents above the Juan de

  11. U, Th, and Pb isotopes in hot springs on the Juan de Fuca Ridge

    SciTech Connect

    Chen, J.H.

    1987-10-10

    The concentrations and isotopic compositions of U, Th, and Pb in three hydrothermal fluids from the Juan de Fuca Ridge were determined. The samples consisted of 10.2--57.6% of the pure hydrothermal end-members based on Mg contents. The Pb contents of the samples ranged from 34 to 87 ng/g, U from 1.3 to 3.0 ng/g, and Th from 0.2 to 7.7 pg/g. These samples showed large enrichments of Pb and Th relative to deep-sea water and some depletion of U. They did not show coherent relationships with Mg, however, indicating nonideal mixings between the hot hydrothermal fluids and cold ambient seawater. Particles filtered from these hydrothermal fluids contained significant amounts of Th and Pb which may effectively increase the concentration of these elements in the fluids when acidified. The /sup 234/U//sup 238/U values in all samples show a /sup 234/U enrichment relative to the equilibrium value and have a seawater signature. The Pb isotopic composition of the Juan de Fuca hydrothermal fluids resembles that of 21 /sup 0/N East Pacific Rise and has a uniform mid-ocean ridge basalt signature. The hydrothermal systems at oceanic spreading ridges have circulated through a large volume of basalts. Therefore Pb in these fluids may represent the best average value of the local oceanic crust. From the effects of U deposition from seawater to the crust and Pb extraction from rock to the ocean, the U/Pb ratio in the hydrothermally altered oceanic crust may be increased significantly. copyright American Geophysical Union 1987

  12. Geochemistry and petrogenesis of basalts from the Juan De Fuca Ridge

    SciTech Connect

    Liias, R.A.; Rhodes, J.M.

    1985-01-01

    The geochemistry of >200 fresh, glassy, zero-age basalts dredged from along the 500 km long Juan de Fuca Ridge (JDFR) illustrates the unique and complex behavior of this active spreading center located on the northern end of the East Pacific Rise. The Cobb-Eickelberg Seamount chain, the trace of the Cobb hot spot, intersects the JDFR at 46/sup 0/N, where a young, volcanically active seamount, astride the ridge, gives clear evidence for continuing hot spot activity. In contrast with other well-documented mantle plume-ridge intersections, there are no systematic geochemical gradients away from the center of maximum volcanism. Petrographic and major element evidence indicates that most JDFR basalts are normal depleted mid-ocean ridge basalts (MORB). However, unlike the vast majority of MORB, the trace element ratios along the JDFR, although highly variable on the scale of single dredge hauls, are predominantly transitional between depleted MORB and enriched oceanic island (or plume) basalts. North of the Cobb Fracture Zone at 48/sup 0/N, the Endeavor segment is chemically distinct form the rest of the JDFR with uniformly enriched trace and rare earth element ratios. Geochemical variability observed along the JDFR requires a heterogeneous mantle source for JDFR basalts. Transitional trace element ratios can be explained by regionally extensive mixing of enriched and normal MORB magmas. Highly evolved basalts, resulting from extensive crystal fractionation requires this mixing be sporadic.

  13. Structure of the southern Juan de Fuca Ridge from seismic reflection records

    USGS Publications Warehouse

    Morton, Janet L.; Sleep, Norman H.; Normark, William R.; Tompkins, Donald H.

    1987-01-01

    Twenty-four-channel seismic reflection records were obtained from the axial region of the southern Juan de Fuca Ridge. Two profiles are normal to the strike of the spreading center and intersect the ridge at latitude 44°40′N and 45°05′N; a third profile extends south along the ridge axis from latitude 45°20′N and crosses the Blanco Fracture Zone. Processing of the axial portions of the cross-strike lines resolved a weak reflection centered beneath the axis. The reflector is at a depth similar to seismically detected magma chambers on the East Pacific Rise and a Lau Basin spreading center; we suggest that the reflector represents the top of an axial magma chamber. In the migrated sections the top of the probable magma chamber is relatively flat and 1–2 km wide, and the subbottom depth of the chamber is greater where the depth to the ridge axis is greater.

  14. Geochemistry of Axial seamount lavas: Magmatic relationship between the Cobb hotspot and the Juan de Fuca Ridge

    SciTech Connect

    Rhodes, J.M.; Morgan, C.; Lilas, R.A. )

    1990-08-10

    Axial seamount, located along the central portion of the Juan de Fuca Ridge axis and at the eastern end of the Cobb-Eickelberg seamount chain, is the current center of the Cobb hotspot. Lava chemistry and bathymetry indicate that Axial seamount is a discrete volcanic unit, with a more productive shallow magmatic plumbing system separate from the adjacent ridge segments. Despite this classic association of spreading center and hotspot volcanic activity, there is no evidence in the lavas for geochemical or isotopic enrichment typical of hotspot or mantle plume activity. The differences in composition between the Axial seamount lavas and the Juan de Fuca Ridge lavas are attributed to melting processes rather than to any fundamental differences in their mantle source compositions. The higher magma production rates, higher Sr, and lower silica saturation in the seamount lavas relative to the ridge lavas are thought to be a consequence of melt initiation at greater depths. The melting column producing the seamount lavas is thought to be initiated in the stability field of spinel peridotite, whereas the ridge lavas are produced from a melting column initiated at shallower levels, possibly within or close to the stability field of plagioclase peridotite. Implicit in this interpretation is the conclusion that the Juan de Fuca Ridge lavas, and by analogy most MORB, are generated at shallow mantle levels, mostly within the stability field of plagioclase peridotite. This interpretation also requires that for the upwelling mantle to intersect the solidus at different depths, the mantle supplying Axial seamount must be hotter than the rest of the Juan de Fuca Ridge. Axial seamount, therefore, reflects a thermal anomaly in the mantle, rather than a geochemically enriched ocean island basalt type mantle plume.

  15. Magmatic effects of the Cobb hot spot on the Juan de Fuca Ridge

    USGS Publications Warehouse

    Chadwick, J.; Perfit, M.; Ridley, I.; Jonasson, I.; Kamenov, G.; Chadwick, W.; Embley, R.; le, Roux P.; Smith, M.

    2005-01-01

    The interaction of the Juan de Fuca Ridge with the Cobb hot spot has had a considerable influence on the magmatism of the Axial Segment of the ridge, the second-order segment that overlies the hot spot. In addition to the construction of the large volcanic edifice of Axial Seamount, the Axial Segment has shallow bathymetry and a prevalence of constructional volcanic features along its 100-km length, suggesting that hot spot-derived magmas supplement and oversupply the ridge. Lavas are generally more primitive at Axial Seamount and more evolved in the Axial Segment rift zones, suggesting that fractional crystallization is enhanced with increasing distance from the hot spot because of a reduced magma supply and more rapid cooling. Although the Cobb hot spot is not an isotopically enriched plume, it produces lavas with some distinct geochemical characteristics relative to normal mid-ocean ridge basalt, such as enrichments in alkalis and highly incompatible trace elements, that can be used as tracers to identify the presence and prevalence of the hot spot influence along the ridge. These characteristics are most prominent at Axial Seamount and decline in gradients along the Axial Segment. The physical model that can best explain the geochemical observations is a scenario in which hot spot and mid-ocean ridge basalt (MORB) magmas mix to varying degrees, with the proportions controlled by the depth to the MORB source. Modeling of two-component mixing suggests that MORB is the dominant component in most Axial Segment basalts. Copyright 2005 by the American Geophysical Union.

  16. Geochemical constraints on the formation of near-ridge Vance seamount chain at the Juan de Fuca Ridge (Invited)

    NASA Astrophysics Data System (ADS)

    Walters, R. L.; Hann, N.; Perfit, M. R.

    2013-12-01

    Observations and sampling of off-axis lava flows and near-ridge seamounts, coupled with the recent discovery of large melt bodies away from ridge axes, attest to the significance of off-axis magmatic phenomena for the formation of the oceanic lithosphere at mid-ocean ridges (MORs). One of the most crucial unsolved questions of oceanic volcanism surrounds the physical mantle processes that cause the initial formation of near-ridge seamounts and sustain volcanism over several million years to produce seamount chains. The Vance Seamounts are just one example of a series of near-ridge seamount chains on the Pacific Plate. The chain comprises six submarine mountains that sit more than 1km above the surrounding oceanic crust just west of the Vance segment of the Juan de Fuca Ridge (JdFR). Dive observations indicate that the seamount chain formed sequentially with the oldest seamount furthest from the ridge axis. The geochemical characteristics of the oldest seamount suggest that the initiation of seamount volcanism was associated with a localized chemical (× thermal) heterogeneity in the mantle. Trace element and isotopic signatures suggest that the chemical heterogeneity was progressively depleted as subsequent seamounts were formed. Central seamount lavas have N-MORB compositions with trace element and isotopic ratios that are significantly more depleted than N-MORB lavas erupted at the JdFR axis. Depletion in the most incompatible elements is so severe for the central seamounts that no physically realistic forward geochemical models involving average depleted MORB mantle can reproduce potential parental melt compositions. The lava compositions from seamounts closest to the ridge reverse the trend in trace element depletion becoming more similar to N-MORB erupted at the current axis. We suggest that excess melt is generated off-axis due to the impingement of a discrete chemical heterogeneity that is more fusible than the DMM matrix. A variety of 2D model ridge

  17. Noble gases in vent water from the Juan de Fuca Ridge

    SciTech Connect

    Kennedy, B.M. )

    1988-07-01

    Hydrothermal vent fluids collected with the DSRV Alvin from the southern limb of the Juan de Fuca Ridge are chemically unique, having chloride concentrations {approximately}2 times ambient seawater. The same fluids contain noble gases in relative abundances like 2{degree}C air-saturated seawater, the expected recharge composition. However, the absolute noble gas abundances are depleted by {approximately}30% relative to seawater. The combination of very high chloride and moderately depleted noble gases appears to require formation of a Cl-rich, gas-free brine by phase separation. This brine is mixed with recharge seawater at temperatures in excess of {approximately}340{degree}C and, therefore, deep in the hydrothermal system.

  18. Ridge asymmetry and deep aqueous alteration at the trench observed from Rayleigh wave tomography of the Juan de Fuca plate

    NASA Astrophysics Data System (ADS)

    Bell, Samuel; Ruan, Youyi; Forsyth, Donald W.

    2016-10-01

    Using Rayleigh wave tomography of noise-removed ocean bottom seismometer data from the Cascadia Initiative, we illuminate the structure of the upper mantle beneath the Juan de Fuca plate. Beneath the Juan de Fuca ridge, there is strong asymmetry, with a pronounced low-velocity zone in the 25-65 km depth range. Extending to the west from the spreading axis, this anomaly has velocities low enough to indicate the presence of melt. The asymmetry in velocity structure and the much greater abundance of seamounts on the west flank of the ridge suggest that dynamic, buoyant upwelling is important, perhaps triggered by thermal or compositional anomalies beneath Axial Seamount. In contrast, there is no evidence for asymmetry in the axial zone or lower than expected velocities beneath the Gorda ridge. On the eastern flank of the Juan de Fuca ridge, the shear velocity in the 25-65 depth range is higher than expected; the lithosphere appears to be colder and thicker than predicted by standard plate cooling models, perhaps caused by the downwelling counterpart of the upwelling on the west side of the ridge. Close to the trench, there is a sharp decrease in shear velocity. We interpret this as aqueous alteration caused by hydrothermal circulation through deep normal faults associated with bending of the plate. Beneath the Astoria and Nitinat fans, where abyssal plain sediment is thickest, the velocity decrease is much smaller, which is consistent with a thick sediment cap that prevents hydrothermal alteration of the plate.

  19. Upper crustal densities derived from sea floor gravity measurements: Northern Juan De Fuca Ridge

    USGS Publications Warehouse

    Holmes, Mark L.; Johnson, H. Paul

    1993-01-01

    A transect of sea floor gravity stations has been analyzed to determine upper crustal densities on the Endeavour segment of the northern Juan de Fuca Ridge. Data were obtained using ALVIN along a corridor perpendicular to the axis of spreading, over crustal ages from 0 to 800,000 years. Calculated elevation factors from the gravity data show an abrupt increase in density with age (distance) for the upper 200 m of crust. This density change is interpreted as a systematic reduction in bulk porosity of the upper crustal section, from 23% for the axial ridge to 10% for the off-axis flanking ridges. The porosity decrease is attributed to the collapse and filling of large-scale voids as the abyssal hills move out of the crustal formation zone. Forward modeling of a plausible density structure for the near-axis region agrees with the observed anomaly data only if the model includes narrow, along-strike, low-density regions adjacent to both inner and outer flanks of the abyssal hills. The required low density zones could be regions of systematic upper crustal fracturing and faulting that were mapped by submersible observers and side-scan sonar images, and whose presence was suggested by the distribution of heat flow data in the same area.

  20. Near-axis crustal structure and thickness of the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Soule, Dax; Wilcock, William S. D.; Toomey, Douglas R.; Hooft, Emilie E. E.; Weekly, Robert T.

    2016-06-01

    A model of crustal thickness and lower crustal velocities is obtained for crustal ages of 0.1-1.2 Ma on the Endeavour Segment of the Juan de Fuca Ridge by inverting travel times of crustal paths and non-ridge-crossing wide-angle Moho reflections obtained from a three-dimensional tomographic experiment. The crust is thicker by 0.5-1 km beneath a 200 m high plateau that extends across the segment center. This feature is consistent with the influence of the proposed Heckle melt anomaly on the spreading center. The history of ridge propagation on the Cobb overlapping spreading center may also have influenced the formation of the plateau. The sharp boundaries of the plateau and crustal thickness anomaly suggest that melt transport is predominantly upward in the crust. Lower crustal velocities are lower at the ends of the segment, likely due to increased hydrothermal alteration in regions influenced by overlapping spreading centers, and possibly increased magmatic differentiation.

  1. Seismic Evidence of Abundant Flank Magmatism at the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Hooft, E. E.; Wells, A. E.; Toomey, D. R.; Wilcock, W. S.

    2013-12-01

    Oceanic crust forms primarily within a narrow, several-kilometer wide, neovolcanic zone at mid-ocean ridges; however, there is an increasing recognition that crustal structure at fast-spreading ridges is modified by off-axis magmatism. Here we use seismic data to show that flank magmatism is also common at an intermediate spreading-rate ridge. We detect several crustal-level, low-velocity, high-attenuation regions on the eastern and western ridge flanks, 7 to 16 km from the neovolcanic zone at the Endeavour segment of the Juan de Fuca Ridge. Seismic refraction data were collected using 64 ocean bottom seismometers (OBSs) and 5,567 airgun shots from the 6600 in3 airgun array of the R/V Marcus G. Langseth in a region extending along the entire ridge segment and out to ~30 km from the rise axis on either side. We observe amplitude anomalies for crustal phases, Pg, for a variety of source-receiver azimuths indicative of numerous anomalous seismic regions on the ridge flanks. We use finite-difference waveform forward modeling to estimate the dimensions, depth, and seismic properties of two of the inferred anomalous regions. The attenuating regions extend horizontally from 2 to 15 km beneath off-axis, ridge-parallel bathymetric highs and from 2 to 4 km below the seafloor. The velocity reduction and the attenuation anomalies suggest the presence of high temperatures and perhaps a small percentage of melt. One anomalous region is associated with a mid-crustal reflector observed in multi-channel seismic data and other mid-crustal reflectors are also present off axis in the region. We attribute the observed seismic anomalies to off-axis magmatic intrusions. Seismic tomography has shown that the upper-crustal, low-velocity layer is thickened on the outer flanks of these highs. This suggests that off-axis volcanism could contribute to the formation of the highs, with erupted lava flowing down the off-axis slopes forming the thicker upper-crustal low-velocity layer. The

  2. Reconstructing Hydrothermal Activity on the Juan de Fuca Ridge over the Last 25ka

    NASA Astrophysics Data System (ADS)

    Mehmel, N.; Costa, K.; McManus, J. F.

    2016-12-01

    Hydrothermal activity on mid-ocean ridges plays a unique role in biogeochemical cycles in the ocean. Hydrothermal vents are a significant source of dissolved Fe, a critical micronutrient in the ocean that supports primary productivity and can modulate the carbon cycle. Little is known about hydrothermal activity in the Last Glacial Maximum (LGM), but new evidence suggests lower sea levels may generate enhanced hydrothermal activity. If hydrothermal activity was higher during the LGM, an Fe fertilized biological pump could have contributed to lower atmospheric CO2 levels. In this study we investigate sediment cores from the Juan de Fuca Ridge (JdFR) to reconstruct hydrothermal activity over the past 25 ka. Five multicores were examined from a spatial array, covering a depth transect along the ridge flank and crest, with a temporal resolution of between 500 and 1000 years. Fe and Cu concentrations were measured by flux fusion, corrected for lithogenic inputs, and normalized to 230Th to calculate hydrothermal fluxes. Hydrothermal flux of Fe and Cu was observed at all times from all sites, suggesting persistent hydrothermal activity on the JdFR. Furthermore, Fe flux into the sediment increases with proximity to the ridge, consistent with a hydrothermal source. The sediment record indicates a stable flux of Fe during the Holocene, compared to flux variations that change by up to 100% between 15 and 20ka. Averaged over 5-7kyr time slices, Cu flux is greater in all 5 records during the LGM than during the Holocene, but in contrast, Fe flux overall appears slightly lower during the LGM than the Holocene. These are the first records from the JdFR to cover the last deglaciation at millennial timescales, and they suggest a more complicated hydrothermal response to glacial sea level changes than observed at other mid-ocean ridges.

  3. Pronounced Shear Velocity Asymmetry in the Mantle Across the Juan de Fuca Ridge and Curious Lack of Features at the Gorda Ridge

    NASA Astrophysics Data System (ADS)

    Bell, S. W.; Ruan, Y.; Forsyth, D. W.

    2015-12-01

    With new Rayleigh-wave tomography results, we have detected a clear and strong asymmetry in the shear velocity structure of the Juan de Fuca ridge. Concentrated in a relatively thin layer with a depth range of ~30-60km, there lies a region of very low shear velocity, with velocities ranging from ~3.8km/s to 4.0km/s. Such low velocities provide strong evidence for the presence of partial melt. This low-velocity region is highly asymmetric, extending much further west than east of the ridge. Especially at shallow depths of ~35 km, this low-velocity region is concentrated just west of the southern portion of the ridge. Peaking near the Axial Seamount, the youngest of the Cobb-Eickelberg Seamounts, it extends south to the region around the small Vance Seamounts just north of the junction with the Blanco Fracture Zone. The Juan de Fuca plate is relatively stationary in the hotspot reference frame, and the Juan de Fuca ridge migrates westward in the hotspot reference frame. Seamounts are overwhelmingly concentrated on the western flank of the ridge, and an asymmetric upwelling driven by migration in the hotspot reference frame has been proposed to explain the seamount asymmetry (i.e. Davis and Karsten, 1986). Our velocity asymmetry, which matches the seamount asymmetry, provides evidence for this asymmetric upwelling and its connection to migration in the absolute hotspot reference frame. In the shear velocity results, the Gorda ridge displays a remarkable lack of features, with no clearly identifiable expression in the subsurface velocity. There is evidence of a broad low-velocity feature beneath Gorda beginning at a depth of ~150 km, but no clear shallow features can be tied to the ridge. At the depths we can resolve (~25-250km), the anisotropy beneath and within the Juan de Fuca plate is small, indicating a deep source of the shear wave splitting results (Bodmer et al., in press), which indicate a fast axis aligned with the Juan de Fuca plate's absolute motion. Around

  4. Hydrological response to a seafloor spreading episode on the Juan de Fuca ridge.

    PubMed

    Davis, Earl; Becker, Keir; Dziak, Robert; Cassidy, John; Wang, Kelin; Lilley, Marvin

    2004-07-15

    Seafloor hydrothermal systems are known to respond to seismic and magmatic activity along mid-ocean ridges, often resulting in locally positive changes in hydrothermal discharge rate, temperature and microbial activity, and shifts in composition occurring at the time of earthquake swarms and axial crustal dike injections. Corresponding regional effects have also been observed. Here we present observations of a hydrological response to seafloor spreading activity, which resulted in a negative formation-fluid pressure transient during and after an earthquake swarm in the sediment-sealed igneous crust of the Middle Valley rift of the northernmost Juan de Fuca ridge. The observations were made with a borehole seal and hydrologic observatory originally established in 1991 to study the steady-state pressure and temperature conditions in this hydrothermally active area. The magnitude of the co-seismic response is consistent with the elastic strain that would be expected from the associated earthquakes, but the prolonged negative pressure transient after the swarm is surprising and suggests net co-seismic dilatation of the upper, permeable igneous crust. The rift valley was visited four weeks after the onset of the seismic activity, but no signature of increased hydrothermal activity was detected in the water column. It appears that water, not magma, filled the void left by this spreading episode.

  5. Submersible observations along the southern Juan de Fuca Ridge: 1984 Alvin program.

    USGS Publications Warehouse

    Normark, William R.; Morton, Janet L.; Ross, Stephanie L.

    1987-01-01

    In September 1984, the research submersible Alvin provided direct observations of three major hydrothermal vent areas along the southernmost segment of the Juan de Fuca Ridge (JFR). The submersible operations focused on specific volcanologie, structural, and hydrothermal problems that had been identified during the preceding 4 years of photographic, dredging, acoustic imaging, and geophysical studies along a 12-km-long section of the ridge. A continuously maintained (from 1981 to the present) net of seafloor-anchored acoustic transponders allowed the observations from Alvin to be directly tied to all previous U.S. Geological Survey data sets and National Oceanic and Atmospheric Administration water column surveys from 1984 to the present. The three vent areas studied are the largest of at least six areas identified by previous deep-towed camera surveys that lie within a deep cleft, which marks the axis of symmetry of the JFR in this region. The cleft appears to be the locus of eruption for this segment of the JFR. The vent areas, at least in part, are localized near what appear to be previous volcanic eruptive centers marked by extensive lava lake collapse features adjacent to the cleft at these sites. Each hydrothermal area has several active discharge sites, and sulfide deposits occur as clusters (15–100 m2) of small chimneys, individual large chimneys, or clusters of large branched chimneys. We review the dive program and present a brief synthesis of the geology of the vent sites together with sample and track line compilations.

  6. Juan de Fuca Ridge: hot spot: propagating rift system: new tectonic geochemical, and magnetic data

    SciTech Connect

    Delaney, J.R.; Johnson, H.P.; Karsten, J.L.

    1981-12-10

    Underway geophysics, deep two camera work, and preliminary geochemical and magnetic studies, from a 1980 cruise to the Juan de Fuca Ridge, allow the following interpretations: (1) the central third (between 45.4/sup 0/N and 46.5/sup 0/N) of the ridge is now actively spreading from a zone which is 10 to 20 km west of the axis bisecting the Brunhes--Matuyama magnetic reversal boundary, (2) the apparent terminus of surficial igneous activity at the northern tip of the active 'Cobb Propagator' has been identified by dredging and camera work; the tip appears curved, or offset slightly, to the west, does not correspond to the northernmost tip of the central magnetic anomaly (Elvers et al., 1974), and spreading has been initiated beneath sediments farther north and (3) iron and titanium in fresh glasses from the active volcanic zone exhibit a progressive enrichment northward, then a pronounced reversal to more 'normal' concentrations in the vicinity of the Cobb Offset.

  7. Sound field near hydrothermal vents on Axial Seamount, Juan de Fuca Ridge. Technical report

    SciTech Connect

    Little, S.A.; Stolzenbach, K.D.; Purdy, G.M.

    1990-08-10

    High-quality acoustic noise measurements were obtained by two hydrophones located 3 m and 40 m from an active hydrothermal vent on Axial Seamount, Juan de Fuca Ridge, in an effort to determine the feasibility of monitoring hydrothermal vent activity through flow noise generation. Most of the measured noise field could be attributed to ambient ocean noise sources of microseisms, distant shipping, and weather, punctuated by local ships and biological sources. Long-period, low-velocity, water/rock interface waves were detected with high amplitudes which rapidly decayed with distance from the seafloor. Detection of vent signals was hampered by unexpected spatial nonstationarity due to the shadowing effects of the calders wall. No continuous vent signals were deemed significant based on a criterion of 90% probability of detection and 5% probability of false alarm. However, a small signal near 40 Hz, with a power level of 0.0001 Pa sq/Hz was noticed on two records taken within 3 m of the Inferno black smoker. The frequency of this signal is consistent with predictions, and the power level suggests the occurrence of jet noise amplification due to convected density inhomogeneities. Keywords: Seamounts; Flow noise; Underwater acoustics; Acoustic measurement; Geothermy/noise; Ocean ridges; Underwater sound signals; Reprints; North Pacific Ocean. (EDC).

  8. Petrological variability of recent magmatism at Axial Seamount summit, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Dreyer, Brian M.; Clague, David A.; Gill, James B.

    2013-10-01

    A combined study of mapping, observational, age constraint, and geochemical data at the summit of Axial Seamount, Juan de Fuca Ridge, has revealed its recent petrological history. Multiple basalt types erupted at the summit in a time sequence. At least three different magma batches have been present beneath the Axial Summit caldera during the last millennium, each with a range in differentiation. The first, prior to 1100 CE, was compositionally diverse, dominantly aphyric T-MORB. The second, from ˜1220 to 1300 CE, was dominantly plagioclase-phyric, more mafic N-MORB erupted mostly in the central portion of the caldera. Since ˜1400 CE, lavas have been more differentiated, and nearly aphyric T-MORB mostly erupted in the caldera's rift zones. Parental magmas vary subtly due to small coupled differences in the degree of melting and sources, but all share a uniform differentiation trend indicating pooling at similar depths. Thus, melts percolate through melt-rich lenses that remain partially isolated in space and/or time. Centennial magmatic timescales at Axial Seamount are similar to those for fast spreading ridge segments. The fluctuation between aphyric and plagioclase-phyric lava likely reflects different pathways or velocities of melt migration.

  9. Geochemistry of some gases in hydrothermal fluids from the southern Juan de Fuca Ridge

    USGS Publications Warehouse

    Evans, William C.; White, L.D.; Rapp, J.B.

    1988-01-01

    Five samples of hydrothermal fluids from two vent areas on the southern Juan de Fuca Ridge were analyzed for dissolved gases. Concentrations in the end-member hydrothermal fluid of H2 (270-527 ??mol/kg), CH4 (82-118 ??mol/kg), and CO2 (3920-4460 ??mol/kg) are well above values in ambient seawater and are similar to concentrations reported for other ridge crest hydrothermal systems. The carbon isotopic ratios of the CH4(??13C=-17.8 to -20.8) and CO2(??13C=-3.6 to -4.7) suggest that at least some of the CH4 and CO2 in the fluids is basalt-derived. The range of ??13C values for the basalt-derived CO2 is -6.8 to -9.7, calculated by assuming conservation of recharge ??CO2 during hydrothermal circulation. Apparent temperatures of equilibration between the CH4 and the basalt-derived CO2 range from 640??C to 750??C. Small amounts of ethane (C2H6/CH4??? 0.9 ?? 10-3-2.2 ?? 10-3), propane, and butane detected in the samples may also have formed in the basalt. One sample of almost pure (95.5%) hydrothermal fluid contained a significant fraction, up to 63% and 74%, respectively, of the recharge Ar and N2. This suggests that the fluid has not undergone extensive vapor-liquid phase separation. -Authors

  10. Tidal Triggering and Statistical Patterns of Microseismicity at Axial Volcano on the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Bohnenstiehl, D. R.; Dziak, R. P.; Caplan-Auerbach, J.; Haxel, J. H.; Mann, M. E.; Pennington, C.; Weis, J.; Womack, N.; Levy, S.

    2015-12-01

    Tidal stress changes are known to modulate the timing of microearthquakes within many mid-ocean ridge volcanic systems. At Axial Volcano, located on the Juan de Fuca Ridge, earthquakes occur preferentially when volumetric extension peaks near times of low ocean tide. Autonomous ocean-bottom hydrophone (OBH, 2007-2011) and cabled ocean bottom seismometer (OBS, Nov. 2014-) data are used to quantify the strength of tidal triggering in time periods before the April 2011 and April 2015 eruptions at Axial Volcano. The mean percent excess at times of low ocean-tide is ~14% (16% std) in the four years prior to the 2011 eruption and ~18% (17% std) in the five months prior to the 2015 eruption. The sensitivity of earthquakes to tidal stress does not evolve systematically prior to either eruption; however, this pattern is disturbed by much larger stress changes associated with the onset of dike intrusion. Following dike injection and eruption, seismicity rates drop sharply. As seismicity rates continue to rise in the months following the 2015 eruption, real-time data available from the cabled OBS network will be used quantify temporal patterns in microearthquake activity as dike induced stresses are relaxed and the magma chamber inflates.

  11. Heat Flux From the Endeavour Segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Thompson, W. J.; McDuff, R. E.; Stahr, F. R.; Yoerger, D. R.; Jakuba, M.

    2005-12-01

    The very essence of a hydrothermal system is transfer of heat by a convecting fluid, yet the flux of heat remains a poorly known quantity. Past studies of heat flux consisted primarily of point measurements of temperature and fluid flow at individual vent sites and inventories of the neutrally buoyant plume above the field. In 2000 the Flow Mow project used the Autonomous Benthic Explorer (ABE) to determine heat flux from Main Endeavour Field (MEF) on the Juan de Fuca Ridge by intersecting the stems of rising buoyant plumes. ABE carries instruments to measure conductivity, temperature and depth, and a MAVS current meter to determine the vertical velocity of the fluid, after correcting for vehicle motion. Complementary work on horizontal fluxes suggests that the vertical flux measured by ABE includes both the primary high buoyancy focused "smoker" sources and also entrained diffuse flow. In 2004, ABE was again used to determine heat flux not only from MEF, but also from the other four fields in the Endeavour Segment RIDGE 2000 Integrated Study Site. In this four year interval the flux of heat from MEF has declined by approximately a factor of two. The High Rise vent field has the greatest heat flux, followed by MEF, then Mothra, Salty Dawg and Sasquatch (of order 500, 300, 100, 50 MW respectively; heat flux at Sasquatch was below detection).

  12. Fluid and chemical fluxes along a buried-basement ridge in the eastern Juan de Fuca Ridge flank

    NASA Astrophysics Data System (ADS)

    Hulme, S.; Wheat, C. G.

    2010-12-01

    Hydrothermal fluid circulation within oceanic crust at low temperatures affects global biogeochemical cycles, with the volume of fluid circulation rivaling that of the world’s water flux to the oceans from rivers. Our work focuses on the best studied low temperature hydrothermal system on the eastern flank of the Juan de Fuca Ridge where a buried basement ridge 100 km from the active spreading axis has been sampled with a variety of mediums. We use data from deep sea drilling, gravity coring, and submersible operations from five sites along-strike of the buried ridge to better constrain the chemical and fluid fluxes along this transect. A transport (advection-diffusion) model is applied to the data, constraining the volumetric fluid flux per unit length within the oceanic crust from 0.05 and 0.2 m3 y-1 cm-1 and identifying conservative elements within this system. Using an average fluid flux, reactive fluxes are determined for non-conservative elements within basaltic crust for twenty-four chemical species. Conservative species include K, Cl, SO4, Ba, Sr, Cs, Mo, and Y. Only Ca and the rare earth elements Ce and Gd are produced by basaltic basement. The remaining chemical species Mg, Na, ammonium, Li, Rb, Mn, Fe, Co, Zn, Cd, U, La and Yb are all consumed within upper basaltic basement. Fluxes of potentially-bioavailable redox species ammonium, Fe, and Mn into the upper basaltic basement are 3 to 20 nmol y-1cm-2. Possible mechanisms of removal are suggested, placing constraints on microbial metabolic activity and biomineralization.

  13. A time history of micro-seismicity leading to volcanic eruption at Axial Volcano, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Haxel, J. H.; Dziak, R. P.; Matsumoto, H.; Fowler, M. J.; Chadwick, B.

    2011-12-01

    A small array of Ocean Bottom Hydrophones (OBHs) has been deployed and annually maintained at Axial Volcano on the Juan de Fuca Ridge in the northeast Pacific Ocean from September 2006 through present. The U.S. Navy's SOSUS hydrophone array has been the main observational tool used to monitor for volcanic seismicity at Axial since 1991. However, several key elements of the SOSUS system have gone offline in recent years, necessitating deployment of an in situ seismic array to record volcanogenic activity. The OBH records have captured increasing rates of local micro-seismicity emerging from the post-eruptive period of seismic quiescence following the 1998 eruption up to a recently discovered (April 2011) volcanic event. The locations of at least 11 earthquake swarms that occurred during the last 5 years leading up to the 2011 volcanic eruption are focused in the southeast region of Axial's caldera with focal depth estimates of ~1.5 km. Of the thousands of local micro-earthquakes recorded by the OBH array at Axial from 2006 to present, only two small events (ML 3.0 and 3.7) associated with the April 2011 seafloor eruption were large enough to be detected by land-based teleseismic stations and a total of four earthquakes were detected on SOSUS hydrophones in the central Pacific. A recent submersible cruise to Axial Volcano recovered two OBH moorings, with a third mooring encased in a new lava flow where it remains buried beneath the seafloor in the southern part of the caldera. Data from the two recovered OBH moorings will provide information regarding the timing, duration and intensity of the most recent volcanic event at Axial Volcano.

  14. Juan de Fuca Plate Ridge-to-Trench Experiment: initial results from active source seismic imaging of the Juan de Fuca plate and Cascadia fore-arc (Invited)

    NASA Astrophysics Data System (ADS)

    Carbotte, S. M.; Canales, J.; Carton, H. D.; Han, S.; Gibson, J. C.; Janiszewski, H. A.; Horning, G.; Nedimovic, M. R.; Abers, G. A.; Trehu, A. M.

    2013-12-01

    Active source seismic data were acquired during the Juan de Fuca Ridge-to-Trench experiment (June-July 2012) to characterize the evolution and structure of the Juan de Fuca plate from formation at the ridge, through evolution in the plate interior, to subduction at the Cascadia trench. The survey provides plate-scale images of the sediments, crust, and shallowest mantle along two ridge-perpendicular transects, one extending from Axial seamount to the Oregon margin near Hydrate Ridge and the other from near Endeavour segment to Grays Harbor offshore Washington. In addition, a 450 km long trench-parallel line ~10 km seaward of the Cascadia deformation front was acquired to characterize variations in plate structure along the margin. Coincident long-streamer (8 km) multi-channel seismic (MCS) and wide-angle ocean bottom seismometer (OBS) data were collected along each transect. Using these data, our current investigations focus on the properties of the thick sediment blanket covering the Juan de Fuca plate and evidence for fluid flow at the deformation front, crustal structure within the plate interior and near the deformation front, and tracking the downgoing plate beneath the margin. Highlights include the discovery of numerous pockmarks on the seafloor providing evidence of active fluid flow up to 60 km west of the deformation front. Along the Oregon transect, a bright decollement horizon is imaged at ~1sec twtt above basement whereas at the Washington margin, protothrusts of the deformation front reach to the top of the oceanic crust. Variations in sediment properties are documented within the margin-parallel transect with changes in the stratigraphic level of decollement. While crustal thickness is quite uniform along the margin (~ 6 km), variations in crustal reflectivity and in shallowest mantle velocities are observed over ~30-50 km length scales that could be related to structural variations in the Cascadia subduction zone. Further landward, the top of the

  15. Lead Isotopic Compositions of the Endeavour Sulfides, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Labonte, F.; Hannington, M. D.; Cousens, B. L.; Blenkinsop, J.; Gill, J. B.; Kelley, D. S.; Lilley, M. D.; Delaney, J. R.

    2006-12-01

    32 sulfide samples from the main structures of the Endeavour vent field, Juan de Fuca Ridge, were analyzed for their Pb isotope composition. The samples were collected from 6 main vent fields between 1985 and 2005 and encompass a strike length of more than 15 km along the ridge crest. The sulfides are typical of black smoker deposits on sediment-starved mid-ocean ridges. Pb isotope compositions of the massive sulfides within the six hydrothermal fields vary within narrow ranges, with 206Pb/204Pb = 18.58 18.75, 207Pb/204Pb = 15.45 15.53 and 208Pb/204Pb = 37.84 38.10. A geographic trend is observed, with the lower Pb ratios restricted mostly to the northern part of the segment (Salty Dawg, Sasquatch and High Rise fields), and the higher Pb ratios restricted mostly to the southern part of the segment (Main Endeavour, Clam Bed and Mothra fields). Variations within individual fields are much smaller than those between fields, and variation within individual sulfide structures is within the uncertainty of the measurements. Therefore, it is unlikely that the ranges of Pb isotope compositions along the length of the segment reflect remobilization, replacement, and recrystallization of sulfides, as suggested for the observed Pb isotope variability in some large seafloor sulfide deposits. Instead, the differences in isotopic compositions from north to south are interpreted to reflect differences in the source rocks exposed to hydrothermal circulation of fluids below the seafloor. Possible sources of the somewhat more radiogenic Pb may be small amounts of buried sediment, either from turbidites or from hemipelagic sediment. This possibility is supported by high concentrations of CH4 and NHC4 found in the high-temperature vent fluids at the Main Endeavour Field, which are interpreted to reflect subseafloor interaction between hydrothermal fluids and organic material in buried sediments. However, the majority of the samples fall below and are approximately parallel to the

  16. Radiogenic isotopes in enriched mid-ocean ridge basalts from Explorer Ridge, northeast Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Cousens, Brian; Weis, Dominique; Constantin, Marc; Scott, Steve

    2017-09-01

    Extreme gradients in topography related to variations in magma supply are observed on the Southern Explorer Ridge (SER), part of the northern Juan de Fuca ridge system. We report radiogenic isotope (Pb, Sr, Nd, Hf) and geochemical data for twenty-four basalt whole-rock and glass samples collected from the length of the SER and from Explorer Deep, a rift to the north of the SER. Lavas from the SER form a north-south geochemical gradient, dominated by E-MORB at the northern axial high, and range from T-MORB to N-MORB towards the southern deepest part of the ridge. Linear relationships between incompatible element ratios and isotopic ratios in MORB along the ridge are consistent with mixing of magmas beneath the ridge to generate the geographic gradient from E- to N-MORB. The E-MORB have high Sr and Pb, and low Nd and Hf isotopic ratios, typical of enriched mantle that includes a FOZO or HIMU isotopic component. The West Valley and Endeavour segments of the northern Juan de Fuca ridge also include this isotopic component, but the proportion of the FOZO or HIMU component is more extreme in the SER basalts. The FOZO or HIMU component may be garnet-bearing peridotite, or a garnet pyroxenite embedded in peridotite. Recycled garnet pyroxenite better explains the very shallow SER axial high, high Nb/La and La/Sm, and the ;enriched; isotopic compositions.

  17. Crustal Structure and Evolution Along the Juan de Fuca Ridge Flanks

    NASA Astrophysics Data System (ADS)

    Nedimović, M.; Carbotte, S.; Diebold, J.; Detrick, R.; Canales, J.; van Ark, E.; Harding, A.; Kent, G.

    2003-12-01

    An extensive seismic investigation of the Juan de Fuca Ridge was carried out in 2002. Here we focus on flank profiles crossing the Endeavour, Northern Symmetric, and Cleft ridge segments. These profiles are a few hundred km-long, extend out to crust about 5 my old, and provide structural information giving insight into crustal evolution. We observe spatial variation in sedimentary cover, tectonic activity, layer 2A thickness, depth to the axial magma chamber and Moho structure. Whereas the western ridge-flank appears to be tectonically stable, normal faults are imaged within the thick sediment section of the eastern flank indicating recent activity well beyond the axial region. Fault offsets diminish upsection suggesting growth faulting caused by long-term slip within the basement structure. In places, imaged fault planes extend through the sediments and crust to the Moho. Reflections from crustal gabbros are not likely unless the rocks are serpentinized at fault planes, which is indicative of fluid flow deep into the crust. Bright Moho where the deep faults plunge into the upper mantle suggests that fluid exchange may extend below the crust. The reflection images show that the western and eastern ridge flanks are evolving in a markedly different way. We believe that the main causes for differential flank evolution are distinct sedimentation and tectonic histories. Massive sediment accumulation on the eastern flank strongly affects the hydrothermal fluid flow regime and the evolution of layer 2A. Faulting profoundly affects the crust by providing new pathways for fluids trapped in the upper crust. Bending of the oceanic slab due to nearby subduction is a likely driving force for the faulting. The density and magnitude of faulting do not monotonously decrease away from the trench, as would be expected from pure slab bending, indicating that other factors contribute to the faulting. Magnetic and bathymetry data tie the faulted areas to propagator wakes. The crust

  18. Seismic Structure of the Shallow Mantle Beneath the Endeavor Segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    VanderBeek, B. P.; Toomey, D. R.; Hooft, E. E.; Wilcock, W. S.; Weekly, R. T.; Soule, D. C.

    2013-12-01

    We present tomographic images of the seismic structure of the shallow mantle beneath the intermediate-spreading Endeavor segment of the Juan de Fuca ridge. Our results provide insight into the relationship between magma supply from the mantle and overlying ridge crest processes. We use seismic energy refracted below the Moho (Pn), as recorded by the Endeavor tomography (ETOMO) experiment, to image the anisotropic and isotropic P wave velocity structure. The ETOMO experiment was an active source seismic study conducted in August 2009 as part of the RIDGE2000 science program. The experimental area extends 100 km along- and 60 km across-axis and encompasses active hydrothermal vent fields near the segment center, the eastern end of the Heck seamount chain, and two overlapping spreading centers (OSCs) at either end of the segment. Previous tomographic analyses of seismic arrivals refracted through the crust (Pg), and reflected off the Moho (PmP), constrain a three-dimensional starting model of crustal velocity and thickness. These Pg and PmP arrivals are incorporated in our inversion of Pn travel-time data to further constrain the isotropic and anisotropic mantle velocity structure. Preliminary results reveal three distinct mantle low-velocity zones, inferred as regions of mantle melt delivery to the base of the crust, that are located: (i) off-axis near the segment center, (ii) beneath the Endeavor-West Valley OSC, and (iii) beneath the Cobb OSC near Split Seamount. The mantle anomalies are located at intervals of ~30 to 40 km along-axis and the low velocity anomalies beneath the OSCs are comparable in magnitude to the one located near the segment center. The direction of shallow mantle flow is inferred from azimuthal variations in Pn travel-time residuals relative to a homogeneous isotropic mantle. Continuing analysis will focus on constraining spatial variations in the orientation of azimuthal anisotropy. On the basis of our results, we will discuss the transport of

  19. Chemistry of hydrothermal solutions from the southern Juan de Fuca Ridge

    SciTech Connect

    Von Damm, K.L.; Bischoff, J.L.

    1987-10-10

    Fluids from three vent fields on the southern Juan de Fuca Ridge were sampled in September 1984 using the DSRV Alvin. The fluids are uniquely high in both chloride, which ranges up to twice the seawater value, and in metal content. Simple vapor-liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids. The cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes: (1) subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and (2) dissolution of a chloride-rich phase combined with a possible small loss of gas during sampling procedures. Although measured temperatures were all less than 300 /sup 0/C, quartz geothermometry suggests that the fluids have equilibrated at greater than 340 /sup 0/C. Quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber. copyright American Geophysical Union 1987

  20. Metagenome sequencing and 98 microbial genomes from Juan de Fuca Ridge flank subsurface fluids

    NASA Astrophysics Data System (ADS)

    Jungbluth, Sean P.; Amend, Jan P.; Rappé, Michael S.

    2017-03-01

    The global deep subsurface biosphere is one of the largest reservoirs for microbial life on our planet. This study takes advantage of new sampling technologies and couples them with improvements to DNA sequencing and associated informatics tools to reconstruct the genomes of uncultivated Bacteria and Archaea from fluids collected deep within the Juan de Fuca Ridge subseafloor. Here, we generated two metagenomes from borehole observatories located 311 meters apart and, using binning tools, retrieved 98 genomes from metagenomes (GFMs). Of the GFMs, 31 were estimated to be >90% complete, while an additional 17 were >70% complete. Phylogenomic analysis revealed 53 bacterial and 45 archaeal GFMs, of which nearly all were distantly related to known cultivated isolates. In the GFMs, abundant Bacteria included Chloroflexi, Nitrospirae, Acetothermia (OP1), EM3, Aminicenantes (OP8), Gammaproteobacteria, and Deltaproteobacteria, while abundant Archaea included Archaeoglobi, Bathyarchaeota (MCG), and Marine Benthic Group E (MBG-E). These data are the first GFMs reconstructed from the deep basaltic subseafloor biosphere, and provide a dataset available for further interrogation.

  1. Metals and isotopes in Juan de Fuca Ridge hydrothermal fluids and their associated solid materials

    SciTech Connect

    Hinkley, T.K.; Tatsumoto, M.

    1987-10-10

    The /sup 87/Sr//sup 86/Sr ratio of the hydrothermal solution (HTS) (0.7034) is larger than that of basalt (0.7025) at the southern vent field of the Juan de Fuca Ridge (SJFR). Both the Sr isotopic ratio for HTS and the water/rock interaction ratio lie between those at two sites farther south on the East Pacific Rise, 13 /sup 0/N and 21 /sup 0/N. These parameters may be closely related to subsurface temperatures and rates of magma ascent and to extent of faulting and surface areas of the frameworks of the hydrothermal systems. For these three Pacific Ocean sites there is no steady geographical progression of these measured parameters, nor of reported spreading rate, with increasing latitude northward. Pb and Nd isotopic measurements are uniform for all samples from the SJFR, ranging only from 18.43 to 18.58 for /sup 206/Pb//sup 204/Pb (fluids and associated solids) and centering near 0.5131 for /sup 143/Nd//sup 144/Nd (only fluids measured). Values for basalts and sulfides from the site have similar values. Relatively high /sup 206/Pb//sup 204/Pb values at the SJFR suggest the potential for the existence of an anomalous radiogenic heat source in the underlying mantle material.

  2. Microbial community structure across fluid gradients in the Juan de Fuca Ridge hydrothermal system.

    PubMed

    Anderson, Rika E; Beltrán, Mónica Torres; Hallam, Steven J; Baross, John A

    2013-02-01

    Physical and chemical gradients are dominant factors in shaping hydrothermal vent microbial ecology, where archaeal and bacterial habitats encompass a range between hot, reduced hydrothermal fluid and cold, oxidized seawater. To determine the impact of these fluid gradients on microbial communities inhabiting these systems, we surveyed bacterial and archaeal community structure among and between hydrothermal plumes, diffuse flow fluids, and background seawater in several hydrothermal vent sites on the Juan de Fuca Ridge using 16S rRNA gene diversity screening (clone libraries and terminal restriction length polymorphisms) and quantitative polymerase chain reaction methods. Community structure was similar between hydrothermal plumes and background seawater, where a number of taxa usually associated with low-oxygen zones were observed, whereas high-temperature diffuse fluids exhibited a distinct phylogenetic profile. SUP05 and Arctic96BD-19 sulfur-oxidizing bacteria were prevalent in all three mixing regimes where they exhibited overlapping but not identical abundance patterns. Taken together, these results indicate conserved patterns of redox-driven niche partitioning between hydrothermal mixing regimes and microbial communities associated with sinking particles and oxygen-deficient waters. Moreover, the prevalence of SUP05 and Arctic96BD-19 in plume and diffuse flow fluids indicates a more cosmopolitan role for these groups in the ecology and biogeochemistry of the dark ocean. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

  3. Metagenome sequencing and 98 microbial genomes from Juan de Fuca Ridge flank subsurface fluids

    PubMed Central

    Jungbluth, Sean P.; Amend, Jan P.; Rappé, Michael S.

    2017-01-01

    The global deep subsurface biosphere is one of the largest reservoirs for microbial life on our planet. This study takes advantage of new sampling technologies and couples them with improvements to DNA sequencing and associated informatics tools to reconstruct the genomes of uncultivated Bacteria and Archaea from fluids collected deep within the Juan de Fuca Ridge subseafloor. Here, we generated two metagenomes from borehole observatories located 311 meters apart and, using binning tools, retrieved 98 genomes from metagenomes (GFMs). Of the GFMs, 31 were estimated to be >90% complete, while an additional 17 were >70% complete. Phylogenomic analysis revealed 53 bacterial and 45 archaeal GFMs, of which nearly all were distantly related to known cultivated isolates. In the GFMs, abundant Bacteria included Chloroflexi, Nitrospirae, Acetothermia (OP1), EM3, Aminicenantes (OP8), Gammaproteobacteria, and Deltaproteobacteria, while abundant Archaea included Archaeoglobi, Bathyarchaeota (MCG), and Marine Benthic Group E (MBG-E). These data are the first GFMs reconstructed from the deep basaltic subseafloor biosphere, and provide a dataset available for further interrogation. PMID:28350381

  4. Metagenome sequencing and 98 microbial genomes from Juan de Fuca Ridge flank subsurface fluids.

    PubMed

    Jungbluth, Sean P; Amend, Jan P; Rappé, Michael S

    2017-03-28

    The global deep subsurface biosphere is one of the largest reservoirs for microbial life on our planet. This study takes advantage of new sampling technologies and couples them with improvements to DNA sequencing and associated informatics tools to reconstruct the genomes of uncultivated Bacteria and Archaea from fluids collected deep within the Juan de Fuca Ridge subseafloor. Here, we generated two metagenomes from borehole observatories located 311 meters apart and, using binning tools, retrieved 98 genomes from metagenomes (GFMs). Of the GFMs, 31 were estimated to be >90% complete, while an additional 17 were >70% complete. Phylogenomic analysis revealed 53 bacterial and 45 archaeal GFMs, of which nearly all were distantly related to known cultivated isolates. In the GFMs, abundant Bacteria included Chloroflexi, Nitrospirae, Acetothermia (OP1), EM3, Aminicenantes (OP8), Gammaproteobacteria, and Deltaproteobacteria, while abundant Archaea included Archaeoglobi, Bathyarchaeota (MCG), and Marine Benthic Group E (MBG-E). These data are the first GFMs reconstructed from the deep basaltic subseafloor biosphere, and provide a dataset available for further interrogation.

  5. The sound field near hydrothermal vents on Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Little, Sarah A.; Stolzenbach, Keith D.; Purdy, G. Michael

    1990-08-01

    High-quality acoustic noise measurements were obtained by two hydrophones located 3 m and 40 m from an active hydrothermal vent on Axial Seamount, Juan de Fuca Ridge, in an effort to determine the feasibility of monitoring hydrothermal vent activity through flow noise generation. Most of the measured noise field could be attributed to ambient ocean noise sources of microseisms, distant shipping, and weather, punctuated by local ships and biological sources. Long-period, low-velocity, water/rock interface waves were detected with high amplitudes which rapidly decayed with distance from the seafloor. Detection of vent signals was hampered by unexpected spatial nonstationarity due to the shadowing effects of the caldera wall. No continuous vent signals were deemed significant based on a criterion of 90% probability of detection and 5% probability of false alarm. However, a small signal near 40 Hz, with a power level of 10-4Pa2/Hz was noticed on two records taken within 3 m of the Inferno black smoker. Hie frequency of this signal is consistent with predictions, and the power level suggests the occurrence of jet noise amplification due to convected density inhomogeneities.

  6. Chemistry of hydrothermal solutions from the southern Juan de Fuca Ridge

    USGS Publications Warehouse

    Von Damm, Karen L.; Bischoff, James L.

    1987-01-01

    Fluids from three vent fields on the southern Juan de Fuca Ridge were sampled in September 1984 using the DSRV Alvin. The fluids are uniquely high in both chloride, which ranges up to twice the seawater value, and in metal content. Simple vapor-liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids. The cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes: (1) subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and (2) dissolution of a chloride-rich phase combined with a possible small loss of gas during sampling procedures. Although measured temperatures were all less than 300°C, quartz geothermometry suggests that the fluids have equilibrated at greater than 340°C. Quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber.

  7. Mineralogy and chemistry of massive sulfide deposits from the Juan de Fuca Ridge.

    USGS Publications Warehouse

    Koski, R.A.; Clague, D.A.; Oudin, E.

    1984-01-01

    Two types of massive sulphide were dredged from one of the six vent sites located in the axial valley of the southern Juan de Fuca ridge. Type A samples are angular slabs of dark grey Zn-rich sulphide with interlayers and a thin, partly-oxidized crust of Fe-sulphide. These layered sulphide aggregates appear to be fragments of a sulphide wall enclosing an active hydrothermal vent. The outer sulphide wall is composed of colloform Fe sulphide and Fe-poor sphalerite deposited under low-T conditions when sea-water and hydrothermal fluid mix above the discharge point. Inside the wall the intensifying hydrothermal sytem deposits a higher-T assemblage of granular Fe-rich sphalerite, wurtzite, pyrite and minor Cu-Fe sulphide. Type B sulphide samples are sub-rounded, spongy-textured fragments composed almost entirely of dendritic aggregates of pale Fe-poor colloform sphalerite and opaline silica. This type of sulphide is deposited in settings peripheral to sites of focused discharge and in open spaces by moderate- to low-T fluid discharging at a slow but variable rate; the fluid becomes increasingly oxidizing, resulting in late-stage deposits of hematite, baryte and sulphur.-L.di H.

  8. On the correlation of electrical conductivity and heat flow in Middle Valley, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Webb, Spahr C.; Edwards, R. Nigel

    1995-11-01

    The near-surface electrical conductivity has been mapped within an area of Middle Valley, a sediment-filled axial valley at the northern end of the Juan de Fuca ridge. The conductivity in the uppermost 20 m of sediment was determined by analyzing the magnetic field signal transmitted between a source coil and a receiver that were towed along the seafloor. The instrument is a version of a time domain electromagnetic (TDEM) sounding system. The heat flow pattern within Middle Valley, with a large central anomaly above a basement high, is reproduced by the conductivity measurements, the result of enhanced pore fluid electrical conductivity due to higher near-surface temperatures in the high heat flow regions. The high correlation between heat flow and conductivity requires that porosity as inferred from Archie's law must be nearly uniform in the central part of the study area. Porosities derived from the conductivity measurements are in close agreement with measurements from the Ocean Drilling Project (ODP) boreholes. Higher near-surface porosities are required in the eastern part of the valley to match the observed heat flow, consistent with the higher porosity seen at ODP site 855. A small region of apparently lower porosity was detected to the west of the center of the valley.

  9. Geology of a vigorous hydrothermal system on the Endeavour segment, Juan de Fuca Ridge

    SciTech Connect

    Delaney, J.R.; Robigou, V.; McDuff, R.E. ); Tivey, M.K. )

    1992-12-10

    A high-precision, high-resolution geologic map explicitly documents relationships between tectonic features and large steep-sided, sulfide-sulfate-silica deposits in the vigorously venting Endeavour hydrothermal field near the northern end of the Juan de Fuca Ridge. Location of the most massive sulfide structures appears to be controlled by intersections of ridge-parallel normal faults and other fracture-fissure sets that trend oblique to, and perpendicular to the overall structural fabric of the axial valley. As presently mapped, the field is about 200 by 400 m on a side and contains at least 15 large (> 1,000 m[sup 3]) sulfide edifices and many tens of smaller, commonly inactive, sulfide structures. The larger sulfide structures are also the most vigorously venting features in the field; they are commonly more than 30 m in diameter and up to 20 m in height. Maximum venting temperatures of 375[degrees]C are associated with the smaller structures in the northern portion of the field are consistently 20[degrees]-30[degrees]C lower. Hydrothermal output from individual active sulfide features varies from no flow in the lower third of the edifice to vigorous output from fracture-controlled black smoker activity near the top of the structures. Two types of diffuse venting in the Endeavour field include a lower temperature 8[degrees]-15[degrees]C output through colonies of large tubeworms and 25[degrees]-50[degrees]C vent fluid that seems to percolate through the tops of overhanging flanges. The large size and steep-walled nature of these structures evidently results from sustained venting in a mature hydrothermal system, coupled with dual mineral depositional mechanisms involving vertical growth by accumulation of chimney sulfide debris and lateral growth by means of flange development.

  10. Detailed heat flow measurements over the Juan de Fuca ridge system

    SciTech Connect

    Davis, E.E.; Lister, C.R.B.; Wade, U.S.; Hyndman, R.D.

    1980-01-10

    Eleven detailed profiles of heat flow measurements have been completed over young oceanic crust of the Juan de Fuca ridge system. Individual measurements were spaced typically 0.4--1 km apart along multiple-penetration lines from 3 to 20 km in total length, and each measurement was located with respect to structural and sedimentary features by simultaneous seismic reflection profiling. In all cases, the average heat flow is well below that predicted by simple conductivity cooled spreading models even when the sediment cover is thick and the nearest basement outcrop is 15 km away. This disparity is attributed to ventilated convective circulation of water in the crust. Large heat flow variability is common along all profiles. Variations are present at two scales. Small-scale variations (from 1 km to a few kilometers between significant heat flow maxima), present in the younger profiles, probably reflect the influence of local venting and permeability variations on permeable layer cellular convection. Large-scale variations (10--20 km between significant heat flow maxima), present in all profiles, may reflect the influence of regional circulation driven by cold water recharge at isolated basement outcrops. Laboratory experimental data indicate that normal celluar convection can coexist with larger-scale bilateral flows, so that there is no simple way to extract the permeable layer thickness from the surface heat flow data. There is a considerable reduction in the amplitude of small-scale heat flow variability over the range of crustal age studied (0.1x12.5 m.y.). This is probably caused by the thermal filtering effects of the sediment cover which increases from about 50 m near the ridge crests to over 700 m on the flanks.

  11. Microbiological characterization of post-eruption "snowblower" vents at Axial Seamount, Juan de Fuca Ridge.

    PubMed

    Meyer, Julie L; Akerman, Nancy H; Proskurowski, Giora; Huber, Julie A

    2013-01-01

    Microbial processes within the subseafloor can be examined during the ephemeral and uncommonly observed phenomena known as snowblower venting. Snowblowers are characterized by the large quantity of white floc that is expelled from the seafloor following mid-ocean ridge eruptions. During these eruptions, rapidly cooling lava entrains seawater and hydrothermal fluids enriched in geochemical reactants, creating a natural bioreactor that supports a subseafloor microbial "bloom." Previous studies hypothesized that the eruption-associated floc was made by sulfide-oxidizing bacteria; however, the microbes involved were never identified. Here we present the first molecular analysis combined with microscopy of microbial communities in snowblower vents from samples collected shortly after the 2011 eruption at Axial Seamount, an active volcano on the Juan de Fuca Ridge. We obtained fluid samples and white flocculent material from active snowblower vents as well as orange flocculent material found on top of newly formed lava flows. Both flocculent types revealed diverse cell types and particulates when examined by phase contrast and scanning electron microscopy (SEM). Distinct archaeal and bacterial communities were detected in each sample type through Illumina tag sequencing of 16S rRNA genes and through sequencing of the sulfide oxidation gene, soxB. In fluids and white floc, the dominant bacteria were sulfur-oxidizing Epsilonproteobacteria and the dominant archaea were thermophilic Methanococcales. In contrast, the dominant organisms in the orange floc were Gammaproteobacteria and Thaumarchaeota Marine Group I. In all samples, bacteria greatly outnumbered archaea. The presence of anaerobic methanogens and microaerobic Epsilonproteobacteria in snowblower communities provides evidence that these blooms are seeded by subseafloor microbes, rather than from microbes in bottom seawater. These eruptive events thus provide a unique opportunity to observe subseafloor microbial

  12. Upper crustal seismic velocity structure and microearthquake depths at the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Barclay, Andrew H.; Wilcock, William S. D.

    2004-01-01

    We present the results of a study to invert microearthquake and explosive shot data from the Endeavour segment of the intermediate-spreading Juan de Fuca Ridge. The average isotropic P wave velocity structure, derived from the shot data, in the uppermost 1.5 km of the oceanic crust is characterized by an increase with age of ˜8% from the axis to at least 0.5 Ma, that is attributed to the sealing of layer 2A porosity by hydrothermal processes. Superimposed on this variation are axis-parallel, 2-km-wide, alternating bands of high and low velocity with a peak-to-peak variation of 5-12%. High and low velocities away from the axis correspond to bathymetric trenches and ridges, respectively and are likely due to variations in layer 2A thickness. P wave azimuthal anisotropy is present in the data that is best fit with a model of 9% anisotropy at 750 m depth, decreasing to 1% at 3 km depth and is likely due to the preferential alignment of vertical cracks and fissures in the along-axis direction. Anisotropy and velocity heterogeneity are coupled; anisotropy alone may explain the form but not the magnitude of the axis-parallel bands. There are strong trade-offs between the hypocentral depths of microearthquakes and the P and S wave velocity structures. Changing the mean hypocentral depth by up to 0.5 km leads to only modest increases in the travel time RMS but the resulting velocity models appear more feasible when the earthquakes are forced deeper than when they are forced shallower.

  13. Frequently Shifting Magma Sources at Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Woodcock, J.; Gill, J.; Ramos, F.; Michael, P.

    2007-12-01

    Different mantle sources and magma batches contribute to crustal growth over short temporal and spatial scales at the 10-km-long summit of the Endeavour segment of the intermediate spreading rate Juan de Fuca Ridge. Based on analyses of >275 basalts collected by submersible, about twenty "chemo-stratigraphic units" have been identified and mapped. Each reflects a different combination of mantle sources, differentiation path, and mixing history. Each represents a different filling of a magma chamber and most include a range in differentiation. Most occur within the <1 km-wide axial valley that is thought to be <10 Ka in age. The maximum along-strike length of any one unit is ~2 km. The flanking ridges differ from each other and from most of the axis in their uppermost basalts. The maximum extent of fractional crystallization within any single chemostratigraphic unit is about 30%; more fractionated magmas do not erupt, or mix in the chamber with subsequent magma batches. Two types of enriched basalts are recognized. E-MORB is enriched in K, LREE, and Nb, and depleted in Y+HREE, but is similar isotopically to axial N-MORB. We attribute it to low degree deep melting of damp peridotite. In contrast, although T-MORB has K/Ti ratios intermediate between N- and E-MORB, this is because of preferential enrichment in HFSE. Its Pb, Sr, Nd, and Hf isotope ratios are maxima, approaching those of FOZO. It is attributed to low degree melting of a chemically distinct component, perhaps pyroxenitic. Both enriched components lie on the same Pb isotope chords so are thought to be similar in age and origin.

  14. Pressures of Partial Crystallization of Magmas from the Juan de Fuca Ridge: Implications for Crustal Accretion

    NASA Astrophysics Data System (ADS)

    Scott, J. L.; Barton, M.

    2010-12-01

    Plate spreading at the mid-ocean ridges is accompanied by intrusion of dikes and eruption of lava along the ridge axis. It has been suggested that the depth of magma chambers that feed the flows and dikes is related to the rate of spreading. As part of a larger effort to examine this hypothesis, we determined the depths of magma chambers beneath the intermediate spreading Juan de Fuca Ridge (JdF) which extends from the Blanco fracture zone at about 44.5 degrees North to the Triple junction of the JdF, Nootka Fault, and the Socanco fracture zone at 48.7 degrees North. Pressures of partial crystallization were determined by comparing the compositions of natural liquids (glasses) with those of experimental liquids in equilibrium with olivine, plagioclase, and clinopyroxene at different pressures and temperatures using the method described by Kelley and Barton (2008). Chemical analyses mid-ocean ridge basalts glasses sampled from along the JdF were used as liquid compositions. Samples with anomalous chemical compositions and samples that yielded pressures associated with unrealistically large uncertainties were filtered out of the database. The calculated pressures for the remaining 533 samples were used to calculate the depths of partial crystallization and to identify the likely location of magma chambers. Preliminary results indicate that the pressure of partial crystallization decreases from 2 to 1±0.5 kbars from the Blanco fracture zone to the north along the Cleft segment of the ridge. Calculated pressures remain approximately constant at 0.87±0.53 kbars along ridge segments to the north of the Cleft. These low pressures for the remaining segments of the ridge are interpreted to indicate magma chambers at depths of 1.3-4.9 km and agree reasonably well with the depths of seismically imaged tops of axial magma chambers (2-3 km) (Canales et al 2009). The higher pressures obtained for lavas erupted along the Cleft segment of the JdF agree very well with recent

  15. Microbial diversity within Juan de Fuca ridge basement fluids sampled from oceanic borehole observatories

    NASA Astrophysics Data System (ADS)

    Jungbluth, S.; Bowers, R.; Lin, H.; Hsieh, C.; Cowen, J. P.; Rappé, M.

    2012-12-01

    Three generations of sampling and instrumentation platforms known as Circulation Obviation Retrofit Kit (CORK) observatories affixed to Ocean Drilling Program (ODP) and Integrated Ocean Drilling Program (IODP) boreholes are providing unrivaled access to fluids originating from 1.2-3.5 million-years (Myr) old basaltic crust of the eastern flank of the Juan de Fuca ridge. Borehole fluid samples obtained via a custom seafloor fluid pumping and sampling system coupled to CORK continuous fluid delivery lines are yielding critical insights into the biogeochemistry and nature of microbial life inhabiting the sediment-covered basement environment. Direct microscopic enumeration revealed microbial cell abundances that are 2-41% of overlying bottom seawater. Snapshots of basement fluid microbial diversity and community structure have been obtained through small subunit ribosomal RNA (SSU rRNA) gene cloning and sequencing from five boreholes that access a range of basement ages and temperatures at the sediment-basement interface. SSU rRNA gene clones were derived from four different CORK installations (1026B, 1301A, 1362A, and 1362B) accessing relatively warmer (65°C) and older (3.5 Myr) ridge flank, and one location (1025C) accessing relatively cooler (39°C) and younger (1.2 Myr) ridge flank, revealing that warmer basement fluids had higher microbial diversity. A sampling time-series collected from borehole 1301A has revealed a microbial community that is temporally variable, with the dominant lineages changing between years. Each of the five boreholes sampled contained a unique microbial assemblage, however, common members are found from both cultivated and uncultivated lineages within the archaeal and bacterial domains, including meso- and thermophilic microbial lineages involved with sulfur cycling (e.g Thiomicrospira, Sulfurimonas, Desulfocapsa, Desulfobulbus). In addition, borehole fluid environmental gene clones were also closely related to uncultivated lineages

  16. Scales of magmatic replenishment and differentiation on an intermediate spreading mid-ocean ridge segment: Endeavour, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Dreyer, B. M.; Gill, J.; Clague, D. A.

    2016-12-01

    The aggregate chemistry of mid-ocean ridge (MOR) basalts cannot be produced by fractional crystallization alone. Recent modeling suggests that repeated magmatic replenishment is required (O'Neill and Jenner, 2012; Coogan and O'Hara, 2015; Shorttle, 2015). Does this inference hold when considering recent advancements in characterizing geological/volcanological context, geochemical variability, and temporal parameters on the scale of individual lava units (Rubin et al., 2009)? We evaluate the scales of magmatic replenishment through examination of compositionally diverse lavas from the Endeavour segment of the Juan de Fuca (JdF) MOR interpreted as comagmatic or coeruptive based on robust geological (Clague et al., 2014), geochemical (Gill et al., 2016), and geochronological (Jamieson et al., 2013; Clague et al., 2014) evidence. This approach is similar to that used for historical MOR eruptions (Rubin et al., 2001). We identified 15 "chemomagmatic" units that are spatially proximate and chemically relatable and separable that collectively represent eruptions since 11ka. Some units may be single lava flows. Other units appear to have erupted batches intermittently over hundreds to thousands of years during which chemically dissimilar lava also erupted. Melt evolution was modeled using MELTS for units with reasonably broad major element variations. Fractional crystallization models can adequately reproduce most of the major and incompatible trace element behavior observed within each unit. Consistent differences in trace element ratios between units argue against intermixing. Thus, magmatic batches typically lie within analytical resolution of fractional crystallizing systems, notwithstanding growing evidence that magmatic systems are repeatedly replenished at the segment scale. Melting and mixing of heterogeneous mantle sources are responsible for the overall compositional diversity at Endeavour. Chemomagmatic units, in contrast, reflect smaller scale processing of

  17. Southern Juan De Fuca Ridge and Escanaba Trough, Gorda Ridge: Comparison of hydrothermal deposits in sediment-free and sediment-covered ridge settings

    SciTech Connect

    Benninger, L.M.; Randolph, M.; Koski, A.; Zierenberg, R.A. )

    1990-06-01

    Southern Juan De Fuca Ridge (SJDF) is a low-relief, sediment-starved ridge axis that has a total opening rate of 6 cm/year and is characterized by lobate and brecciated sheet flows and pillows of MORB composition. Sulfide deposits form at {approximately}2,200 m water depth and are concentrated within a narrow graben centered within the ridge axial valley. Solitary and coalesced chimneys (0.25 to 12 m high) rise directly from the basalt basement and are composed predominantly of Zn sulfide accompanied by Fe and Cu-Fe sulfide and traces of Pb sulfide. Anhydrite occurs as a minor phase in some chimneys. Sulfide chimneys were formed by rapid-venting of high temperature ({approximately}285{degree}C) fluids. These acidic fluids (pH {approximately}3.5) are enriched in Cl, Na, and Ca and are depleted in Cu and Zn. In contrast to SJDF, Escanaba Trough (ET) is spreading at {approximately}2.3 cm/year and has the high relief and axial graben morphology typical of the slow-spreading Mid-Atlantic Ridge. The floor of the axial valley is buried by up to 500 m of clay and terrigenous silt. Rare basement exposures reveal unbrecciated sheet flows and pillow basalts of MORB composition. Large chimney-topped sulfide mounds up to 20 m high and hundreds of meters in extent occur at {approximately}3,250 m water depth at the base of sediment hills; sulfide veins, small chimneys, and clastic deposits occur on, and within, the sediment between hills. Two distinct sulfide types occur at ET. Pyrrhotite-rich sulfide is enriched in Fe, Cu, and As and is associated with low-velocity venting of warm (<220{degree} C) alkaline (pH {approximately}5.4) fluids that are currently depositing anhydrite and barite sinter deposits on top of the sulfide mounds.

  18. New Insights into Diking Processes from High Resolution Bathymetry of Pillow Ridges on the Juan de Fuca and Gorda Ridges

    NASA Astrophysics Data System (ADS)

    Yeo, I. A.; Clague, D. A.; Paduan, J. B.; Caress, D. W.

    2010-12-01

    Recently developed methods of acquiring high resolution bathymetry allow scientists to observe seafloor morphology at mid-ocean ridges at unprecedented resolution. We remapped the boundaries of four historic eruptions at three intermediate-rate segments of the Gorda and Juan de Fuca spreading centers and identify an additional 17 prehistoric pillow mound eruptions using 1-m resolution bathymetry. Previous studies underestimated flow volumes of the historic flows by almost an order of magnitude. We find that they range in area from 0.3 to 3.8 km2 and volume from 0.017 to 0.258 km3. Prehistoric flow areas range from 0.1 to 1.8 km2 and in volume from 0.004 to 0.158 km3. Our new estimates indicate that average eruption rates during the CoAxial and North Gorda eruptions ranged from 14,000 - 50,000 m3/hr per km of fissure and that these rates are comparable to those observed at Hawaiian fissure eruptions. Flow mapping demonstrates that eruptions do not occur continuously along the fissures, but instead form a number of discrete pillow mounds. The lack of young lavas and fissures between these mounds suggests that magma traveling though the dike is undergoing flow focusing before it reaches the surface. Two scales of flow focusing are observed at the four historic pillow ridges: irregular focusing within the dike produces discrete pillow mounds, while a finer scale focusing produces regularly spaced vents on the largest mounds. The first order mound distribution is probably due to a combination of irregular melt supply and a sinuous dike form which allows viscosity variations to develop and eventual solidification where heat loss to the dike walls is highest. The second order variation probably occurs after a steady melt supply to sections of the dike is developed as a result of fluctuations in melt supply rate, which allow the development of flow instabilities that eventually lead to flow localization.

  19. Gabbroic xenoliths and host ferrobasalt from the southern Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Dixon, Jacqueline Eaby; Clague, David A.; Eissen, Jean-Philippe

    1986-03-01

    Rare isotropic gabbroic xenoliths occur in sheet and lobate flow fragments of nearly aphyric ferrobasalt collected along a 12-km section of the southern Juan de Fuca Ridge. Xenoliths comprise ≪ 1% of the dredge contents and range in size from 1 cm3 (glomerocryst) to 240 cm3. The xenoliths have ophitic to intersertal texture with 5-50% interstitial glass of ferrobasaltic composition more evolved than the host lava. On the basis of texture and mineralogy, the xenoliths have been subdivided into three types: type I, plagioclase + olivine + glass; type II, plagioclase + augite + glass ± olivine; and type III, plagioclase + augite + olivine + glass ± pigeonite (partially inverted) + Fe-Ti oxides. Mineral and glass inclusion compositions suggest a sequence of evolution for the three xenolith types in which type I is the least evolved and type III is the most evolved. Application of a graphical pyroxene geothermometer to augite in xenolith types II and III yields crystallization temperatures of 1100°-1200°C and to host-lamellae pairs in inverted pigeonite yields subsolidus equilibrium temperatures of 1100°-1150°C. Coexisting titanomagnetite-ilmenite pairs in type III xenoliths yield temperature estimates of 1000°-1070°C and log f02 = -9.7 to -10.8. We infer that the xenoliths represent the partially crystalline "mush" boundary zone of a magma chamber based on the abundance of interstitial glass, zonation of mineral grains in the most crystalline samples, and coherence of chemical trends between interstitial glass, glass inclusions, and mineral phases. The evolved composition of the xenoliths provides evidence for the presence of melts more fractionated than the host ferrobasalt in the magma chamber. The erupted ferrobasalt is a hybrid lava formed by mixing these highly evolved melts with more primitive melts.

  20. Hydrothermal fluid composition at Middle Valley, Northern Juan de Fuca Ridge: Temporal and spatial variability

    NASA Astrophysics Data System (ADS)

    Cruse, Anna M.; Seewald, Jeffrey S.; Saccocia, Peter J.; Zierenberg, Robert

    Hydrothermal fluids were collected in July 2000 from the Dead Dog and Ore Drilling Program (ODP) Mound vent fields at Middle Valley, a sediment-covered spreading center on the northern Juan de Fuca Ridge. Measured fluid temperatures varied from 187° to 281°C in focused flow vents and 40°C in ODP Hole 1035F. Cl concentrations indicate that ODP Mound fluids undergo phase separation in the subsurface, whereas Dead Dog fluids do not. The lack of phase separation at Dead Dog is consistent with other geochemical indicators of lower subsurface temperatures. Cooling and equilibration with quartz after phase separation at the ODP Mound results in exit temperatures and silica concentrations that are indistinguishable from those at Dead Dog. The sulfur isotopic composition of aqueous ΣH2S indicates extensive reduction of seawater SO4 and leaching of basaltic sulfur at both areas. A new area of venting, which resulted from drilling operations during ODP Leg 169, was discovered on the eastern side of the ODP Mound. The fluids in the new area have compositions that are similar to those of Hole 1035H and Shiner Bock, except for lower H2 and higher H2S concentrations. These differences reflect the conversion of pyrite to pyrrhotite in the ODP Mound as fluids react with sulfide minerals during upflow. Fluid temperatures and compositions have remained constant between 1990 and 2000 indicating that subsurface reaction zone conditions did not change over this period. Near constant concentrations of sediment-derived mobile trace elements suggest that the residence time of fluids in a high-temperature reservoir exceeds 10 years.

  1. Temperature and Redox Effect on Mineral Colonization in Juan de Fuca Ridge Flank Subsurface Crustal Fluids.

    PubMed

    Baquiran, Jean-Paul M; Ramírez, Gustavo A; Haddad, Amanda G; Toner, Brandy M; Hulme, Samuel; Wheat, Charles G; Edwards, Katrina J; Orcutt, Beth N

    2016-01-01

    To examine microbe-mineral interactions in subsurface oceanic crust, we evaluated microbial colonization on crustal minerals that were incubated in borehole fluids for 1 year at the seafloor wellhead of a crustal borehole observatory (IODP Hole U1301A, Juan de Fuca Ridge flank) as compared to an experiment that was not exposed to subsurface crustal fluids (at nearby IODP Hole U1301B). In comparison to previous studies at these same sites, this approach allowed assessment of the effects of temperature, fluid chemistry, and/or mineralogy on colonization patterns of different mineral substrates, and an opportunity to verify the approach of deploying colonization experiments at an observatory wellhead at the seafloor instead of within the borehole. The Hole U1301B deployment did not have biofilm growth, based on microscopy and DNA extraction, thereby confirming the integrity of the colonization design against bottom seawater intrusion. In contrast, the Hole U1301A deployment supported biofilms dominated by Epsilonproteobacteria (43.5% of 370 16S rRNA gene clone sequences) and Gammaproteobacteria (29.3%). Sequence analysis revealed overlap in microbial communities between different minerals incubated at the Hole U1301A wellhead, indicating that mineralogy did not separate biofilm structure within the 1-year colonization experiment. Differences in the Hole U1301A wellhead biofilm community composition relative to previous studies from within the borehole using similar mineral substrates suggest that temperature and the diffusion of dissolved oxygen through plastic components influenced the mineral colonization experiments positioned at the wellhead. This highlights the capacity of low abundance crustal fluid taxa to rapidly establish communities on diverse mineral substrates under changing environmental conditions such as from temperature and oxygen.

  2. Microbial diversity within basement fluids of the sediment-buried Juan de Fuca Ridge flank.

    PubMed

    Jungbluth, Sean P; Grote, Jana; Lin, Huei-Ting; Cowen, James P; Rappé, Michael S

    2013-01-01

    Despite its immense size, logistical and methodological constraints have largely limited microbiological investigations of the subseafloor basement biosphere. In this study, a unique sampling system was used to collect fluids from the subseafloor basaltic crust via a Circulation Obviation Retrofit Kit (CORK) observatory at Integrated Ocean Drilling Program borehole 1301A, located at a depth of 2667 m in the Pacific Ocean on the eastern flank of the Juan de Fuca Ridge. Here, a fluid delivery line directly accesses a 3.5 million years old basalt-hosted basement aquifer, overlaid by 262 m of sediment, which serves as a barrier to direct exchange with bottom seawater. At an average of 1.2 × 10(4) cells ml(-1), microorganisms in borehole fluids were nearly an order of magnitude less abundant than in surrounding bottom seawater. Ribosomal RNA genes were characterized from basement fluids, providing the first snapshots of microbial community structure using a high-integrity fluid delivery line. Interestingly, microbial communities retrieved from different CORKs (1026B and 1301A) nearly a decade apart shared major community members, consistent with hydrogeological connectivity. However, over three sampling years, the dominant gene clone lineage changed from relatives of Candidatus Desulforudis audaxviator within the bacterial phylum Firmicutes in 2008 to the Miscellaneous Crenarchaeotic Group in 2009 and a lineage within the JTB35 group of Gammaproteobacteria in 2010, and statistically significant variation in microbial community structure was observed. The enumeration of different phylogenetic groups of cells within borehole 1301A fluids supported our observation that the deep subsurface microbial community was temporally dynamic.

  3. Geology and hydrothermal evolution of the Mothra Hydrothermal Field, Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Glickson, Deborah A.; Kelley, Deborah S.; Delaney, John R.

    2007-06-01

    Detailed characterization of the Mothra Hydrothermal Field, the most southern and spatially extensive field on the Endeavour Segment of the Juan de Fuca Ridge, provides new insights into its geologic and hydrothermal development. Meter-scale bathymetry, side-scan sonar imagery, and direct dive observations show that Mothra is composed of six actively venting sulfide clusters spaced 40-200 m apart. Chimneys within each cluster have similar morphology and venting characteristics, and all clusters host a combination of active and extinct sulfide structures. Black smoker chimneys venting fluids above 300°C are rare, while more common lower-temperature, diffusely venting chimneys support dense colonies of macrofauna and bacterial mat. Hydrothermal sediment and extinct sulfide debris cover 10-15 m of the seafloor surrounding each vent cluster, obscuring the underlying basaltic substrate of light to moderately sedimented pillow, lobate, sheet, and chaotic flows, basalt talus, and collapse terrain. Extinct sulfide chimneys and debris between the clusters indicate that hydrothermal flow was once more widespread and that it has shifted spatially over time. The most prominent structural features in the axial valley at Mothra are regional (020°) trending faults and fissures and north-south trending collapse basins. The location of actively venting clusters within the field is controlled by (1) localization of fluid upflow along the western boundary fault zone, and diversion of these fluids by antithetic faults to feed vent clusters near the western valley wall, and (2) tapping of residual magmatic heat in the central part of the axial valley, which drives flow beneath vent clusters directly adjacent to the collapse basins 70-90 m east of the western valley wall. These processes form the basis for a model of axial valley and hydrothermal system development at Mothra, in which the field is initiated by an eruptive-diking episode and sustained through intense microseismicity

  4. Microbial diversity within basement fluids of the sediment-buried Juan de Fuca Ridge flank

    PubMed Central

    Jungbluth, Sean P; Grote, Jana; Lin, Huei-Ting; Cowen, James P; Rappé, Michael S

    2013-01-01

    Despite its immense size, logistical and methodological constraints have largely limited microbiological investigations of the subseafloor basement biosphere. In this study, a unique sampling system was used to collect fluids from the subseafloor basaltic crust via a Circulation Obviation Retrofit Kit (CORK) observatory at Integrated Ocean Drilling Program borehole 1301A, located at a depth of 2667 m in the Pacific Ocean on the eastern flank of the Juan de Fuca Ridge. Here, a fluid delivery line directly accesses a 3.5 million years old basalt-hosted basement aquifer, overlaid by 262 m of sediment, which serves as a barrier to direct exchange with bottom seawater. At an average of 1.2 × 104 cells ml−1, microorganisms in borehole fluids were nearly an order of magnitude less abundant than in surrounding bottom seawater. Ribosomal RNA genes were characterized from basement fluids, providing the first snapshots of microbial community structure using a high-integrity fluid delivery line. Interestingly, microbial communities retrieved from different CORKs (1026B and 1301A) nearly a decade apart shared major community members, consistent with hydrogeological connectivity. However, over three sampling years, the dominant gene clone lineage changed from relatives of Candidatus Desulforudis audaxviator within the bacterial phylum Firmicutes in 2008 to the Miscellaneous Crenarchaeotic Group in 2009 and a lineage within the JTB35 group of Gammaproteobacteria in 2010, and statistically significant variation in microbial community structure was observed. The enumeration of different phylogenetic groups of cells within borehole 1301A fluids supported our observation that the deep subsurface microbial community was temporally dynamic. PMID:22791235

  5. Microbial Primary Productivity in Hydrothermal Vent Chimneys at Middle Valley, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Olins, H. C.; Rogers, D.; Frank, K. L.; Girguis, P. R.; Vidoudez, C.

    2012-12-01

    Chemosynthetic primary productivity supports hydrothermal vent ecosystems, but the extent of that productivity has not been well measured. To examine the role that environmental temperature plays in controlling carbon fixation rates, and to assess the degree to which microbial community composition, in situ geochemistry, and mineralogy influence carbon fixation, we conducted a series of shipboard incubations across a range of temperatures (4, 25, 50 and 90°C) and at environmentally relevant geochemical conditions using material recovered from three hydrothermal vent chimneys in the Middle Valley hydrothermal vent field (Juan de Fuca Ridge). Net rates of carbon fixation (CFX) were greatest at lower temperatures, and were similar among structures. Rates did not correlate with the mineralogy or the geochemical composition of the high temperature fluids at each chimney. No obvious patterns of association were observed between carbon fixation rates and microbial community composition. Abundance of selected functional genes related to different carbon fixation pathway exhibited striking differences among the three study sites, but did not correlate with rates. Natural carbon isotope ratios implicate the Calvin Benson Bassham Cycle as the dominant mechanism of primary production in these systems, despite the abundance of genes related to other pathways (and presumably some degree of activity). Together these data reveal that primary productivity by endolithic communities does not exhibit much variation among these chimneys, and further reveal that microbial activity cannot easily be related to mineralogical and geochemical assessments that are made at a coarser scale. Indeed, the relationships between carbon fixation rates and community composition/functional gene abundance were also likely obfuscated by differences in scale at which these measurements were made. Regardless, these data reveal the degree to which endolithic, anaerobic carbon fixation contributes to

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

    NASA Astrophysics Data System (ADS)

    Jamieson, John W.; Hannington, Mark D.; Clague, David A.; Kelley, Deborah S.; Delaney, John R.; Holden, James F.; Tivey, Margaret K.; Kimpe, Linda E.

    2013-07-01

    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.

  7. Temperature and Redox Effect on Mineral Colonization in Juan de Fuca Ridge Flank Subsurface Crustal Fluids

    PubMed Central

    Baquiran, Jean-Paul M.; Ramírez, Gustavo A.; Haddad, Amanda G.; Toner, Brandy M.; Hulme, Samuel; Wheat, Charles G.; Edwards, Katrina J.; Orcutt, Beth N.

    2016-01-01

    To examine microbe-mineral interactions in subsurface oceanic crust, we evaluated microbial colonization on crustal minerals that were incubated in borehole fluids for 1 year at the seafloor wellhead of a crustal borehole observatory (IODP Hole U1301A, Juan de Fuca Ridge flank) as compared to an experiment that was not exposed to subsurface crustal fluids (at nearby IODP Hole U1301B). In comparison to previous studies at these same sites, this approach allowed assessment of the effects of temperature, fluid chemistry, and/or mineralogy on colonization patterns of different mineral substrates, and an opportunity to verify the approach of deploying colonization experiments at an observatory wellhead at the seafloor instead of within the borehole. The Hole U1301B deployment did not have biofilm growth, based on microscopy and DNA extraction, thereby confirming the integrity of the colonization design against bottom seawater intrusion. In contrast, the Hole U1301A deployment supported biofilms dominated by Epsilonproteobacteria (43.5% of 370 16S rRNA gene clone sequences) and Gammaproteobacteria (29.3%). Sequence analysis revealed overlap in microbial communities between different minerals incubated at the Hole U1301A wellhead, indicating that mineralogy did not separate biofilm structure within the 1-year colonization experiment. Differences in the Hole U1301A wellhead biofilm community composition relative to previous studies from within the borehole using similar mineral substrates suggest that temperature and the diffusion of dissolved oxygen through plastic components influenced the mineral colonization experiments positioned at the wellhead. This highlights the capacity of low abundance crustal fluid taxa to rapidly establish communities on diverse mineral substrates under changing environmental conditions such as from temperature and oxygen. PMID:27064928

  8. Preliminary Analysis of Multibeam, Subbottom, and Water Column Data Collected from the Juan de Fuca Plate and Gorda Ridge Earthquake Swarm Sites, March-April 2008.

    NASA Astrophysics Data System (ADS)

    Merle, S. G.; Dziak, R. P.; Embley, R. W.; Lupton, J. E.; Greene, R. R.; Chadwick, W. W.; Lilley, M.; Bohnenstiehl, D. R.; Braunmiller, J.; Fowler, M.; Resing, J.

    2008-12-01

    Two oceanographic expeditions were undertaken in the northeast Pacific during April and September of 2008 to collect a variety of scientific data at the sites of intense earthquake swarms that occurred from 30 March to 9 April 2008. The earthquake swarms were detected by the NOAA/PMEL and US Navy SOSUS hydrophone system in the northeast Pacific. The first swarm occurred within the central Juan de Fuca Plate, ~280 km west of the Oregon coast and ~70 km north of the Blanco Transform Fault Zone (BTFZ). Time history of the events indicate this swarm was not a typical mainshock-aftershock sequence, and was the largest SOSUS detected swarm within the intraplate. This intraplate swarm activity was followed by three distinct clusters of earthquakes located along the BTFZ. Two of the clusters, which began on 10 and 12 April, were initiated by MW 5+ earthquakes suggesting these were mainshock-aftershock sequences, and the number of earthquakes on the BTFZ were small relative to the intraplate swarm. On 22 April, another intense earthquake swarm began on the northern Gorda Ridge segment adjacent to the BTFZ. The Gorda swarm produced >1000 SOSUS detected earthquakes over a five-day duration, with activity distributed between the mid-segment high and the ridge-transform intersection. This swarm was of special interest because of previous magmatic activity near its location in 1996. Overall, the March-April earthquake activity showed an interesting spatio-temporal progression, beginning at the intraplate, to the transform, then to a spreading event at the ridge. This pattern once again demonstrates the Juan de Fuca plate is continually moving and converging with North America at the Cascadia Subduction Zone. As the initial swarm was not focused on the ridge crest, it was not interpreted as a significant eruptive event, and we did not advocate a large-scale Ridge2000 response effort. The earthquake activity, however, did have an unusual character and therefore a short (four

  9. Uniformity and diversity in the composition of mineralizing fluids from hydrothermal vents on the southern Juan de Fuca Ridge.

    USGS Publications Warehouse

    Philpotts, J.A.; Aruscavage, P. J.; Von Damm, Karen L.

    1987-01-01

    Abundances of Li, Na, K, Rb, Ca, Sr, Ba, Mn, Fe, Zn, and Si have been determined in fluid samples from 7 vents located in three areas on the southern Juan de Fuca Ridge. The hydrothermal component estimated from the Mg contents of the samples ranges from 7% to 76%. Concentrations of Fe and Si, among other elements, in acid-stabilized solutions appear to be generally representative of the parental hydrothermal fluids, but some Zn determinations and most Ba values appear to be too low.-from Authors

  10. Monitoring Change on Hydrothermal Edifices by Photogrammetric Time Series: Case Studies from the Endeavour Segment (Juan de Fuca Ridge)

    NASA Astrophysics Data System (ADS)

    Heesemann, M.; Kwasnitschka, T.; Kelley, D. S.; Mihaly, S. F.

    2015-12-01

    High-resolution photogrammetric surveys derived from ROV or AUV imagery yield seafloor geometry at centimeter resolution with full color texture while modeling overhangs and crevasses, generating vastly more detailed terrain models compared to most acoustic methods. The models furthermore serve as geographic reference frames for localized studies. Repetitive surveys consequently facilitate the precise, quantitative study of edifice buildup and erosion as well as the development of the biological habitat. We compare data gathered by the Ocean Networks Canada maintenance cruises with earlier surveys at two sites (Mothra, Main Endeavour Field) along the Endeavour Segment of the Juan de Fuca Ridge.

  11. Low-Temperature Weathering of Hydrothermal Sulfide Minerals at Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Toner, B. M.; Santelli, C. M.; Rogers, D. R.; Edwards, K. J.

    2005-12-01

    Phylogenetically and metabolically diverse microbial communities have been identified in several deep ocean settings, including the seafloor at mid-ocean ridge flanks. The microorganisms present in these environments appear to participate in geochemical processes, such as mineral dissolution and mineral precipitation, over geological time scales. The purpose of our study was to characterize the initial alteration products and geochemical signatures of hydrothermal sulfide minerals exposed at the seafloor near hydrothermal venting at the Juan de Fuca Ridge, and to identify those weathering products specific to microbial metabolism. Biominerals are notoriously difficult to characterize, often possessing structural defects and small particle size, and are commonly only one of many constituents within natural particles and biofilms. Given these challenges, focused beam X-ray absorption spectroscopic (XAS) techniques provide important capabilities for identifying microbial weathering products by (1) effectively simplifying the chemistry of the sample through examination of chemically discrete areas, (2) identifying co-occurring elements of interest, (3) providing complementary structural information from co-occurring elements, and (4) examining samples at the natural micro- to millimeter spatial scale of mineralogical heterogeneity. We collected 2-dimensional X-ray fluorescence (XRF) elemental maps of experimentally weathered sulfide minerals in cross section. For these experiments, fresh, unweathered sulfide minerals were incubated at low temperatures for a two month period and then collected for mineralogical and microbiological analysis. Previous work on these samples showed that abundant Fe oxide minerals (principally 2-line ferrihydrite) accumulated during weathering, and correlated with dense cell aggregates at the mineral surface. Additionally, a diverse collection of Fe oxidizing bacteria were cultured from these and other similar samples incubated or collected

  12. Porosity estimates of the upper crust in the Endeavour segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Kim, E.; Toomey, D. R.; Hooft, E. E. E.; Wilcock, W. S. D.; Weekly, R. T.; Lee, S. M.; Kim, Y.

    2015-12-01

    We estimate upper crustal porosity variations using the differential effective medium (DEM) theory to interpret the observed seismic velocity variations for the Endeavour segment of the Juan de Fuca Ridge, an intermediate spreading center [Weekly et al., 2014]. We use six P-wave vertical velocity profiles averaged within 5 km × 10 km areas to estimate the porosity at depths from 0.4 km to 2 km. The profile regions cover on-axis, east and west flanks of the central Endeavour segment and three regions of the segment ends including the Endeavour-West Valley (E-WV) and the Cobb overlapping spreading centers (OSCs) and the relict Middle Valley. At the segment center, our calculated porosities on-axis and on the east and west flanks agree well with the apparent bulk porosities measured in Hole 504B at intermediate-spreading Costa Rica Rift [Becker, 1990] and decrease from 5-15% to 2-7% from 0.5 km to 1 km depth and seal by 2 km depth. At all depths, our calculated porosities on the east and west flanks are lower than those on-axis by ~1.3-3%. This indicates the infilling of cracks by mineral precipitation associated with near-axis hydrothermal circulation [Newman et al., 2011]. At the segment ends, upper crustal velocities are lower than those in the segment center at depths < 2 km. These lower velocities are attributed to higher porosities (10-20% at 0.4 km decreasing to 3-6% at 2 km depth). This may indicate that fracturing in the OSCs strongly affects porosity at shallow depths. Between 0.7 km and 1 km, porosities estimated in all regions using pore aspect ratios of 0.05, 0.1 and 0.2 are higher than those from Hole 504B indicating that the aspect ratio of cracks may be smaller than 0.05. There also appears to be a spreading rate dependence to upper crustal porosity structure. On-axis at the Endeavour segment, the calculated porosities from 0.4 km to 2 km are higher than those at the Lucky Strike segment, a slow spreading center [Seher et al., 2010]. Specifically at 2

  13. High-Resolution Imaging of Axial Volcano, Juan de Fuca ridge.

    NASA Astrophysics Data System (ADS)

    Arnulf, A. F.; Harding, A. J.; Kent, G. M.

    2014-12-01

    To date, seismic experiments have been key in our understanding of the internal structure of volcanic systems. However, most experiments, especially subaerial-based, are often restricted to refraction geometries with limited numbers of sources and receivers, and employ smoothing constraints required by tomographic inversions that produce smoothed and blurry images with spatial resolutions well below the length scale of important features that define these magmatic systems. Taking advantage of the high density of sources and receivers from multichannel seismic (MCS) data should, in principle, allow detailed images of velocity and reflectivity to be recovered. Unfortunately, the depth of mid-ocean ridges has the detrimental effect of concealing critical velocity information behind the seafloor reflection, preventing first arrival travel-time tomographic approaches from imaging the shallowest and most heterogeneous part of the crust. To overcome the limitations of the acquisition geometry, here we are using an innovative multistep approach. We combine a synthetic ocean bottom experiment (SOBE), 3-D traveltime tomography, 2D elastic full waveform and a reverse time migration (RTM) formalism, and present one of the most detailed imagery to date of a massive and complex magmatic system beneath Axial seamount, an active submarine volcano that lies at the intersection of the Juan de Fuca ridge and the Cobb-Eickelberg seamount chain. We present high-resolution images along 12 seismic lines that span the volcano. We refine the extent/volume of the main crustal magma reservoir that lies beneath the central caldera. We investigate the extent, volume and physical state of a secondary magma body present to the southwest and study its connections with the main magma reservoir. Additionally, we present a 3D tomographic model of the entire volcano that reveals a subsiding caldera floor that provides a near perfect trap for the ponding of lava flows, supporting a "trapdoor

  14. Diffuse heat flux on the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Pruis, M. J.; Johnson, H. P.; Hautala, S. L.; Garcia-Berdeal, I.

    2001-12-01

    While determining the proportion the total heat budget attributable to diffuse flow has proven difficult, previous estimates have indicated that up to 90% of the total heat loss at a mid-ocean ridge may be by diffuse flow. A key problem in estimating diffuse flow can be traced back to the lack of a large-scale systematic survey of diffuse venting sites over a sufficiently large surfical area to characterize fluid crustal circulation paths and, subsequently, a representative number of point measurements of the diffuse heat flux within the survey area, to integrate over the entire survey area. In July, 2001, we concluded a two-year field program to the Endeavour Segment of the Juan de Fuca Ridge where we made quantitative measurements of diffuse heat flux over a large area of the axial valley floor including regions surrounding the large / active Main Endeavour and High Rise vent fields and the diffusely-venting Clam Bed, Beach and the southern New Field sites. Detailed bathymetric mapping and a large-scale acoustic scintillation (AST) experiment over the entire segment (between the Beach hydrothermal site to the south and the active High Rise vent field to the north) mapped the distribution, areal coverage and frequency of low-temperature diffuse vents. Measurements of vertical heat flux require determination of both near-bottom temperature gradients and fluid motions to constrain possible thermal models. Using 20 MAVS-3 three-axis acoustic current meters designed specifically for co-registered thermal boundary temperature measurements (in the bottom 1m), we have made thirty single-point measurements of the diffuse heat flux over time scales of days to one year. In this presentation we will show preliminary diffuse heat flux estimates and discuss possible implications for the partitioning of the total heat output in areas near large high-temperature hydrothermal fields and smaller, more isolated vent fields. We will also discuss the degree of variability of the

  15. Precipitation and growth of barite within hydrothermal vent deposits from the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Jamieson, John William; Hannington, Mark D.; Tivey, Margaret K.; Hansteen, Thor; Williamson, Nicole M.-B.; Stewart, Margaret; Fietzke, Jan; Butterfield, David; Frische, Matthias; Allen, Leigh; Cousens, Brian; Langer, Julia

    2016-01-01

    Hydrothermal vent deposits form on the seafloor as a result of cooling and mixing of hot hydrothermal fluids with cold seawater. Amongst the major sulfide and sulfate minerals that are preserved at vent sites, barite (BaSO4) is unique because it requires the direct mixing of Ba-rich hydrothermal fluid with sulfate-rich seawater in order for precipitation to occur. Because of its extremely low solubility, barite crystals preserve geochemical fingerprints associated with conditions of formation. Here, we present data from petrographic and geochemical analyses of hydrothermal barite from the Endeavour Segment of the Juan de Fuca Ridge, northeast Pacific Ocean, in order to determine the physical and chemical conditions under which barite precipitates within seafloor hydrothermal vent systems. Petrographic analyses of 22 barite-rich samples show a range of barite crystal morphologies: dendritic and acicular barite forms near the exterior vent walls, whereas larger bladed and tabular crystals occur within the interior of chimneys. A two component mixing model based on Sr concentrations and 87Sr/86Sr of both seawater and hydrothermal fluid, combined with 87Sr/86Sr data from whole rock and laser-ablation ICP-MS analyses of barite crystals indicate that barite precipitates from mixtures containing as low as 17% and as high as 88% hydrothermal fluid component, relative to seawater. Geochemical modelling of the relationship between aqueous species concentrations and degree of fluid mixing indicates that Ba2+ availability is the dominant control on mineral saturation. Observations combined with model results support that dendritic barite forms from fluids of less than 40% hydrothermal component and with a saturation index greater than ∼0.6, whereas more euhedral crystals form at lower levels of supersaturation associated with greater contributions of hydrothermal fluid. Fluid inclusions within barite indicate formation temperatures of between ∼120 °C and 240 °C during

  16. Small-Scale Mantle Heterogeneities Beneath the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Harris, C. R.; Gill, J.; Woodcock, J.; Anderson, R.

    2008-12-01

    The Endeavour segment of the Juan de Fuca Ridge samples at least two different geochemical heterogeneities unrelated to adjacent hot spots. One is FOZO-like in isotopes and HFSE-rich. Another is K+LREE-rich. Both are sampled randomly in short spatial (few-km) and temporal succession through separate MORB melting events, but the FOZO-like MORB is restricted to axial magmas that rise along a major fault and by-pass the axial magma chamber. The large geochemical diversity and high density of submersible-collected samples creates opportunity for constraining melting processes and mantle dynamics beneath an intermediate spreading-rate ridge. Basalts from the Endeavour Axial Ridge Volcano (EARV) can be divided into N-type (normal) MORBs (K2O/TiO2 < 0.15), transitional, or T-MORBs (K2O/TiO2 = 0.15 - 0.25), and enriched, or E-MORBs (K2O/TiO2 > 0.25). N-MORBs have highest Zr/Nb and E-MORBs the lowest Zr/Nb. Recently we discovered the most trace element depleted N- MORB yet at Endeavour. This sample originates from the base of the western wall of the axial valley south of the Mothra vent field, located in the southern-most part of the EARV. However, none of the samples are as depleted as those from the sea floor beyond the ridge flanks or from the Heckle Seamounts to the north. Two subgroups of N-MORBs and three subgroups of T-MORBs are defined by consistent major and trace element characteristics. For example, T1 MORBs have the lowest SiO2; the T2 group has the lowest Na2O and higher Fe8 than T3. Trace element differences among the various groups can not be explained by crystal fractionation alone. Pb isotopes do not correlate with K2O/TiO2. T1 MORBs have the highest 206Pb/204Pb ratios and T3 MORBs generally have the lowest 206Pb/204Pb and lowest 143Nd/144Nd ratios. Pb isotopes of bulk rocks and sulfides define an array beneath the Northern Hemispheric Reference Line. The sulfide data (LaBonte et al., 2006; Cook, 1994; Tivey and Delaney, 1985) indicate deposition from

  17. Endeavour Segment, Juan de Fuca Ridge, Integrated Studies Site (ISS) Update and Opportunities

    NASA Astrophysics Data System (ADS)

    Butterfield, D.; Ridge Community

    2003-12-01

    The Ridge 2000 (R2K) Integrated Studies bull's eye on the Juan de Fuca Ridge is focused on the Main Endeavour hydrothermal field, located on the central portion of the Endeavour Segment. This vent field is one of the most vigorously venting systems along the global mid-ocean ridge spreading network, hosting at least 18 large sulfide structures that contains more than100 smokers. Prior to a magmatic event in 2000 some of the edifices had been venting 380C, volatile-rich fluids with extremely low chlorinities for a decade. In addition to the Main Endeavour Field there are four other known high temperature vent fields spaced approximately 2 kilometers apart along the segment (with hints of more) and abundant areas of diffuse flow, both nearby and distal to the high temperature venting. Diffuse flow from the structures and from a variety of basaltic-hosted sites provides rich habitats abundant with microbial and macrofaunal communities. There are well-developed gradients in volatile concentrations along axis that may reflect influence from a sedimentary source to the north, and high chlorinity fluids vent from the most southern (Mothra) and northern fields (Sasquatch). Twenty years of research have laid a firm base for the 5-year plans of R2K at this site, which include examining the response of this segment to perturbations induced by tectonic and magmatic events, identification of the reservoirs, fluxes, and feedbacks of mass and energy at this site, and predictive modeling coupled with field observations. Since designation as an IS site, high-resolution bathymetric mapping (EM300) and an extensive multi-channel seismic survey have been conducted along the entire segment. Smaller focused areas have also been mapped at meter resolution by SM2000 sonar. Intense field programs in 2003 established the first in-situ seismic array along a mid-ocean ridge, which includes installation of a buried broadband seismometer and 7 short-period seismometers emplaced within basaltic

  18. Spatial and temporal evolution of magmatic systems beneath the Endeavor Segment, Juan de Fuca Ridge: Tectonic and petrologic constraints

    SciTech Connect

    Karsten, J.L. ); Delaney, J.R. ); Rhodes, J.M.; Liias, R.A. )

    1990-11-10

    Major and trace element data for a suite of lavas have been used to investigate the geometry and evolution of magmatic systems beneath the Endeavour Segment, Juan de Fuca Ridge. The morphology of the Endeavour Segment between the northward propagating Cobb Offset and the recently formed (<0.2 m.y.) Endeavour Offset is dominated by a shallow, rifted, elongate crestal volcano (Endeavour Ridge) that deepens along-strike into a broad, deep basin at each offset. Lavas from the current axis of the Endeavour Segment are moderately fractionated (MgO: 6-8.5 wt %) and have generally higher SiO{sub 2}, Al{sub 2}O{sub 3}, Na{sub 2}O, and K{sub 2}O, and lower FeO than lavas from south of the Cobb Offset (SOCO lavas). Incompatible trace element abundances and ratios indicate the Endeavour lavas are primarily enriched E-MORBs and T-MORBs in contrast with the SOCO lavas, which are more depleted in character. Thus, the 30-km wide Cobb Offset appears to mark a major geochemical boundary beneath the Juan de Fuca Ridge. In contrast with the Endeavour Segment axial lavas, samples from adjacent abyssal hills are more similar to the SOCO lavas in their major and trace element characteristics. These observations suggest that the parental magmas of the Endeavour Segment exhibit temporal variability, with more enriched material arriving only recently beneath the ridge axis. Pronounced compositional variability is observed at small spatial scales within the Endeavour Segment axial lavas, which does not correlate with axial morphology. Small scale heterogeneity along-strike seems incompatible with models of centralized upwelling of melts beneath the summit region of the ridge axis, with shallow lateral injection of melts to distal ends of the segment, unless these spatial variations actually reflect temporal variations in the source composition and collapse of the shallow magmatic systems toward the summit region as rift failure has progressed.

  19. Hot spot-ridge crest convergence in the northeast Pacific

    SciTech Connect

    Karsten, J.L.; Delaney, J.R. )

    1989-01-10

    Evolution of the Juan de Fuca Ridge during the past 7 m.y. has been reconstructed taking into account both the propagating rift history and migration of the spreading center in the 'absolute' (fixed hot spot) reference frame. Northwestward migration of the spreading center (at a rate of 30 km/m.y.) has resulted in progressive encroachment of the ridge axis on the Cobb Hot Spot and westward jumping of the central third of the ridge axis more recently than 0.5 Ma. Seamounts in the Cobb-Eickelberg chain are predicted to display systematic variations in morphology and petrology, and a reduction in the age contrast between the edifice and underlying crust, as a result of the ridge axis approach. Relative seamount volumes also indicate that magmatic output of the hot spot varied during this interval, with a reduction in activity between 2.5 and 4.5 Ma, compared with relatively more robust activity before and after this period. Spatial relationships determined in this reconstruction allow hypotheses relating hot spot activity and rift propagation to be evaluated. In most cases, rift propagation has been directed away from the hot spot during the time period considered. Individual propagators show some reduction in propagation rate as separation between the propagating rift tip and hot spot increases, but cross comparison of multiple propagators does not uniformly display the same relationship. No obvious correlation exists between propagation rate and increasing proximity of the hot spot to the ridge axis or increasing hot spot output. Taken together, these observations do not offer compelling support for the concept of hot spot driven rift propagation. However, short-term reversals in propagation direction at the Cobb Offset coincide with activity of the Heckle melting anomaly, suggesting that local propagation effects may be related to excess magma supply at the ridge axis.

  20. Vent Field Distribution and Evolution Along the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Kelley, D. S.; Delaney, J. R.; Lilley, M. D.; Butterfield, D. A.

    2001-12-01

    Five major vent fields have now been discovered along the Endeavour Segment of the Juan de Fuca Ridge. From the north to the south they include Sasquatch, Salty Dawg, High Rise, Main Endeavour, and Mothra. Spacing between the distinct, high-temperature fields increases from the north to the south. For example Sasquatch is located 1.6 km north of Salty Dawg and Mothra is 2.7 km south of the Main Endeavour Field. In addition to changes in spacing of the vent fields along axis there are also dramatic changes in the style, intensity, and thermal-chemical characteristics of venting. The newly discovered Sasquatch field extends for >200 m in length, and venting is limited to a few isolated, small structures that reach 284° C. Active venting is confined to the northern portion of the field. In contrast, extinct, massive sulfide edifices and oxidized sulfide talus can be followed continuously for over 200 m along a 25-30 m wide, 020 trending ridge indicating that this field was very active in the past. In contrast to the delicate active structures, older extinct structures reach at least 25 m in height and the aspect ratios are similar to active pillars in the Mothra Field 7.5 km, to the south. It is unclear if venting at this site represents rejuvenation of the field, or whether it is in a waning stage. Within Salty Dawg, vent fluid temperatures reach 296° C and vigorous venting is constrained to a few, multi-flanged edifices that reach 25 m in height and 25 m in length. The field hosts over 25 structures, oxidized sulfide is abundant, and diffuse flow is dominant. Fluid compositions and temperatures are consistent with Salty Dawg being in a waning stage of evolution. Venting intensity and incidence of venting increase dramatically at High Rise where numerous multi-flanged structures are active; temperatures reach 343° C. The most intense and active of the fields is the Main Endeavour, with at least 21 actively venting, multi-flanged edifices that contain at least 100

  1. Direct Measurements of Hydrothermal Heat Output at Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Germanovich, L. N.; di Iorio, D.; Genc, G.; Hurt, R. S.; Lowell, R. P.; Holden, J. F.; Butterfield, D. A.; Olson, E. J.

    2009-12-01

    Heat output and fluid flow are key parameters for characterizing seafloor hydrothermal systems at oceanic spreading centers. In particular, they are essential for examining partition of heat and geochemical fluxes between discrete and diffuse flow components. Hydrothermal heat output also constrains permeability of young oceanic crust and thickness of the conductive boundary layer separating hydrothermal circulation from the underlying magmatic heat source. Over the past several years, we have deployed a number of relatively simple devices to make direct measurements of focused and diffuse flow. Most recently, we have used cup anemometer and turbine flow meters to measure fluid flow and heat flux at individual high-temperature vents and diffuse flow sites. The turbine flow meter (Figure 1) includes a titanium rotor assembly housed within a stainless steel tube and supported by sapphire bearings. The device can be used at different seafloor settings for measurements of both diffuse and focused flow. The spin of the rotor blades is videotaped to acquire the angular velocity, which is a function of the flow rate determined through calibration. We report data obtained during four cruises to the Main Endeavor and High Rise vent fields, Juan de Fuca Ridge (JdFR), between 2007 and 2009. Overall more than 50 successful measurements of heat flow have been made on a variety of high-, medium-, and low-temperature hydrothermal sites on the Endeavor, Mothra, and High Rise structures. For example, the velocity of diffuse flow at Endeavor ranged from ~1 to ~10 cm/sec. The flow velocity from black smokers varied from ~10 cm/sec to ~1 m/sec, which appears to be similar to EPR 9°N. Typical measurements of heat flux obtained at JdFR ranged from ~1 kW for diffuse flow to ~1 MW for black smokers. Although it is difficult to extrapolate the data and obtain the integrated heat output for a vent field on JdFR, the data are used to characterize the heat fluxes from individual vent

  2. Magma Dynamics at Axial Seamount, Juan de Fuca Ridge, from Seafloor Deformation Data

    NASA Astrophysics Data System (ADS)

    Baumgardt, E.; Nooner, S. L.; Chadwick, W.

    2014-12-01

    Axial Seamount is located about 480 km west of the Oregon coast at the intersection of the Cobb hotspot and the Juan de Fuca Ridge. Two eruptions have been observed since routine observations began in the 1990's, one in January 1998 and the other in April 2011. Precise bottom pressure measurements have documented an inflation/deflation cycle within Axial's summit caldera. The slow inflation observed at the center of the caldera was punctuated by sudden rapid deflation of 3.2 m during the 1998 eruption and 2.4 m during the 2011 eruption. Pressure data collected in September 2013 from continuously recording bottom pressure recorders and campaign-style measurements with an ROV indicates that Axial Seamount inflated 1.57 m from April 2011 to September 2013 at an average inflation rate of 61 cm/yr, meaning it had already recovered more than 65% of the deflation from the 2011 eruption within just 2.4 years. The geometry and location of the deformation source is not well constrained by the spatially-sparse pressure data, particularly for the most recent co-eruption deflation and post-eruption inflation signals. Here, we use geodetic data collected in September 2013 to test the fit of multiple numerical models of increasing complexity. We show that for this time period (since April 2011) neither a simple point deformation source (Mogi model) nor an oblate spheroid (penny-shaped crack) provide a good fit to the data. We then use finite element models to build more complex inflation geometries, guided by recent seismically imaged magma reservoirs, in an attempt to understand the source(s) of the observed deformation pattern. The recent seismic data provide good constraints on magma reservoir geometry and show the most robust melt occurs under the southeast part of the caldera at Axial. However, previous geodetic measurements at Axial have consistently shown a deformation source near the caldera center. We use numerical modeling to attempt to reconcile these differences.

  3. Estimating Heat Transfer from Grotto Mound, NEPTUNE Canada Cabled Observatory, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Rona, P. A.; Bemis, K. G.; Xu, G.

    2012-12-01

    Heat flux is a fundamental property of a seafloor hydrothermal system that relates to magnitude of sub-seafloor heat source and biosphere conditions, to distribution and style of seafloor venting and benthic biota, to chemical flux, plume formation, and dispersal of biological matter in the water column. We are working to estimate heat flux from Grotto mound, the site of the NEPTUNE Canada Cabled Observatory in the Main Endeavour Field on the Juan de Fuca Ridge. The mound is formed of two sulfide edifices that lie between ~2190 and 2180 m isobaths: 1) an elliptical edifice with major NE-SW-trending axis ~30 m long and minor axis ~ 14 m wide (area ~ 330 m2); 2) a columnar edifice ~ 10 m in diameter and 10 m high (area ~80 m2) named the North Tower, situated across a narrow (~5 m wide) saddle (area ~40 m2) at the W end of the elliptical edifice. Several black smokers discharge relatively small plumes at the E end of the elliptical edifice. A cluster of vigorous black smokers discharge from the top of North Tower and merge to form a large plume. Patchy diffuse flow occurs in areas around all of the black smokers and in the saddle between the two edifices. We are in process of measuring heat flux from components of hydrothermal discharge on Grotto mound, as follows: 1) for smokers on the North Tower an integrated heat flux of 28-55 MW is calculated based on temperature measurements in the initial 20 m rise of the plume assuming that the highest temperatures measured are closest to those of the plume centerline ; 2) for smokers on the E end of the elliptical edifice based on measurements of flow rate from video and acoustic Doppler phase shift, video of vent diameters, and in situ temperature measurements; 3) for discharge from flanges on some chimneys based on video of flow and in situ temperature measurements; 4) for diffuse flow based on area measured by Acoustic Scintillation Thermography and direct measurements of temperature and flow rate. We are evaluating

  4. Heat flux from black smokers on the Endeavour and Cleft segments, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Ginster, Ursula; Mottl, Michael J.; von Herzen, Richard P.

    1994-03-01

    We have estimated the heat flux from black smoker vents on the Juan de Fuca Ridge to evaluate their importance for heat transfer from young oceanic crust. The velocity and temperature of smoker effluent were measured from the manned submersible Alvin within a few centimeters of vent orifices, using a turbine flowmeter with an attached temperature probe. Exit velocity was calculated from a simple plume model, and vent orifices were measured in photographs and video records. The estimated power output from smokers alone is 49 plus or minus 13 MW for the Plume site, Vent 1 and Vent 3 on the southern Cleft segment near 45 deg N; 364 plus or minus 73 MW for the main vent field on the Endeavour Segment near 48 deg N; and 122 plus or minus 61 MW for the Tubeworm field 2 km north. The estimates for the Cleft and Tubeworm fields could be too low because of undiscovered vents. These values constitute only 4% to 14% of the total advective heat flux estimated for these vent fields from measurements in the nonbuoyant plume and of diffuse flow at the seafloor, indicating that most of the heat advected at these hydrothermal vent sites is carried by diffuse rather than focused flow. Values for individual smokers vary from 0.1 to 94 MW, with an average of 6.2 MW at the Endeavour field and 3.1 MW at the Cleft field. Our estimates agree well at all scales with those of Bemis et al. (1993) based on measurements made during the same dives, in some cases simultaneously, up to 50 m high in the buoyant plume. The good agreement between the two techniques implies that little diffuse flow at either high or low temperature is incorporated into the buoyant plumes generated by smokers at these sites. Velocity-temperature measurements at vents excavated by Alvin could not be modeled successfully, suggesting that vent structures may grow in equilibrium with the force of the exiting water such that orifice size is determined by volume flux. At the Endeavour field the heat flux is focused by

  5. Seismic and Tectonic Monitoring of the Endeavour Ridge Segment—Recent and Future Expansion of Ocean Networks Canada's NEPTUNE Observatory on the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Heesemann, M.; Davis, E. E.; Scherwath, M.; Kao, H.; Coogan, L. A.; Rogers, G. C.; Wilcock, W. S. D.

    2016-12-01

    Ocean Networks Canada's (ONC) NEPTUNE observatory provides real-time access to sensors on the Endeavour Ridge Segment (Endeavour)—a focus site on the Juan de Fuca Ridge System that is complementary to one on Axial Volcano that is connected through the Ocean Observatories Initiative's (OOI) Cabled Array. While first instruments (including cameras, a short-period seismometer, and vent monitoring instruments) installed at the Main Endeavour vent field have been sending data since summer 2010, unreliable extension cables precluded continuous time-series from other nearby locations. With the successful installation of four extension cables, the summer of 2016 represents an important milestone in the instrumentation of the Endeavour Ridge Segment. We will present an overview of the data that are available in near real-time from Endeavour and new instrumentation that is scheduled for installation in 2017, and highlight first results derived from the new seismo-tectonic network now in operation. This network consists of three short-period seismometers (Mothra Field, Main Endeavour Field, Regional Circulation North), one broadband seismometer (western Ridge Flank), and four bottom pressure recorders (Mothra Field, Regional Circulation South, Main Endeavour Field, western Ridge Flank). The pressure recorders will provide both seismic and oceanographic data, and allow to measure differential vertical motion among the sites. We will also highlight a new technique to determine long period seafloor deformation from broadband seismometer mass-position measurements, using data from the Ridge Flank instrument as an example.

  6. Free-living bacterial communities associated with tubeworm (Ridgeia piscesae) aggregations in contrasting diffuse flow hydrothermal vent habitats at the Main Endeavour Field, Juan de Fuca Ridge.

    PubMed

    Forget, Nathalie L; Kim Juniper, S

    2013-04-01

    We systematically studied free-living bacterial diversity within aggregations of the vestimentiferan tubeworm Ridgeia piscesae sampled from two contrasting flow regimes (High Flow and Low Flow) in the Endeavour Hydrothermal Vents Marine Protected Area (MPA) on the Juan de Fuca Ridge (Northeast Pacific). Eight samples of particulate detritus were recovered from paired tubeworm grabs from four vent sites. Most sequences (454 tag and Sanger methods) were affiliated to the Epsilonproteobacteria, and the sulfur-oxidizing genus Sulfurovum was dominant in all samples. Gammaproteobacteria were also detected, mainly in Low Flow sequence libraries, and were affiliated with known methanotrophs and decomposers. The cooccurrence of sulfur reducers from the Deltaproteobacteria and the Epsilonproteobacteria suggests internal sulfur cycling within these habitats. Other phyla detected included Bacteroidetes, Actinobacteria, Chloroflexi, Firmicutes, Planctomycetes, Verrucomicrobia, and Deinococcus-Thermus. Statistically significant relationships between sequence library composition and habitat type suggest a predictable pattern for High Flow and Low Flow environments. Most sequences significantly more represented in High Flow libraries were related to sulfur and hydrogen oxidizers, while mainly heterotrophic groups were more represented in Low Flow libraries. Differences in temperature, available energy for metabolism, and stability between High Flow and Low Flow habitats potentially explain their distinct bacterial communities. © 2013 The Authors. Published by Blackwell Publishing Ltd.

  7. Free-living bacterial communities associated with tubeworm (Ridgeia piscesae) aggregations in contrasting diffuse flow hydrothermal vent habitats at the Main Endeavour Field, Juan de Fuca Ridge

    PubMed Central

    Forget, Nathalie L; Kim Juniper, S

    2013-01-01

    We systematically studied free-living bacterial diversity within aggregations of the vestimentiferan tubeworm Ridgeia piscesae sampled from two contrasting flow regimes (High Flow and Low Flow) in the Endeavour Hydrothermal Vents Marine Protected Area (MPA) on the Juan de Fuca Ridge (Northeast Pacific). Eight samples of particulate detritus were recovered from paired tubeworm grabs from four vent sites. Most sequences (454 tag and Sanger methods) were affiliated to the Epsilonproteobacteria, and the sulfur-oxidizing genus Sulfurovum was dominant in all samples. Gammaproteobacteria were also detected, mainly in Low Flow sequence libraries, and were affiliated with known methanotrophs and decomposers. The cooccurrence of sulfur reducers from the Deltaproteobacteria and the Epsilonproteobacteria suggests internal sulfur cycling within these habitats. Other phyla detected included Bacteroidetes, Actinobacteria, Chloroflexi, Firmicutes, Planctomycetes, Verrucomicrobia, and Deinococcus–Thermus. Statistically significant relationships between sequence library composition and habitat type suggest a predictable pattern for High Flow and Low Flow environments. Most sequences significantly more represented in High Flow libraries were related to sulfur and hydrogen oxidizers, while mainly heterotrophic groups were more represented in Low Flow libraries. Differences in temperature, available energy for metabolism, and stability between High Flow and Low Flow habitats potentially explain their distinct bacterial communities. PMID:23401293

  8. Stable isotope studies of vent fluids and chimney minerals, southern Juan de Fuca Ridge: Sodium metasomatism and seawater sulfate reduction

    SciTech Connect

    Shanks W.C. III; Seyfried W.E. Jr.

    1987-10-10

    Sulfur isotope values (delta/sup 34/S) or H/sub 2/S in vent fluids from the southern Juan de Fuca Ridge hydrothermal sites range from 4.0 to 7.4% and are variably /sup 34/S-enriched with respect to coexisting inner wall chimney sulfides. Chimney sulfides range from 1.6 to 5.7%. The chimneys consist of Fe-sphalerite zoned to inner zinc sulfide and chalcopyrite ( +- isocubanite)-pyrrhotite lining channels. Sulfide from inner walls of type A chimneys have the lightest delta/sup 34/S values. Type B chimneys (porous, unzoned, low-Fe-sphalerite) have the isotopically heaviest chimney sulfides and occur at vent sites distal to the along-axis shallow point of the ridge crest, hence distal to the magma chamber. These variations are largely ascribed to sulfate reduction by ferrous iron in the hydrothermal fluid in chimneys of substrate mounds, probably due to transitory entrainment of ambient sulfate-bearing seawater. The delta/sup 18/O values of end-member hydrothermal fluids range from 0.6 to 0.8%, significantly lower than the delta/sup 18/O values at 21 /sup 0/N vent fluids. The deltaD values of the fluid samples range from -2.5 to 0.5%. Isotopic differences from the 21 /sup 0/N fluids may be due to slightly higher water/rock ratios, approximately 1.0, in the southern Juan de Fuca Ridge hydrothermal system. Admixture of a small amount of residual brine from an earlier phase separation even may have contributed water with low deltaD values.

  9. The concentration and isotopic composition of carbon in basaltic glasses from the Juan de Fuca Ridge, Pacific Ocean

    NASA Technical Reports Server (NTRS)

    Blank, Jennifer G.; Delaney, John R.; Des Marais, David J.

    1993-01-01

    The abundance and C-13/C-12 ratios of carbon were analyzed in basaltic glass from twenty locations along the Juan de Fuca Ridge using a 3-step combustion/extraction technique. Carbon released during the first two combustion steps at 400-500 C and 600-650 C is interpreted to be secondary, and only the carbon recovered during a final combustion step at about 1200 C is thought to be indigenous to the samples. For carbon released at about 1200 C, glasses analyzed as 1-2 mm chips contained 23-146 ppm C with delta C-13 values of -4.8 to -9.3 per mil, whereas samples crushed to 38-63 microns or 63-90 microns yielded 56-103 ppm C with delta C-13 values of -6.1 to -9.2 per mil. The concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean-ridge basalts. The Juan de Fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor. Evidence of disequilibrium includes (1) a large range of carbon contents among glasses collected at similar depths, (2) a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample, and (3) a lack of correlation between vesicle abundance, carbon concentration, and depth of eruption. Variations in carbon concentration and delta C-13 ratios along the ridge do not correlate with major element chemistry. The observed relationship between carbon concentrations and delta C-13 values may be explained by late-stage, variable degrees of open-system (Rayleigh-like) degassing.

  10. The concentration and isotopic composition of carbon in basaltic glasses from the Juan de Fuca Ridge, Pacific Ocean.

    PubMed

    Blank, J G; Delaney, J R; Des Marais, D J

    1993-02-01

    The abundance and 13C/12C ratios of carbon were analyzed in basaltic glass from twenty locations along the Juan de Fuca Ridge using a 3-step combustion/extraction technique. Carbon released during the first two combustion steps at 400-500 degrees C and 600-650 degrees C is interpreted to be secondary, and only the carbon recovered during a final combustion step at approximately 1200 degrees C is thought to be indigenous to the samples. For carbon released at approximately 1200 degrees C, glasses analyzed as 1-2 mm chips contained 23-146 ppm C with delta 13C values of -4.8 to -9.3%, whereas samples crushed to 38-63 microns or 63-90 microns yielded 56-103 ppm C with delta 13C values of -6.1 to -9.2%. The concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean-ridge basalts. The Juan de Fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor. Evidence of disequilibrium includes (1) a large range of carbon contents among glasses collected at similar depths, (2) a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample, and (3) a lack of correlation between vesicle abundance, carbon concentration, and depth of eruption. Variations in carbon concentration and delta 13C ratios along the ridge do not correlate with major element chemistry. The observed relationship between carbon concentrations and delta 13C values may be explained by late-stage, variable degrees of open-system (Rayleigh-like) degassing.

  11. The concentration and isotopic composition of carbon in basaltic glasses from the Juan de Fuca Ridge, Pacific Ocean

    NASA Technical Reports Server (NTRS)

    Blank, Jennifer G.; Delaney, John R.; Des Marais, David J.

    1993-01-01

    The abundance and C-13/C-12 ratios of carbon were analyzed in basaltic glass from twenty locations along the Juan de Fuca Ridge using a 3-step combustion/extraction technique. Carbon released during the first two combustion steps at 400-500 C and 600-650 C is interpreted to be secondary, and only the carbon recovered during a final combustion step at about 1200 C is thought to be indigenous to the samples. For carbon released at about 1200 C, glasses analyzed as 1-2 mm chips contained 23-146 ppm C with delta C-13 values of -4.8 to -9.3 per mil, whereas samples crushed to 38-63 microns or 63-90 microns yielded 56-103 ppm C with delta C-13 values of -6.1 to -9.2 per mil. The concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean-ridge basalts. The Juan de Fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor. Evidence of disequilibrium includes (1) a large range of carbon contents among glasses collected at similar depths, (2) a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample, and (3) a lack of correlation between vesicle abundance, carbon concentration, and depth of eruption. Variations in carbon concentration and delta C-13 ratios along the ridge do not correlate with major element chemistry. The observed relationship between carbon concentrations and delta C-13 values may be explained by late-stage, variable degrees of open-system (Rayleigh-like) degassing.

  12. Detailed study of the Cobb offset of the Juan de Fuca ridge: evolution of a propagating rift

    SciTech Connect

    Johnson, H.P.; Karsten, J.L.; Delaney, J.R.; Davis, E.E.; Currie, R.G.; Chase, R.L.

    1983-03-10

    The Cobb Offset on the northern portion of the Juan de Fuca Ridge has been identified as the tip of a northward propagating rift (Hey and Wilson, 1982). Map compilations of magnetic and seismic data from four new cruises define the present locus of spreading and volcanism on the two ridge segments abutting the Offset and permit detailed modeling of the recent evolution within this transform zone. The axis of recent spreading on the southern ridge segment bends from the normal rdige trend (N20/sup 0/E) to a N-S trend, north of 47/sup 0/15'N. The spreading axis on the northern ridge segment generally defines a N20/sup 0/E trend, except at the southern terminus, where the spreading center is offset slightly to the east. The two spreading centers overlap by about 33 km in the Offset vicinity, and there is evidence of recent volcanism on both segments. Present ridge axis morphology exhibits a transitional sequence from a symmetrical, axial high along the more 'normal' portions of each ridge segment to a grabenlike depression as the tip is approached. The magnetic anomaly patterns observed in the Cobb Offset vicinity are not consistent with the patterns predicted by models of continuous, northward propagation. The magnetic anomaly patterns of the Brunhes Epoch require an event of rapid northward propagation about 0.7 m.y. B.P., followed by a more gradual southward propagation in the middle Brunhes Epoch; most recently, the spreading center on the southern ridge has extended northward to its present configuration. Prior to the Brunhes Epoch, modeling of the magnetic anomaly patterns does not indicate a unique solution; however, net propagation has been northward. We present alternative models for the period beginning 1.7 m.y. B.P.

  13. Variable crustal structure along the Juan de Fuca Ridge; influence of on-axis hotspots and absolute plate motions

    NASA Astrophysics Data System (ADS)

    Carbotte, S. M.; Nedimovic, M.; Canales, J. P.

    2007-12-01

    Observations of crustal structure along the Juan de Fuca Ridge (JdFR) reveal influence of on-axis hotspots and absolute motion of the spreading ridge on axial melt distribution. Multi-channel reflection seismic and bathymetric data are used to constrain axial structure and spreading history for past 4-8 Ma within 3 spreading corridors crossing Cleft, Northern Symmetric (NSymm) and Endeavour segments. Along-axis data reveal south-to-north gradients in seafloor relief, depth and presence of the crustal magma lens which indicate a warmer axial regime at Cleft segment than at the northerly NSymm and Endeavour segments. South-to-north gradients are also observed within individual ridge segments with shallower ridge axis and crustal magma lens located to the south within most segments. Cross-axis lines reveal differences in inferred crustal thickness with higher average two- way travel times (twtt) to Moho found at Cleft and Endeavour segments (2300 and 2200 msec) coincident with distinct plateau, 32 and 40 km wide. Further on the ridge flanks, Moho twtt are similar at all 3 segments (~2100 +/- 100 msec) indicating little difference in inferred crustal thickness prior to ~0.6-0.7 Ma. We attribute the recent increase in crustal production at Cleft and Endeavour segments to initiation of ridge axis-centered melt anomalies associated with the Cobb HS and the Heckle melt anomaly. Rapid along-axis channeling of the Cobb mantle anomaly, preferentially to the south to influence melt production at Cleft segment 160 km away is implied. The northwesterly absolute motion of the JdFR axis could account for preferential southward directed along-axis asthenospheric flow. The regional and within-segment scale south to north gradients in seafloor and sub- seafloor structure along the JdFR may also reflect the influence of absolute motion of the ridge axis on sub-axial melt distribution.

  14. A detailed study of the Cobb Offset of the Juan de Fuca Ridge: Evolution of a propagating rift

    NASA Astrophysics Data System (ADS)

    Johnson, H. Paul; Karsten, Jill L.; Delaney, John R.; Davis, Earl E.; Currie, Ralph G.; Chase, Richard L.

    1983-03-01

    The Cobb Offset on the northern portion of the Juan de Fuca Ridge has been identified as the tip of a northward propagating rift [Hey and Wilson, 1982]. Map compilations of magnetic and seismic data from four new cruises define the present locus of spreading and volcanism on the two ridge segments abutting the Offset and permit detailed modeling of the recent evolution within this transform zone. The axis of recent spreading on the southern ridge segment bends from the normal ridge trend (N20°E) to a N-S trend, north of 47°15'N. The spreading axis on the northern ridge segment generally defines a N20°E trend, except at the southern terminus, where the spreading center is offset slightly to the east. The two spreading centers overlap by about 33 km in the Offset vicinity, and there is evidence of recent volcanism on both segments. Present ridge axis morphology exhibits a transitional sequence from a symmetrical, axial high along the more `normal' portions of each ridge segment to a grabenlike depression as the tip is approached. The magnetic anomaly patterns observed in the Cobb Offset vicinity are not consistent with the patterns predicted by models of continuous, northward propagation. The magnetic anomaly patterns of the Brunhes Epoch require an event of rapid northward propagation about 0.7 m.y. B.P., followed by a more gradual southward propagation in the middle Brunhes Epoch; most recently, the spreading center on the southern ridge has extended northward to its present configuration. Prior to the Brunhes Epoch, modeling of the magnetic anomaly patterns does not indicate a unique solution; however, net propagation has been northward. We present alternative models for the period beginning 1.7 m.y. B.P. In the first model, the Cobb Offset has evolved by a series of northward and southward events of propagation, with net advance to the north. In the second model, stable asymmetric spreading from overlapping ridge segments has evolved into a transform fault

  15. Uniformity and diversity in the composition of mineralizing fluids from hydrothermal vents on the southern Juan de Fuca Ridge

    SciTech Connect

    Philpotts, J.A.; Aruscavage, P.J.; Von Damm, K.L.

    1987-10-10

    Abundances of Li, Ni, K, Rb, Ca, Sr, Ba, Mn, Fe, Zn, and Si have been determined in fluid samples from seven vents located in three areas on the southern Juan de Fuca Ridge. The hydrothermal component estimated from the Mg contents of the samples ranges from 7% to 76%. Concentrations of Fe and Si, among the other elements, in acid-stabilized solutions appear to be generally representative of the parental hydrothermal fluids, but some Zn determinations and most Ba values appear to be too low. Thermodynamic calculations indicate that the acidified samples remain supersaturated with respect to silica, barite, and pyrite; unacidified samples are supersaturated, in addition with respect to ZnS, FeS, and many silicate phases. Within the constraints of limited sampling there appear to be differences in fluid compositions both within and between the three vent areas. Some uniform differences in the elemental abundances predicted for hydrothermal end-member fluids might be due to inmixing of fresh seawater at depth in the hydrothermal system. The Juan de Fuca hydrothermal fluids contain more Fe but otherwise have relative elemental abundances fairly similar to those in 13 /sup 0/N (East Pacific Rise) fluids, albeit at higher levels. In contrast, fluids from 21 /sup 0/N (East Pacific Rise) and Galapagos have lower K/Rb and much lower Sr and Na abundances; these compositional features probably result from interaction of these fluids with a different mineral assemblage, possibly more mature greenstone. copyright American Geophysical Union 1987

  16. Understanding Plume Bending at Grotto Vent on the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Bemis, K. G.; Xu, G.; Rabinowitz, J.; Rona, P. A.; Jackson, D. R.; Jones, C. D.

    2011-12-01

    Our improved understanding of black smoker plume bending derives from acoustic imaging of the plume at Grotto, a 30 m diameter vent cluster in the Main Endeavour Field, Juan de Fuca Ridge. In July 2000, the VIP2000 cruise collected 15 acoustic images over 24 hours. In September 2010, the Cabled Observatory Vent Imaging Sonar (COVIS) was connected to the NEPTUNE Canada Endeavour Observatory and acquired a 29 day time series capturing plume bending in 479 independent images. Inclination and declination are extracted for one or more plumes from the acoustic images using 2D Gaussian fitting. The bending of the large plume above the northwest end of Grotto is consistent with a dominant tidal sloshing and secondary rift valley inflow based a spectral analysis of the COVIS time series compared with a spectral analysis of current data from 2.9 km north of Grotto. The smaller plume above the eastern end of Grotto behaves in a more complicated fashion as it sometimes bends towards the larger plume. The overall shape of the larger plume is highly variable: sometimes the plume just leans in the direction of the presumed ambient current; other times, the plume bends-over and, in a few cases, the plume bends in two or more directions (forming a sinusoidal shape). Several factors influence bending direction, magnitude and shape. First, for a fluctuating plume, the instantaneous plume centerline wiggles around within the time-averaged plume boundaries; this will certainly produce a "sinusoidal" shape and may be the best explanation for the small scale multi-directional bending observed in individual acoustic images. Second, the transition from jet to plume could produce a change in bending magnitude (but not direction); however, this is unlikely to be visible on the acoustic images as the transition from jet to plume is anticipated to occur within the first 1 m of rise. Third, the ratio of rise velocity W to cross-flow velocity U controls the magnitude and direction of bending

  17. Geochemistry and petrology of andesites from the north rift zone of Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Smithka, I. N.; Perfit, M. R.; Clague, D. A.; Wanless, V. D.

    2014-12-01

    In 2013, the ROV Doc Ricketts onboard R/V Western Flyer explored ~4 km of an elongate pillow ridge up to ~300 m high along the eastern edge of the north rift zone of Axial Seamount. The steep-sided volcanic ridge is constructed of large pillow lavas up to 2-3 m in diameter and smaller elongated pillow tubes. Of the 27 samples collected during dive D526, all but one are andesites making it one of the largest confirmed high-silica exposures along a mid-ocean ridge (MOR). Based on radiocarbon ages of sediment on top of flows, the mounds are at least ~1390 years old. This minimum age is much younger than the 56 Ka age calculated based on distance from the rift axis, indicating eruption off-axis through older, colder crust and supporting the hypothesis and model calculations that extensive fractional crystallization (>85%) caused the high silica content. The andesitic lavas are primarily glassy, highly vesicular, crusty, and sparsely phyric with small (~1 mm) plagioclase crystals and olivine, clinopyroxene, and Fe-Ti oxide microphenocrysts. Microprobe analyses of glasses are similar to wax-core samples previously collected from this area but are more compositionally variable. Excluding one basalt (7.7 wt% MgO) sampled between mounds, the lavas are basaltic andesites and andesites (53-59 wt% SiO2) with <3 wt% MgO and 12.8-15.7 wt% FeO concentrations. Incompatible trace element abundances are ~4-6 times more enriched than in Axial Seamount T-MORB. Primitive mantle-normalized patterns are similar to those of high-silica lavas from other MORs (southern Juan de Fuca Ridge, 9N East Pacific Rise) with significant positive U anomalies, large negative Sr anomalies, small negative Eu anomalies, and slight positive Zr-Hf anomalies. The andesites are more enriched in light rare earth elements than basalts from Axial Seamount ((La/Yb)N 1.35-1.4 vs. 0.7-1.27) and N-MORB from the southern Juan de Fuca Ridge. The andesites also have high Cl (~0.3-0.6 wt%) and H2O (~1.60-1.71 wt

  18. Mineralogical studies of sulfide samples and volatile concentrations of basalt glasses from the southern Juan de Fuca Ridge

    NASA Technical Reports Server (NTRS)

    Brett, Robin; Evans, Howard T., Jr.; Wandless, M. V.; Gibson, E. K., Jr.; Hedenquist, Jeffrey W.

    1987-01-01

    Sulfide samples obtained from Alvin dives on the southern Juan de Fuca Ridge were examined, showing the presence of two previously undiscovered minerals, both formed at low temperatures. The first detection of lizardite, starkeyite, and anatase in such an environment is also reported. Sulfide geothermometry involving the Cu-Fe-S system shows a vent temperature of less than 328 C for one sample. Ice-melting temperatures on inclusions from this sample are about -2.8 C, and fluid inclusion studies on crystals near this sample show pressure-corrected homogenization temperatures of 268 and 285 C. Volatile concentrations from vesicle-free basalt glass from the vent field are found to be about 0.0013 wt pct CO2 and 0.16 wt pct H2O.

  19. 210Po and 210Pb disequilibrium in the hydrothermal vent fluids and chimney deposits from Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Hussain, N.; Church, T. M.; Luther, G. W., III; Moore, W. S.

    Significantly deficient 210Po/210Pb activity ratios (0.14±0.14) are measured in the hydrothermal vent fluids collected from Juan de Fuca Ridge. Chimney deposits generally showed <5 dpm of excess 210Po. However, one sample from the outermost layer of a sealed spire yielded >1200 dpm g-1 of excess 210Po.If the observed 210Po-210Pb disequilibrium in vent fluids is a result of 210Po removal by the precipitates, residence time of polonium with respect to its irreversible removal from hot fluids is estimated to be of the order of a few minutes. Alternatively, if the disequilibrium is a result of an insufficient growth of 210Po from in-situ 210Pb following heating, the residence time of hot fluids within the hydrothermal system can be shown to be less than 30 days, which is considerably lower than previously reported values.

  20. Regional patterns of hydrothermal alteration of sediments as interpreted from seafloor reflection coefficients, Middle Valley, Juan De Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Rohr, Kristin M. M.; Schmidt, Ulrike; Groschel-Becker, Henrike

    1993-09-01

    Reflection coefficients of the seafloor have been calculated from three multi-channel seismic reflection profiles across Middle Valley of the Juan de Fuca ridge. Seafloor reflection coefficients in this sedimented rift valley are high over an active hydrothermal vent and adjacent to major offset faults. Comparison of our measurements to drilling results from Leg 139 shows that high reflection coefficients over an active vent mound are produced by cemented sediments. Large reflection coefficients adjacent to major faults may have a similar origin and indicate that ongoing faulting creates pathways for hydrothermal fluids which alter the sediments and result in higher densities and velocities. Since 30 Hz seismic energy responds to the top 50 m of sediments, we are looking at the integrated response of hydrothermal alteration over tens of thousands of years. This is the first time seafloor reflection coefficients have been used to identify highly altered sediments in a region of deep-water hydrothermal activity.

  1. Seismic Anisotropy and Mantle Flow from Ridge to Trench Below the Gorda-Juan de Fuca Plate System

    NASA Astrophysics Data System (ADS)

    Martin-Short, R.; Allen, R. M.; Bastow, I. D.; Richards, M. A.; Totten, E. J.

    2015-12-01

    Tectonic plates are underlain by a low viscosity layer of the mantle, the asthenosphere, which flows. Flow in the asthenosphere may be induced by motion of the overriding plate, or by deeper mantle convection. Measurement of seismic anisotropy, the directional dependence of seismic wave speed, is an important tool in understanding mantle structure and dynamics, and is often used to infer information about asthenospheric flow geometry. However, isolation of asthenospheric signals is challenging because most seismometers are located on the continents, whose complex structure influences seismic waves en-route to the surface. Thus the challenge is to record seismic data on oceanic lithosphere, which is much thinner and simpler. We present stacked shear wave splitting results from phases 1 to 3 of the Cascadia Initiative: An ambitious, large-scale deployment of offshore seismometers across the Gorda and Juan-de-Fuca plates. Fast splitting directions (FSD) can approximate mantle flow geometry, thus for the first time allowing an interpretation of flow beneath an ocean basin from ridge to trench. The Juan-de-Fuca plate appears able to influence mantle flow: FSD rotate towards the absolute plate motion direction (APM) with increasing distance from the ridge. In contrast, Gorda FSD align with the motion of the adjacent Pacific plate rather than Gorda APM. These observations suggest that drag caused by motion the Pacific plate controls asthenospheric flow beneath Gorda, and thus that the Gorda plate may be decoupled from the asthenosphere. We also construct a simple geodynamic model of this situation, which supports its plausibility. Our findings imply that tectonic plates must reach a minimum size and speed before they are able to exert influence on asthenospheric flow.

  2. Spatial and temporal evolution of magmatic systems beneath the endeavour segment, Juan de Fuca Ridge: Tectonic and petrologic constraints

    NASA Astrophysics Data System (ADS)

    Karsten, Jill L.; Delaney, John R.; Rhodes, J. Michael; Liias, Raimo A.

    1990-11-01

    Major and trace element data for a suite of lavas from fifty-six dredges and ALVEN dives on the ridge axis and adjacent abyssal hills have been used to investigate the geometry and evolution of magmatic systems beneath the Endeavour Segment, Juan de Fuca Ridge. The morphology of the Endeavour Segment between the northward propagating Cobb Offset and the recently formed (<0.2 m.y.) Endeavour Offset is dominated by a shallow, rifted, elongate crestal volcano (Endeavour Ridge) that deepens along-strike into a broad, deep basin at each offset. A set of ridges, interpreted to be previous crestal volcanoes rifted apart by spreading, flank the Endeavour Ridge and chronicle the "dueling" propagator history of the Cobb Offset The tectonic evidence strongly suggests that a large portion of the Endeavour Segment may be a failing rift segment at this time. Lavas from the current axis of the Endeavour Segment are moderately fractionated (MgO: 6-8.5 wt %) and have generally higher SiO2, Al2O3, Na2O, and K2O, and lower FeO* man lavas from south of the Cobb Offset (SOCO lavas). Incompatible trace element abundances and ratios indicate the Endeavour lavas are primarily enriched E-MORBs and T-MORBs (e.g., Zr/Nb: 7-24; Zr/Y: 2.5-5.9; and Ba/TiO2: 6-64), in contrast with the SOCO lavas, which are more depleted in character. Thus, the 30-km wide Cobb Offset appears to mark a major geochemical boundary beneath the Juan de Fuca Ridge. In contrast with the Endeavour Segment axial lavas, samples from adjacent abyssal hills are more similar to the SOCO lavas in their major and trace element characteristics. These observations suggest that the parental magmas of the Endeavour Segment exhibit temporal variability, with more enriched material arriving only recently beneath the ridge axis. Pronounced compositional variability is observed at small spatial scales within the Endeavour Segment axial lavas, which does not correlate with axial morphology. This variability is interpreted to reflect

  3. Variable crustal structure along the Juan de Fuca Ridge: Influence of on-axis hot spots and absolute plate motions

    NASA Astrophysics Data System (ADS)

    Carbotte, Suzanne M.; Nedimović, Mladen R.; Canales, Juan Pablo; Kent, Graham M.; Harding, Alistair J.; Marjanović, Milena

    2008-08-01

    Multichannel seismic and bathymetric data from the Juan de Fuca Ridge (JDFR) provide constraints on axial and ridge flank structure for the past 4-8 Ma within three spreading corridors crossing Cleft, Northern Symmetric, and Endeavour segments. Along-axis data reveal south-to-north gradients in seafloor relief and presence and depth of the crustal magma lens, which indicate a warmer axial regime to the south, both on a regional scale and within individual segments. For young crust, cross-axis lines reveal differences between segments in Moho two-way traveltimes of 200-300 ms which indicate 0.5-1 km thicker crust at Endeavour and Cleft compared to Northern Symmetric. Moho traveltime anomalies extend beyond the 5-15 km wide axial high and coincide with distinct plateaus, 32 and 40 km wide and 200-400 m high, found at both segments. On older crust, Moho traveltimes are similar for all three segments (˜2100 ± 100 ms), indicating little difference in average crustal production prior to ˜0.6 and 0.7 Ma. The presence of broad axis-centered bathymetric plateau with thickened crust at Cleft and Endeavour segments is attributed to recent initiation of ridge axis-centered melt anomalies associated with the Cobb hot spot and the Heckle melt anomaly. Increased melt supply at Cleft segment upon initiation of Axial Volcano and southward propagation of Endeavour segment during the Brunhes point to rapid southward directed along-axis channeling of melt anomalies linked to these hot spots. Preferential southward flow of the Cobb and Heckle melt anomalies and the regional-scale south-to-north gradients in ridge structure along the JDFR may reflect influence of the northwesterly absolute motion of the ridge axis on subaxial melt distribution.

  4. Crustal Thickness and Lower Crustal Velocity Structure Beneath the Endeavour Segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Hill, R.; Soule, D. C.; Wilcock, W. S. D.; Toomey, D. R.; Hooft, E. E. E.; Weekly, R. T.

    2014-12-01

    In 2009, a multi-scale seismic tomography experiment was conducted on the Endeavour segment of the Juan de Fuca Ridge aboard the R/V Marcus G. Langseth. Ocean bottom seismometers were deployed at 64 sites and recorded 5567 shots of a 36-element, 6600 in.3 airgun array. The experiment extended 100 km along-axis and 60 km cross-axis. Two crustal tomographic analyses have previously been completed using data from the experiment. First, 93,000 manually picked crustal refraction arrivals (Pg) were used to develop a three-dimensional model of crustal velocity and thickness in the upper crust (Weekly et al. 2014). Second, this model was used as the starting model in an analysis that incorporated ~19,000 Moho reflection arrivals (PmP) for non-ridge crossing paths to image lower crustal velocity structure and crustal thickness off-axis. A key feature of this model is a ~0.5-1 km increase in crustal thickness beneath a bathymetric plateau that extends to either side of the central portion of the Endeavour segment. We present a tomographic inversions that incorporates ridge-crossing paths to examine spatial variations in lower crustal velocity and crustal thickness beneath the ridge axis. The preliminary results from an inversion that incorporates ~8700 manually picked ridge-crossing PmP arrival times reveals a ~10-km-wide low velocity zone extending throughout the lower crust with a velocity anomaly of -0.3 to -0.5 km/s at ≥4 km depth. This low velocity zone extends both to the north and south of the axial magma chamber reflector imaged previously beneath the central Endeavour. The inversion also shows significant variations in apparent crustal thickness along axis but additional analysis is required to understand whether these variations are well resolved.

  5. Upper crustal seismic structure of the Endeavour segment, Juan de Fuca Ridge from traveltime tomography: Implications for oceanic crustal accretion

    NASA Astrophysics Data System (ADS)

    Weekly, Robert T.; Wilcock, William S. D.; Toomey, Douglas R.; Hooft, Emilie E. E.; Kim, Eunyoung

    2014-04-01

    isotropic and anisotropic P wave velocity structure of the upper oceanic crust on the Endeavour segment of the Juan de Fuca Ridge is studied using refracted traveltime data collected by an active-source, three-dimensional tomography experiment. The isotropic velocity structure is characterized by low crustal velocities in the overlapping spreading centers (OSCs) at the segment ends. These low velocities are indicative of pervasive tectonic fracturing and persist off axis, recording the history of ridge propagation. Near the segment center, velocities within the upper 1 km show ridge-parallel bands with low velocities on the outer flanks of topographic highs. These features are consistent with localized thickening of the volcanic extrusive layer from eruptions extending outside of the axial valley that flow down the fault-tilted blocks that form the abyssal hill topography. On-axis velocities are generally relatively high beneath the hydrothermal vent fields likely due to the infilling of porosity by mineral precipitation. Lower velocities are observed beneath the most vigorous vent fields in a seismically active region above the axial magma chamber and may reflect increased fracturing and higher temperatures. Seismic anisotropy is high on-axis but decreases substantially off axis over 5-10 km (0.2-0.4 Ma). This decrease coincides with an increase in seismic velocities resolved at depths ≥1 km and is attributed to the infilling of cracks by mineral precipitation associated with near-axis hydrothermal circulation. The orientation of the fast-axis of anisotropy is ridge-parallel near the segment center but curves near the segment ends reflecting the tectonic fabric within the OSCs.

  6. Amino acid abundances and stereochemistry in hydrothermally altered sediments from the Juan de Fuca Ridge, northeastern Pacific Ocean.

    PubMed

    Andersson, E; Simoneit, B R; Holm, N G

    2000-09-01

    The Juan de Fuca Ridge is a hydrothermally active, sediment covered, spreading ridge situated a few hundred kilometres off the west coast of North America in the northeastern Pacific Ocean. Sediments from seven sites drilled during the Ocean Drilling Program (ODP) Legs 139 and 168 were analyzed for total hydrolyzable amino acids (THAA), individual amino acid distributions, total organic C (TOC) and total N (TN) contents. The aim was to evaluate the effects of hydrothermal stress on the decomposition and transformation of sedimentary amino acids. Hydrolyzable amino acids account for up to 3.3% of the total organic C content and up to 12% of the total N content of the upper sediments. The total amounts of amino acids decrease significantly with depth in all drilled holes. This trend is particularly pronounced in holes with a thermal gradient of around 0.6 degrees C/m or higher. The most abundant amino acids in shallow sediments are glycine, alanine, lysine, glutamic acid, valine and histidine. The changes in amino acid distributions in low temperature holes are characterized by increased relative abundances of non-protein beta-alanine and gamma-aminobutyric acid. In high temperature holes the amino acid compositions are characterized by high abundances of glycine, alanine, serine, ornithine and histidine at depth. D/L ratios of samples with amino acid distributions similar to those found in acid hydrolysates of kerogen, indicate that racemization rates of amino acids bound by condensation reactions may be diminished.

  7. Draft Genome Sequences of Pseudoalteromonas telluritireducens DSM 16098 and P. spiralis DSM 16099 Isolated from the Hydrothermal Vents of the Juan de Fuca Ridge

    PubMed Central

    Liu, Rui; Wang, Mengqiang; Wang, Hao; Gao, Qiang; Hou, Zhanhui; Zhou, Zhi; Gao, Dahai

    2016-01-01

    This report describes the draft genome sequences of two strains, Pseudoalteromonas telluritireducens DSM 16098 and P. spiralis DSM 16099, which were isolated from hydrothermal vents of the Juan de Fuca Ridge. The reads generated by an Ion Torrent PGM were assembled into contigs with total sizes of 4.4 Mb and 4.1 Mb for DSM 16098 and DSM 16099, respectively. PMID:27563045

  8. Draft Genome Sequences of Pseudoalteromonas telluritireducens DSM 16098 and P. spiralis DSM 16099 Isolated from the Hydrothermal Vents of the Juan de Fuca Ridge.

    PubMed

    Zhang, Huan; Liu, Rui; Wang, Mengqiang; Wang, Hao; Gao, Qiang; Hou, Zhanhui; Zhou, Zhi; Gao, Dahai; Wang, Lingling

    2016-08-25

    This report describes the draft genome sequences of two strains, Pseudoalteromonas telluritireducens DSM 16098 and P. spiralis DSM 16099, which were isolated from hydrothermal vents of the Juan de Fuca Ridge. The reads generated by an Ion Torrent PGM were assembled into contigs with total sizes of 4.4 Mb and 4.1 Mb for DSM 16098 and DSM 16099, respectively. Copyright © 2016 Zhang et al.

  9. Fluid rare earth element anlayses from geothermal wells located on the Reykjanes Peninsula, Iceland and Middle Valley seafloor hydrothermal system on the Juan de Fuca Ridge.

    DOE Data Explorer

    Andrew Fowler

    2015-05-01

    Results for fluid rare earth element analyses from four Reykjanes peninsula high-temperature geothermal fields. Data for fluids from hydrothermal vents located 2400 m below sea level from Middle Valley on the Juan de Fuca Ridge are also included. Data have been corrected for flashing. Samples preconcentrated using a chelating resin with IDA functional group (InertSep ME-1). Analyzed using an Element magnetic sector inductively coupled plasma mass spectrometry (ICP-MS).

  10. Evidence of off-axis volcanism and hydrothermal venting along the cleft segment of the southern Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Stakes, D.; Perfit, M.; Wheat, C.; Ramirez, T.; Koski, R.; Hein, J.

    2003-04-01

    High-resolution mapping and systematic ROV-based geological observation and sampling, of the Cleft Segment, Juan de Fuca Ridge, provide a unique perspective on crustal evolution and off-axis hydrothermal activity along this moderate spreading-rate ridge. Simrad EM300 multibeam bathymetric maps with a 30- m pixel size provide sufficiently high resolution to trace magmatic, tectonic, and hydrothermal events over geologically short time scales (50--100,000 years). During a series of 13 dives in 2000 and 2002 using the MBARI ROV Tiburon, we collected samples of basalt and hydrothermal precipitates along six transects across the ridge axis extending up to 5 km off-axis. The rift-valley walls consist of a series of inward-facing bounding faults, separated by blocks of oceanic crust that exhibit little or no deformation. Unlike the axial valley where sheetflows are predominant, these off-axis blocks are unfaulted constructional pillow ridges, mounds, and hornitos. Field observations provide evidence for off-axis volcanism along eruptive fissures and from point-sources related to rift-bounding faults. Other volcanic constructions in the first series of abyssal hills are interpreted to be syntectonic lava flows erupted along "volcanic growth faults". Thick ridge-flank flows of intact pillows originated from near-axis bounding faults. The contact between the massive pillowed units and the older sheet flows (approximately three kilometers to the east) is clearly delineated by both sediment cover and lava-flow morphology and is the site of diffusive low-temperature hydrothermal venting. Measured temperatures of shimmering fluids at this eastern site were 3--20^oC above ambient. A large Fe-Mn mound with dramatic chemical gradients was discovered 4 km west of the spreading axis on the flank of a ridge-parallel horst capped with syntectonic pillowed flows. The hydrothermal mounds are characterized by layered flocculent masses of microbial filaments encrusted with amorphous and

  11. Dissolved Carbon Species in Diffuse and Focused Flow Hydrothermal Vents at the Main Endeavour Field, Northern Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Foustoukos, D. I.; Seyfried, W. E.; Ding, K.; Pester, N. J.

    2006-12-01

    The magmatic and tectonic event of 1999 had a significant impact on the chemical composition of vent fluids issuing from the Main Endeavour Field (MEF), Juan de Fuca Ridge. Here, we report dissolved concentrations of H2, CO2, CO and C1-C3 alkanes measured in low and high-temperature hydrothermal fluids collected in August 2005 during an RV Atlantis/DSV Alvin expedition at MEF. In comparison with time series data, temperatures of the 2005 vent fluids were slightly lower than those recorded in the aftermaths of the tectonic event of 1999. The possible cooling of the hydrothermal subseafloor reaction zone is consistent with the observed increase in dissolved Cl to pre-1999 values. Converging compositional trends to pre-1999 conditions are also suggested for dissolved CO2 concentrations (~20 mmol/kg) in Puffer, Sully, Bastille and S&M vent fluids. In these focused flow and high-temperature vent fluids, dissolved CO2 is in thermodynamic equilibrium with CO(aq). The systematics of organic species in diffuse flow fluids, however, appears to be closely related to processes occurring within the near-seafloor environment. For example, excess CO(aq) observed in the diffuse flow fluids at Easter Island is attributed to sluggish CO- CO2(aq) equilibria at low temperatures, suggesting hydrothermal circulation of short-residence times. Short-lived hydrothermal circulation is further supported by the nearly identical C1/(C2+C3) ratios between focused and diffuse flow fluids. Furthermore, alkane distribution in the MEF diffuse flow fluids suggests direct mixing between seawater and hydrothermal fluid with minimal biological inputs, in contrast with the greater effect of microbial methanogenesis proposed in other ridge-crest hydrothermal environments. Thus, the coupling of CO2(aq)-CO(aq) redox equilibrium with dissolved carbon species in low- temperature vent fluids could provide a better understanding of the effect of subsurface microbial communities upon the composition of mid

  12. Compressional and Shear Wave Structure of the Upper Crust Beneath the Endeavour Segment, Juan De Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Kim, E.; Toomey, D. R.; Hooft, E. E. E.; Wilcock, W. S. D.; Weekly, R. T.; Lee, S. M.; Kim, Y.

    2014-12-01

    We present tomographic images of the compressional (Vp) and shear (Vs) wave velocity structure of the upper crust beneath the Endeavour segment of the Juan de Fuca Ridge. This ridge segment is bounded by the Endeavour and Cobb overlapping spreading centers (OSCs) to the north and south, respectively. Near the segment center an axial magma chamber (AMC) reflector underlies 5 hydrothermal vent fields. Our analysis uses data from the Endeavour tomography (ETOMO) experiment. A prior study of the Vp structure indicates that the shallow crust of the Endeavour segment is strongly heterogeneous [Weekly et al., 2014]. Beneath the OSCs Vp is anomalously low, indicating tectonic fracturing. Near the segment center, upper crustal Vp is relatively high beneath the hydrothermal vent fields, likely due to infilling of porosity by mineral precipitation. Lower velocities are observed immediately above the AMC, reflecting increased fracturing or higher temperatures. Anisotropic tomography reveals large amplitude ridge-parallel seismic anisotropy on-axis (>10%), but decreases in the off-axis direction over 5-10 km. Here we use crustal S-wave phases (Sg) — generated by P-to-S conversions near the seafloor — to better constrain crustal properties. Over half the OBSs in the ETOMO experiment recorded horizontal data on two channels that are of sufficiently high quality that we can orient the geophones using the polarizations of water waves from shots within 12 km. For these OBSs, crustal Sg phases are commonly visible out to ranges of ~20-25 km. We invert the Sg data separately for Vs structure, and also jointly invert Pg and Sg data to constrain the Vp/Vs ratio. Preliminary inversions indicate that Vs and Vp/Vs varies both laterally and vertically. These results imply strong lateral variations in both the physical (e.g., crack density and aspect ratio) and chemical (e.g., hydration) properties of oceanic crust.

  13. Comparison of Volatile and Major Element Concentrations in Melt Inclusions from Juan de Fuca Ridge Seamounts and the Adjacent Ridge Axis

    NASA Astrophysics Data System (ADS)

    Wanless, V. D.; Behn, M. D.; Perfit, M. R.; Clague, D. A.

    2014-12-01

    Here we present volatile (CO2, H2O, F, S, Cl) and major element data from >200 naturally glassy, olivine-hosted melt inclusions and glasses erupted from five seamounts proximal to the Juan de Fuca Ridge. This includes 90 analyses of melt inclusions from the Vance Seamount chain and 126 analyses from two small, mafic (glass MgO > 9 wt%) near-axis cones (T461 and T881). We provide geochemical constraints on both the compositional variations and the depths of crystallization beneath the seamounts using vapor-saturation pressures derived from CO2-H2O concentrations. These data suggest crystallization occurs beneath the two near-axis cones from seafloor pressures to 6400 bars corresponding to depths up to 9 km below the seafloor. This range of crystallization is similar to that calculated from olivine-hosted melt inclusions from the adjacent Juan de Fuca Ridge axis. By contrast, crystallization pressures from Vance Seamounts are more limited with pressures ranging from 400 to 1300 bars or depths of 0.7 to 3.8 km below seafloor. The Vance Seamounts have a prominent peak in depths of crystallization at ~2-3 km below seafloor in histograms, perhaps suggesting that it is the preferred depth of melt storage and crystallization beneath seamounts chains. By contrast, crystallization peaks beneath the small, near-axis cones are less prominent and occur slightly deeper at 3-4 km below seafloor. Overall, S and F concentrations in the seamount melt inclusions are similar to on-axis inclusions; however, Cl concentrations in the seamounts are remarkably low. On-axis inclusions have an average of 61 ppm Cl and range from 4-163 ppm. By contrast, Cl concentrations in the seamounts range from 3-82 ppm, but have an average of only 11 ppm. Excess Cl in mid-ocean ridge lavas is often attributed to contamination by seawater or brines associated with hydrothermal circulation. We suggest that the low Cl concentrations in the seamount inclusions may result from either a seamount mantle source

  14. Quantitative estimate of heat flow from a mid-ocean ridge axial valley, Raven field, Juan de Fuca Ridge: Observations and inferences

    NASA Astrophysics Data System (ADS)

    Salmi, Marie S.; Johnson, H. Paul; Tivey, Maurice A.; Hutnak, Michael

    2014-09-01

    A systematic heat flow survey using thermal blankets within the Endeavour segment of the Juan de Fuca Ridge axial valley provides quantitative estimates of the magnitude and distribution of conductive heat flow at a mid-ocean ridge, with the goal of testing current models of hydrothermal circulation present within newly formed oceanic crust. Thermal blankets were deployed covering an area of 700 by 450 m in the Raven Hydrothermal vent field area located 400 m north of the Main Endeavour hydrothermal field. A total of 176 successful blanket deployment sites measured heat flow values that ranged from 0 to 31 W m-2. Approximately 53% of the sites recorded values lower than 100 mW m-2, suggesting large areas of seawater recharge and advective extraction of lithospheric heat. High heat flow values were concentrated around relatively small "hot spots." Integration of heat flow values over the Raven survey area gives an estimate of conductive heat output of 0.3 MW, an average of 0.95 W m-2, over the survey area. Fluid circulation cell dimensions and scaling equations allow calculation of a Rayleigh number of approximately 700 in Layer 2A. The close proximity of high and low heat flow areas, coupled with previous estimates of surficial seafloor permeability, argues for the presence of small-scale hydrothermal fluid circulation cells within the high-porosity uppermost crustal layer of the axial seafloor.

  15. Activity and abundance of denitrifying bacteria in the subsurface biosphere of diffuse hydrothermal vents of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Bourbonnais, A.; Juniper, S. K.; Butterfield, D. A.; Devol, A. H.; Kuypers, M. M. M.; Lavik, G.; Hallam, S. J.; Wenk, C. B.; Chang, B. X.; Murdock, S. A.; Lehmann, M. F.

    2012-04-01

    Little is known about nitrogen (N) transformations in general, and the elimination of N in particular, at diffuse vents where anoxic hydrothermal fluids have mixed with oxygenated crustal seawater prior to discharge. Oceanic N sinks that remove bio-available N ultimately affect chemosynthetic primary productivity in these ecosystems. Using 15N paired isotope techniques, we determined potential rates of fixed N-loss pathways (denitrification, anammox) and dissimilative nitrate reduction to ammonium (DNRA) in sulfidic hydrothermal vent fluids discharging from the subsurface at several sites at Axial Volcano and the Endeavour Segment on the Juan de Fuca Ridge. We also measured physico-chemical parameters (i.e. temperature, pH, nutrients, H2S and N2O concentrations) as well as the biodiversity and abundance of chemolithotrophic nitrate-reducing, sulfur-oxidizing γ-proteobacteria (SUP05 cluster) using sequence analysis of amplified small subunit ribosomal RNA (16S rRNA) genes in combination with taxon-specific quantitative polymerase chain reaction (qPCR) assays. Denitrification was the dominant N-loss pathway in the subsurface biosphere of the Juan de Fuca Ridge, with rates of up to ~1000 nmol N l-1 day-1. In comparison, anammox rates were always <5 nmol N l-1 day-1 and below the detection limit at most of the sites. DNRA rates were up to 152 nmol N l-1 day-1. These results suggest that bacterial denitrification out-competes anammox in sulfidic hydrothermal vent waters. Taxon-specific qPCR revealed that γ-proteobacteria of the SUP05 cluster sometimes dominated the microbial community (SUP05/total bacteria up to 38%). Significant correlation existed between fixed N-loss (i.e., denitrification, anammox) rates and in-situ nitrate and dissolved inorganic nitrogen (DIN) deficits in the fluids, indicating that DIN availability may ultimately regulate N-loss in the subsurface. Based on our rate measurements, and on published data on hydrothermal fluid fluxes and residence

  16. Activity and abundance of denitrifying bacteria in the subsurface biosphere of diffuse hydrothermal vents of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Bourbonnais, A.; Juniper, S. K.; Butterfield, D. A.; Devol, A. H.; Kuypers, M. M. M.; Lavik, G.; Hallam, S. J.; Wenk, C. B.; Chang, B. X.; Murdock, S. A.; Lehmann, M. F.

    2012-11-01

    Little is known about fixed nitrogen (N) transformation and elimination at diffuse hydrothermal vents where anoxic fluids are mixed with oxygenated crustal seawater prior to discharge. Oceanic N sinks that remove bio-available N ultimately affect chemosynthetic primary productivity in these ecosystems. Using 15N paired isotope techniques, we determined potential rates of fixed N loss pathways (denitrification, anammox) and dissimilatory nitrate reduction to ammonium (DNRA) in sulfidic hydrothermal vent fluids discharging from the subsurface at several sites at Axial Volcano and the Endeavour Segment on the Juan de Fuca Ridge. We also measured physico-chemical parameters (i.e., temperature, pH, nutrients, H2S and N2O concentrations) as well as the biodiversity and abundance of chemolithoautotrophic nitrate-reducing, sulfur-oxidizing γ-proteobacteria (SUP05 cluster) using sequence analysis of amplified small subunit ribosomal RNA (16S rRNA) genes in combination with taxon-specific quantitative polymerase chain reaction (qPCR) assays. Denitrification was the dominant N loss pathway in the subsurface biosphere of the Juan de Fuca Ridge, with rates of up to ~1000 nmol N l-1 day-1. In comparison, anammox rates were always < 5 nmol N l-1 day-1 and below the detection limit at most of the sites. DNRA rates were up to ~150 nmol N l-1 day-1. These results suggest that bacterial denitrification out-competes anammox in sulfidic hydrothermal vent waters. Taxon-specific qPCR revealed that γ-proteobacteria of the SUP05 cluster sometimes dominated the microbial community (SUP05/total bacteria up to 38%). Significant correlations were found between fixed N loss (i.e., denitrification, anammox) rates and in situ nitrate and dissolved inorganic nitrogen (DIN) deficits in the fluids, indicating that DIN availability may ultimately regulate N loss in the subsurface. Based on our rate measurements, and on published data on hydrothermal fluid fluxes and residence times, we estimated

  17. Fine-scale heat flow, shallow heat sources, and decoupled circulation systems at two sea-floor hydrothermal sites, Middle Valley, northern Juan de Fuca Ridge

    SciTech Connect

    Stein, J.S.; Fisher, A.T.; Langseth, M.; Jin, W.; Iturrino, G.; Davis, E.

    1998-12-01

    Fine-scale heat-flow patterns at two areas of active venting in Middle Valley, a sedimented rift on the northern Juan de Fuca Ridge, provide thermal evidence of shallow hydrothermal reservoirs beneath the vent fields. The extreme variability of heat flow is explained by conductive heating immediately adjacent to vents and shallow circulation within sediments above the reservoir. This secondary circulation is hydrologically separated from the deeper system feeding the vents by a shallow conductive lid within the sediments. A similar separation of shallow and deep circulation may also occur at sediment-free ridge-crest hydrothermal environments.

  18. Morphometric variability within the axial zone of the southern Juan de Fuca Ridge: Interpretation from Sea MARC II, Sea MARC I, and deep-sea photography

    USGS Publications Warehouse

    Kappel, Ellen S.; Normark, William R.

    1987-01-01

    The morphometric characteristics of the axial regions of oceanic spreading centers are determined by (1) the type of volcanic flows, (2) the relation between primary volcanic relief (on a scale of a few meters to tens of meters) and degree of sediment cover, and (3) the extent of surficial expression and timing of tectonic disruption of the young oceanic crust. Even within a single, continuous, linear spreading-ridge segment with relatively uniform axial valley dimensions over a distance of 50 or more kilometers, such as along the southern Juan de Fuca Ridge, the changes in morphometric characteristics along axis within the youngest crust indicate distinct variation in tectonic and volcanic activity over short distances within short time periods. An integrated analysis of Sea MARC I, Sea MARC II, and photographic data for the southernmost continuous segment of the Juan de Fuca Ridge shows that generalizations about tectonic and volcanic processes at spreading ridges must consider both the temporal scale of processes as well as the physical scales of observations if predictive models are to be successful. Comparison of the morphometric expression within the major hydrothermal vent area and the rest of the southernmost ridge segment suggests that the mapped distribution of hydrothermal vents may reflect the extent of survey effort rather than uniqueness of geologic setting.

  19. Submarine fissure eruptions and hydrothermal vents on the southern Juan de Fuca Ridge: preliminary observations from the submersible Alvin

    USGS Publications Warehouse

    Normark, W.R.

    1986-01-01

    The submersible Alvin was used to investigate 3 active hydrothermal discharge sites along the S Juan de Fuca Ridge in September 1984. The hydrothermal zones occur within a 10-30m-deep, 30-50m-wide cleft marking the center of the axial valley. This cleft is the eruptive locus for the axial valley. The hydrothermal vents coincide with the main eruptive vents along the cleft. Each hydrothermal zone has multiple discharge sites extending as much as 500m along the cleft. Sulfide deposits occur as clusters (15-100m2 area) of small chimneys (= or <2m high) and as individual and clustered fields of large, branched chimneys (= or <10m high). Recovered sulfide samples are predominantly the tops of chimneys and spires and typically contain more than 80% sphalerite and wurtzite with minor pyrrhotite, pyrite, marcasite, isocubanite, chalcopyrite, anhydrite, anhydrite, and amorphous silica. The associated hydrothermal fluids have the highest chlorinity of any reported to date.-Authors

  20. Microbial diversity of a sulfide black smoker in main endeavour hydrothermal vent field, Juan de Fuca Ridge.

    PubMed

    Zhou, Huaiyang; Li, Jiangtao; Peng, Xiaotong; Meng, Jun; Wang, Fengping; Ai, Yuncan

    2009-06-01

    Submarine hydrothermal vents are among the least-understood habitats on Earth but have been the intense focus of research in the past 30 years. An active hydrothermal sulfide chimney collected from the Dudley site in the Main Endeavour vent Field (MEF) of Juan de Fuca Ridge was investigated using mineralogical and molecular approaches. Mineral analysis indicated that the chimney was composed mainly of Fe-, Zn-and Cu-rich sulfides. According to phylogenetic analysis, within the Crenarchaeota, clones of the order Desulfurococcales predominated, comprising nearly 50% of archaeal clones. Euryarchaeota were composed mainly of clones belonging to Thermococcales and deep-sea hydrothermal vent Euryarchaeota (DHVE), each of which accounted for about 20% of all clones. Thermophilic or hyperthermophilic physiologies were common to the predominant archaeal groups. More than half of bacterial clones belonged to epsilon-Proteobacteria, which confirmed their prevalence in hydrothermal vent environments. Clones of Proteobacteria (gamma-, delta-, beta-), Cytophaga-Flavobacterium-Bacteroides (CFB) and Deinococcus-Thermus occurred as well. It was remarkable that methanogens and methanotrophs were not detected in our 16S rRNA gene library. Our results indicated that sulfur-related metabolism, which included sulfur-reducing activity carried out by thermophilic archaea and sulfur-oxidizing by mesophilic bacteria, was common and crucial to the vent ecosystem in Dudley hydrothermal site.

  1. Vertical distribution and characterization of aerobic phototrophic bacteria at the Juan de Fuca Ridge in the Pacific Ocean.

    PubMed

    Rathgeber, Christopher; Lince, Michael T; Alric, Jean; Lang, Andrew S; Humphrey, Elaine; Blankenship, Robert E; Verméglio, André; Plumley, F Gerald; Van Dover, Cindy L; Beatty, J Thomas; Yurkov, Vladimir

    2008-09-01

    The vertical distribution of culturable anoxygenic phototrophic bacteria was investigated at five sites at or near the Juan de Fuca Ridge in the Pacific Ocean. Twelve similar strains of obligately aerobic phototrophic bacteria were isolated in pure culture, from depths ranging from 500 to 2,379 m below the surface. These strains appear morphologically, physiologically, biochemically, and phylogenetically similar to Citromicrobium bathyomarinum strain JF-1, a bacterium previously isolated from hydrothermal vent plume waters. Only one aerobic phototrophic strain was isolated from surface waters. This strain is morphologically and physiologically distinct from the strains isolated at deeper sampling locations, and phylogenetic analysis indicates that it is most closely related to the genus Erythrobacter. Phototrophs were cultivated from three water casts taken above vents but not from two casts taken away from active vent sites. No culturable anaerobic anoxygenic phototrophs were detected. The photosynthetic apparatus was investigated in strain JF-1 and contains light-harvesting I and reaction center complexes, which are functional under aerobic conditions.

  2. Influence of Igneous Basement on Deep Sediment Microbial Diversity on the Eastern Juan de Fuca Ridge Flank.

    PubMed

    Labonté, Jessica M; Lever, Mark A; Edwards, Katrina J; Orcutt, Beth N

    2017-01-01

    Microbial communities living in deeply buried sediment may be adapted to long-term energy limitation as they are removed from new detrital energy inputs for thousands to millions of years. However, sediment layers near the underlying oceanic crust may receive inputs from below that influence microbial community structure and/or activity. As part of the Census of Deep Life, we used 16S rRNA gene tag pyrosequencing on DNA extracted from a spectrum of deep sediment-basement interface samples from the subsurface of the Juan de Fuca Ridge flank (collected on IODP Expedition 327) to examine this possible basement influence on deep sediment communities. This area experiences rapid sedimentation, with an underlying basaltic crust that hosts a dynamic flux of hydrothermal fluids that diffuse into the sediment. Chloroflexi sequences dominated tag libraries in all sediment samples, with variation in the abundance of other bacterial groups (e.g., Actinobacteria, Aerophobetes, Atribacteria, Planctomycetes, and Nitrospirae). These variations occur in relation to the type of sediment (clays versus carbonate-rich) and the depth of sample origin, and show no clear connection to the distance from the discharge outcrop or to basement fluid microbial communities. Actinobacteria-related sequences dominated the basalt libraries, but these should be viewed cautiously due to possibilities for imprinting from contamination. Our results indicate that proximity to basement or areas of seawater recharge is not a primary driver of microbial community composition in basal sediment, even though fluids diffusing from basement into sediment may stimulate microbial activity.

  3. Spuriously shallow NRM inclinations of hydrothermally altered Juan de Fuca Ridge sediment - secondary magnetization or disruption of the sediment fabric

    NASA Astrophysics Data System (ADS)

    Urbat, M.; Brandau, A.

    2003-04-01

    The marine sediment of the active Dead Dog Vent Field in Middle Valley, Juan de Fuca Ridge (ODP Holes 1036A-C), is strongly altered due to focused hydrothermal fluid circulation. A detailed paleo- and rockmagnetic study of the sediment indicates that the magnetic signal (iron oxides and secondary iron sulfides) sensitively reflects both thermally accelerated rates of diagenesis and direct reaction with the fluids. The explanation of NRM directions, however, in some of the lithologically homogeneous intervals is not straightforward. In these hydrothermally altered intervals the paleomagnetic record displays spuriously shallow or even negative inclinations, and a detailed analysis of the AF-demagnetization behavior does not indicate a true recording of the Earth magnetic field. We explore several potential causes for the NRM directions including authigenic precipitation of new magnetic minerals or the disruption of the sedimentary fabric and concomitant distortion of the NRM record. Spuriously shallow inclinations in all three holes correspond to inclinations of the minimum axes of the AMS ellipsoid that significantly deviates from vertical (i.e. 90° as would be expected for an undisturbed marine sedimentary fabric). We discuss, whether the secondary precipitation of (non-) magnetic minerals can explain the NRM behavior, if the volume of the original minerals is changed.

  4. Distribution and composition of hydrothermal plume particles from the ASHES Vent Field at Axial Volcano, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Feely, R. A.; Geiselman, T. L.; Baker, E. T.; Massoth, G. J.; Hammond, S. R.

    1990-08-01

    In 1986 and 1987, buoyant and neutrally buoyant hydrothermal plume particles from the ASHES vent field within Axial Volcano were sampled to study their variations in composition with height above the seafloor. Individual mineral phases were identified using standard X ray diffraction procedures. Elemental composition and particle morphologies were determined by X ray fluorescence spectrometry and scanning electron microscopy/X ray energy spectrometry techniques. The vent particles were primarily composed of sphalerite, anhydrite, pyrite, pyrrhotite, chalcopyrite, barite, hydrous iron oxides, and amorphous silica. Grain size analyses of buoyant plume particles showed rapid particle growth in the first few centimeters above the vent orifice, followed by differential sedimentation of the larger sulfide and sulfate minerals out of the buoyant plume. The neutrally buoyant plume consisted of a lower plume, which was highly enriched in Fe, S, Zn, and Cu, and an upper plume, which was highly enriched in Fe and Mn. The upper plume was enriched in Fe and Mn oxyhydroxide particles, and the lower plume was enriched in suspended sulfide particles in addition to the Fe and Mn oxyhydroxide particles. The chemical data for the water column particles indicate that chemical scavenging and differential sedimentation processes are major factors controlling the composition of the dispersing hydrothermal particles. Short-term sediment trap experiments indicate that the fallout from the ASHES vent field is not as large as some of the other vent fields on the Juan de Fuca Ridge.

  5. Time-series measurement of hydrothermal heat flux at the Grotto mound, Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Xu, Guangyu; Jackson, Darrell R.; Bemis, Karen G.; Rona, Peter A.

    2014-10-01

    Continuous time-series observations are key to understanding the temporal evolution of a seafloor hydrothermal system and its interplay with thermal and chemical processes in the ocean and Earth interior. In this paper, we present a 26-month time series of the heat flux driving a hydrothermal plume on the Endeavour Segment of the Juan de Fuca Ridge obtained using the Cabled Observatory Vent Imaging Sonar (COVIS). Since 2010, COVIS has been connected to the North East Pacific Time-series Underwater Networked Experiment (NEPTUNE) observatory that provides power and real-time data transmission. The heat flux time series has a mean value of 18.10 MW and a standard deviation of 6.44 MW. The time series has no significant global trend, suggesting the hydrothermal heat source remained steady during the observation period. The steadiness of the hydrothermal heat source coincides with reduced seismic activity at Endeavour observed in the seismic data recorded by an ocean bottom seismometer from 2011 to 2013. Furthermore, first-order estimation of heat flux based on the temperature measurements made by the Benthic and Resistivity Sensors (BARS) at a neighboring vent also supports the steadiness of the hydrothermal heat source.

  6. Window into Sediment-Buried Basement Biosphere: Fluid Sampling from CORK Observatory Seafloor Platforms, Juan de Fuca Ridge Flanks

    NASA Astrophysics Data System (ADS)

    Cowen, J. P.; Lin, H.; Rappe, M.; Jungbluth, S.; Glazer, B. T.; Matzinger, M.; Amend, J. P.; Boettger, J.

    2010-12-01

    Studies of the deep basement biosphere are technologically challenging, requiring complementary approaches to provide sufficient access to allow precision analyses and experimentation. Our NSF-funded ‘Microbial Observatory’ has focused on IODP Circulation Obviating Retrofit Kit (CORK) observatories to obtain pristine samples of fluids from sediment-buried basement environments. We have developed instruments and samplers to interface with CORK fluid delivery lines, including a ROV/HOV-borne Mobile Pumping System and autonomous (e.g., GeoMICROBE) instrument sensor/sampler systems. These systems are providing high quality (e.g., depleted Mg++, <6 mM) samples of basement fluids from 3.5 mA old upper basement, on the flanks of the Juan de Fuca Ridge, for geochemical and microbial studies. Relative to bottom seawater, these fluids are also depleted in O2, SO42-, PO43-, NO3- and NO2-, while enriched in NH4+, H2S, Mn and Fe. In situ voltammetric analyses obtained during sample collection, revealed the presence of micromolar levels of sulfide (0.5 µm) in the fluids. Dissolved organic carbon in basement fluids is about half that of local bottom seawater, low molecular weight organic acids are below detection limits, while total amino acids are also low in concentration, but the relative abundance of specific amino acids varies from that of bottom seawater. Overall, the sediment-buried basement environments appears to be organic-carbon depleted and low energy, yet still dynamic. The microbial communities from CORK 1301A (47deg 45N, 127deg 45W) in consecutive years are heterogeneous, but share common groups. Different CORKs sampled a decade apart share major lineages, consistent with hydrogeologic connectivity. Samples collected from a new CORK installation at borehole 1026B contain a subset of members found a decade previously from an older style CORK at the same site. Communities retrieved from the CORK at 1025C (47deg 53N, 128deg 39W), in 1.4 My ridge flank basement

  7. Seismic reflection images of a near-axis melt sill within the lower crust at the Juan de Fuca ridge.

    PubMed

    Canales, J Pablo; Nedimović, Mladen R; Kent, Graham M; Carbotte, Suzanne M; Detrick, Robert S

    2009-07-02

    The oceanic crust extends over two-thirds of the Earth's solid surface, and is generated along mid-ocean ridges from melts derived from the upwelling mantle. The upper and middle crust are constructed by dyking and sea-floor eruptions originating from magma accumulated in mid-crustal lenses at the spreading axis, but the style of accretion of the lower oceanic crust is actively debated. Models based on geological and petrological data from ophiolites propose that the lower oceanic crust is accreted from melt sills intruded at multiple levels between the Moho transition zone (MTZ) and the mid-crustal lens, consistent with geophysical studies that suggest the presence of melt within the lower crust. However, seismic images of molten sills within the lower crust have been elusive. Until now, only seismic reflections from mid-crustal melt lenses and sills within the MTZ have been described, suggesting that melt is efficiently transported through the lower crust. Here we report deep crustal seismic reflections off the southern Juan de Fuca ridge that we interpret as originating from a molten sill at present accreting the lower oceanic crust. The sill sits 5-6 km beneath the sea floor and 850-900 m above the MTZ, and is located 1.4-3.2 km off the spreading axis. Our results provide evidence for the existence of low-permeability barriers to melt migration within the lower section of modern oceanic crust forming at intermediate-to-fast spreading rates, as inferred from ophiolite studies.

  8. Microbiological characterization of post-eruption “snowblower” vents at Axial Seamount, Juan de Fuca Ridge

    PubMed Central

    Meyer, Julie L.; Akerman, Nancy H.; Proskurowski, Giora; Huber, Julie A.

    2013-01-01

    Microbial processes within the subseafloor can be examined during the ephemeral and uncommonly observed phenomena known as snowblower venting. Snowblowers are characterized by the large quantity of white floc that is expelled from the seafloor following mid-ocean ridge eruptions. During these eruptions, rapidly cooling lava entrains seawater and hydrothermal fluids enriched in geochemical reactants, creating a natural bioreactor that supports a subseafloor microbial “bloom.” Previous studies hypothesized that the eruption-associated floc was made by sulfide-oxidizing bacteria; however, the microbes involved were never identified. Here we present the first molecular analysis combined with microscopy of microbial communities in snowblower vents from samples collected shortly after the 2011 eruption at Axial Seamount, an active volcano on the Juan de Fuca Ridge. We obtained fluid samples and white flocculent material from active snowblower vents as well as orange flocculent material found on top of newly formed lava flows. Both flocculent types revealed diverse cell types and particulates when examined by phase contrast and scanning electron microscopy (SEM). Distinct archaeal and bacterial communities were detected in each sample type through Illumina tag sequencing of 16S rRNA genes and through sequencing of the sulfide oxidation gene, soxB. In fluids and white floc, the dominant bacteria were sulfur-oxidizing Epsilonproteobacteria and the dominant archaea were thermophilic Methanococcales. In contrast, the dominant organisms in the orange floc were Gammaproteobacteria and Thaumarchaeota Marine Group I. In all samples, bacteria greatly outnumbered archaea. The presence of anaerobic methanogens and microaerobic Epsilonproteobacteria in snowblower communities provides evidence that these blooms are seeded by subseafloor microbes, rather than from microbes in bottom seawater. These eruptive events thus provide a unique opportunity to observe subseafloor microbial

  9. Geochronology and petrogenesis of MORB from the Juan de Fuca and Gorda ridges by 238U230Th disequilibrium

    USGS Publications Warehouse

    Goldstein, S.J.; Murrell, M.T.; Janecky, D.R.; Delaney, J.R.; Clague, D.A.

    1991-01-01

    A highly precise mass spectrometric method of analysis was used to determine 238U234U230Th232Th in axial and off-axis basalt glasses from Juan de Fuca (JDF) and Gorda ridges. Initial 230Th activity excesses in the axial samples range from 3 to 38%, but generally lie within a narrow range of 12 to 15%. Secondary alteration effects were evaluated using ??234U and appear to be negligible; hence the 230Th excesses are magmatic in origin. Direct dating of MORB was accomplished by measuring the decrease in excess 230Th in off-axis samples. 238U230Th ages progressively increase with distance from axis. Uncertainties in age range from 10 to 25 ka for UTh ages of 50 to 200 ka. The full spreading rate based on UTh ages for Endeavour segment of JDF is 5.9 ?? 1/2 cm/yr, with asymmetry in spreading between the Pacific (4.0 ?? 0.6 cm/yr) and JDF (1.9 ?? 0.6 cm/yr) plates. For northern Gorda ridge, the half spreading rate for the JDF plate is found to be 3.0 ?? 0.4 cm/yr. These rates are in agreement with paleomagnetic spreading rates and topographic constraints. This suggests that assumptions used to determine ages, including constancy of initial 230Th 232Th ratio over time, are generally valid for the areas studied. Samples located near the axis of spreading are typically younger than predicted by these spreading rates, which most likely reflects recent volcanism within a 1-3 km wide zone of crustal accretion. Initial 230Th/232Th ratios and 230Th activity were also used to examine the recent Th/U evolution and extent of melting of mantle sources beneath these ridges. A negative anomaly in 230Th 232Th for Axial seamount lavas provides the first geochemical evidence of a mantle plume source for Axial seamount and the Cobb-Eickelberg seamount chain and indicates recent depletion of other JDF segment sources. Large 230Th activity excesses for lavas from northern Gorda ridge and Endeavour segment indicate formation from a lower degree of partial melting than other segments. An

  10. Hydrothermal scavenging on the Juan de Fuca Ridge: {sup 230}Th{sub xs}, {sup 10}Be, and REEs in ridge-flank sediments

    SciTech Connect

    German, C.R.; Colley, S.; Higgs, N.C.; Ludford, E.M.

    1997-10-01

    We have investigated the geochemistry of a hydrothermally enriched sediment core recovered from the western flank of the N.Cleft Segment, Juan de Fuca Ridge, {approximately}8km west of the {open_quotes}MegaPlume{close_quotes} area previously identified near 45{degrees}N. The core contains varying biogenic, lithogenic, and hydrothermal components, as reflected in CaCO{sub 3}, Al, and Fe contents, respectively. Horizons of pronounced hydrothermal input, in core-top sediments and at depth, exhibit increased concentrations of Fe, Cu, Zn, and Pb and shifts in Pb isotopic compositions toward nonradiogenic (MORB/hydrothermal) values. REE concentrations co-vary with hydrothermal Fe down-core, and shale-normalised REE distribution patterns exhibit both negative Ce-anomalies and positive Eu-anomalies, indicative of input from plume-particle fall-out. Unsupported {sup 230}Th{sub xs} activities down-core are consistent with continuous slow sediment accumulation rates of 0.54 cm/ky for 200 ky since the deposition of the deeper Fe-rich horizon. {sup 10}Be{sub (0)}, and {sup 9}Be isotope concentrations also co-vary with hydrothermal Fe down-core and exhibit {sup 10}Be{sub (0)} ratios which approach that of Pacific Ocean deep water, indicative of a seawater-scavenging source. 49 refs., 9 figs., 7 tabs.

  11. Lead isotope relations in oceanic Ridge basalts from the Juan de Fuca-Gorda Ridge area N.E. Pacific Ocean

    USGS Publications Warehouse

    Church, S.E.; Tatsumoto, M.

    1975-01-01

    Lead isotopic analyses of a suite of basaltic rocks from the Juan de Fuca-Gorda Ridge and nearby seamounts confirm an isotopically heterogeneous mantle known since 1966. The process of mixing during partial melting of a heterogeneous mantle necessarily produces linear data arrays that can be interpreted as secondary isochrons. Moreover, the position of the entire lead isotope array, with respect to the geochron, requires that U/Pb and Th/Pb values are progressively increased over the age of the earth. Partial melting theory also dictates analogous behavior for the other incompatible trace elements. This process explains not only the LIL element character of MOR basalts, but also duplicates the spread of radiogenic lead data collected from alkali-rich oceanic basalts. This dynamic, open-system model of lead isotopic and chemical evolution of the mantle is believed to be the direct result of tectonic flow and convective overturn within the mantle and is compatible with geophysical models of a dynamic earth. ?? 1975 Springer-Verlag.

  12. Effects of hydrothermal alteration on the magnetic mineralogy of mid-ocean ridge basalts, IODP Site 1301B, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Linville, L. M.; Housen, B.; Sager, W.

    2005-12-01

    Pairs of young (3.5 Ma) altered and unaltered MORB from the Juan de Fuca Ridge collected from IODP Expedition 301, Hole 1301B were studied to better understand how hydrothermal alteration affects the magnetization of oceanic crust. Thermomagnetic analysis (performed with both a VSM and Kappabridge) revealed characteristically different Curie temperatures and degree of non-reversibility between altered and unaltered samples. Magnetic contributions outlined by these methods, in addition to IRM and hysteresis parameters, indicate that samples are dominated by single domain titanomagnetite and titanomaghemite, with a titanium content of approximately TM45. Petrological analysis with a SEM confirmed the presence of abundant Fe-Ti oxides. Despite the preponderance of titanomagnetite in unaltered samples, shrinkage cracks, which offer direct evidence of maghemitization, were seen in both altered and unaltered samples, indicating (as do irreversible cooling curves for all samples) that even supposedly unaltered samples have undergone some degree of low temperature oxidation. Preliminary paleomagnetic data in related samples indicates normal polarity and inclinations that are approximately what is expected for this site. The samples also exhibit both streaked and well defined, non-streaked magnetizations. This study intends to utilize the information obtained by procedures described above to test for correlations between characteristic magnetization directions and degree of oxidation, in order to further our understanding of the effect maghemitization has on the paleomagnetism of oceanic rocks.

  13. Evidence of active ground deformation on the mid-ocean ridge: Axial seamount, Juan de Fuca Ridge, April-June 1988

    SciTech Connect

    Fox, C.G. )

    1990-08-10

    Since September 1987 a precision bottom pressure recorder (BPR) has been deployed within the summit caldera of Axial seamount. The instrument is capable of measuring pressure of 1 mbar resolution and recording these measurements at 64 samples per hour for up to 15 months. Any significant change in the pressure record should indicate a change of depth associated with vertical ground movement, commonly indicative of active inflation or deflation of underlying magma bodies. Results from the first 9 months of the BPR deployment revealed a significant change in pressure, which is interpreted to represent a 15-cm subsidence of the caldera floor during two 2- to 3-week periods in April-June 1988. Also during these periods, an anomalous decline in temperature at the site was recorded that is correlated with an apparent increase in current velocity at the Axial Seamount Hydrothermal Emissions Study (ASHES) vent field, suggesting vigorous advection of cold water into the caldera. Concurrent oceanographic data from Geosat and from current meter arrays do not indicate any large-scale oceanographic phenomena capable of generating these simultaneous events. One mechanism to explain simultaneous ground subsidence and temperature decline at the caldera center and increased bottom current at the caldera margin is the generation of a buoyant parcel of heated water in response to the intrusion or the eruption of magma associated with volcanic deflation. Similar volcanic events also may have generated large midwater plumes that have been described previously along the southern Juan de Fuca Ridge.

  14. Seafloor tilt induced by ocean tidal loading inferred from broadband seismometer data from the Cascadia subduction zone and Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Davis, Earl E.; Heesemann, Martin; Lambert, Anthony; He, Jianheng

    2017-04-01

    Mass-balancing voltages from four buried broadband seismometers connected to the NEPTUNE Canada seafloor cable are being recorded at 24-bit resolution. Sites are located on the Vancouver Island continental shelf, the nearby Cascadia accretionary prism, the eastern flank of the Juan de Fuca Ridge, and the western flank close to the Juan de Fuca Ridge axis. Tidal variations are present throughout the records. Variations in vertical acceleration at three of the sites match predicted gravitational attraction variations very well; those at the fourth site show a small residual that is probably caused by sensitivity to tilt resulting from sensor inclination. Horizontal accelerations, which at tidal periods are sensitive primarily to tilt, are anomalously large relative to standard-earth model results. After removal of predicted tidal body and ocean attraction and loading terms, the residuals are seen to follow ocean pressure variations. Responses range from 0.4 μrad dbar-1 (0.04 μrad kPa-1) at 10° true (down under positive load) at the continental shelf site, to 0.6 μrad dbar-1 at 243° at the Cascadia prism, 0.4 μrad dbar-1 at 90° at the eastern Juan de Fuca Ridge flank, and 0.2 μrad dbar-1 at 116° true on the western ridge flank. Except at the continental shelf site, tilts are roughly perpendicular to structural strike. The tilt observations can be explained by loading-induced deformation in the presence of local lithologic gradients or by the influence of faults or structurally controlled anisotropic elastic properties. The observations highlight the utility of using mass position data from force-feedback broad-band seismometers for geodynamic studies.

  15. Shear wave splitting observations across the Juan de Fuca plate system: Ridge- to-trench constraints on mantle flow from 2 years of Cascadia Initiative OBS data

    NASA Astrophysics Data System (ADS)

    Bodmer, M.; Toomey, D. R.; Hooft, E. E. E.

    2014-12-01

    We present SKS splitting measurements for the first two years of data collected by the Cascadia Initiative (CI) amphibious array. Our analysis includes observations from over 100 ocean bottom seismometers (OBS), as well as 31 onshore stations, and spans both the Juan de Fuca and Gorda plates. The CI dataset is unique in that it includes several regions that can distinctly influence anisotropic fabric development such as: the upwelling mantle beneath the Juan de Fuca and Gorda ridges, the young evolving oceanic lithosphere of the plate interior, the Blanco transform fault, and the Cascadia subduction zone. For the first time, we are able to analyze these regions with a single dataset, and using a common methodology. Splitting measurements are routinely done on land sites, but have been completed on relatively few OBS stations. This is largely due to the low signal to noise present in OBS data, which can obscure the splitting results. To address that nearly all the OBS data exceeds the global high noise limit at the frequencies used for splitting, we implement a rigorous quality control scheme. Our method specifically takes into account the response of common splitting methods to high noise data and addresses known issues such as cycle skipping, false minima, low transverse energy, and near-null measurements. Individual measurements are filtered at 0.03-0.1 Hz, manually checked for quality, and stacked. Preliminary results show trench perpendicular onshore measurements consistent with previous studies. Oceanic measurements in the plate interior show a coherent fast axis roughly aligned with absolute plate motion. Several measurements near the ridge and trench appear to be rotated in the ridge and trench parallel directions. Continuing work will integrate splitting measurements from the final two years of the CI with these findings, which will be used to characterize the ridge-to-trench mantle flow across the Juan de Fuca plate system.

  16. Elastic Full Waveform Inversion reveals the fine-scale structure of Axial Volcano on the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Arnulf, A. F.; Harding, A. J.; Kent, G.

    2012-12-01

    Axial volcano (sometimes referred to as "Axial seamount" or "Axial") is located at 46N, 130W at the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg seamount chain. It is the most recent eruptive center of the Cobb hotspot, which last erupted in 2011. The volcano rises ~700 m above the adjacent ridge axis and its summit features a U-shaped caldera open to the southeast, which hosts an active hydrothermal field and very young lava flows. Located at the junction of a mid-ocean ridge and a volcanic hotspot, Axial volcano is atypical and its internal structure remains poorly understood. Here, we present results from an elastic full waveform inversion (FWI) along multiple seismic lines that span the whole volcano. We have used a multi-stage FWI, inverting successively wide-angle reflections and refractions arrivals from downward extrapolated streamer data, then windowed short offset reflections from the underlying magma chamber. Our final models show fine scale velocity structures with spatial resolutions of tens of meters. Our results indicate that Layer 2A thickness is extremely heterogeneous (350-900 m) within the volcano with abrupt vertical throws of >300 m beneath the caldera walls that suggests the tectonic thinning of a geologically defined Layer 2A. Interestingly, Layer 2A appears to be extremely thin beneath the active hydrothermal field and the most recent lava flows, on the southeast end of the caldera, where sheeted dikes might lay <100 m beneath the seafloor. On the other hand, the nearby caldera center is filled by successive lava sequences (~450 m thick) that further appear to be micro faulted, suggesting a constant interplay between magmatic and tectonic processes. Surface velocities show limited variation over the whole volcano and may suggest relative recent formation, considering the rapid increase in layer 2A velocity with age. Finally, our velocity structures image a wide and complex magma chamber system beneath the volcano at depth

  17. Permeabilities of Young Oceanic Crust on the Flanks of the Juan de Fuca Ridge and Costa Rica Rift Determined from Borehole Temperature and Pressure Measurements

    NASA Astrophysics Data System (ADS)

    Becker, K.; Davis, E. E.

    2002-12-01

    In 1996, long-term CORK hydrological observatories were installed in four cased holes drilled by the Ocean Drilling Program through sediment cover into young oceanic crust east of the Juan de Fuca Ridge. Initial temperature measurements indicated vertical fluid flow in all of the holes prior to sealing with CORKs. Warm water was being produced from igneous crust of two sediment-covered basement ridges, and cool seawater was being drawn into basement at the other two holes. Rates were estimated from the perturbed temperature profiles at ~60 to 200 m/hr. Pressure differentials driving the flow were also measured with the CORK installations, allowing estimates of permeabilities of the upper crustal sections penetrated by the holes. Values vary systematically with age, ranging from about 10-10 m2 in the youngest site (0.9 Ma) to 10-12 m2 in the oldest site (3.6 Ma), confirming an apparent reduction of permeability with age determined with packer experiments at three of the same sites. Combined with other estimates of permeabilities in the same holes using methods with different scales of investigation, the new permeability estimates provide further evidence for a significant scale dependence of permeability in the upper oceanic crust. In 2001, wireline-deployable analogs of the CORK experiments were installed in two cased holes in well-sedimented ~6-m.y.-old crust on the south flank of the Costa Rica Ridge. The structural setting was very similar to the older pair of the four Juan de Fuca CORKs, and the results from initial temperature measurements were also comparable: warm water was produced from a hole in a sediment-covered basement ridge and cool seawater was being drawn into a neighboring hole in a basement trough. Rates of flow were slower than at the Juan de Fuca sites, probably because the holes had been left open for years. Pressure data are scheduled to be collected in November 2002 using DSV Alvin and should allow permeability calculations similar to those

  18. Mineralogical studies of sulfide samples and volatile concentrations of basalt glasses from the southern Juan de Fuca Ridge.

    PubMed

    Brett, R; Evans, H T; Gibson, E K; Hedenquist, J W; Wandless, M V; Sommer, M A

    1987-10-10

    Sulfide samples obtained from the U.S. Geological Survey's DSRV Alvin dives on the southern Juan de Fuca Ridge closely resemble those from the same area described by Koski et al. (1984). Major minerals include sphalerite, wurtzite, pyrite, marcasite, isocubanite, anhydrite, and chalcopyrite. Equilibrium, if attained at all, during deposition of most sulfides was a transient event over a few tens of micrometers at most and was perturbed by rapid temperature and compositional changes of the circulating fluid. Two new minerals were found: one, a hydrated Zn, Fe hydroxy-chlorosulfate, and the other, a (Mn, Mg, Fe) hydroxide or hydroxy-hydrate. Both were formed at relatively low temperatures. Lizardite, starkeyite, and anatase were found for the first time in such an environment. Sulfide geothermometry involving the system Cu-Fe-S indicates a vent temperature of <328 degrees C for one sample. Fluid inclusion studies on crystals from the same vicinity of the same sample give pressure-corrected homogenization temperatures of 268 degrees and 285 degrees C. Ice-melting temperatures on inclusions from the same sample are about -2.8 degrees C, indicating that the equivalent salinity of the trapped fluid is about 50% greater than that of seawater. Volatile concentrations from vesicle-free basalt glass from the vent field are about 0.013 wt% CO2 and 0.16 wt% H2O, CO2 contents in these samples yield an entrapment depth of 2200 m of seawater, which is the depth from which the samples were collected.

  19. GeoChip-based analysis of metabolic diversity of microbial communities at the Juan de Fuca Ridge hydrothermal vent

    PubMed Central

    Wang, Fengping; Zhou, Huaiyang; Meng, Jun; Peng, Xiaotong; Jiang, Lijing; Sun, Ping; Zhang, Chuanlun; Van Nostrand, Joy D.; Deng, Ye; He, Zhili; Wu, Liyou; Zhou, Jizhong; Xiao, Xiang

    2009-01-01

    Deep-sea hydrothermal vents are one of the most unique and fascinating ecosystems on Earth. Although phylogenetic diversity of vent communities has been extensively examined, their physiological diversity is poorly understood. In this study, a GeoChip-based, high-throughput metagenomics technology revealed dramatic differences in microbial metabolic functions in a newly grown protochimney (inner section, Proto-I; outer section, Proto-O) and the outer section of a mature chimney (4143-1) at the Juan de Fuca Ridge. Very limited numbers of functional genes were detected in Proto-I (113 genes), whereas much higher numbers of genes were detected in Proto-O (504 genes) and 4143-1 (5,414 genes). Microbial functional genes/populations in Proto-O and Proto-I were substantially different (around 1% common genes), suggesting a rapid change in the microbial community composition during the growth of the chimney. Previously retrieved cbbL and cbbM genes involved in the Calvin Benson Bassham (CBB) cycle from deep-sea hydrothermal vents were predominant in Proto-O and 4143-1, whereas photosynthetic green-like cbbL genes were the major components in Proto-I. In addition, genes involved in methanogenesis, aerobic and anaerobic methane oxidation (e.g., ANME1 and ANME2), nitrification, denitrification, sulfate reduction, degradation of complex carbon substrates, and metal resistance were also detected. Clone libraries supported the GeoChip results but were less effective than the microarray in delineating microbial populations of low biomass. Overall, these results suggest that the hydrothermal microbial communities are metabolically and physiologically highly diverse, and the communities appear to be undergoing rapid dynamic succession and adaptation in response to the steep temperature and chemical gradients across the chimney. PMID:19273854

  20. GeoChip-based analysis of metabolic diversity of microbial communities at the Juan de Fuca Ridge hydrothermal vent.

    PubMed

    Wang, Fengping; Zhou, Huaiyang; Meng, Jun; Peng, Xiaotong; Jiang, Lijing; Sun, Ping; Zhang, Chuanlun; Van Nostrand, Joy D; Deng, Ye; He, Zhili; Wu, Liyou; Zhou, Jizhong; Xiao, Xiang

    2009-03-24

    Deep-sea hydrothermal vents are one of the most unique and fascinating ecosystems on Earth. Although phylogenetic diversity of vent communities has been extensively examined, their physiological diversity is poorly understood. In this study, a GeoChip-based, high-throughput metagenomics technology revealed dramatic differences in microbial metabolic functions in a newly grown protochimney (inner section, Proto-I; outer section, Proto-O) and the outer section of a mature chimney (4143-1) at the Juan de Fuca Ridge. Very limited numbers of functional genes were detected in Proto-I (113 genes), whereas much higher numbers of genes were detected in Proto-O (504 genes) and 4143-1 (5,414 genes). Microbial functional genes/populations in Proto-O and Proto-I were substantially different (around 1% common genes), suggesting a rapid change in the microbial community composition during the growth of the chimney. Previously retrieved cbbL and cbbM genes involved in the Calvin Benson Bassham (CBB) cycle from deep-sea hydrothermal vents were predominant in Proto-O and 4143-1, whereas photosynthetic green-like cbbL genes were the major components in Proto-I. In addition, genes involved in methanogenesis, aerobic and anaerobic methane oxidation (e.g., ANME1 and ANME2), nitrification, denitrification, sulfate reduction, degradation of complex carbon substrates, and metal resistance were also detected. Clone libraries supported the GeoChip results but were less effective than the microarray in delineating microbial populations of low biomass. Overall, these results suggest that the hydrothermal microbial communities are metabolically and physiologically highly diverse, and the communities appear to be undergoing rapid dynamic succession and adaptation in response to the steep temperature and chemical gradients across the chimney.

  1. Linkages between mineralogy, fluid chemistry, and microbial communities within hydrothermal chimneys from the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Lin, T. J.; Ver Eecke, H. C.; Breves, E. A.; Dyar, M. D.; Jamieson, J. W.; Hannington, M. D.; Dahle, H.; Bishop, J. L.; Lane, M. D.; Butterfield, D. A.; Kelley, D. S.; Lilley, M. D.; Baross, J. A.; Holden, J. F.

    2016-02-01

    Rock and fluid samples were collected from three hydrothermal chimneys at the Endeavour Segment, Juan de Fuca Ridge to evaluate linkages among mineralogy, fluid chemistry, and microbial community composition within the chimneys. Mössbauer, midinfrared thermal emission, and visible-near infrared spectroscopies were utilized for the first time to characterize vent mineralogy, in addition to thin-section petrography, X-ray diffraction, and elemental analyses. A 282°C venting chimney from the Bastille edifice was composed primarily of sulfide minerals such as chalcopyrite, marcasite, and sphalerite. In contrast, samples from a 300°C venting chimney from the Dante edifice and a 321°C venting chimney from the Hot Harold edifice contained a high abundance of the sulfate mineral anhydrite. Geochemical modeling of mixed vent fluids suggested the oxic-anoxic transition zone was above 100°C at all three vents, and that the thermodynamic energy available for autotrophic microbial redox reactions favored aerobic sulfide and methane oxidation. As predicted, microbes within the Dante and Hot Harold chimneys were most closely related to mesophilic and thermophilic aerobes of the Betaproteobacteria and Gammaproteobacteria and sulfide-oxidizing autotrophic Epsilonproteobacteria. However, most of the microbes within the Bastille chimney were most closely related to mesophilic and thermophilic anaerobes of the Deltaproteobacteria, especially sulfate reducers, and anaerobic hyperthermophilic archaea. The predominance of anaerobes in the Bastille chimney indicated that other environmental factors promote anoxic conditions. Possibilities include the maturity or fluid flow characteristics of the chimney, abiotic Fe2+ and S2- oxidation in the vent fluids, or O2 depletion by aerobic respiration on the chimney outer wall.

  2. Space-time relations of hydrothermal sulfide-sulfate-silica deposits at the northern Cleft Segment, Juan de Fuca Ridge

    SciTech Connect

    Koski, R.A.; Smith, V.K. ); Embley, R.W. ); Jonasson, I.R. ); Kadko, D.C. . Rosenstiel School of Marine and Atmospheric Science)

    1993-04-01

    Submersible investigations along the northern Cleft Segment of the Juan de Fuca Ridge indicate that a newly erupted sheet flow and two recent megaplume events are spatially related to a NNE-trending fissure system that is now the locus for active hydrothermal venting and deposition of massive sulfide mounds and chimneys. Samples from active high-temperature vent sites located east and north of the sheet flow terrain include zoned Cu-sulfide-rich chimneys (Type 1), bulbous anhydrite-rich chimneys (Type 2), and columnar Zn-sulfide-rich chimneys (Type 3). Type 1 chimneys with large open channelways result from the focused discharge of fluid at temperatures between 310 and 328 C from the Monolith sulfide mound. Type 2 chimneys are constructed on the Monolith and Fountain mounds where discharge of fluid at temperatures between 293 and 315 C is diffuse and sluggish. Type 3 chimneys, characterized by twisting narrow channelways, are deposited from focused and relatively low-temperature fluid discharging directly from basalt substrate. Inactive sulfide chimneys (Type 4) located within 100 m of the fissure system have bulk compositions, mineral assemblages, colloform and bacteroidal textures, and oxygen isotope characteristics consistent with low-temperature (< 250 C ) deposition from less robust vents. Field relations and [sup 210]Pb ages (> 100 years) indicate that the Type 4 chimneys formed prior to the sheet flow eruption. The sulfide mounds and Type 1 and Type 2 chimneys at the Monolith and Fountain vents, however, are an expression of the same magmatic event that caused the sheet flow eruption and megaplume events.

  3. Heat flux measured acoustically at Grotto Vent, a hydrothermal vent cluster on the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Xu, G.; Jackson, D. R.; Bemis, K. G.; Rona, P. A.

    2013-12-01

    Over the past several decades, quantifying the heat output has been a unanimous focus of studies at hydrothermal vent fields discovered around the global ocean. Despite their importance, direct measurements of hydrothermal heat flux are very limited due to the remoteness of most vent sites and the complexity of hydrothermal venting. Moreover, almost all the heat flux measurements made to date are snapshots and provide little information on the temporal variation that is expected from the dynamic nature of a hydrothermal system. The Cabled Observatory Vent Imaging Sonar (COVIS, https://sites.google.com/a/uw.edu/covis/) is currently connected to the Endeavour node of the NEPTUNE Canada observatory network (http://www.neptunecanada.ca) to monitor the hydrothermal plumes issuing from a vent cluster (Grotto) on the Endeavour Segment of the Juan de Fuca Ridge. COVIS is acquiring a long-term (20-months to date) time series of the vertical flow rate and volume flux of the hydrothermal plume above Grotto through the Doppler analysis of the acoustic backscatter data (Xu et al., 2013). We then estimate the plume heat flux from vertical flow rate and volume flux using our newly developed inverse method. In this presentation, we will briefly summarize the derivation of the inverse method and present the heat-flux time series obtained consequently with uncertainty quantification. In addition, we compare our heat-flux estimates with the one estimated from the plume in-situ temperatures measured using a Remotely Operative Vehicle (ROV) in 2012. Such comparison sheds light on the uncertainty of our heat flux estimation. Xu, G., Jackson, D., Bemis, K., and Rona, P., 2013, Observations of the volume flux of a seafloor hydrothermal plume using an acoustic imaging sonar, Geochemistry, Geophysics Geosystems, 2013 (in press).

  4. Assimilation of Seawater in Basaltic Magmas: Evidence Found in a Lava Pillar From Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Schiffman, P.; Zierenberg, R.; Chadwick, W. W.; Clague, D. A.

    2008-12-01

    A lava pillar formed during the 1998 eruption at Axial Seamount exhibits compositional and textural evidence consistent with the direct assimilation of seawater under magmatic conditions. Glass immediately adjacent to anastomosing microfractures within 1 cm of the inner pillar wall is oxidized and significantly enriched in both Na and Cl (and depleted in Fe and K) with respect to that in selvages from the (unaffected) outer pillar wall. The affected glass contains up to 1 wt. % Cl and is enriched by ca. 2 wt. % Na2O relative to unaffected glass, consistent with a nearly 1:1 (molar) assimilation of NaCl. Glass not adjacent to microfractures in the inner pillar wall is depleted in Na, but enriched in K, with respect to the NaCl-enriched, inner pillar wall glass and the unaffected outer pillar wall glass. The 87Sr/86Sr ratio of the NaCl-enriched glass (ca. 0.704 +/- .001), as determined by LA ICPMS, is slightly elevated with respect to that of unaffected glass (ca. .703) consistent with the incorporation of a seawater-derived fluid. The presence of tiny (< 10 mm) grains of Cu-Fe- and Fe-sulfides as well as elemental Ni, Ag, and Au in the Na-depleted, K-enriched glass of the inner pillar wall implies significant reduction of this glass, presumably by hydrogen generated during seawater assimilation and oxidation of magma adjacent to microfractures. We interpret that the chemical anomalies we see in the glass of the interior pillar wall are caused by nearly instantaneous assimilation of seawater into the magma during pillar growth. Other lava pillars we have examined from Axial Seamount and elsewhere on the Juan de Fuca Ridge do not display similar features, although we have not examined a statistically significant number of samples to ascertain how widespread a process this is for seawater assimilation.

  5. High-resolution near-bottom vector magnetic anomalies over Raven Hydrothermal Field, Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Tivey, Maurice A.; Johnson, H. Paul; Salmi, Marie S.; Hutnak, Michael

    2014-10-01

    High-resolution, near-bottom vector magnetic data were collected by remotely operated vehicle Jason over the Raven hydrothermal vent field (47°57.3'N 129°5.75'W) located north of Main Endeavour vent field on the Endeavour segment of the Juan de Fuca Ridge. The survey was part of a comprehensive heat flow study of the Raven site using innovative thermal blanket technology to map the heat flux and crustal fluid pathways around a solitary hydrothermal vent field. Raven hydrothermal activity is presently located along the western axial valley wall, while additional inactive hydrothermal deposits are found to the NW on the upper rift valley wall. Magnetic inversion results show discrete areas of reduced magnetization associated with both active and inactive hydrothermal vent deposits that also show high conductive heat flow. Higher spatial variability in the heat flow patterns compared to the magnetization is consistent with the heat flow reflecting the currently active but ephemeral thermal environment of fluid flow, while crustal magnetization is representative of the static time-averaged effect of hydrothermal alteration. A general NW to SE trend in reduced magnetization across the Raven area correlates closely with the distribution of hydrothermal deposits and heat flux patterns and suggests that the fluid circulation system at depth is likely controlled by local crustal structure and magma chamber geometry. Magnetic gradient tensor components computed from vector magnetic data improve the resolution of the magnetic anomaly source and indicate that the hydrothermally altered zone directly beneath the Raven site is approximately 15 × 106 m3 in volume.

  6. Influence of Igneous Basement on Deep Sediment Microbial Diversity on the Eastern Juan de Fuca Ridge Flank

    PubMed Central

    Labonté, Jessica M.; Lever, Mark A.; Edwards, Katrina J.; Orcutt, Beth N.

    2017-01-01

    Microbial communities living in deeply buried sediment may be adapted to long-term energy limitation as they are removed from new detrital energy inputs for thousands to millions of years. However, sediment layers near the underlying oceanic crust may receive inputs from below that influence microbial community structure and/or activity. As part of the Census of Deep Life, we used 16S rRNA gene tag pyrosequencing on DNA extracted from a spectrum of deep sediment-basement interface samples from the subsurface of the Juan de Fuca Ridge flank (collected on IODP Expedition 327) to examine this possible basement influence on deep sediment communities. This area experiences rapid sedimentation, with an underlying basaltic crust that hosts a dynamic flux of hydrothermal fluids that diffuse into the sediment. Chloroflexi sequences dominated tag libraries in all sediment samples, with variation in the abundance of other bacterial groups (e.g., Actinobacteria, Aerophobetes, Atribacteria, Planctomycetes, and Nitrospirae). These variations occur in relation to the type of sediment (clays versus carbonate-rich) and the depth of sample origin, and show no clear connection to the distance from the discharge outcrop or to basement fluid microbial communities. Actinobacteria-related sequences dominated the basalt libraries, but these should be viewed cautiously due to possibilities for imprinting from contamination. Our results indicate that proximity to basement or areas of seawater recharge is not a primary driver of microbial community composition in basal sediment, even though fluids diffusing from basement into sediment may stimulate microbial activity. PMID:28824568

  7. Degassing and Vesiculation during the 2011 Eruption of Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Jones, M.; Soule, S. A.

    2015-12-01

    The dependency of CO2 disequilibrium in mid-ocean ridge basalts (MORB) on magma ascent and emplacement rates makes volatile analysis a valuable tool for evaluating submarine eruption dynamics. This study examines volatile content and vesicle size distributions in a suite of samples collected from the 2011 eruption of Axial Seamount. The samples exhibit a wide range of dissolved CO2 concentrations (68 - 339 ppm), low H2O concentrations (0.17 - 0.26 wt %), and consistent supersaturation relative to the expected CO2-H2O phase equilibrium in basaltic melts. The vesicularity, characteristic bubble radii, and bubble number density correlate with the dissolved volatile concentrations and indicate that bubble nucleation and growth occur within a closed system. The extent of degassing increases with distance from the eruptive vent and variations are also observed along the eruptive fissure providing a spatially resolved record of eruption dynamics. A bubble growth model is used to constrain the minimum ascent rates, eruption duration, and flow rates for the 2011 eruption. These results are compared to similar data from the global mid-ocean ridge system to evaluate differences in timescales of emplacement and ascent in MOR eruptions.

  8. Complete Genome Sequence of the Hyperthermophilic Archaeon Pyrococcus sp. Strain ST04, Isolated from a Deep-Sea Hydrothermal Sulfide Chimney on the Juan de Fuca Ridge

    PubMed Central

    Jung, Jong-Hyun; Lee, Ju-Hoon; Holden, James F.; Seo, Dong-Ho; Shin, Hakdong; Kim, Hae-Yeong; Kim, Wooki; Ryu, Sangryeol

    2012-01-01

    Pyrococcus sp. strain ST04 is a hyperthermophilic, anaerobic, and heterotrophic archaeon isolated from a deep-sea hydrothermal sulfide chimney on the Endeavour Segment of the Juan de Fuca Ridge in the northeastern Pacific Ocean. To further understand the distinct characteristics of this archaeon at the genome level (polysaccharide utilization at high temperature and ATP generation by a Na+ gradient), the genome of strain ST04 was completely sequenced and analyzed. Here, we present the complete genome sequence analysis results of Pyrococcus sp. ST04 and report the major findings from the genome annotation, with a focus on its saccharolytic and metabolite production potential. PMID:22843576

  9. Complete genome sequence of the hyperthermophilic archaeon Pyrococcus sp. strain ST04, isolated from a deep-sea hydrothermal sulfide chimney on the Juan de Fuca Ridge.

    PubMed

    Jung, Jong-Hyun; Lee, Ju-Hoon; Holden, James F; Seo, Dong-Ho; Shin, Hakdong; Kim, Hae-Yeong; Kim, Wooki; Ryu, Sangryeol; Park, Cheon-Seok

    2012-08-01

    Pyrococcus sp. strain ST04 is a hyperthermophilic, anaerobic, and heterotrophic archaeon isolated from a deep-sea hydrothermal sulfide chimney on the Endeavour Segment of the Juan de Fuca Ridge in the northeastern Pacific Ocean. To further understand the distinct characteristics of this archaeon at the genome level (polysaccharide utilization at high temperature and ATP generation by a Na(+) gradient), the genome of strain ST04 was completely sequenced and analyzed. Here, we present the complete genome sequence analysis results of Pyrococcus sp. ST04 and report the major findings from the genome annotation, with a focus on its saccharolytic and metabolite production potential.

  10. Mixing of Mantle Sources Preserved in Melt Inclusions at Coaxial Segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Schwartz, D. M.; Wanless, V. D.; Lytle, M. L.; Clague, D. A.

    2016-12-01

    Coaxial segment of the Juan de Fuca Ridge (JdFR) has a poorly defined axial rift, a wide rift valley, and erupts primarily pillow lavas, suggesting relatively low magma supply compared to more magmatically robust ridge segments to the south. To evaluate magma supply at Coaxial, we have analyzed olivine-hosted melt inclusions (MIs; N=113) and host glasses (N=7) for major, trace and volatile element contents, which we compare with new and existing data from Vance and Cleft segments of the JdFR. Of the three segments, Coaxial has the most diverse range of MI compositions. We divide the Coaxial MIs into two categories based on major and trace element systematics: NMORB (La/Sm > 0.5 and K2O/TiO2 > 0.05; N=68) and DMORB (La/Sm ≤ 0.5 and K2O/TiO2 ≤ 0.05; N=45), with the NMORB inclusions more closely resembling those of Cleft and Vance. DMORB inclusions are also characterized by higher mean FeO/MgO (0.93) and H2O/Ce (0.076) compared to NMORB (FeO/MgO =1.1 and H2O/Ce = 0.032). As a whole, the MIs from Coaxial have relatively low equilibration depths in the crust (average of 1656 m; determined by vapor saturation pressures of CO2-H2O) compared to the depth of the seismically imaged melt lens (2329 m; Carbotte et al., 2008). However, when considered separately, NMORB have peak MI depths consistent with the melt lens, similar to the other segments investigated, while the DMORB MI have a shallower peak resulting from lower CO2 concentrations. We suggest that the lower La/Sm and CO2/Nb ratios in the DMORB indicate the presence of a depleted mantle source, consistent with reported mantle values (e.g., Shimizu et al., 2016) that result in anomalously low equilibration pressures. However, the lower average FeO/MgO of the DMORB MIs support their early, likely deep, entrapment compared to the majority of NMORB inclusions. While DMORB compositions have been explained by high extents of melting of a normal mantle component, we favor a hypothesis where MIs are derived by mixing a

  11. Upper Crustal Structure of the Cleft Segment of the Juan de Fuca Ridge using 2D Streamer travel time tomography

    NASA Astrophysics Data System (ADS)

    Ghosh, S.; Canales, J.; Carbotte, S. M.; Nedimovic, M. R.

    2009-12-01

    We use long off-set (6 km) multichannel seismic reflection data to obtain the P-wave seismic structure of the upper ~2 km of the crust along the southern part of the intermediate-spreading Juan de Fuca Ridge (Cleft segment). Along this segment, the top of the Axial Magma Chamber (AMC) deepens from south to north from about 2.0 km at the southern end of the segment to about 2.3 km at the northern end. Both segment ends are characterized by high-temperature hydrothermal venting. Our objective is to study the effects of high temperature hydrothermal circulation on the seismic structure of the shallow crust. We jointly inverted refracted and reflected travel times (from the top of the AMC) to obtain the 2 dimensional velocity structure of the earth along ~60 km of the ridge axis. Prior to tomographic inversion, processing of marine seismic data included trace editing, trapezoidal band pass filtering (3-5-15-30 Hz), formation of partial off-set stacks of 5 shots (i.e, supershots) to increase the signal to noise ratio and downward continuation of the wavefield to a datum just above the sea floor (i.e, phase shift in the frequency-wave number domain of both source and receiver gathers to extract travel time information from refracted arrivals at near offset. Traveltime picking of the arrivals was done using a semi automated first break routine. The picked travel times of the first refracted arrivals and the reflected arrivals from the AMC are then input into a tomography inversion algorithm to build a 2D velocity model. Our results do not show detectable velocity variations associated with the presence of active high-temperature hydrothermal discharge, probably because the length scale of hydrothermal alteration is smaller than the resolving power of traveltime tomography. However our results are a first step towards higher-resolution seismic imaging models using waveform inversion. We will also present results from off-axis data to understand the early evolution of the

  12. Subsurface fluids from basement basalt of the Juan de Fuca Ridge possess microbial communities that are distinct from overlying sediments and surrounding seawater

    NASA Astrophysics Data System (ADS)

    Jungbluth, S.; Bowers, R. M.; Lin, H.; Hsieh, C.; Cowen, J. P.; Rappe, M. S.

    2013-12-01

    Hydrothermal circulation of fluids through the porous and permeable ocean basement fuels a deep subsurface microbial community that remains poorly characterized due to the logistical and methodological constraints associated with sampling the sediment-covered seafloor. Ocean Drilling Program and Integrated Ocean Drilling Program holes penetrating 1.2-3.5 million-years old sediment-covered basaltic crust of the Juan de Fuca Ridge flank fitted with Circulation Obviation Retrofit Kit (CORK) borehole observatories have enabled sampling of chemically-reducing basement fluids over the course of multiple years (2008-2013). Consistent and reliable access to pristine fluids from the ocean crust is due to improvements to CORK observatories, through incorporation of microbiologically-friendly materials, and fluid sampling techniques and equipment. By analyzing ~1.7 million reads of the small subunit ribosomal RNA (SSU rRNA) gene by next-generation Illumina sequencing from marine sediment, deep seawater, and 24 crustal fluid samples spanning multiple years and boreholes (1025C, U1301A, U1362A, and U1362), a distinct subseafloor biosphere dominated by the domain Bacteria was uncovered. Fluids from borehole U1301A sampled annually over the course of three years each had distinct microbial community structure and were dominated by the Proteobacteria. In contrast, fluids from boreholes 1362A and 1362B, located ~500 meters to the northeast, contained lineages phylogenetically related to the phylum Nitrospirae in highest abundance. The domain Archaea was was dominated by either the phylum Crenarchaeota (borehole U1301A) or the Euryarchaeota (boreholes 1025C, U1362A and U1362B). SSU rRNA genes phylogenetically affiliated with known lineages of methane producing Euryarchaeota (e.g. Methanobacteria) were the most abundant archaeal group detected in fluids from Holes U1362A and U1362B, predominantly within samples originating from the deepest subsurface sampling horizon (~200 meters sub

  13. Modeling mid-ocean ridge hydrothermal response to earthquakes, tides, and ocean currents: a case study at the Grotto mound, Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Xu, G.; Bemis, K. G.

    2014-12-01

    Seafloor hydrothermal systems feature intricate interconnections among oceanic, geological, hydrothermal, and biological processes. The advent of the NEPTUNE observatory operated by Ocean Networks Canada at the Endeavour Segment, Juan de Fuca Ridge enables scientists to study these interconnections through multidisciplinary, continuous, real-time observations. The multidisciplinary observatory instruments deployed at the Grotto Mound, a major study site of the NEPTUNE observatory, makes it a perfect place to study the response of a seafloor hydrothermal system to geological and oceanic processes. In this study, we use the multidisciplinary datasets recorded by the NEPTUNE Observatory instruments as observational tools to demonstrate two different aspects of the response of hydrothermal activity at the Grotto Mound to geological and oceanic processes. First, we investigate a recent increase in venting temperature and heat flux at Grotto observed by the Benthic and Resistivity Sensors (BARS) and the Cabled Observatory Vent Imaging Sonar (COVIS) respectively. This event started in Mar 2014 and is still evolving by the time of writing this abstract. An initial interpretation in light of the seismic data recorded by a neighboring ocean bottom seismometer on the NEPTUNE observatory suggests the temperature and heat flux increase is probably triggered by local seismic activities. Comparison of the observations with the results of a 1-D mathematical model simulation of hydrothermal sub-seafloor circulation elucidates the potential mechanisms underlying hydrothermal response to local earthquakes. Second, we observe significant tidal oscillations in the venting temperature time series recorded by BARS and the acoustic imaging of hydrothermal plumes by COVIS, which is evidence for hydrothermal response to ocean tides and currents. We interpret the tidal oscillations of venting temperature as a result of tidal loading on a poroelastic medium. We then invoke poroelastic

  14. Geologic setting of massive sulfide deposits and hydrothermal vents along the southern Juan de Fuca Ridge

    SciTech Connect

    Normark, W.R.; Morton, J.L.; Delaney, J.R.

    1982-01-01

    This report incorporates data from two cruises of the USGS vessel SP LEE: (1) L12-80-WF from 29 October to 13 November 1980, and (2) L11-81-WF from 4 to 15 September 1981. The 1980 cruise occurred long after the optimum weather window for this region. The natural results was that no photographic or sample stations could be attempted during nearly continuous gale- and storm-force winds, which twice forced the vessel to depart the work area for safety. A detailed bathymetric survey of a 35-km segment of the ridge axial zone was completed nonetheless, and the bathymetric map compiled from this survey was used as the base for our second cruise in 1981. The second visit to the area was blessed with fair weather, and most of the cruise effort was devoted to photography and sampling, including dredging and hydrocasts in the axial valley segment, which is the central part of the area surveyed in 1980.

  15. Large Lava Pond Complex on the Juan de Fuca Ridge: an Effusive, Energetic Eruption that Drained Away

    NASA Astrophysics Data System (ADS)

    Paduan, J. B.; Clague, D. A.; Davis, A. S.; Chadwick, W.; Cousens, B. L.; Embley, R. W.

    2005-12-01

    We explored an unusually large, deep, drained lava lake complex on the south rift of Axial Seamount on the Juan de Fuca Ridge during three dives with the ROV Tiburon in August 2005. The complex of five large ponds, first identified from EM300 multibeam bathymetry, is 5 km long and more than 1 km wide. The ponds are separated from one another by narrow levees that rise about 90 meters above the pond floors. The levees are all about the same depth, which suggests that the ponds formed at the same time. The volume of the lake, prior to draining, was 0.2-0.4 km3, making it the largest lava lake known along the ridge system. The outer slopes of the pond levees are constructed of elongate pillows that flowed down the steep slopes. The rims are narrow, level plateaus of lobate flows with many collapses. The inner walls are vertical cliffs, overhanging in places, with horizontal shelves from the top of the levees down to the floors of the ponds. Left like bathtub rings, these shelves mark former surfaces of the lava pond as it drained away while the lava was still molten. In many places, this veneer has collapsed to reveal truncated lobate flows and pillows. The floor of one small pond was entirely talus blocks. However, the floors of the other, larger ponds had little talus and, instead, were vast expanses of thin broken crusts, lobate flows, and very fluid, chaotic, folded and jumbled sheet flows. The lavas from each pond have abundant large feldspar and rarer olivine crystals, suggesting that all were from the same eruption. This eruption apparently began with sheet flows whose advance was limited by topography. It then ponded and built up the levees that were left when the lava drained away. On the floor of one pond we found a deposit several meters tall that was delicate and difficult to sample, and turned out to be agglutinated spatter. Limu o Pele (lava bubble wall fragments) was abundant in all the sediment samples in and around the ponds. The spatter and limu

  16. Chlorine stable isotopic composition of basement fluids of the eastern flank of the Juan de Fuca Ridge (ODP Leg 168)

    NASA Astrophysics Data System (ADS)

    Bonifacie, Magali; Monnin, Christophe; Jendrzejewski, Nathalie; Agrinier, Pierre; Javoy, Marc

    2007-08-01

    This paper presents chlorine stable isotope compositions (δ 37Cl) of sediment pore waters collected by squeezing sediment cores from the sediment-basement interface along an East-West transect through the eastern flank of the Juan de Fuca Ridge (ODP Leg 168). These "near basement fluids" (NBF) are generally thought to be representative of low-temperature fluids circulating in the off-axis basaltic crust. The δ 37Cl value of the fluid directly sampled from a flow at the base of Site 1026 (WSTP1026) is also reported. NBF display δ 37Cl values between - 2.09‰ and - 0.12‰ relative to the Standard Mean Ocean Chloride (SMOC defined as 0‰) and small variations in chlorinity (˜ 4%). These data contrast with the homogeneity of δ 37Cl values associated with highly variable chlorinities observed in high-temperature on-axis fluids [M. Bonifacie, J.L. Charlou, N. Jendrzejewski, P. Agrinier, J.P. Donval, Chlorine isotopic compositions of ridge axis high temperature hydrothermal vent fluids, Chem. Geol. 221(2005) 279-288.]. The NBF δ 37Cl values show a general decreasing trend with distance from the ridge-axis except for two fluids. When plotted against δ 18O values, the δ 37Cl of the NBF show two different trends. This paper discusses the possible contributions on NBF δ 37Cl values of fluid-mixing, water-rock interactions and transport processes (diffusion, ion membrane filtration) that can occur in the igneous basement. However, as none of these processes can fully explain the observed δ 37Cl variations, the potential effect of the sediment cover is also investigated. At site 1026, the interstitial pore fluid displays a δ 37Cl signature significantly lower than that of the fluid discharge sample (- 1.90‰ and - 0.28‰, respectively). This difference, demonstrated here cannot be an artifact of the sampling method, rather indicates the influence of the sediment cover on NBF δ 37Cl values. The potential contributions of physical processes associated with

  17. The birth and death of the oceanic lithosphere: Geochemical and tectonic investigations of the Juan de Fuca Ridge and Mariana Trench

    NASA Astrophysics Data System (ADS)

    Hulme, Samuel M.

    The research I conducted for my dissertation addresses specifically: (1) the role of fluid alteration of the ocean crust during its maturing stages near a spreading center using the Juan de Fuca Ridge as the model; and (2) the role of fluids in the demise of the crust as it is recycled within a subduction zone, using the non-accretioanry Mariana system as the model. The first 2 chapters detail the progressive alteration of a region of young oceanic crust (at the Juan de Fuca Ridge) by combining the results of multiple deep-sea drilling legs, long-term borehole observatory sampling, and hydrothermal vent chemistry. The third chapter examines fluid transfer during serpentinization of the suprasubduction lithosphere, based on the relationship between trace-element patterns and serpentine phases in serpentinite mud pore fluids and serpentinite mud/rocks collected at serpentinite mud volcanoes on the Mariana forearc. The final chapter presents detailed bathymetric and Hybrid Remote Operated Vehicle (HROV) Nereus surveys conducted in the deepest regions of the Mariana Trench (and therefore the world) that are interpreted to explain the regional tectonic processes and to guide future exploration efforts. These new efforts may lead to further discoveries of unique geologic features that will allow researchers to better understand the ongoing evolution of the Earth.

  18. Evolution of the Mothra Hydrothermal Field, Endeavour Segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Glickson, D.; Kelley, D. S.; Delaney, J.

    2005-12-01

    The Mothra Hydrothermal Field (MHF) is a 600 m long, high-temperature hydrothermal field. It is located 2.7 km south of the Main Endeavour Field at the southern end of the central Endeavour Segment. Mothra is the most areally extensive field along the Endeavour Segment, composed of six active sulfide clusters that are 40-200 m apart. Each cluster contains rare black smokers (venting up to 319°C), numerous diffusely venting chimneys, and abundant extinct chimneys and sulfide talus. From north to south, these clusters include Cauldron, Twin Peaks, Faulty Towers, Crab Basin, Cuchalainn, and Stonehenge. As part of the Endeavour Integrated Study Site (ISS), the MHF is a site of intensive interdisciplinary studies focused on linkages among geology, geochemistry, fluid chemistry, seismology, and microbiology. Axial valley geology at MHF is structurally complex, consisting of lightly fissured flows that abut the walls and surround a core of extensively fissured, collapsed terrain. Fissure abundance and distribution indicates that tectonism has been the dominant process controlling growth of the axial graben. Past magmatic activity is shown by the 200 m long chain of collapse basins between Crab Basin and Stonehenge, which may have held at least ~7500 m3 of lava. Assuming a flow thickness of 0.5 m, this amount of lava could cover over half the valley floor during a single volcanic event. At a local scale, MHF clusters vary in size, activity, and underlying geology. They range in size from 400-1600 m2 and consist of isolated chimneys and/or coalesced cockscomb arrays atop ramps of sulfide talus. In the northern part of the field, Cauldron, Twin Peaks, Faulty Towers, and Crab Basin are located near the western valley wall, bounded by basalt talus and a combination of collapsed sheet flows, intermixed lobate and sulfide, disrupted terrain, and isolated pillow ridges. The southern clusters, Cuchalainn and Stonehenge, are associated with collapse basins in the central valley

  19. Geochemistry of low-molecular weight hydrocarbons in hydrothermal fluids from Middle Valley, northern Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Cruse, Anna M.; Seewald, Jeffrey S.

    2006-04-01

    Hydrothermal vent fluids from Middle Valley, a sediment-covered vent field located on the northern Juan de Fuca Ridge, were sampled in July, 2000. Eight different vents with exit temperatures of 186-281 °C were sampled from two areas of venting: the Dead Dog and ODP Mound fields. Fluids from the Dead Dog field are characterized by higher concentrations of ΣNH 3 and organic compounds (C 1-C 4 alkanes, ethene, propene, benzene and toluene) compared with fluids from the ODP Mound field. The ODP Mound fluids, however, are characterized by higher C 1/(C 2 + C 3) and benzene:toluene ratios than those from the Dead Dog field. The aqueous organic compounds in these fluids have been derived from both bacterial processes (methanogenesis in low temperature regions during recharge) as well as from thermogenic processes in higher temperature portions of the subsurface reaction zone. As the sediments undergo hydrothermal alteration, carbon dioxide and hydrocarbons are released to solution as organic matter degrades via a stepwise oxidation process. Compositional and isotopic differences in the aqueous hydrocarbons indicate that maximum subsurface temperatures at the ODP Mound are greater than those at the Dead Dog field. Maximum subsurface temperatures were calculated assuming that thermodynamic equilibrium is attained between alkenes and alkanes, benzene and toluene, and carbon dioxide and methane. The calculated temperatures for alkene-alkane equilibrium are consistent with differences in the dissolved Cl concentrations in fluids from the two fields, and confirm that subsurface temperatures at the ODP Mound are hotter than those at the Dead Dog field. Temperatures calculated assuming benzene-toluene equilibrium and carbon dioxide-methane equilibrium are similar to observed exit temperatures, and do not record the hottest subsurface conditions. The difference in subsurface temperatures estimated using organic geochemical thermometers reflects subsurface cooling processes via

  20. Flow and hydrography at a hydrothermally-active axial valley in the northern Juan de Fuca Ridge.

    NASA Astrophysics Data System (ADS)

    Garcia Berdeal, I.; Hautala, S. L.

    2006-12-01

    High-resolution transects of flow and hydrography over a 3-km hydrothermally-active portion of Endeavour Segment (Juan de Fuca Ridge) are presented. The measurements span the bottom 300 m, including the 100- m deep axial valley. The hydrographic sections reveal background gradients in temperature, salinity and density with colder, saltier, and denser water to the south and east of the axial valley. Coincident with the along-valley density gradient is a bottom-intensified, northward along-valley current. The vertical shear of this current scales with the thermal wind shear derived from the cross-valley density gradient, and the flow is aligned with the baroclinic pressure gradient associated with the along-valley density gradient. Both the density gradient and along-valley flow are observed in repeated sections taken at different times. In order to maintain a steady state momentum balance necessary for the persistence of the along-valley current on long timescales, the baroclinic pressure gradient force could be balanced by vertical friction or advection of momentum, or lateral friction along the valley sidewalls. Hydrothermal plumes in their rising, laterally spreading, and equilibrated stages are also observed in the sections. Rising plumes are evidenced by density inversions, convergent flow surrounding their cores, and cyclonic vorticity of magnitude 10 times the Coriolis parameter. From the limited number of rising plumes that were detected in the towyo surveys over each vent field, it appears that plume salinity and buoyancy anomalies vary from north to south, as plumes over the northern High Rise field are fresher and more buoyant than those over the Main Endeavour field to the south. Considerable temporal and spatial variability in the maximum vertical extent of the plumes is evident in repeated sections, and is likely caused by tidal advection and the inherent intermittency of the plumes themselves. Near the level of neutral buoyancy, thin layers of

  1. Imaging hydrothermal roots along the Endeavour segment of the Juan de Fuca ridge using elastic full waveform inversion.

    NASA Astrophysics Data System (ADS)

    Arnulf, A. F.; Harding, A. J.; Kent, G. M.

    2016-12-01

    The Endeavour segment is a 90 km-long, medium-spreading-rate, oceanic spreading center located on the northern Juan de Fuca ridge (JDFR). The central part of this segment forms a 25-km-long volcanic high that hosts five of the most hydrothermally active vent fields on the MOR system, namely (from north to south): Sasquatch, Salty Dawg, High Rise, Main Endeavour and Mothra. Mass, heat and chemical fluxes associated to vigorous hydrothermal venting are large, however the geometry of the fluid circulation system through the oceanic crust remains almost completely undefined. To produce high-resolution velocity/reflectivity structures along the axis of the Endeavour segment, here, we combined a synthetic ocean bottom experiment (SOBE), 2-D traveltime tomography, 2D elastic full waveform and reverse time migration (RTM). We present velocity and reflectivity sections along Endeavour segment at unprecedented spatial resolutions. We clearly image a set of independent, geometrically complex, elongated low-velocity regions linking the top of the magma chamber at depth to the hydrothermal vent fields on the seafloor. We interpret these narrow pipe-like units as focused regions of hydrothermal fluid up-flow, where acidic and corrosive fluids form pipe-like alteration zones as previously observed in Cyprus ophiolites. Furthermore, the amplitude of these low-velocity channels is shown to be highly variable, with the strongest velocity drops observed at Main Endeavour, Mothra and Salty Dawg hydrothermal vent fields, possibly suggesting more mature hydrothermal cells. Interestingly, the near-seafloor structure beneath those three sites is very similar and highlights a sharp lateral transition in velocity (north to south). On the other hand, the High-Rise hydrothermal vent field is characterized by several lower amplitudes up-flow zones and relatively slow near-surface velocities. Last, Sasquatch vent field is located in an area of high near-surface velocities and is not

  2. Microbially-Mediated Sulfur Oxidation in Diffuse Hydrothermal Vent Fluids at Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Akerman, N. H.; Butterfield, D. A.; Huber, J. A.

    2011-12-01

    Diffusely venting hydrothermal fluids can act as a window to the subseafloor microbial environment, where chemically-reduced hydrothermal fluids mixing with oxygenated seawater in the shallow crust creates chemical disequilibria that chemotrophic microorganisms can exploit for energy gain. At Axial Seamount, an active deep-sea volcano located on the Juan de Fuca Ridge, sulfide concentrations have been measured as high as 5770 μM, and sulfide oxidation is quantitatively the most important chemical energy source for microbial metabolism. In addition, studies of microbial population structure indicate that diffuse fluids at Axial are dominated by putative sulfur- and sulfide-oxidizing bacteria belonging to the Epsilonproteobacteria. To further study this important microbial process, we surveyed diffuse vent samples from Axial over a range of temperature, pH, and sulfide concentrations for the presence and expression of sulfide-oxidizing bacteria using a functional gene approach. Dissolved oxygen concentrations decrease exponentially above 40°C and lower the potential for sulfide oxidation, so we identified six sites of different temperatures, two each in the low (< 30°C), medium (~30°C), and high temperature (30 - 50°C) range. The low temperature sites had sulfide-to-temperature ratios of 1 - 26, the medium from 15 - 29, and the high from 26 - 36. PCR primers were designed to target the sulfur oxidation gene soxB specifically from Epsilonproteobacteria and five of the six sites were positive for soxB in the DNA fraction. Bulk RNA was also extracted from the same sites to examine in situ expression of soxB. Data from these analyses, along with quantification of the soxB gene abundance and expression using quantitative PCR, are currently being carried out. Together, this data set of soxB gene diversity, expression, and abundance along with geochemical data will allow us to quantitatively determine the functional dynamics of sulfide oxidation in the subseafloor at

  3. A Comparative Study of the 2011 and 2015 Eruptions of Axial Volcano, Juan de Fuca Ridge, From Seafloor Hydrophones

    NASA Astrophysics Data System (ADS)

    Caplan-Auerbach, J.; Dziak, R. P.; Bohnenstiehl, D. R.; Chadwick, W.; Lau, T. K. A.

    2015-12-01

    Axial volcano, on the Juan de Fuca ridge, erupted in April 2011, and again in April 2015. Both eruptions were captured on ocean bottom hydrophones (OBHs). The 2011 eruption was recorded by three OBHs deployed near or within the caldera, although one instrument was overrun by lava and its data could not be recovered. The 2015 eruption was captured in real time by a network of ocean bottom seismometers and hydrophones deployed as part of the Ocean Observatories Initiative Cabled Array. Intense seismicity preceded and accompanied both eruptions. Earthquakes are recognizable in the hydroacoustic record by the timing of surface reflections: secondary and tertiary pulses are consistent with arrivals coming from below the hydrophone and reflecting off of the sea surface. The 2015 eruption also produced signals that initiate in the water column, interpreted as water-lava interactions. Surface reflections for these water column events are consistent with a more distant source, and the relative polarity of arrivals on the co-located OBH and OBSs are consistent with a signal traveling through the water rather than the subsurface. Comparisons of arrivals on the hydroacoustic and seismic channels show that there is little energy on the EW seismic channel, consistent with an impulsive signal arriving from the north. These water column events are absent from the 2011 eruption, despite the fact that preliminary estimates suggest that the eruptions were of comparable volume. Also observed during the 2015 event were a number of a diffuse broadband (10-100 Hz) signals that last from several minutes to over an hour. These events appear similar to hydroacoustic signals recorded in association with explosive degassing at other submarine volcanoes including NW Rota-1 (Marianas) and West Mata (Lau Basin). A comparison of hydroacoustic data recorded in the two events indicates that the 2015 eruption was more vigorous than the 2011 event and resulted in more explosive lava

  4. Uranium-series disequilibria of inflated sections of the Juan de Fuca Ridge: Implications for mantle melting

    NASA Astrophysics Data System (ADS)

    Dreyer, B. M.; Gill, J. B.; Ramos, F. C.; Clague, D. A.; Scott, S. R.

    2010-12-01

    U-Th disequilibria are reported for the two inflated portions (defined by bathymetric highs) of the Juan de Fuca Ridge (JdFR): Axial Seamount and the northern Endeavour segment. Both have broad axis-centered bathymetric plateaus, commonly attributed to the influence of the adjacent Heckle and Cobb melt anomalies, respectively. We explore structural and geochemical contrasts between them that imply fundamental differences in magma plumbing and/or transport processes. The depth to the axial magma chamber (AMC) within the JdFR crust is shallowest beneath Axial Seamount and deepest and most variable beneath Endeavour. Lavas from Endeavour include the most enriched and diverse compositions of the JdFR. Endeavour N-MORBs are most similar to Axial basalts in K2O/TiO2, La/Yb, Na8, and Fe8 although most Axial basalts have lower MgO. Major element trends suggest clinopyroxene saturation at higher MgO at Endeavour. Additional basalt types from Endeavour (i.e., those with K2O/TiO2 >0.15), the West Valley segment to the north, and Southwest Seamount to the west share similar enrichments in incompatible trace elements (Th, Nb) and radiogenic-Pb. Similar characteristics are absent from basalts from the adjacent Heck and Heckle seamount chains, which are highly-depleted N-MORBs, precluding the hypothesis that thickened and inflated crust at Endeavour is associated with increased melt supply due to transit over the seamount source. In contrast, Axial basalts are more chemically homogeneous, and share selected geochemical characteristics with the adjacent Cobb seamount chain. New uranium-series data suggest fundamental differences in melting parameters between inflated and non-inflated portions of the JdFR. Average Th/U at Endeavour (3.03 ± 6, n=10) is nearly indistinguishable from Axial (2.83 ± 9, n=17), but both are distinct from elsewhere on the JdFR (~2.1-2.5). That is, basalts erupted from regions of inflated crust have higher Th/U. Despite high overall compositional

  5. In-situ Chemistry of Hydrothermal Fluids from Black Smokers in Main Endeavour Field, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Ding, K.; Seyfried, W. E.; Zhang, Z.; Foustoukos, D.; Pester, N. J.

    2005-12-01

    After an off-axis earthquake swarm in 1999, dramatic changes were observed in vent fluids of Main Endeavour Field, Juan de Fuca Ridge. Three month latter, we also recorded this sudden variation using a high temperature in-situ chemical sensor. The results at that time indicated some of the vent temperatures as high as 374°C. This change was also characterized by relatively high in-situ pH, high dissolved H2, and H2S concentrations in the fluids that were in excess of 5, 0.7 mmol/kg and 20 mmol/kg respectively. In order to further track time dependent changes over the past 6 years, we revisited Main Endeavour Field during the recent AT 11-31 cruise in Aug.~Sept. 2005. The high temperature chemical sensor was again used on selected dives with DSV Alvin to conduct in-situ measurements of pH, dissolved H2 and H2S concentrations along with temperatures. The data were obtained in a real time mode of 3 seconds per-reading from a series of measurements at high temperature conditions in the depth of 2200 m. Conventional gas-tight samples were also collected for verification and further study. In this study, Puffer, Sully and Bastille black smoker vent sites were specifically investigated owing to the high fluid temperatures that characterize these vents in comparison with other vents in the area. The measured temperatures for these vents were 362°C, 358°C, and 361°C respectively, which were generally about 20~30°C higher than the others currently in the area, but approximately 10°C lower than the highest temperatures measured in the aftermath of the 1999 seismic-magmatic event. Although the drops in vent temperatures were not substantial, the measured in-situ chemistry showed large departures from previous reported data. The in-situ pH values in these vents ranged from 4.43 to 4.89, in comparison with values above 5 in 1999. This difference may be linked directly to the decrease in temperature. The measured in-situ dissolved H2 and H2S concentrations were 0

  6. Geological and hydrothermal controls on the distribution of megafauna in Ashes Vent Field, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Arquit, Anne M.

    1990-08-01

    A computerized data base was constructed to aid in the interpretation of biological and geological observations recorded from 7662 photographs taken of Ashes vent field (located along the SW wall of the summit caldera of Axial Volcano, Juan de Fuca Ridge) during 1985-1986 using the Pisces IV submersible and a towed camera system. The transition region between the locus of high-temperature vents in Ashes vent field (i.e., Inferno, 326°C; Hell, 301°C; and Virgin Mound, 298°C) and more typical environmental conditions for the summit caldera of Axial Volcano as a whole is zoned spatially with respect to sediment type and organism assemblage. Three general ecological zones are identified within the vent field: (1) the central vent zone (within 100 m of a high-temperature vent), dominated by vent-associated organisms (vestimentiferan tube worms, clams, bacterial mats) and sedimentation (high-temperature, plume-derived and low-temperature, in situ deposits); (2) the distal vent zone (100-725 m from any high-temperature vent), characterized by extensive fields of iron oxide, iron silicate and silica chimneys and sediment (nontronite assemblage material), as well as maximum densities of most nonvent fauna; and (3) the nonvent impact zone (725-1300 m), indicated by elevated densities of nonvent organisms relative to regional (i.e., caldera-wide) values and maximum Bathydorus sp. sponge densities. The distribution of vestimentiferan tube worms is limited to within 90 m of known high-temperature venting (central vent zone); and anemones were observed only between 30 and 40 m from hot vents. Clams and microbial mats are concentrated in the central vent zone, as well, but occur sporadically up to 1250 m from the hot vents in association with hydrothermal nontronite that is probably precipitating in situ from <60°C vent fluid; thus megafaunal distributions are a useful indicator of poorly defined, often diffuse low-temperature hydrothermal activity on the seafloor. Maximum

  7. Analysis of off-axis low-velocity zones on the flanks of the Endeavour segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Wells, A. E.; Hooft, E. E.; Toomey, D. R.; Wilcock, W. S.; Weekly, R. T.

    2011-12-01

    At mid-ocean ridges of all spreading rates, oceanic crust forms primarily within a 1-2 km wide neovolcanic zone; however, there is an increasing recognition that crustal structure is modified by off-axis volcanism. We present seismic data from the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge that reveal several crustal-level, low-velocity regions on the eastern and western flanks 7 to 16 km from the neovolcanic zone. The ~90 km long Endeavour segment lies between the Cobb and Endeavour overlapping spreading centers (OSCs). Seismic reflection data indicates the center of the segment is on a ~40 km wide plateau of greater crustal thickness that is interpreted to have developed when the Juan de Fuca Ridge overrode the melting anomaly associated with the Heckle seamount chain. Using the three-dimensional geometry of the Endeavour active source seismic tomography experiment conducted in 2009, we examine the travel times and amplitude anomalies of the Pg phase for a wide variety of source-receiver azimuths. In several locations on the eastern and western flanks of the Endeavour segment we observe significant and localized decreases in the amplitude of P waves, suggesting diffraction of energy around low-velocity bodies in the mid-crust. We model ray paths to estimate the depth of the anomalous regions. We also generate synthetic seismograms using finite difference waveform propagation through the three-dimensional seismic velocity structure that includes the seafloor topography. We test how low-velocity zones with various dimensions, depths, and physical properties affect the amplitudes and waveforms of crustal phases. We compare these synthetics with the observed anomalous regions to constrain the properties and geometry of the low velocity zones. We infer that the observed low velocity bodies are due to magma complexes at 2 to 3 km depth beneath bathymetric highs. On the eastern flank, three magma complexes are located 9 to 11 km from the axis

  8. Measurement of crustal thickness using PmP arrivals from an active source experiment at the Endeavour Segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Soule, D. C.; Wilcock, W. S.; Hooft, E. E.; Toomey, D. R.; Wells, A. E.; Weekly, R. T.

    2011-12-01

    In August 2009, we conducted a multi-scale seismic tomography experiment on the Endeavour segment of the Juan de Fuca Ridge aboard the R/V Marcus G. Langseth. During the experiment, 68 four-component ocean bottom seismometers (OBSs) were deployed at 64 sites throughout a 90x50 km2 area to record seismic energy from 5567 shots of the 36-element, 6600 in.3 airgun array. The experimental geometry was designed to image crustal thickness variations within 30 km of the ridge axis (0 to 1 Ma). Good quality data were recorded at all but two sites on either the vertical or hydrophone channel. Clear PmP arrivals are observed at ranges beyond 20 km, but the waveform shapes and amplitudes exhibit complex variations. Many ray paths, including those that cross the ridge axis, have PmP arrivals that are delayed relative to the times predicted for models constructed by combining a three dimensional inversion of Pg arrival times for upper crustal structure with a constant velocity of 7.2 km/s in a lower crust extending both 6 and 7 km below the seafloor. We will use PmP arrivals to examine spatial variations in crustal thickness and lower crustal velocity structure under the Endeavour segment of the Juan de Fuca ridge and thus constrain the history of segment-scale magma supply. These data will allow us to determine whether short wavelength, ridge-perpendicular variations in bathymetry are linked to variations in crustal thickness, which would support a cyclical model for crustal production rates. Two-way vertical incidence travel times measured in a recent reflection experiment have been interpreted in terms of a 0.5 - 1 km increase in crustal thickness beneath an area of elevated bathymetry located about the central Endeavour that may be linked to the Heckle melt anomaly. Wide-angle PmP arrivals will allow us to discriminate between changes in crustal thickness and variations in lower crustal velocity.

  9. Crustal magnetization and the subseafloor structure of the ASHES vent field, Axial Seamount, Juan de Fuca Ridge: Implications for the investigation of hydrothermal sites

    NASA Astrophysics Data System (ADS)

    Caratori Tontini, Fabio; Crone, Timothy J.; de Ronde, Cornel E. J.; Fornari, Daniel J.; Kinsey, James C.; Mittelstaedt, Eric; Tivey, Maurice

    2016-06-01

    High-resolution geophysical data have been collected using the Autonomous Underwater Vehicle (AUV) Sentry over the ASHES (Axial Seamount Hydrothermal Emission Study) high-temperature ( 348°C) vent field at Axial Seamount, on the Juan de Fuca Ridge. Multiple surveys were performed on a 3-D grid at different altitudes above the seafloor, providing an unprecedented view of magnetic data resolution as a function of altitude above the seafloor. Magnetic data derived near the seafloor show that the ASHES field is characterized by a zone of low magnetization, which can be explained by hydrothermal alteration of the host volcanic rocks. Surface manifestations of hydrothermal activity at the ASHES vent field are likely controlled by a combination of local faults and fractures and different lava morphologies near the seafloor. Three-dimensional inversion of the magnetic data provides evidence of a vertical, pipe-like upflow zone of the hydrothermal fluids with a vertical extent of 100 m.

  10. Preliminary Results from Downhole Osmotic Samplers in a Gas Tracer Injection Experiment in the Upper Oceanic Crust on the Eastern Flank of the Juan de Fuca Ridge.

    NASA Astrophysics Data System (ADS)

    de Jong, M. T.; Clark, J. F.; Neira, N. M.; Fisher, A. T.; Wheat, C. G.

    2015-12-01

    We present results from a gas tracer injection experiment in the ocean crust on the eastern flank of the Juan de Fuca Ridge, in an area of hydrothermal circulation. Sulfur hexafluoride (SF6) tracer was injected in Hole 1362B in 2010, during IODP Expedition 327. Fluid samples were subsequently collected from a borehole observatory (CORK) installed in this hole and similar CORKs in three additional holes (1026B, 1362A, and 1301A), located 300 to 500 m away. This array of holes is located on 3.5 My old seafloor, as an array oriented subparallel to the Endeavor Segment of Juan de Fuca Ridge. Borehole fluid samples were collected in copper coils using osmotic pumps. In addition to pumps at seafloor wellheads, downhole sampling pumps were installed in the perforated casing in the upper ocean crust. These downhole samplers were intended to produce a high-resolution continuous record of tracer concentrations, including records from the first year after tracer injection in Holes 1362A and 1362B. In contrast, wellhead samplers were not installed on these CORKs holes until 2011, and wellhead records from all CORKs have a record gap of up to one year, because of a delayed expedition in 2012. The downhole samples were recovered with the submersible Alvin in August 2014. SF6 concentrations in downhole samples recovered in 2014 are generally consistent with data obtained from wellhead samples. Of particular interest are the results from Hole 1362B, where a seafloor valve was opened and closed during various recovery expeditions. High resolution tracer curves produced from the 1362B downhole samples confirm that these operations produced an SF6 breakthrough curve corresponding to a classic push-pull test used to evaluate contaminant field locations in terrestrial setting. Complete analyses of downhole samples from these CORKs are expected to produce high-resolution breakthrough curves that will allow more precise analysis and modeling of hydrothermal flow in the study area.

  11. Hydrothermal Temperature Changes at South Cleft, Juan de Fuca Ridge, Associated with Blanco Transform Seismicity: More Evidence of Far-Field Effects Induced by Earthquakes

    NASA Astrophysics Data System (ADS)

    Dziak, R. P.; Chadwick, W. W.; Embley, R. W.; Fox, C. G.; Hammond, S. R.

    2001-12-01

    The regional impact of transform earthquakes on ridge-crest hydrothermal venting is investigated using a sequence of 170 western Blanco Transform earthquakes that occurred from June 1-7, 2000. The earthquakes were recorded on both the SOSUS hydrophone array and land-based seismic networks. The mainshock (Mw6.2) occurred at 11:13Z on June 2, exhibited a right-lateral strike-slip mechanism, and was the largest event detected from the western Blanco Transform in the past 40 yrs. The mainshock nucleated ~10 km east of a cluster of 80 foreshocks, and from the aftershock distribution, appears to have ruptured the entire western transform strike-slip fault segment ( ~56 km). Two HOBO high-temperature probes were positioned within black smoker chimneys at the Vent1 and Plume hydrothermal fields along the southern Cleft segment, Juan de Fuca Ridge, recording temperatures about once per hour. These two hydrothermal vent fields are ~1.8 km apart and ~42 km northwest of the acoustic location of the mainshock. The Plume HOBO record shows an abrupt temperature decrease from 240.5° C to 235.5° C between 12:00Z and 00:00Z on June 2-3 (immediately after the Blanco earthquake) after several prior months of a very gradual decrease in temperature. This perturbation lasts about a week before the temperature rejoins its previous trend. The Vent1 HOBO record shows that after 7 mos of steady readings (272° C +/- 3° ), temperatures decreased 5° C from May 25 to June 9, and decreased another 20° C from June 9 to 19, after which temperatures were steady for two weeks until the probe was retrieved. A Coloumb failure model indicates the mainshock should have caused a regional stress reduction of 0.02 MPa along the southern Juan de Fuca Ridge. Since stress reduction in the crust might also decrease pore pressure and therefore the mass flow rate in a hydrothermal system, this stress reduction might have caused the observed temperature declines. These findings are consistent with recent

  12. The Cleft revealed: Geologic, magnetic, and morphologic evidence for construction of upper oceanic crust along the southern Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Stakes, Debra S.; Perfit, Michael R.; Tivey, Maurice A.; Caress, David W.; Ramirez, Tony M.; Maher, Norman

    2006-04-01

    The geology and structure of the Cleft Segment of the Southern Juan de Fuca Ridge (JdFR) have been examined using high-resolution mapping systems, observations by remotely operated vehicle (ROV), ROV-mounted magnetometer, and the geochemical analysis of recovered lavas. Bathymetric mapping using multibeam (EM300) coupled with in situ observations that focused on near-axis and flank regions provides a detailed picture of 0 to 400 ka upper crust created at the southern terminus of the JdFR. A total of 53 rock cores and 276 precisely located rock or glass samples were collected during three cruises that included sixteen ROV dives. Our observations of the seafloor during these dives suggest that many of the unfaulted and extensive lava flows that comprise and/or cap the prominent ridges that flank the axial valley emanate from ridge parallel faults and fissures that formed in the highly tectonized zone that forms the walls of the axial valley. The geochemically evolved and heterogeneous nature of these near-axis and flank eruptions is consistent with an origin within the cooler distal edges of a crustal magma chamber or mush zone. In contrast, the most recent axial eruptions are more primitive (higher MgO), chemically homogeneous lobate, sheet, and massive flows that generate a distinct magnetic high over the axial valley. We suggest that the syntectonic capping volcanics observed off-axis were erupted from near-axis and flank fissures and created a thickened extrusive layer as suggested by the magnetic and seismic data. This model suggests that many of the lavas that comprise the elevated ridges that bound the axial valley of the Cleft Segment were erupted during the collapse of a magmatic cycle not during the robust phase that established a new magmatic cycle.

  13. Unique Thermophiles Supported by the Ocean Crustal Fluids Exiting From a Borehole in the Eastern Flank of Juan de Fuca Ridge.

    NASA Astrophysics Data System (ADS)

    Nakagawa, S.; Inagaki, F.; Suzuki, Y.; Takai, K.; Horikoshi, K.

    2005-12-01

    Very little is known about the potential of ocean crustal fluids on ridge flanks to sustain microbial ecosystem. An unprecedented chance to investigate the occurrence of microbes within the crustal fluids is given by a borehole observatory, CORK (Circulation Obviation Retrofit Kit). The CORK consists of two parts: instruments installed in the sealed part of the cased borehole drilled by the Ocean Drilling Program (ODP), and a data logger and fluids sampling port sitting on the seafloor. Recently, a study using the CORK suggested the presence of unique microorganisms in ~64 deg C of crustal fluids emanated from a 295-meter-deep borehole in the eastern flank of Juan de Fuca Ridge (35 Ma crust) (Cowen et al., 2003, Science, 299, 120-123). Most of the 16S rRNA gene detected in the fluids related to sulfate-reducing genera (Desulfotomaculum, Ammonifex, and Desulfonatronovibrio), implying that fluids circulating within aging ocean crust potentially support microbial sulfate-reduction. When we recovered the CORK during the Juan de Fuca cruise of Integrated Ocean Drilling Program (IODP), sulfide deposits attached to the CORK body was found. The microbial community in the sulfide deposits inferred by clone sequencing of environmental 16S rRNA genes was distinct from those hitherto reported in other microbial habitats including natural deep-sea vents on ridge crests and subduction zones, but similar in part with that reported in the fluids emanated from the same CORK. Most frequently retrieved clones of bacterial and archaeal 16S rRNA gene were related to Ammonifex and Methanococcales, respectively. Semi-quantitative cultivation experiments revealed that over 103 cells per cm3 of the sulfide deposits were culturable. Surprisingly, none of the microbes widely distributing in natural deep-sea hydrothermal environments, i.e. Thermococcales, Aquificales, and epsilon-Proteobacteria, could be detected or cultured. Culturable microbial community consisted mainly of

  14. Geology, mineralogy, and chemistry of sediment-hosted clastic massive sulfides in shallow cores, Middle Valley, northern Juan de Fuca Ridge

    SciTech Connect

    Goodfellow, W.D.; Franklin, J.M. )

    1993-12-01

    Middle Valley is a sediment-covered rift near the northern end of Juan de Fuca Ridge. Hydrothermal fluids are presently being discharged at two vent fields about 3 km apart, Bent Hill and the area of active venting. The hydrothermally active chimneys at both Bent Hill and the area of active venting consist of anhydrite and Mg-rich silicates with minor pyrite, Cu-Fe sulfide, sphalerite, and galena. Hydrothermal discharge in these areas appears to be focused along extensional faults. At the Bent Hill massive sulfide deposit, clastic sulfide layers are interbedded with hydrothermally altered and unaltered hemipelagic and turbiditic sediment along the flanks of the sulfide mound. Sulfide textures and mineralogy suggest that the Bent Hill sulfide mound formed by the build-up and collapse of sulfide chimneys, the resedimentation of sulfide debris and the formation of clastic sulfide layers, and the infilling and replacement of clastic sulfides by hydrothermal fluids near vents. Sulfur isotope values that are consistently more positive than basaltic sulfur support the addition of seawater sulfur. Pb isotope values for the Bent Hill deposit that are transitional between midocean ridge basalt (MORB) and Middle Valley sediments indicate that the sulfides probably formed from fluids which originated in the oceanic crust but which have been modified by reaction with lower temperature (<274 C) fluids generated in the sedimentary pile, similar to those now venting in Middle Valley.

  15. Dissolved Organic Carbon Distribution in Two Hydrothermal Systems - West Mata, NE Lau Basin during an eruption event and basement fluids from sediment-buried Juan de Fuca Ridge flanks

    NASA Astrophysics Data System (ADS)

    Lin, H.; Cowen, J. P.; Butterfield, D. A.; Embley, R. W.; Resing, J.

    2009-12-01

    Hydrothermal systems have profound influence in regulating seawater chemistry. However, the extent hydrothermal systems have impact on deep ocean DOC remains unclear. This study will provide data on dissolved organic carbon distribution in two very different hydrothermal systems. The first is hydrothermal fluids produced from a near-arc volcano in Northeast Lau Basin. Samples were collected with the Butterfield fluid sampler during an eruption event at West Mata during May 2009. The eruption event allowed collection of fluids from both new and established vents, high temperature focused and low temperature diffused vents. This unique opportunity should shed light on DOC changes in nascent hydrothermal systems in accordance with early microbiological community succession. The second hydrothermal environment is a 3.5 Myr-sediment-covered basement aquifer located on the east flank of Juan de Fuca Ridge. Basement Fluids were collected from basement ~280 mbsf (~20 m below sediment-basement interface) using 0.25” stainless steal fluid delivery lines of the Circulation Obviating Retrofit Kit (CORK) observatories at Ocean Drilling program borehole 1301A; samples were drawn up the FDL by a new clean pumping system (Mobile Pump Valve Unit or MPVU) and collected in an acid-cleaned 60-L Large Volume Bag Sampler (LVBS). Due to the effective hydraulic barrier of the 260 m thick of sediment over-lying the basement at this site, the basement fluid here does not readily exchange with bottom seawater. In contrast to vent fluid in Lau vent field, the basement fluid has been circulating in the basement, on average, several thousand years. DOC data will be presented from these hydrothermal fluids and discussed with respect to the DOC cycle in the deep ocean.

  16. Insights on the Biology of the Eastern Lau Spreading Center from Studies on the East Pacific Rise and Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Fisher, C. R.; Sen, A.; Becker, E.

    2011-12-01

    A primary goal of the Ridge 2000 program was to conduct comparable interdisciplinary studies at a few fundamentally different sites that would facilitate comparisons among sites and development of concepts with broad application across deep ocean ridge spreading centers. Although the Eastern Lau Spreading Center (ELSC) was the least known of the three Integrated Study Sites, we were able to make amazingly fast progress on understanding this system because we could draw on technology and experience developed during the RIDGE program to plan and conduct the work, and now interpret our findings in the context of the rich literature and Ridge 2000 studies on East Pacific Rise (EPR) , Juan de Fuca Ridge (JdFR), and Mid Atlantic Ridge communities. The ELSC communities not only house different species than those of the other regions, but unlike the often tubeworm dominated E. Pacific vents, they are structured by symbiont reliant species that are mobile; snails and mussels. Although there is some variation with lava type on the ELSC, the 4 species of large, symbiont-containing snails largely occupy the niches filled by tubeworms and mussels on the EPR, while the niche of the mussel in the W. Pacific vents is quite different from that of its EPR cousin. Although we have not observed any significant tectonic or magmatic events during our studies of the ELSC, 4 years of study considered in the context of what we have learned on the EPR and JdFR allow us to formulate and begin testing hypotheses about temporal change and succession in these very different and much less visited ecosystems. Furthermore, athough Paralvinella fijiensis are only found in limited areas on some chimneys and flanges, unlike the situation on the EPR and JdFR ,the ELSC chimney communities are largely composed of the same species as are found in diffuse flow on the lavas. The ELSC chimney communities are also remarkably stable, hosting some of the largest and apparently oldest individuals found on the

  17. Off-axis Crustal Thickness and Lower Crustal Velocity Structure from Seismic Tomography on the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Soule, D. C.; Wilcock, W. S.; Toomey, D. R.; Hooft, E. E.; Weekly, R. T.

    2013-12-01

    In August 2009, we conducted a seismic tomography experiment on the Endeavour segment of the Juan de Fuca Ridge to constrain the processes of crustal accretion. The experiment footprint extended 100 km along- and 60 km across-axis and covered the hydrothermally active central portion of the segment, two large overlapping spreading centers and the eastern end the Heck seamount chain. A total of 68 four-component ocean bottom seismometers were deployed at 64 sites and recorded 5567 shots of the 36-element, 6600 in.3 airgun array of the R/V Marcus G. Langseth. The data return rate was high, with good quality data recorded on either the vertical or hydrophone channel at all but two sites. In a prior study, 93,000 manually picked crustal refraction arrivals (Pg) were used to invert for three-dimensional upper crustal velocity. Here we add wide-angle PmP arrival times for non-ridge crossing paths in order to constrain the velocity of the lower crust and crustal thickness on both the Pacific and Juan de Fuca plates at crustal ages of 0.1-1.0 Ma. The starting model was obtained by extending the three-dimensional upper crustal model obtained from the Pg data downward, assuming no vertical velocity gradient in the lower crust and by adding a Moho at 6.3 km depth. Preliminary results using ~7000 PmP arrivals with reflection points at ages of 0.3-1.0 Ma show that crustal thicknesses varies from 6.1 to 7.6 km. The thickest crust is found beneath a 40-km-wide plateau located on the central portion of the Endeavour Segment. This region has been previously interpreted as a region of enhanced crustal production associated with the Heckle melt anomaly. Velocities at the base of the crust range from 6.9-7.2 km/s and tend to be slightly higher beneath the bathymetric plateau consistent with decreased levels of magmatic differentiation near the segment center. Thickened crust is also found on the Juan de Fuca plate beneath a failed propagator of the Cobb overlapping spreading center

  18. Constraining the velocity structure of the Juan de Fuca plate from ridge to trench with a 2D tomographic study of wide angle OBS data

    NASA Astrophysics Data System (ADS)

    Boulahanis, B.; Canales, J. P.; Carbotte, S. M.; Carton, H. D.; Han, S.; Nedimovic, M. R.

    2016-12-01

    We conduct a two-dimensional travel time tomography study of a cross-plate, 300-km long, ocean bottom seismometer (OBS) transect collected as part of the Ridge to Trench (R2T) program to investigate the structure, evolution and state of hydration of the Juan de Fuca (JdF) plate from the ridge axis to subduction at the Cascadia margin offshore Washington. Our study employs the methodology of Korenaga et al. (2000) to derive a P-wave velocity model using wide-angle data from 15 OBSs spaced on average 15 km apart, spanning from the Endeavour segment of the JdF ridge to the Cascadia accretionary prism. A top down modeling approach is employed, first assessing velocities of the sediment layer, then the crust, and finally the upper mantle; at each stage of the inversion we fix the structure of the overlaying layers. Quality of data fit is evaluated using the root mean square value of the difference between predicted and observed travel times normalized by pick uncertainty. Previous studies provide a well-resolved multi-channel seismic (MCS) reflection image of this transect (Han et al., 2016), affording good constraints of the location of basement and Moho reflectors while allowing for comparison of the relationship between velocities and crustal structure. MCS results along this transect suggest evidence of little bending faulting confined to the sediment and upper-middle crust. An initial velocity model of the sediment layer above igneous crust is constructed utilizing the MCS derived sediment velocities. A one-dimensional velocity starting model of the oceanic crust is generated using the results of Horning et al. (in press) from a quasi-parallel cross-plate transect also acquired as part of the R2T study. Seismic velocities are compared to predicted velocities for crustal and mantle lithologies at temperatures estimated from a plate-cooling model and are used to provide constraints on water contents in these layers.

  19. Contrasting two-dimensional and three-dimensional models of outcrop-to-outcrop hydrothermal circulation on the eastern flank of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Fisher, A. T.; Winslow, D. M.; Stauffer, P. H.; Gable, C. W.; Zyvoloski, G.

    2015-12-01

    We present results from two-dimensional and three-dimensional coupled (fluid and heat flow) simulations of ridge-flank hydrothermal circulation on the eastern flank of the Juan de Fuca Ridge. Field studies in this region demonstrate the existence of an active hydrothermal siphon operating between two seamounts separated by ~50 km, and provide quantitative constraints that help to determine which simulations are successful in replicating known properties and processes. Constraints from field observations include (a) the flow rate between the outcrops, (b) the presence of secondary convection within the basement aquifer, leading to simultaneous recharge and discharge through a single outcrop (in additional to siphon flow between outcrops), (c) direct measurements of crustal permeability in basement boreholes, and (d) the lack of a regional seafloor heat flux anomaly as a consequence of outcrop-to-outcrop circulation. New simulations include an assessment of crustal permeability and thickness, outcrop permeability, and a comparison of simulation results using different geometries. Three-dimensional simulations are more consistent with field observations than their two-dimensional counterparts and indicate a crustal aquifer of ≤300 m thick having a bulk permeability between 3×10-13 and 2×10-12 m2, values consistent with borehole measurements. In addition, we find fluid flow rates and crustal cooling efficiencies that are an order of magnitude greater in three-dimensional simulations than inferred from two-dimensional simulations using equivalent properties. These results show that three-dimensional simulations of outcrop-to-outcrop hydrothermal circulation on a ridge flank improves the geological and geometric accuracy of results, in comparison to models run in two dimensions.

  20. Hydrothermal recharge and discharge guided by basement outcrops on 0.7-3.6 Ma seafloor east of the Juan de Fuca Ridge: Observations and numerical models

    NASA Astrophysics Data System (ADS)

    Hutnak, M.; Fisher, A. T.; Zühlsdorff, L.; Spiess, V.; Stauffer, P. H.; Gable, C. W.

    2006-07-01

    The nature of ridge-flank hydrothermal circulation guided by basement outcrops protruding through thick sediments is constrained on the eastern flank of the Juan de Fuca Ridge using combined bathymetric, seismic, and thermal observations and analytical and numerical calculations of coupled fluid-heat flow. Observational data near the western edge of the survey area indicate that young, cool hydrothermal fluids circulate rapidly through upper basement, probably both across-strike and along-strike of dominant structural trends. Data from the eastern end of survey coverage (Second Ridge (SR)) indicate that upper basement is regionally nearly isothermal. A small number of basement outcrops in this area host focused hydrothermal discharge, as do additional basement outcrops to the north and south of the SR area. Numerical models of individual recharging and discharging outcrops, patterned after the Baby Bare and Grizzly Bare outcrops, suggest that local convection alone cannot explain observed patterns of seafloor heat flux near these features. Forced-flow simulations show that reasonable rates of hydrothermal recharge and discharge, inferred from independent observations, can explain nearby seafloor heat flux, provided that upper basement permeability within and near the outcrops falls within a range of 10-13 to 10-11 m2. Free-flow simulations of fluid circulation between paired outcrops separated by 50 km, as are Baby Bare and Grizzly Bare outcrops, are most consistent with observations when regional basement permeability is 10-11 to 10-10 m2. These simulations illustrate how sensitive these systems are to selection of appropriate properties and boundary and initial conditions.

  1. Seismic reflection imaging of the Juan de Fuca plate from ridge to trench: New constraints on the distribution of faulting and evolution of the crust prior to subduction

    NASA Astrophysics Data System (ADS)

    Han, Shuoshuo; Carbotte, Suzanne M.; Canales, Juan Pablo; Nedimović, Mladen R.; Carton, Hélène; Gibson, James C.; Horning, Greg W.

    2016-03-01

    We present prestack time-migrated multichannel seismic images along two cross-plate transects from the Juan de Fuca (JdF) Ridge to the Cascadia deformation front (DF) offshore Oregon and Washington from which we characterize crustal structure, distribution and extent of faults across the plate interior as the crust ages and near the DF in response to subduction bending. Within the plate interior, we observe numerous small offset faults in the sediment section beginning 50-70 km from the ridge axis with sparse fault plane reflections confined to the upper crust. Plate bending due to sediment loading and subduction initiates at ~120-150 km and ~65-80 km seaward of the DF, respectively, and is accompanied by increase in sediment fault offsets and enhancement of deeper fault plane reflectivity. Most bend faulting deformation occurs within 40 km from the DF; on the Oregon transect, bright fault plane reflections that extend through the crust and 6-7 km into the mantle are observed. If attributed to serpentinization, ~0.12-0.92 wt % water within the uppermost 6 km of the mantle is estimated. On the Washington transect, bending faults are confined to the sediment section and upper-middle crust. The regional difference in subduction bend-faulting and potential hydration of the JdF plate is inconsistent with the spatial distribution of intermediate-depth intraslab seismicity at Cascadia. A series of distinctive, ridgeward dipping (20°-40°) lower crustal reflections are imaged in ~6-8 Ma crust along both transects and are interpreted as ductile shear zones formed within the ridge's accretionary zone in response to temporal variations in mantle upwelling, possibly associated with previously recognized plate reorganizations at 8.5 Ma and 5.9 Ma.

  2. Widespread hydrothermal ash deposits in sediment cores from Axial Seamount, Juan de Fuca Ridge record deep-marine caldera formation 1300-800 yr BP

    NASA Astrophysics Data System (ADS)

    Portner, R. A.; Dreyer, B. M.; Clague, D. A.

    2016-12-01

    Sediment core archives from the flanks of Axial Seamount (1400 mbsl) on the Juan de Fuca Ridge preserve widespread dispersal of basaltic ash. Ash is mid-ocean ridge basalt (MORB) glass. It typically occurs with hydrothermal and pelagic sedimentary components, which together form up to 2 meter thick bedded stratigraphic sequences. Compared to other lithofacies the overall finer grain size of ash shards ( 110 um) and notable presence of lithic components (e.g., crystalline basalt) co-occurring with hydrothermal sediment (e.g. Fe-smectite) suggests that hydrothermal ash lithofacies record high energy fragmentation processes where hydrothermal fluids were present. This lithofacies is most pronounced around the caldera rim where it is most abundant and thickest. Radiocarbon dating of pelagic foraminifera from the cores indicates that a significant amount of hydrothermal ash was deposited 1300-800 yr BP around the caldera. Moreover, chemical stratigraphy of glass shards below, within and above the hydrothermal ash bed indicates that the seamount produced primitive (high MgO) melts for a brief period shortly after hydrothermal ash deposition. The chronologic, lithologic and chemical characteristics of hydrothermal ash lithofacies and its unique spatial association to caldera rims suggest that its deposition is associated with ring-fault development, hydrothermal circulation and magma fragmentation. Caldera ring-faults would have hosted important recharge-discharge cells vital to hydrothermal circulation. Magma-water interactions along the roots of these ring-faults likely lead to phreatomagmatic fragmentation and wide-dispersal of hydrothermal ash from vents around the caldera rim. If magma chamber depth is generally 2-3 km depth, the upper surfaces of sub-seamount magma chambers are shallower than the critical point of seawater (<29 MPa), where magma-water interactions can occur. The absence of hydrothermal ash marker beds on normal mid-ocean ridge axes (>2000 mbsl) may

  3. Seismic reflection imaging of the Juan de Fuca plate from ridge to trench: new constraints on the distribution of faulting and evolution of the crust prior to subduction

    NASA Astrophysics Data System (ADS)

    Han, S.; Carbotte, S. M.; Canales, J. P.; Nedimovic, M. R.; Carton, H. D.; Gibson, J. C.

    2016-12-01

    To characterize the evolution of the Juan de Fuca (JdF) plate from ridge to trench, quantify its hydration state prior to subduction, and assess the relationship between along-strike variations in plate structure and Cascadia subduction zone processes, the JdF Ridge-to-Trench Experiment, a joint long streamer multi-channel seismic (MCS) and wide-angle ocean bottom seismometer (OBS) survey was conducted in 2012. This study provides plate-scale images and seismic velocity of the sediments, crust, and shallowest mantle along two ridge-perpendicular transects offshore Oregon and Washington and an 400 km long trench-parallel line 10-15 km seaward of the Cascadia deformation front (DF). Here we present prestack time migrated MCS images of the three transects. Within the plate interior, we observe numerous small offset faults in the sediment section beginning 50-70 km from the ridge axis with sparse fault plane reflections confined to the upper crust. As the plate bends due to sediment loading and subduction, bright fault plane reflections that extend through the crust and 6-7 km into the mantle are imaged on the Oregon Transect within 40 km from the DF; on the Washington Transect, bending faults are confined to the sediment section and upper-middle crust. The reflection image of the along-strike transect shows more abundant reflectivity south of 45°50'N coincident with reduced seismic velocity in the lower crust derived from the OBS data (Canales et al., 2016) suggesting more faulted and hydrated crust off Oregon prior to subduction. This regional difference coincides with the plate interface transition from well locked to partially creeping at Cascadia. A series of distinctive, ridgeward-dipping (20°-40°) lower crustal reflections are imaged in 6-8 Ma crust along two cross-plate transects and are interpreted as ductile shear zones formed at the JdF ridge in response to temporal variations in mantle upwelling, possibly associated with previously recognized plate

  4. A Diverse Community of Metal(loid) Oxide Respiring Bacteria Is Associated with Tube Worms in the Vicinity of the Juan de Fuca Ridge Black Smoker Field.

    PubMed

    Maltman, Chris; Walter, Graham; Yurkov, Vladimir

    2016-01-01

    Epibiotic bacteria associated with tube worms living in the vicinity of deep sea hydrothermal vents of the Juan de Fuca Ridge in the Pacific Ocean were investigated for the ability to respire anaerobically on tellurite, tellurate, selenite, selenate, metavanadate and orthovanadate as terminal electron acceptors. Out of 107 isolates tested, 106 were capable of respiration on one or more of these oxides, indicating that metal(loid) oxide based respiration is not only much more prevalent in nature than is generally believed, but also is an important mode of energy generation in the habitat. Partial 16S rRNA gene sequencing revealed the bacterial community to be rich and highly diverse, containing many potentially new species. Furthermore, it appears that the worms not only possess a close symbiotic relationship with chemolithotrophic sulfide-oxidizing bacteria, but also with the metal(loid) oxide transformers. Possibly they protect the worms through reduction of the toxic compounds that would otherwise be harmful to the host.

  5. A Diverse Community of Metal(loid) Oxide Respiring Bacteria Is Associated with Tube Worms in the Vicinity of the Juan de Fuca Ridge Black Smoker Field

    PubMed Central

    Maltman, Chris; Walter, Graham; Yurkov, Vladimir

    2016-01-01

    Epibiotic bacteria associated with tube worms living in the vicinity of deep sea hydrothermal vents of the Juan de Fuca Ridge in the Pacific Ocean were investigated for the ability to respire anaerobically on tellurite, tellurate, selenite, selenate, metavanadate and orthovanadate as terminal electron acceptors. Out of 107 isolates tested, 106 were capable of respiration on one or more of these oxides, indicating that metal(loid) oxide based respiration is not only much more prevalent in nature than is generally believed, but also is an important mode of energy generation in the habitat. Partial 16S rRNA gene sequencing revealed the bacterial community to be rich and highly diverse, containing many potentially new species. Furthermore, it appears that the worms not only possess a close symbiotic relationship with chemolithotrophic sulfide-oxidizing bacteria, but also with the metal(loid) oxide transformers. Possibly they protect the worms through reduction of the toxic compounds that would otherwise be harmful to the host. PMID:26914590

  6. Geology of the northern Cleft segment, Juan de Fuca Ridge: Recent lava flows, sea-floor spreading, and the formation of megaplumes

    SciTech Connect

    Embley, R.W. ); Chadwick, W. ); Perfit, M.R. ); Baker, E.T. )

    1991-08-01

    Geologic mapping and lava sampling were carried out after the discovery of large bursts of hydrothermal fluids (megaplumes) over the southern Juan de Fuca Ridge in 1986 and 1987. These investigations of the northernmost section of the Cleft segment have discovered: (1) semicontinuous low-temperature venting and one major high-temperature vent site along 17 km of the neovolcanic zone and (2) very glassy, lightly sedimented sheet flows and pillow mounds superimposed on older terrain over about 24 km along the northern-most part. The pillow mounds are documented to have erupted between 1981 and 1987. The occurrence of the megaplumes during this same time period strengthens the hypothesis that megaplumes are caused by sea-floor extension events. Although the basalts from the entire length of the neovolcanic zone of the Cleft segment appear to have been derived from the same mantle source, a systematic northward increase in Mg number along the segment within the neovolcanic zone indicates less shallow-level differentiation to the north, possibly related to the development of new magma chambers during the recent phase of sea-floor spreading that has occurred there.

  7. Phylogenetic diversity of microorganisms in subseafloor crustal fluids from Holes 1025C and 1026B along the Juan de Fuca Ridge flank

    PubMed Central

    Jungbluth, Sean P.; Lin, Huei-Ting; Cowen, James P.; Glazer, Brian T.; Rappé, Michael S.

    2014-01-01

    To expand investigations into the phylogenetic diversity of microorganisms inhabiting the subseafloor biosphere, basalt-hosted crustal fluids were sampled from Circulation Obviation Retrofit Kits (CORKs) affixed to Holes 1025C and 1026B along the Juan de Fuca Ridge (JdFR) flank using a clean fluid pumping system. These boreholes penetrate the crustal aquifer of young ocean crust (1.24 and 3.51 million years old, respectively), but differ with respect to borehole depth and temperature at the sediment-basement interface (147 m and 39°C vs. 295 m and 64°C, respectively). Cloning and sequencing of PCR-amplified small subunit ribosomal RNA genes revealed that fluids retrieved from Hole 1025C were dominated by relatives of the genus Desulfobulbus of the Deltaproteobacteria (56% of clones) and Candidatus Desulforudis of the Firmicutes (17%). Fluids sampled from Hole 1026B also contained plausible deep subseafloor inhabitants amongst the most abundant clone lineages; however, both geochemical analysis and microbial community structure reveal the borehole to be compromised by bottom seawater intrusion. Regardless, this study provides independent support for previous observations seeking to identify phylogenetic groups of microorganisms common to the deep ocean crustal biosphere, and extends previous observations by identifying additional lineages that may be prevalent in this unique environment. PMID:24723917

  8. Identification and characterization of a novel thermostable gh-57 gene from metagenomic fosmid library of the Juan de Fuca Ridge hydrothemal vent.

    PubMed

    Wang, Hui; Gong, Yingxue; Xie, Wei; Xiao, Wenjuan; Wang, Junmei; Zheng, Yangyang; Hu, Jia; Liu, Zehuan

    2011-08-01

    A novel glycoside hydrolases family 57 gene (gh-57) was found from a metagenomic fosmid library constructed from a black smoker chimney sample 4143-1 from the Mothra hydrothermal vent at the Juan de Fuca Ridge. Sequence and homology analysis using BLAST revealed that it had high similarity to gh-57 family. Conserved domain research revealed that the novel gh-57 contained a Glyco-hydro-57 domain and five conserved regions, including two putative catalytic residues Glu¹⁵⁴ and Asp²⁶³. The three-dimensional features of the protein and its homologue from Pyrococcus horikoshii OT3 known as α-amylase were generated by homology modeling. The gh-57 gene was cloned, expressed, and purified in Escherichia coli using pQE system. Enzyme activity revealed that the recombinant protein could hydrolyze soluble starch and demonstrated amylase activity. It showed an optimal pH of 7.5, an optimal temperature of 90 °C, and its thermostability at 90 °C could remain over 50% enzyme activity for 4 h. The enzyme activity could be increased by DTT and Mg²⁺ while an inhibitory effect was observed with EDTA, ATP, and Ca²⁺. These results showed that the gh-57 gene was a novel thermostable amylase from oceanic microorganisms.

  9. Origin of minor and trace element compositional diversity in anorthitic feldspar phenocrysts and melt inclusions from the Juan de Fuca Ridge

    USGS Publications Warehouse

    Adams, David T.; Nielsen, Roger L.; Kent, Adam J.R.; Tepley, Frank J.

    2011-01-01

    Melt inclusions trapped in phenocryst phases are important primarily due to their potential of preserving a significant proportion of the diversity of magma composition prior to modification of the parent magma array during transport through the crust. The goal of this investigation was to evaluate the impact of formational and post-entrapment processes on the composition of melt inclusions hosted in high anorthite plagioclase in MORB. Our observations from three plagioclase ultra-phyric lavas from the Endeavor Segment of the Juan de Fuca Ridge document a narrow range of major elements and a dramatically greater range of minor and trace elements within most host plagioclase crystals. Observed host/inclusion partition coefficients for Ti are consistent with experimental determinations. In addition, observed values of DTi are independent of inclusion size and inclusion TiO2 content of the melt inclusion. These observations preclude significant effects from the re-homogenization process, entrapment of incompatible element boundary layers or dissolution/precipitation. The observed wide range of TiO2 contents in the host feldspar, and between bands of melt inclusions within individual crystals rule out modification of TiO contents by diffusion, either pre-eruption or due to re-homogenization. However, we do observe comparatively small ranges for values of K2O and Sr compared to P2O5 and TiO2 in both inclusions and crystals that can be attributed to diffusive processes that occurred prior to eruption.

  10. Distribution and composition of hydrothermal plume particles from the ASHES vent field at Axial Volcano, Juan de Fuca Ridge. [Axial Seamount Hydrothermal Emission Study

    SciTech Connect

    Feely, R.A.; Geiselman, T.L.; Baker, E.T.; Massoth, G.J. ); Hammond, S.R. )

    1990-08-10

    In 1986 and 1987, buoyant and neutrally buoyant hydrothermal plume particles from the ASHES vent field within Axial Volcano were sampled to study their variations in composition with height above the seafloor. Individual mineral phases were identified using standard X ray diffraction procedures. Elemental composition and particle morphologies were determined by X ray fluorescence spectrometry and scanning electron microscopy/X ray energy spectrometry techniques. The vent particles were primarily composed of sphalerite, anhydrite, pyrite, pyrrhotite, chalcopyrite, barite, hydrous iron oxides, and amorphous silica. Grain size analyses of buoyant plume particles showed rapid particle growth in the first few centimeters above the vent orifice, followed by differential sedimentation of the larger sulfide and sulfate minerals out of the buoyant plume. The neutrally buoyant plume consisted of a lower plume, which was highly enriched in Fe, S, Zn, and Cu, and an upper plume, which was highly enriched in Fe and Mn. The upper plume was enriched in Fe and Mn oxyhydroxide particles, and the lower plume was enriched in suspended sulfide particles in addition to the Fe and Mn oxyhydroxide particles. The chemical data for the water column particles indicate that chemical scavenging and differential sedimentation processes are major factors controlling the composition of the dispersing hydrothermal particles. Short-term sediment trap experiments indicate that the fallout from the ASHES vent field is not as large as some of the other vent fields on the Juan de Fuca Ridge.

  11. Phylogenetic diversity of microorganisms in subseafloor crustal fluids from Holes 1025C and 1026B along the Juan de Fuca Ridge flank.

    PubMed

    Jungbluth, Sean P; Lin, Huei-Ting; Cowen, James P; Glazer, Brian T; Rappé, Michael S

    2014-01-01

    To expand investigations into the phylogenetic diversity of microorganisms inhabiting the subseafloor biosphere, basalt-hosted crustal fluids were sampled from Circulation Obviation Retrofit Kits (CORKs) affixed to Holes 1025C and 1026B along the Juan de Fuca Ridge (JdFR) flank using a clean fluid pumping system. These boreholes penetrate the crustal aquifer of young ocean crust (1.24 and 3.51 million years old, respectively), but differ with respect to borehole depth and temperature at the sediment-basement interface (147 m and 39°C vs. 295 m and 64°C, respectively). Cloning and sequencing of PCR-amplified small subunit ribosomal RNA genes revealed that fluids retrieved from Hole 1025C were dominated by relatives of the genus Desulfobulbus of the Deltaproteobacteria (56% of clones) and Candidatus Desulforudis of the Firmicutes (17%). Fluids sampled from Hole 1026B also contained plausible deep subseafloor inhabitants amongst the most abundant clone lineages; however, both geochemical analysis and microbial community structure reveal the borehole to be compromised by bottom seawater intrusion. Regardless, this study provides independent support for previous observations seeking to identify phylogenetic groups of microorganisms common to the deep ocean crustal biosphere, and extends previous observations by identifying additional lineages that may be prevalent in this unique environment.

  12. Three-dimensional modeling of outcrop-to-outcrop hydrothermal circulation on the eastern flank of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Winslow, D. M.; Fisher, A. T.; Stauffer, P. H.; Gable, C. W.; Zyvoloski, G. A.

    2016-03-01

    We present three-dimensional simulations of coupled fluid and heat transport in the ocean crust, to explore patterns and controls on ridge-flank hydrothermal circulation on the eastern flank of the Juan de Fuca Ridge. Field studies have shown that there is large-scale fluid flow in the volcanic ocean crust in this region, including local convection and circulation between two basement outcrops separated by ~50 km. New simulations include an assessment of crustal permeability and aquifer thickness, outcrop permeability, the potential influence of multiple discharging outcrops, and a comparison between two-dimensional (profile) and three-dimensional representations of the natural system. Field observations that help to constrain new simulations include a modest range of flow rates between recharging and discharging outcrops, secondary convection adjacent to the recharging outcrop, crustal permeability determinations made in boreholes, and the lack of a regional seafloor heat flux anomaly as a consequence of advective heat loss from the crust. Three-dimensional simulations are most consistent with field observations when models use a crustal permeability of 3 × 10-13 to 2 × 10-12 m2, and the crustal aquifer is ≤300 m thick, values consistent with borehole observations. We find fluid flow rates and crustal cooling efficiencies that are an order of magnitude greater in three-dimensional simulations than in two-dimensional simulations using equivalent properties. Simulations including discharge from an additional outcrop can also replicate field observations but tend to increase the overall rate of recharge and reduce the flow rate at the primary discharge site.

  13. Eruptive and tectonic history of the Endeavour Segment, Juan de Fuca Ridge, based on AUV mapping data and lava flow ages

    NASA Astrophysics Data System (ADS)

    Clague, David. A.; Dreyer, Brian M.; Paduan, Jennifer B.; Martin, Julie F.; Caress, David W.; Gill, James B.; Kelley, Deborah S.; Thomas, Hans; Portner, Ryan A.; Delaney, John R.; Guilderson, Thomas P.; McGann, Mary L.

    2014-08-01

    High-resolution bathymetric surveys from autonomous underwater vehicles ABE and D. Allan B. were merged to create a coregistered map of 71.7 km2 of the Endeavour Segment of the Juan de Fuca Ridge. Radiocarbon dating of foraminifera in cores from three dives of remotely operated vehicle Doc Ricketts provide minimum eruption ages for 40 lava flows that are combined with the bathymetric data to outline the eruptive and tectonic history. The ages range from Modern to 10,700 marine-calibrated years before present (yr BP). During a robust magmatic phase from >10,700 yr BP to ˜4300 yr BP, flows erupted from an axial high and many flowed >5 km down the flanks; some partly buried adjacent valleys. Axial magma chambers (AMCs) may have been wider than today to supply dike intrusions over a 2 km wide axial zone. Summit Seamount formed by ˜4770 yr BP and was subsequently dismembered during a period of extension with little volcanism starting ˜4300 yr BP. This tectonic phase with only rare volcanic eruptions lasted until ˜2300 yr BP and may have resulted in near-solidification of the AMCs. The axial graben formed by crustal extension during this period of low magmatic activity. Infrequent eruptions occurred on the flanks between 2620-1760 yr BP and within the axial graben since ˜1750 yr BP. This most recent phase of limited volcanic and intense hydrothermal activity that began ˜2300 yr BP defines a hydrothermal phase of ridge development that coincides with the present-day 1 km wide AMCs and overlying hydrothermal vent fields.

  14. Eruptive and tectonic history of the Endeavour Segment, Juan de Fuca Ridge, based on AUV mapping data and lava flow ages

    USGS Publications Warehouse

    Clague, David A.; Dreyer, Brian M; Paduan, Jennifer B; Martin, Julie F; Caress, David W; Gillespie, James B.; Kelley, Deborah S; Thomas, Hans; Portner, Ryan A; Delaney, John R; Guilderson, Thomas P.; McGann, Mary L.

    2014-01-01

    High-resolution bathymetric surveys from autonomous underwater vehicles ABE and D. Allan B. were merged to create a coregistered map of 71.7 km2 of the Endeavour Segment of the Juan de Fuca Ridge. Radiocarbon dating of foraminifera in cores from three dives of remotely operated vehicle Doc Ricketts provide minimum eruption ages for 40 lava flows that are combined with the bathymetric data to outline the eruptive and tectonic history. The ages range from Modern to 10,700 marine-calibrated years before present (yr BP). During a robust magmatic phase from >10,700 yr BP to ~4300 yr BP, flows erupted from an axial high and many flowed >5 km down the flanks; some partly buried adjacent valleys. Axial magma chambers (AMCs) may have been wider than today to supply dike intrusions over a 2 km wide axial zone. Summit Seamount formed by ~4770 yr BP and was subsequently dismembered during a period of extension with little volcanism starting ~4300 yr BP. This tectonic phase with only rare volcanic eruptions lasted until ~2300 yr BP and may have resulted in near-solidification of the AMCs. The axial graben formed by crustal extension during this period of low magmatic activity. Infrequent eruptions occurred on the flanks between 2620–1760 yr BP and within the axial graben since ~1750 yr BP. This most recent phase of limited volcanic and intense hydrothermal activity that began ~2300 yr BP defines a hydrothermal phase of ridge development that coincides with the present-day 1 km wide AMCs and overlying hydrothermal vent fields.

  15. Seismic Structure of the Endeavour Segment, Juan de Fuca Ridge: Correlations of Crustal Magma Chamber Properties With Seismicity, Faulting, and Hydrothermal Activity

    NASA Astrophysics Data System (ADS)

    van Ark, E. M.; Detrick, R. S.; Canales, J. P.; Carbotte, S. M.; Diebold, J. B.; Harding, A.; Kent, G.; Nedimovic, M. R.; Wilcock, W. S.

    2003-12-01

    Multichannel seismic reflection data collected in July 2002 at the RIDGE2000 Integrated Studies Site at the Endeavour segment, Juan de Fuca Ridge show a high-amplitude, mid-crustal reflector underlying all of the known hydrothermal vent fields at this segment. This reflector, which has been identified with a crustal magma body [Detrick et al., 2002], is found at a two-way travel time of 0.85-1.5 s (1.9-4.0 km) below the seafloor and extends approximately 25 km along axis although it is only 1-2 km wide on the cross-axis lines. The reflector is shallowest (2.5 km depth on the along-axis line) beneath the central, elevated part of the Endeavour segment and deepens toward the segment ends, with a maximum depth of 4 km. The cross axis lines show the mid-crustal reflector dipping from 9 to 50? to the east with the shallowest depths under the ridge axis and greater depths under the eastern flank of the ridge. The amplitude-offset behavior of this mid-crustal axial reflector is consistent with a negative impedance contrast, indicating the presence of melt or a crystallizing mush. We have constructed partial offset stacks at 2-3 km offset to examine the variation of melt-mush content of the axial magma chamber along axis. We see a decrease in P-wave amplitudes with increasing offset for the mid-crustal reflector beneath the Mothra and Main Endeavour vent fields and between the Salty Dawg and Sasquatch vent fields, indicating the presence of a melt-rich body. Beneath the High Rise, Salty Dawg, and Sasquatch vent fields P-wave amplitudes vary little with offset suggesting the presence of a more mush-rich magma chamber. Hypocenters of well-located microseismicity in this region [Wilcock et al., 2002] have been projected onto the along-axis and cross-axis seismic lines, revealing that most axial earthquakes are concentrated in a depth range of 1.5 - 2.7 km, just above the axial magma chamber. In general, seismicity is distributed diffusely within this zone indicating thermal

  16. Major- and minor-metal composition of three distinct solid material fractions associated with Juan de Fuca hydrothermal fluids (northeast Pacific), and calculation of dilution fluid samples

    USGS Publications Warehouse

    Hinkley, T.K.; Seeley, J.L.; Tatsumoto, M.

    1988-01-01

    Three distinct types of solid material are associated with each sample of the hydrothermal fluid that was collected from the vents of the Southern Juan de Fuca Ridge. The solid materials appear to be representative of deposits on ocean floors near mid-ocean ridges, and interpretation of the chemistry of the hydrothermal solutions requires understanding of them. Sr isotopic evidence indicates that at least two and probably all three of these solid materials were removed from the solution with which they are associated, by precipitation or adsorption. This occurred after the "pure" hydrothermal fluid was diluted and thoroughly mixed with ambient seawater. The three types of solid materials, are, respectively, a coarse Zn- and Fe-rich material with small amounts of Na and Ca; a finer material also rich in Zn and Fe, but with alkali and alkaline-earth metals; and a scum composed of Ba or Zn, with either considerable Fe or Si, and Sr. Mineral identification is uncertain because of uncertain anion composition. Only in the cases of Ba and Zn were metal masses greater in solid materials than in the associated fluids. For all other metals measured, masses in fluids dwarf those in solids. The fluids themselves contain greater concentrations of all metals measured, except Mg, than seawater. We discuss in detail the relative merits of two methods of determining the mixing proportions of "pure" hydrothermal solution and seawater in the fluids, one based on Sr isotopes, and another previously used method based on Mg concentrations. Comparison of solute concentrations in the several samples shows that degree of dilution of "pure" hydrothermal solutions by seawater, and amounts of original solutes that were removed from it as solid materials, are not related. There is no clear evidence that appreciable amounts of solid materials were not conserved (lost) either during or prior to sample collection. ?? 1988.

  17. Crustal structure of Axial Volcano on the Juan de Fuca Ridge, from seafloor depths to the bottom of the magma chamber, using Elastic Full Waveform Inversion.

    NASA Astrophysics Data System (ADS)

    Arnulf, Adrien; Harding, Alistair; Kent, Graham

    2013-04-01

    Axial volcano is located at 46˚N, 130˚W at the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg seamount chain. It is the most recent eruptive center of the Cobb hotspot, which last erupted in 2011. The volcano rises ~700 m above the adjacent ridge axis and its summit features a 8-km-long, U-shaped caldera with an opening to the southeast where there is an active hydrothermal field and very young lava flows. Located at the junction of a mid-ocean ridge and a volcanic hotspot, Axial volcano is atypical and its internal structure remains poorly understood. Here, we present results from an elastic full waveform inversion (FWI) along multiple seismic lines that span the whole volcano. We have used a multi-stage FWI, inverting successively wide-angle reflections and refractions arrivals from downward extrapolated streamer data, then windowed short offset reflections from the underlying magma chamber. Our final models show fine scale velocity structures with spatial resolutions of tens of meters. Our results indicate that Layer 2A thickness is extremely heterogeneous (350-900 m) within the volcano with abrupt vertical offsets of >300 m at the caldera walls, consistent with faulting of a geologically defined Layer 2A. Interestingly, Layer 2A appears to be extremely thin beneath the active hydrothermal field, where sheeted dikes might lay <100 m beneath the seafloor. On the other hand, the ever-dropping floor of the caldera appears to be a perfect trap for the ponding of lava flows: the thickness of the lava flows increase gradually to the northwest reaching ~450 m at end of the caldera. Surface velocities are low and exhibit limited variation over the whole volcano suggesting relative recent formation, as layer 2A velocity increases rapidly with age at slightly greater depths. Crustal aging (increase in layer 2A velocity with age) appears to be controlled by pipe-like pattern of focused hydrothermal mineralization. Finally, RTM images reveal a large melt

  18. Submarine geology of Hana Ridge and Haleakala Volcano's northeast flank, Maui

    USGS Publications Warehouse

    Eakins, Barry W.; Robinson, Joel E.

    2006-01-01

    We present a morphostructural analysis of the submarine portions of Haleakala Volcano and environs, based upon a 4-year program of geophysical surveys and submersible explorations of the underwater flanks of Hawaiian volcanoes that was conducted by numerous academic and governmental research organizations in Japan and the U.S. and funded primarily by the Japan Agency for Marine–Earth Science and Technology. A resulting reconnaissance geologic map features the 135-km-long Hana Ridge, the 3000 km2 Hana slump on the volcano's northeast flank, and island-surrounding terraces that are the submerged parts of volcanic shields. Hana Ridge below 2000 m water depth exhibits the lobate morphology typical of the subaqueously erupted parts of Hawaiian rift zones, with some important distinctions: namely, subparallel crestlines, which we propose result from the down-rift migration of offsets in the dike intrusion zone, and an amphitheater at its distal toe, where a submarine landslide has embayed the ridge tip. Deformation of Haleakala's northeast flank is limited to that part identified as the Hana slump, which lies downslope from the volcano's submerged shield, indicating that flank mobility is also limited in plan, inconsistent with hypothesized volcanic spreading driven by rift-zone dilation. The leading edge of the slump has transverse basins and ridges that resemble the thrust ramps of accretionary prisms, and we present a model to describe the slump's development that emphasizes the role of coastally generated fragmental basalt on gravitational instability of Haleakala's northeast flank and that may be broadly applicable to other ocean-island slumps.

  19. Evolution and hydration of the Juan de Fuca crust and uppermost mantle: a plate-scale seismic investigation from ridge to trench

    NASA Astrophysics Data System (ADS)

    Carbotte, S. M.; Canales, J.; Carton, H. D.; Nedimovic, M. R.; Han, S.; Marjanovic, M.; Gibson, J. C.; Janiszewski, H. A.; Horning, G.; Delescluse, M.; Watremez, L.; Farkas, A.; Biescas Gorriz, B.; Bornstein, G.; Childress, L. B.; Parker, B.

    2012-12-01

    The evolution of oceanic lithosphere involves incorporation of water into the physical and chemical structure of the crust and shallow mantle through fluid circulation, which initiates at the mid-ocean ridge and continues on the ridge flanks long after crustal formation. At subduction zones, water stored and transported with the descending plate is gradually released at depth, strongly influencing subduction zone processes. Cascadia is a young-lithosphere end member of the global subduction system where relatively little hydration of the downgoing Juan de Fuca (JdF) plate is expected due to its young age and presumed warm thermal state. However, numerous observations support the abundant presence of water within the subduction zone, suggesting that the JdF plate is significantly hydrated prior to subduction. Knowledge of the state of hydration of the JdF plate is limited, with few constraints on crustal and upper mantle structure. During the Cascadia Ridge-to-Trench experiment conducted in June-July 2012 over 4000 km of active source seismic data were acquired as part of a study of the evolution and state of hydration of the crust and shallow mantle of the JdF plate prior to subduction at the Cascadia margin. Coincident long-streamer (8 km) multi-channel seismic (MCS) and wide-angle ocean bottom seismometer (OBS) data were acquired in a two-ship program with the R/V Langseth (MGL1211), and R/V Oceanus (OC1206A). Our survey included two ridge-perpendicular transects across the full width of the JdF plate, a long trench-parallel line ~10 km seaward of the Cascadia deformation front, as well as three fan lines to study mantle anisotropy. The plate transects were chosen to provide reference sections of JdF plate evolution over the maximum range of JdF plate ages (8-9 Ma), offshore two contrasting regions of the Cascadia Subduction zone, and provide the first continuous ridge-to-trench images acquired at any oceanic plate. The trench-parallel line was designed to

  20. Metalloid reducing bacteria isolated from deep ocean hydrothermal vents of the Juan de Fuca Ridge, Pseudoalteromonas telluritireducens sp. nov. and Pseudoalteromonas spiralis sp. nov.

    PubMed

    Rathgeber, Christopher; Yurkova, Natalia; Stackebrandt, Erko; Schumann, Peter; Humphrey, Elaine; Beatty, J Thomas; Yurkov, Vladimir

    2006-11-01

    Five strains of Gram-negative, rod, curved rod and spiral-shaped bacteria were isolated from the vicinity of deep ocean hydrothermal vents along the Main Endeavour Segment of the Juan de Fuca Ridge in the Pacific Ocean. All strains showed remarkable resistance to high levels of toxic metalloid oxyanions, and were capable of reducing the oxyanions tellurite and selenite to their less toxic elemental forms. Phylogenetic analysis of four strains identified these isolates as close relatives of the genus Pseudoalteromonas within the class Gammaproteobacteria. Pseudoalteromonas agarivorans was the closest relative of strains Te-1-1 and Se-1-2-redT, with, respectively, 99.5 and 99.8% 16S rDNA sequence similarity. Strain Te-2-2T was most closely related to Pseudoalteromonas paragorgicola, with 99.8% 16S rDNA sequence similarity. The DNA G+C base composition was 39.6 to 41.8 mol%, in agreement with other members of the genus Pseudoalteromonas. However, the isolates showed important morphological and physiological differences from previously described species of this genus, with one group forming rod-shaped bacteria typical of Pseudoalteromonas and the other forming vibrioid- to spiral-shaped cells. Based on these differences, and on phylogenetic data, we propose the creation of the new species Pseudoalteromonas telluritireducens sp. nov., with strain Se-1-2-redT (DSMZ = 16098T = VKM B-2382T) as the type strain, and Pseudoalteromonas spiralis sp. nov., with strain Te-2-2T (DSMZ = 16099T = VKM B-2383T) as the type strain.

  1. Desulfurobacterium crinifex sp. nov., a novel thermophilic, pinkish-streamer forming, chemolithoautotrophic bacterium isolated from a Juan de Fuca Ridge hydrothermal vent and amendment of the genus Desulfurobacterium.

    PubMed

    Alain, Karine; Rolland, Sophie; Crassous, Philippe; Lesongeur, Françoise; Zbinden, Magali; le Gall, Christian; Godfroy, Anne; Page, Antoine; Juniper, S Kim; Cambon-Bonavita, Marie-Anne; Duchiron, Francis; Querellou, Joël

    2003-10-01

    A novel thermophilic, chemolithoautotrophic bacterium, designated as NE1206(T), was isolated from a Juan de Fuca Ridge hydrothermal vent sample (tubes of the annelid polychaete Paralvinella sulfincola attached to small pieces of hydrothermal chimney). The cells were rod-shaped (1.2-3.5 x 0.4-0.7 microm), occurring as single motile rods or forming macroscopic aggregates visible as pinkish to brownish streamers. The new isolate was anaerobic. It grew between 50 and 70 degrees C (optimum 60-65 degrees C; doubling time approximately 1 h 15 min at 60 degrees C), between pH 5.0 and 7.5 (optimum pH around 6.0-6.5) and at sea salts concentrations between 20 and 40 g l(-1 )(optimum 30 g l(-1)). Cells grew chemolithoautotrophically in an H(2)/CO(2) atmosphere (80/20, v/v; 200 kPa). Molecular hydrogen was the sole electron donor used by the strain. Nitrate and elemental sulfur served as electron acceptors, yielding ammonia and hydrogen sulfide, respectively (nitrate reduction supported higher growth rates than sulfur reduction). The G+C content of the genomic DNA was 36.7+/-0.8 mol%. Phylogenetic analyses of the 16S rRNA gene located the strain within the genus Desulfurobacterium. However, the novel isolate possesses physiological and biochemical characteristics that differ from the previously described species of this genus. We propose that the isolate represents a novel species, Desulfurobacterium crinifex sp. nov. The type strain is NE1206(T) (DSM 15218(T), CIP 107649(T)). An amendment of the genus Desulfurobacterium description is proposed, based on the phenotypic characteristics of the novel species.

  2. A preliminary 1-D model investigation of tidal variations of temperature and chlorinity at the Grotto mound, Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Xu, G.; Larson, B. I.; Bemis, K. G.; Lilley, Marvin D.

    2017-01-01

    Tidal oscillations of venting temperature and chlorinity have been observed in the long-term time series data recorded by the Benthic and Resistivity Sensors (BARS) at the Grotto mound on the Juan de Fuca Ridge. In this study, we use a one-dimensional two-layer poroelastic model to conduct a preliminary investigation of three hypothetical scenarios in which seafloor tidal loading can modulate the venting temperature and chlorinity at Grotto through the mechanisms of subsurface tidal mixing and/or subsurface tidal pumping. For the first scenario, our results demonstrate that it is unlikely for subsurface tidal mixing to cause coupled tidal oscillations in venting temperature and chlorinity of the observed amplitudes. For the second scenario, the model results suggest that it is plausible that the tidal oscillations in venting temperature and chlorinity are decoupled with the former caused by subsurface tidal pumping and the latter caused by subsurface tidal mixing, although the mixing depth is not well constrained. For the third scenario, our results suggest that it is plausible for subsurface tidal pumping to cause coupled tidal oscillations in venting temperature and chlorinity. In this case, the observed tidal phase lag between venting temperature and chlorinity is close to the poroelastic model prediction if brine storage occurs throughout the upflow zone under the premise that layers 2A and 2B have similar crustal permeabilities. However, the predicted phase lag is poorly constrained if brine storage is limited to layer 2B as would be expected when its crustal permeability is much smaller than that of layer 2A.

  3. Compositions, growth mechanisms, and temporal realtions of hydrothermal sulfide-sulfate-silica chimneys at the northern Cleft segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Koski, Randolph A.; Jonasson, Ian R.; Kadko, David C.; Smith, Virginia K.; Wong, Florence L.

    1994-03-01

    Three active hydrothermal vents forming sulfide mounds and chimneys (Monolith, Fountain, and Pipe Organ) and more widely distributed inactive chimneys are spatially related to a system of discontinuous fissures and young sheet flow lavas at the northern Cleft segment, Juan de Fuca Ridge. The formation of zoned tubular Curich chimneys (type I) on the Monolith sulfide mound is related to focused flow of high-temperature (to 328 C) fluid. Bulbous chimneys (type II or 'beehives') at the Monolith and Fountain vents are products of diffuse high-temperature (to 315 C) discharge. A broader zone of vigorous mixing between the hydrothermal fluid and seawater results in quench crystallization of anhydrite-rich shells. Columnar Zn-sulfide-rich chimneys with narrow channelways (type III) are constructed where focused and relatively low-temperature (261 C) fluid vents directly from the basalt substrate. The bulk chemistry (low Cu; high Pb, Ag, and SiO2 contents), mineralogy (pyrite-marcasite-wurtzite-amorphous silica-anglesite), colloform and filamentous textures, and oxygen isotope characteristics of inactive (type IV) chimneys indicate a low-temperature (less than 250 C) origin involving diffuse and sluggish flow patterns and conductive cooling. Seafloor observations and Pb-210 data indicate that (1) type IV chimneys are products of an earlier period of hydrothermal activity that ended no more than 60 years ago but prior to the sheet flow eruption; (2) the high-temperature Monolith and Fountain vents are manifestations of the same heating event (shallow emplacement of magma) that led to the sheet flow eruption and recent megaplumes; and (3) the Pipe Organ Vent is in a very youthful stage of development, and chimney deposition postdates the sheet flow eruption.

  4. Constraining Seasonal and Vertical Distributions of Planktonic Foraminifera for Paleoclimate Reconstruction Since MIS3 at the Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Chen, S. L.; Ravelo, A. C.; Clague, D. A.

    2015-12-01

    The California Current is an upwelling region with dynamic interactions between circulation, biological productivity and ecology. A 77 cm piston push core was taken from the Juan de Fuca Ridge Axial Seamount using a Remotely Operated Vehicle (ROV) (2213m, 45.55º N, 130.08º W), an active submarine volcano ~480 km off Oregon's coast. Five radiocarbon dates indicate that the sediment ranges from 42.6 ka at 77 cm to 17.6 ka at 15 cm, with an average sediment accumulation rate of 2.47 cm/ka from 77-15 cm, and an average rate of 0.85 cm/ka during the postglacial period (<17.6 ka). Multiple species of planktic foraminifera from the core representing subtropical, subartic, and arctic fauna have been used to constrain changes in vertical and seasonal temperature since Marine Isotope Stage 3 (MIS3). Measurements of δ18O of the upwelling species Globigerina bulloides, the thermocline dwelling species Neogloboquadrina dutertrei, and the warm mixed-layer species Orbulina universa are offset from each other, reflecting vertical and seasonal variation among the planktonic foraminifera. Of the three species, G. bulloides shows the least variation in δ18O, possibly indicating that marked changes in temperature are masking changes in the δ18O of seawater due to global ice volume changes. G. bulloides and O. universa δ18O values are similar in MIS 3 and diverge with time, indicating the development of strong seasonal succession of species, since the last glacial maximum. Bulk nitrogen isotopes and nitrogen flux provide additional constraints on upwelling strength and insight into local biological productivity and nutrient dynamics. Obtaining Mg/Ca data will clarify the δ 18O interpretation except deep in the core where metal-bearing authigenic precipitates affect Mg concentrations. These climatic proxies together provide insight into how global climate change and local seamount volcanism impacts regional productivity in the California Current.

  5. Volatile, Major and Trace Element Chemistry of Olivine-Hosted Melt Inclusions and Host Glasses in Cleft and Coaxial Segments of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Schwartz, D. M.; Wanless, V. D.; Lytle, M. L.

    2015-12-01

    To assess the influence of hotspot anomalies on crustal accretion along the Juan de Fuca Ridge, we examine lavas and olivine-hosted melt inclusions (MIs) erupted at segments adjacent to (Coaxial) and isolated from (Cleft) the Cobb Hotspot, which currently intersects the ridge at Axial Seamount. Coaxial samples (host basalt N = 7; MIs N=113) were collected from the center of an axial rise, ~60 km north of Axial Seamount. Cleft samples were collected within the axial graben, ~100 km south of Axial Seamount (host basalts N=3; MIs N=38). The MIs and host glasses were analyzed for major, trace and volatile element concentrations. Vapor-saturation pressures of each MI were determined using CO2-H2O concentrations. Entrapment depths for Coaxial MIs range from 0-16 km below seafloor (bsf) with a broad frequency peak centered about 1.5 km bsf. By contrast, the Cleft segment MIs have a narrower range of entrapment depths (0 to 12 km bsf), with a narrow and deeper frequency distribution centered around 3 km bsf. The average rare-earth element (REE) concentrations for the MIs closely resemble those of the host-basalt glasses. Coaxial MIs display variably depleted light and heavy REE patterns and indicate variable degrees of fractional crystallization. The Cleft MIs are uniformly depleted in light REEs only, and span a narrower compositional range, indicating similar crystallization histories. This suggests a model of accretion at Cleft, where relatively homogeneous mantle melts crystallize from ~10 km bsf to the seafloor, with significant storage and crystallization in a shallow (3 km depth) melt lens. At Coaxial, crystallization begins at greater depths (~15 km bsf) with a broader, shallower peak of MI entrapment depths and more variable trace element patterns. The peaks in crystallization depths are broadly consistent with the depths for seismically imaged melt lenses (Carbotte et al., 2006) at both segments. The broader peak of MI entrapment depths observed at Coaxial may

  6. Numerical Modeling of Two-Phase Flow at the Main Endeavour Field, Juan de Fuca Ridge: Quasi-Steady State and Thermal Decline of the Vent Field

    NASA Astrophysics Data System (ADS)

    Singh, S.; Lowell, R. P.; Lewis, K. C.

    2012-12-01

    The Main Endeavour Field (MEF) on the Juan de Fuca Ridge consists of a large number of chimney structures occupying an area approximately 400 m x 150 m along the ridge axis. For nearly a decade, the MEF exhibited quasi-steady north-south trending spatial gradients of both temperature and salinity. We have constructed 2-D across-axis numerical models of two-phase flow using the code FISHES to investigate possible causes for this variation. We considered the effect of bottom boundary temperature and both a homogeneous permeability structure and a geometry incorporating a more-permeable layer 2A. From these model results we argue that such a trend is more likely to be the result of heterogeneous permeability structure of the shallow oceanic crust than a result of bottom boundary temperature variations. After a magmatic event in 1999, this trend was disrupted; and thermal data using the Autonomous Benthic Explorer (ABE) indicates that there has been a significant decline in the heat output from a value of approximately 450 MW in 2000 to approximately 300 MW in 2004. In the southern part of the vent field, vent salinities have also increased from values well below those of seawater to values close to seawater. We therefore extend our investigation to include the effect of a temporally-decaying basal heat flow, which may result from cooling, crystallizing magma chamber, on the system. Our aim is to determine whether such a phenomenon could cause the observed rapid decline of heat flow and changes in vent salinity at the MEF. We find that the thermal inertia in the system is such that changes in basal heat flow would be difficult to detect in the given time frame, if magma replenishment ceased following the 1999 magmatic event. The time delay between changes in bottom conditions and the observed decay in observed heat output suggests that the 1999 event represented a small replenishment event and that the AMC may have begun cooling some time before that. Moreover, because

  7. Microearthquakes beneath the Hydrothermal Vent Fields on the Endeavour Segment of the Juan de Fuca Ridge: Results from the Keck Seismic/Hydrothermal Observatory

    NASA Astrophysics Data System (ADS)

    Bowman, D.; Parker, J.; Wilcock, W.; Hooft, E.; Barclay, A.; Toomey, D.; McGill, P.; Stakes, D.; Schmidt, C.; Patel, H.

    2005-12-01

    The W.M. Keck Foundation is supporting the operation of a small seismic network in the vicinity of the hydrothermal vent fields on the central portion of the Endeavour Segment of the Juan de Fuca Ridge. This is part of a program to conduct prototype seafloor observatory experiments to monitor the relationships between episodic deformation, fluid venting and microbial productivity at oceanic plate boundaries. The Endeavour seismic network was installed in the summer of 2003 and comprises seven GEOSense three-component short-period corehole seismometers and one buried Guralp CMG-1T broadband seismometer. A preliminary analysis of the first year of data was undertaken as part of an undergraduate research apprenticeship class taught at the University of Washington's Friday Harbor Laboratories and additional analysis has since been completed by two of the apprentices and by two IRIS undergraduate interns. Over 12,000 earthquakes were located along the ridge-axis of the Endeavour, of which ~3,000 occur within or near the network and appear to be associated with the hydrothermal systems. The levels of seismicity are strongly correlated with the intensity of venting with particularly high rates of seismicity beneath the Main and High Rise Fields and substantially lower rates to the north beneath the relatively inactive Salty Dawg and Sasquatch fields. We have used both HYPOINVERSE and a grid search algorithm to investigate the distribution of focal depths assuming a variety of one-dimensional velocity models. The preliminary results show that the majority of earthquakes occur within a narrow depth range and may represent an intense zone of seismicity within a reaction overlying the axial magma chamber at ~2.5 km depth. However, the mean focal depth is strongly dependent on the relative weights assigned to the S arrivals. We infer from the inspection of residuals that no combination of the P- and S-wave velocity models we have so far investigated are fully consistent with

  8. Age, Episodicity and Migration of Hydrothermal Activity within the Axial Valley, Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Jamieson, J. W.; Hannington, M. D.; Kelley, D. S.; Clague, D. A.; Holden, J. F.; Tivey, M. K.; Delaney, J. R.

    2011-12-01

    Hydrothermal sulfide deposits record the history of high-temperature venting along the Endeavour Segment. Active venting is currently located within five discreet vent fields, with minor diffuse venting occurring between the fields. However, inactive and/or extinct sulfide structures are found throughout the entire axial valley of the ridge segment, suggesting that hydrothermal activity has been more vigorous in the past or focused venting has migrated with time. Here, we present age constraints from U-series dating of 44 sulfide samples collected by manned submersible from between the Mothra Field in the south to Sasquatch in the north. Samples are dated using 226Ra/Ba ratios from hydrothermal barite that precipitates along with the sulfide minerals. Most samples have been collected from within or near the active vent fields. Fifteen samples from the Main Endeavour Field (MEF) show a spectrum of ages from present to 2,430 years old, indicating that this field has been continuously active for at least ~2,400 years. MEF appears to be oldest currently active field. This minimum value for the age of hydrothermal activity also provides a minimum age of the axial valley itself. Ages from thirteen samples from the High-Rise Field indicate continuous venting for at least the past ~1,250 years. These age data are used in conjunction with age constraints of the volcanic flows to develop an integrated volcanic, hydrothermal and tectonic history of the Endeavour Segment. The total volume of hydrothermal sulfide within the axial valley, determined from high-resolution bathymetry, is used in conjunction with the age constraints of the sulfide material to determine the mass accumulation rates of sulfide along the Endeavour Segment. These data can be used to calibrate the efficiency of sulfide deposition from the hydrothermal vents, and provide a time-integrated history of heat, fluid and chemical fluxes at the ridge-segment scale. The comparison of time-integrated rates with

  9. Very High Resolution Bathymetric Mapping at the Ridge 2000 Integrated Study Sites: Acquisition and Processing Protocols Developed During Recent Alvin Field Programs to the East Pacific Rise and Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Ferrini, V.; Fornari, D. J.; Shank, T.; Tivey, M.; Kelley, D. S.; Glickson, D.; Carbotte, S. M.; Howland, J.; Whitcomb, L. L.; Yoerger, D.

    2004-12-01

    Recent field programs at the East Pacific Rise and Juan de Fuca Ridge have resulted in the refinement of data processing protocols that enable the rapid creation of high-resolution (meter-scale) bathymetric maps from pencil-beam altimetric sonar data that are routinely collected during DSV Alvin dives. With the development of the appropriate processing tools, the Imagenex sonar, a permanent sensor on Alvin, can be used by a broad range of scientists permitting the analysis of various data sets within the context of high-quality bathymetric maps. The data processing protocol integrates depth data recorded with Alvin's Paroscientific pressure sensor with bathymetric soundings collected with an Imagenex 675 kHz articulating (scanning) sonar system, and high-resolution navigational data acquired with DVLNAV, which includes bottom lock Doppler sonar and long baseline (LBL) navigation. Together these data allow us, for the first time, to visualize portions of Ridge 2000 Integrated Study Sites (ISS) at 1-m vertical and horizontal resolution. These maps resolve morphological details of structures within the summit trough at scales that are relevant to biological communities (e.g. hydrothermal vents, lava pillars, trough walls), thus providing the important geologic context necessary to better understand spatial patterns associated with integrated biological-hydrothermal-geological processes. The Imagenex sonar is also a permanent sensor on the Jason2 ROV, which is also equipped with an SM2000 (200 kHz) near-bottom multibeam sonar. In the future, it is envisioned that near-bottom multibeam sonars will be standard sensors on all National Deep Submergence Facility (NDSF) vehicles. Streamlining data processing protocols makes these datasets more accessible to NDSF users and ensures broad compatibility between data formats among NDSF vehicle systems and allied vehicles (e.g. ABE). Establishing data processing protocols and software suites, routinely calibrating sensors (e

  10. AUV Mapping of Axial Seamount, Juan de Fuca Ridge: The Southern Caldera Floor and Upper South Rift

    NASA Astrophysics Data System (ADS)

    Clague, D. A.; Caress, D.; Paduan, J. B.; Chadwick, W. W.; Butterfield, D. A.; Thomas, H.; Conlin, D.; Thompson, D. R.

    2007-12-01

    During September 2006 and August 2007 NOAA NeMO cruises, we conducted 7 high-resolution near-bottom seafloor mapping surveys of Axial Seamount using the MBARI Mapping AUV D. Allan B. The 200 kHz multibeam and 110 kHz sidescan surveys of the south caldera and upper south rift, conducted at 50 m vehicle altitude, achieved sub-meter resolution bathymetry and sidescan imagery. Numerous previous and concurrent submersible or ROV dives provide ground-truth of what the maps depict. A companion poster presents the AUV surveys of the north caldera and northeastern caldera rim. The southern caldera wall is buried beneath at least 5 voluminous lava flows, including the 1998 flow, each erupted from fissures extending along the southeastern edge of the caldera roughly parallel to the upper south rift zone. The caldera wall here was not as tall as on the southwest, north, and northeast of the caldera, and may have been as low as 35 m tall before it was buried. Active and inactive hydrothermal vents are generally located along the inferred buried caldera wall. Eruptive fissures are characterized by series of depressions aligned along each fissure; no ramparts or other constructional edifices were constructed along them. The aligned depressions suggest that lava drained back down the fissures at the end of the eruptions. The fissure eruptions were large volume and had large effusion rates as seen by their interwoven channels and the extent of the flows. Most of these flows have central channels of lineated sheet flows, bordered by folded and then jumbled sheet flows, surrounded by lobate flows with lava pillars and collapse structures and pillowed flow margins. As an example, the 1998 eruption in and near the caldera issued from 5 en echelon fissures extending at least 3 km. The largest flow lobe extending to the south was mapped along its entire western boundary using JASON II, but the flow extends to the southeast beyond the mapped region. An unusual km-across feature was mapped

  11. Competing styles of deep-marine explosive eruptions revealed from Axial seamount and Juan De Fuca ridge push core records

    NASA Astrophysics Data System (ADS)

    Portner, R. A.; Clague, D. A.; Paduan, J. B.; Martin, J. F.

    2012-12-01

    extremely fine-grained, angular-sliver shaped and locally concentrated into reverse graded laminae. Fluidal shards are rare. Plagioclase fragments are locally abundant up to 15%. A significant component of hydrothermal grains also occurs and consists of pale greenish-blue clay aggregates, reddish-orange botryoidal grains, anyhydrite, barite or zeolite, and pyrite. X-ray diffraction analysis indicates that the muddy host contains minor nontronite or saponite, and chlorite. This mineral association is in stark contrast to quartz-illite bearing sediment samples from adjacent ridge segments, and supports the interpretation that the ashy mud deposits on Axial seamount preserve hydrothermal activity. Analogous to a phreatomagmatic eruption on land, we envisage shallow circulation of hydrothermal fluids below the vent and hydrovolcanic fragmentation during ascent through the conduit. Lamination and grading criteria suggest that beds were deposited via dilute turbidity flows and reworked by ocean bottom currents. Associations of the two pyroclastic lithofacies with interbedded fossiliferous-bioturbated mud, indicates relatively quiescent periods between separate magmatic or phreatomagmatic eruptions. These eruptive modes extend our knowledge about the range in deep-marine explosive activity.

  12. Seismicity Along the Endeavour Segment of the Juan de Fuca Ridge: Automated Event Locations for an Ocean-Bottom Seismometer Network

    NASA Astrophysics Data System (ADS)

    Weekly, R. T.; Wilcock, W. S.; Hooft, E. E.; Toomey, D. R.; McGill, P. R.

    2004-12-01

    From 2003-2006, the W.M. Keck Foundation supported the operation of a network of eight ocean-bottom seismometers (OBSs) that were deployed with a remotely operated vehicle along the central portion of the Endeavour Segment of the Juan de Fuca mid-ocean ridge as part of a multidisciplinary prototype NEPTUNE experiment. Data from 2003-2004 were initially analyzed during a research apprenticeship class at the University of Washington's Friday Harbor Laboratories. Eight student analysts located ~13,000 earthquakes along the Endeavour Segment. Analysis of data from 2004-2005 has to date been limited to locating ~6,000 earthquakes associated with a swarm in February-March 2005 near the northern end of the Endeavour Segment. The remaining data includes several significant swarms and it is anticipated that tens of thousands of earthquakes still need to be located. In order to efficiently obtain a complete catalog of high-quality locations for the 3-year experiment, we are developing an automatic method for earthquake location. We first apply a 5-Hz high-pass filter and identify triggers when the ratio of the root-mean square (RMS) amplitudes in short- and long- term windows exceeds a specified threshold. We search for events that are characterized by triggers within a short time interval on the majority of stations and use the signal spectra to eliminate events that are the result of 20-Hz Fin and Blue whale vocalizations. An autoregressive technique is applied to a short time window centered on the trigger time to pick P-wave times on each station's vertical channel. We locate the earthquake with these picks and either attempt to repick or eliminate arrivals with unacceptable residuals. Preliminary S-wave picks are then made on the horizontal channels by applying a 5-12 Hz bandpass filter, identifying the peak RMS amplitude for a short running window, and making a pick at the time the RMS amplitude rises above 50% of this value. The picks are refined using the

  13. Seismicity Along the Endeavour Segment of the Juan de Fuca Ridge: Automated Event Locations for an Ocean-Bottom Seismometer Network

    NASA Astrophysics Data System (ADS)

    Weekly, R. T.; Wilcock, W. S.; Hooft, E. E.; Toomey, D. R.; McGill, P. R.

    2007-12-01

    From 2003-2006, the W.M. Keck Foundation supported the operation of a network of eight ocean-bottom seismometers (OBSs) that were deployed with a remotely operated vehicle along the central portion of the Endeavour Segment of the Juan de Fuca mid-ocean ridge as part of a multidisciplinary prototype NEPTUNE experiment. Data from 2003-2004 were initially analyzed during a research apprenticeship class at the University of Washington's Friday Harbor Laboratories. Eight student analysts located ~13,000 earthquakes along the Endeavour Segment. Analysis of data from 2004-2005 has to date been limited to locating ~6,000 earthquakes associated with a swarm in February-March 2005 near the northern end of the Endeavour Segment. The remaining data includes several significant swarms and it is anticipated that tens of thousands of earthquakes still need to be located. In order to efficiently obtain a complete catalog of high-quality locations for the 3-year experiment, we are developing an automatic method for earthquake location. We first apply a 5-Hz high-pass filter and identify triggers when the ratio of the root-mean square (RMS) amplitudes in short- and long- term windows exceeds a specified threshold. We search for events that are characterized by triggers within a short time interval on the majority of stations and use the signal spectra to eliminate events that are the result of 20-Hz Fin and Blue whale vocalizations. An autoregressive technique is applied to a short time window centered on the trigger time to pick P-wave times on each station's vertical channel. We locate the earthquake with these picks and either attempt to repick or eliminate arrivals with unacceptable residuals. Preliminary S-wave picks are then made on the horizontal channels by applying a 5-12 Hz bandpass filter, identifying the peak RMS amplitude for a short running window, and making a pick at the time the RMS amplitude rises above 50% of this value. The picks are refined using the

  14. Microbial and Mineral Descriptions of the Interior Habitable Zones of Active Hydrothermal Chimneys from the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Holden, J. F.; Lin, T.; Ver Eecke, H. C.; Breves, E.; Dyar, M. D.; Jamieson, J. W.; Hannington, M. D.; Butterfield, D. A.; Bishop, J. L.; Lane, M. D.

    2013-12-01

    Actively venting hydrothermal chimneys and their associated hydrothermal fluids were collected from the Endeavour Segment, Juan de Fuca Ridge to determine the mineralogy, chemistry and microbial community composition of their interiors. To characterize the mineralogy, Mössbauer, FTIR, VNIR and thermal emission spectroscopies were used for the first time on this type of sample in addition to thin-section petrography, x-ray diffraction and elemental analyses. A chimney from the Bastille edifice was Fe-sulfide rich and composed primarily of chalcopyrite, marcasite-sphalerite, and pyrrhotite while chimneys from the Dante and Hot Harold edifices were Fe-sulfide poor and composed primarily of anhydrite. The bulk emissivity and reflectance spectroscopies corroborated well with the petrography and XRD analyses. The microbial community in the interior of Bastille was most closely related to mesophilic-to-thermophilic anaerobes of the deltaproteobacteria and hyperthermophilic archaea while those in the interiors of Dante and Hot Harold were most closely related to mesophilic-to-thermophilic aerobes of the beta-, gamma- and epsilonproteobacteria. The fluid temperatures (282-321°C) and chemistries of the three chimneys were very similar suggesting that differences in mineralogy and microbial community compositions were more dependent on fluid flow characteristics and paragenesis within the chimney. Thin-section petrography of the interior of another hydrothermal chimney collected from the Dante edifice (emitting 336°C fluid) shows a thin coat of Fe3+ oxide associated with amorphous silica on the exposed outer surfaces of pyrrhotite, sphalerite and chalcopyrite in pore spaces, along with anhydrite precipitation in the pores that is indicative of seawater ingress. The Fe-sulfide minerals were likely oxidized to ferrihydrite with increasing pH and Eh due to cooling and seawater exposure, providing reactants for bioreduction. Culture-based most-probable-number estimates of

  15. Joint Inversion for VP/VS Structure of the Upper Oceanic Crust beneath the Endeavour Segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Kim, E.; Toomey, D. R.; Hooft, E. E. E.; Wilcock, W. S. D.; Weekly, R. T.; Lee, S. M.; Kim, Y.

    2016-12-01

    We have obtained models of VP and VS in the upper oceanic crust beneath the Endeavour segment of the Juan de Fuca Ridge by simultaneously inverting first arriving Pg and P-to-S converted Sg travel times obtained during a seismic tomography experiment. In the inversion, two types of VP to VS coupling are tested. First, VP/VS variations are assumed to be spatially smooth. Second, dlnVs/dlnVp is assumed to be constant. Of the two approaches, the constant dlnVs/dlnVp recovers VP/VS anomalies and also reduces Sg misfits the most. Preliminary results show that the horizontally averaged VP/VS in a 10 km by 20 km area at the center segment decreases from 3.0 in the seismic layer 2A (≤ 0.4 km depth) to 1.72 at the bottom of the seismic layer 2B (2 km). To understand the VP/VS variations with depth, we model the relationship between porosity and VP/VS using differential effective medium (DEM) theory. To explain our seismic observation, we use basalt (VP = 6.4 km/s, VS = 3.5 km/s, density = 2971 kg/m3 [Johnston and Christensen, 1997]) and seawater (VP = 1.5 km/s, VS = 0 km/s, density = 1030 kg/m3 [Telford and Sheriff, 1990]) as a host medium and fluid-filled crack (aligned vertically). At zero porosity (φ = 0%), VP/VS of basalt is set to 1.83. The observed VP/VS of 3.0 in the layer 2A can be explained by increased porosity of 0.8%, 2.3%, 7%, or 22% due to water-filled cracks with an aspect ratio (d) of 0.001, 0.002, 0.005, or 0.01, respectively. These crack aspect ratios are consistent with a porosity that is reduced to 0.1%, 0.3%, 1.1%, or 3.3% at the top of the layer 2B (0.6 km) where the observed VP/VS is 2.0. We also estimate variations in crack density with depth. The crack density of thin cracks (d ≤ 0.01) abruptly decreases by 85% between the layers 2A and 2B, whereas that of thick cracks (d ≥ 0.1) decreases by only 27%. Based on the modeling result, the observed variations in VP/VS of the layer 2 can be explained by the presence and sealing characters of cracks

  16. Tectonic evolution of Gorda Ridge inferred from sidescan sonar images

    USGS Publications Warehouse

    Masson, D.G.; Cacchione, D.A.; Drake, D.E.

    1988-01-01

    Gorda Ridge is the southern segment of the Juan de Fuca Ridge complex, in the north-east Pacific. Along-strike spreading-rate variation on Gorda Ridge and deformation of Gorda Plate are evidence for compression between the Pacific and Gorda Plates. GLORIA sidescan sonographs allow the spreading fabric associated with Gorda Ridge to be mapped in detail. Between 5 and 2 Ma, a pair of propagating rifts re-orientated the northern segment of Gorda Ridge by about 10?? clockwise, accommodating a clockwise shift in Pacific-Juan de Fuca plate motion that occurred around 5 Ma. Deformation of Gorda Plate, associated with southward decreasing spreading rates along southern Gorda Ridge, is accommodated by a combination of clockwise rotation of Gorda Plate crust, coupled with left-lateral motion on the original normal faults of the ocean crust. Segments of Gorda Plate which have rotated by different amounts are separated by narrow deformation zones across which sharp changes in ocean fabric trend are seen. Although minor lateral movement may occur on these NW to WNW structures, no major right-lateral movement, as predicted by previous models, is observed. ?? 1988 Kluwer Academic Publishers.

  17. The Cobb-Eickelberg seamount chain: Hotspot volcanism with mid-ocean ridge basalt affinity

    SciTech Connect

    Desonie, D.L.; Duncan, R.A. )

    1990-08-10

    Cobb hotspot, currently located beneath Axial seamount on the Juan de Fuca ridge, has the temporal but not the isotopic characteristics usually attributed to a mantle plume. The earlier volcanic products of the hotspot, form eight volcanoes in the Cobb-Eickelberg seamount (CES) chain, show a westward age progression away from the hotspot and a westward increase in the age difference between the seamounts and the crust on which they formed. These results are consistent with movement of the Pacific plate over a fixed Cobb hotspot and eventual encroachment by the westwardly migrating Juan de Fuca ridge. CES lavas are slightly enriched in alkalies and incompatible elements relative to those of the Juan de Fuca ridge but they have Sr, Nd, and Pb isotopic compositions virtually identical to those found along the ridge. Therefore, Cobb hotspot is a stationary, upper mantle melting anomaly whose volcanic products show strong mid-ocean ridge basalt (MORB) affinity. These observations can be explained by low degrees of partial melting of entrained heterogeneous upper mantle MORB source material within a thermally driven lower mantle diapir or by an intrinsic MORB-like composition of the deeper mantle source region from which northeast Pacific plumes rise.

  18. A long-term record of magma compositions at the Juan de Fuca ridge from analysis of sediment hosted volcanic glass: tests of the effects of sea level on melt production

    NASA Astrophysics Data System (ADS)

    Ferguson, D.; Li, Y.; Langmuir, C. H.; Costa, K.; McManus, J. F.; Huybers, P. J.

    2015-12-01

    It is hypothesized that the pressure changes caused by sea level variations during glacial cycles can influence long-term rates of magmatism in ocean basins. This proposed coupling between oceanic magmatism and climate has important implications for temporal trends in rates of mid-ocean ridge (MOR) volcanism, the structure of the oceanic crust and the composition of oceanic magmas, including the flux of volatile elements from the mantle. Testing the extent to which climate cycles may or may not modulate the compositions of oceanic magmas is difficult, as it requires compositional records that stretch over timescales comparable to those of glacial cycles (i.e. 10s of kyrs), which do not currently exist. In this study we use fragments of volcanic glass found in sediment cores to construct compositional time-series for lavas erupted at the Juan de Fuca ridge, NW Pacific. These provide continuous records of magmatism over several 10s kyrs, with a temporal resolution of a few kyrs. The longest record in our current dataset spans ~80 kyrs and records two significant step-wise changes in the average compositions of the erupted magmas, linked to both variations in the extent of crustal fractionation (i.e. MgO) and also the composition of primary mantle melts (i.e. K2O/TiO2). These changes occur rapidly and are decoupled in time, with the MgO shift happening around ~20 kyrs before the change in K2O/TiO2. Compositional variations such as these, and the temporal offset between them, are generally consistent with models of the effect of sea-level variation on magma chemistry, which can modulate the melt flux to the ridge and the extent of mantle melting. To place our results in a chronological and climatic context we will compare our data to oxygen-isotope records collected from the same sediment horizons and chemical analysis of the host sediments. Our study demonstrates the potential of this method for investigating the magmatic behaviour of ridges over long timescales.

  19. Ridges

    NASA Image and Video Library

    2003-04-15

    Tall narrow ridges snake between mesas and buttes in this image from NASA Mars Odyssey. Where one such ridge crosses a flat-topped mesa in the lower center of the image, the mesa surface is split into two surfaces of different heights.

  20. Investigating the effects of climate variations on bacillary dysentery incidence in northeast China using ridge regression and hierarchical cluster analysis

    PubMed Central

    Huang, Desheng; Guan, Peng; Guo, Junqiao; Wang, Ping; Zhou, Baosen

    2008-01-01

    Background The effects of climate variations on bacillary dysentery incidence have gained more recent concern. However, the multi-collinearity among meteorological factors affects the accuracy of correlation with bacillary dysentery incidence. Methods As a remedy, a modified method to combine ridge regression and hierarchical cluster analysis was proposed for investigating the effects of climate variations on bacillary dysentery incidence in northeast China. Results All weather indicators, temperatures, precipitation, evaporation and relative humidity have shown positive correlation with the monthly incidence of bacillary dysentery, while air pressure had a negative correlation with the incidence. Ridge regression and hierarchical cluster analysis showed that during 1987–1996, relative humidity, temperatures and air pressure affected the transmission of the bacillary dysentery. During this period, all meteorological factors were divided into three categories. Relative humidity and precipitation belonged to one class, temperature indexes and evaporation belonged to another class, and air pressure was the third class. Conclusion Meteorological factors have affected the transmission of bacillary dysentery in northeast China. Bacillary dysentery prevention and control would benefit from by giving more consideration to local climate variations. PMID:18816415

  1. Investigating the effects of climate variations on bacillary dysentery incidence in northeast China using ridge regression and hierarchical cluster analysis.

    PubMed

    Huang, Desheng; Guan, Peng; Guo, Junqiao; Wang, Ping; Zhou, Baosen

    2008-09-25

    The effects of climate variations on bacillary dysentery incidence have gained more recent concern. However, the multi-collinearity among meteorological factors affects the accuracy of correlation with bacillary dysentery incidence. As a remedy, a modified method to combine ridge regression and hierarchical cluster analysis was proposed for investigating the effects of climate variations on bacillary dysentery incidence in northeast China. All weather indicators, temperatures, precipitation, evaporation and relative humidity have shown positive correlation with the monthly incidence of bacillary dysentery, while air pressure had a negative correlation with the incidence. Ridge regression and hierarchical cluster analysis showed that during 1987-1996, relative humidity, temperatures and air pressure affected the transmission of the bacillary dysentery. During this period, all meteorological factors were divided into three categories. Relative humidity and precipitation belonged to one class, temperature indexes and evaporation belonged to another class, and air pressure was the third class. Meteorological factors have affected the transmission of bacillary dysentery in northeast China. Bacillary dysentery prevention and control would benefit from by giving more consideration to local climate variations.

  2. Evidence of Volcanism and Extensive Low-Temperature Off-Axis Hydrothermal Venting along the Cleft Segment of the Southern Juan de Fuca Ridge (JdFR)

    NASA Astrophysics Data System (ADS)

    Stakes, D. S.; Perfit, M.; Wheat, G.; Delong, E.; Tivey, M. A.; Ramirez, T. M.

    2002-12-01

    Systematic geological observations and off-axis sampling of the Cleft Segment of the southern JdFR made with the MBARI ROV Tiburon provide a unique perspective on the crustal evolution along this typical moderate spreading-rate ridge. The rift valley walls are comprised of a series of major bounding faults, separated by blocks of oceanic crust that exhibit little or no deformation. Unlike the present axis that is dominated by sheet and lobate flows, these blocks are almost entirely comprised of unfaulted, constructional pillow ridges, mounds and hornitos some of which formed along off-axis eruptive fissures and from point-sources that appear related to the formation of rift-bounding faults. Other volcanic constructs seem to be related to the formation of the first series of abyssal hills, consistent with "volcanic growth faults" draped with syntectonic lava flows. Observations with Tiburon combined with high-resolution Simrad EM300 bathymetry suggests that the inflated flank topography that characterizes the Cleft Segment was created by extensive constructional volcanism that formed pillowed flow fronts tens to hundreds of meters high Approximately three kilometers east and west of the axis, a contact between the massive pillowed units and older sheet flows is clearly delineated both by increased sediment cover and by the change in lava flow morphology. Close to this contact on the east side of the ridge flank, a linear mound of altered and fractured sheet flows coated with flocculent precipitates was observed with curtains of shimmering fluid emanating from its porous interior. Several more ridges 6-8 m tall, discovered and sampled in 2002 extend over a few hundred meters and are actively venting low-temperature fluids. The venting at the "Flyer Field" is characterized by ubiquitous amorphous Fe-rich precipitates and by weakly diffuse fluid flow with temperatures 3-20 degrees C above ambient. Microbial mats are conspicuous and intermixed with green precipitates

  3. An estimate of hydrothermal fluid residence times and vent chimney growth rates based on 210Pb Pb ratios and mineralogic studies of sulfides dredged from the Juan de Fuca Ridge

    USGS Publications Warehouse

    Kadko, D.; Koski, R.; Tatsumoto, M.; Bouse, R.

    1985-01-01

    The 210Pb Pb ratios across two sulfide samples dredged from the Juan de Fuca Ridge are used to estimate the growth rate of the sulfide material and the residence time of the hydrothermal fluid within the oceanic crust from the onset of basalt alteration. 210Pb is added to the hydrothermal fluid by two processes: (1) high-temperature alteration of basalt and (2) if the residence time of the fluid is on the order of the 22.3-year half-life of 210Pb, by in-situ growth from 222Rn (Krishnaswami and Turekian, 1982). Stable lead is derived only from the alteration of basalt. The 210Pb Pb ratio across one sample was ??? 0.5 dpm/10-6 g Pb, and across the other it was ??? 0.4 dpm/10-6 g Pb. These values are quite close to the 238U Pb ratios of basalts from the area, suggesting that the residence time of the hydrothermal fluid from the onset of basalt alteration is appreciably less than the mean life of 210Pb, i.e., the time required for ingrowth from the radon. An apparent growth rate of 1.2 cm/yr is derived from the slope of the 210Pb Pb curve for one of the samples. This is consistent with its mineralogy and texture which suggest an accretionary pattern of development. There is no obvious sequential growth pattern, and virtually no gradient in 210Pb Pb across the second sample. This is consistent with alteration of the original 210Pb Pb distribution by extensive remobilization reactions which are inferred from the mineralogic and textural relationships of the sample. ?? 1985.

  4. Re-evaluating across-axis geochemical variations at the East Pacific Rise and Juan de Fuca Ridge: on- and off-axis melt delivery

    NASA Astrophysics Data System (ADS)

    Perfit, M. R.; Walters, R. L.

    2014-12-01

    High spatial density geochemical data sets from the N-EPR and S-JdFR are used to re-evaluate the across-axis geochemical variations in major and trace elements at mid-ocean ridges (MORs). At two axial melt lens (AML) segments, north and south, at the 9-10°N EPR, N-MORB MgO varies across-axis from the most primitive above the AML to more evolved away from the axis. This trend is distinct at the northern (magmatically more robust) segment with an axial MgO range of 8-9 wt% and off-axis (>2km) range of 6.5-8 wt%. This decrease is also reflected in E-MORB MgO variation. There is more variability at the southern segment but, off-axis progression to more evolved MgO is still evident. Interestingly, the Cleft segment, JdFR, displays similar geochemical behavior to the EPR with an axial MgO range of 7-8.5 wt% and off-axis (>2km) range of 6-7.5 wt%. EPR geochemical studies over the past 30 years have described models of upper crustal accumulation ranging from eruptions limited to the axis, to temporal variation in the composition of magma in the AML, to multiple eruption sites across the ridge crest and flanks (<5km). Eruptions limited to the axis, with topographically controlled flow off-axis, cannot reproduce the observed off-axis change to more evolved N-MORB. Time-dependence could explain one instance of evolved lavas off-axis but, similar geochemical behavior is observed at two separate AML segments. Multiple instances of consistent compositional variability at multiple AML segments, and at different ridges, point to a common process of crustal accretion at MORs. In light of recent geophysical discoveries of Off-axis AMLs (OAMLs) at the EPR and JdFR, we propose that the trend of more evolved lavas for the majority of N-MORB lavas with distance from the axis is controlled by thermal distribution in the underlying crystal mush zone (CMZ). Higher magma flux beneath the axis facilitates higher temperatures and high porosity melt pathways, reducing crustal residence times

  5. Phylogenetic and Physiological Diversity of Subseafloor Microbial Communities at Axial Seamount, Juan de Fuca Ridge: Summary of Results From the New Millenium Observatory (NeMO), 1998-2004

    NASA Astrophysics Data System (ADS)

    Baross, J. A.; Huber, J. A.; Mehta, M. P.; Opatkiewicz, A.; Bolton, S. A.; Butterfield, D. A.; Sogin, M. L.; Embley, R. W.

    2005-12-01

    Axial Seamount (45 ° 58' N; 130 ° 00' W) is an active submarine volcano located on the Juan de Fuca Ridge, approximately 300 miles off the coast of Oregon. Lying at the intersection of a seamount chain and a spreading axis, Axial is a unique study site from both the geological and biological perspective. In January of 1998, Axial experienced a week-long series of earthquakes, and subsequent water column and seafloor observations on the southeast portion of the caldera found temperature and chemical anomalies, extensive new seafloor lava flows, large "snow blower" type vents, and other characteristics commonly associated with diking-eruptive events. Due to its high activity and close proximity to shore, Axial was chosen as a site for a multi-year observatory (New Millenium Observatory, NeMO) to document changes and interactions between geology, chemistry, and biology on the mid-ocean ridge system. From 1998 through 2004, we extensively sampled diffuse vents at Axial Seamount to determine the physiological and phylogenetic diversity of subseafloor microbial communities and their relationship to the geochemical environment. Here we present a summary of those studies, including molecular-based phylogenetic surveys of bacteria, archaea, and potential nitrogen-fixing organisms, culturing results of thermophiles and hyperthermophiles from over 20 sites, and the distribution of one particular group of hyperthermophiles at diffuse vents throughout the caldera and how that distribution may be linked to the geochemical habitat. Results indicate that Axial supports a diverse subseafloor microbial community, including hydrogen and sulfur oxidizers, hyperthermophilic methane producers and heterotrophs, and many organisms with the potential to fix nitrogen. In addition, we find that the species composition of the microbial community changes in response to changes in the physical and chemical conditions at each vent site. The extent of seawater mixing with hydrothermal fluids

  6. Phylogenetic Diversity of Nitrogenase (nifH) Genes in Deep-Sea and Hydrothermal Vent Environments of the Juan de Fuca Ridge

    PubMed Central

    Mehta, Mausmi P.; Butterfield, David A.; Baross, John A.

    2003-01-01

    The subseafloor microbial habitat associated with typical unsedimented mid-ocean-ridge hydrothermal vent ecosystems may be limited by the availability of fixed nitrogen, inferred by the low ammonium and nitrate concentrations measured in diffuse hydrothermal fluid. Dissolved N2 gas, the largest reservoir of nitrogen in the ocean, is abundant in deep-sea and hydrothermal vent fluid. In order to test the hypothesis that biological nitrogen fixation plays an important role in nitrogen cycling in the subseafloor associated with unsedimented hydrothermal vents, degenerate PCR primers were designed to amplify the nitrogenase iron protein gene nifH from hydrothermal vent fluid. A total of 120 nifH sequences were obtained from four samples: a nitrogen-poor diffuse vent named marker 33 on Axial Volcano, sampled twice over a period of 1 year as its temperature decreased; a nitrogen-rich diffuse vent near Puffer on Endeavour Segment; and deep seawater with no detectable hydrothermal plume signal. Subseafloor nifH genes from marker 33 and Puffer are related to anaerobic clostridia and sulfate reducers. Other nifH genes unique to the vent samples include proteobacteria and divergent Archaea. All of the nifH genes from the deep-seawater sample are most closely related to the thermophilic, anaerobic archaeon Methanococcus thermolithotrophicus (77 to 83% amino acid similarity). These results provide the first genetic evidence of potential nitrogen fixers in hydrothermal vent environments and indicate that at least two sources contribute to the diverse assemblage of nifH genes detected in hydrothermal vent fluid: nifH genes from an anaerobic, hot subseafloor and nifH genes from cold, oxygenated deep seawater. PMID:12571018

  7. Phylogenetic diversity of nitrogenase (nifH) genes in deep-sea and hydrothermal vent environments of the Juan de Fuca Ridge.

    PubMed

    Mehta, Mausmi P; Butterfield, David A; Baross, John A

    2003-02-01

    The subseafloor microbial habitat associated with typical unsedimented mid-ocean-ridge hydrothermal vent ecosystems may be limited by the availability of fixed nitrogen, inferred by the low ammonium and nitrate concentrations measured in diffuse hydrothermal fluid. Dissolved N2 gas, the largest reservoir of nitrogen in the ocean, is abundant in deep-sea and hydrothermal vent fluid. In order to test the hypothesis that biological nitrogen fixation plays an important role in nitrogen cycling in the subseafloor associated with unsedimented hydrothermal vents, degenerate PCR primers were designed to amplify the nitrogenase iron protein gene nifH from hydrothermal vent fluid. A total of 120 nifH sequences were obtained from four samples: a nitrogen-poor diffuse vent named marker 33 on Axial Volcano, sampled twice over a period of 1 year as its temperature decreased; a nitrogen-rich diffuse vent near Puffer on Endeavour Segment; and deep seawater with no detectable hydrothermal plume signal. Subseafloor nifH genes from marker 33 and Puffer are related to anaerobic clostridia and sulfate reducers. Other nifH genes unique to the vent samples include proteobacteria and divergent Archaea. All of the nifH genes from the deep-seawater sample are most closely related to the thermophilic, anaerobic archaeon Methanococcus thermolithotrophicus (77 to 83% amino acid similarity). These results provide the first genetic evidence of potential nitrogen fixers in hydrothermal vent environments and indicate that at least two sources contribute to the diverse assemblage of nifH genes detected in hydrothermal vent fluid: nifH genes from an anaerobic, hot subseafloor and nifH genes from cold, oxygenated deep seawater.

  8. The NeMO Explorer Web Site: Interactive Exploration of a Recent Submarine Eruption and Hydrothermal Vents, Axial Volcano, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Weiland, C.; Chadwick, W. W.; Embley, R. W.

    2001-12-01

    To help visualize the submarine volcanic landscape at NOAA's New Millennium Observatory (NeMO), we have created the NeMO Explorer web site: http://www.pmel.noaa.gov/vents/nemo/explorer.html. This web site takes visitors a mile down beneath the ocean surface to explore Axial Seamount, an active submarine volcano 300 miles off the Oregon coast. We use virtual reality to put visitors in a photorealistic 3-D model of the seafloor that lets them view hydrothermal vents and fresh lava flows as if they were really on the seafloor. At each of six virtual sites there is an animated tour and a 360o panorama in which users can view the volcanic landscape and see biological communities within a spatially accurate context. From the six sites there are hyperlinks to 50 video clips taken by a remotely operated vehicle. Each virtual site concentrates on a different topic, including the dynamics of the 1998 eruption at Axial volcano (Rumbleometer), high-temperature hydrothermal vents (CASM and ASHES), diffuse hydrothermal venting (Marker33), subsurface microbial blooms (The Pit), and the boundary between old and new lavas (Castle vent). In addition to exploring the region geographically, visitors can also explore the web site via geological concepts. The concepts gallery lets you quickly find information about mid-ocean ridges, hydrothermal vents, vent fauna, lava morphology, and more. Of particular interest is an animation of the January 1998 eruption, which shows the rapid inflation (by over 3 m) and draining of the sheet flow. For more info see Fox et al., Nature, v.412, p.727, 2001. This project was funded by NOAA's High Performance Computing and Communication (HPCC) and Vents Programs. Our goal is to present a representative portion of the vast collection of NOAA's multimedia imagery to the public in a way that is easy to use and understand. These data are particularly challenging to present because of their high data rates and low contextual information. The 3-D models create

  9. Continuing evolution of the Pacific-Juan de Fuca-North America slab window system-A trench-ridge-transform example from the Pacific Rim

    USGS Publications Warehouse

    McCrory, P.A.; Wilson, D.S.; Stanley, R.G.

    2009-01-01

    Many subduction margins that rim the Pacific Ocean contain complex records of Cenozoic slab-window volcanism combined with tectonic disruption of the continental margin. The series of slab windows that opened beneath California and Mexico starting about 28.5 Ma resulted from the death of a series of spreading ridge segments and led to piecewise destruction of a subduction regime. The timing and areal extent of the resultant slab-window volcanism provide constraints on models that depict the subsequent fragmentation and dispersal of the overlying continental margin. The initial Pioneer slab window thermally weakened the overlying western Transverse Ranges and California Borderlands region starting about 28.5 Ma. A second thermal pulse occurred in the same region starting about 19 Ma during growth of the Monterey slab window. This additional heating, combined with the capture of a partially subducted Monterey plate fragment by the Cocos plate, initiated the pulling apart and rotation of the adjacent continental margin. Similarly, the capture of Guadalupe and Magdalena plate fragments by the Pacific plate and initiation of the Guadalupe-Magdalena slab window about 12.5 Ma are coeval with Baja California pulling away from the Mexico continental margin, with the break along the Comondú arc, in crust already thermally weakened by about 10 My of volcanism. In coastal California, distributed crustal extension and subsidence accompanied the new transform plate boundary, and continued until the slab windows cooled and plate motion coalesced along a through-going system of strike-slip faults. The transform boundary continues to evolve, and forward modeling predicts an instability with the current configuration as a result of convergence between the Sierra Nevada and Peninsular Ranges batholiths, starting about 2 My in the future. The instability may be resolved by a shift in the locus of transform motion from the San Andreas fault to the eastern California shear zone, or by

  10. Continuing evolution of the Pacific-Juan de Fuca-North America slab window system—A trench-ridge-transform example from the Pacific Rim

    NASA Astrophysics Data System (ADS)

    McCrory, Patricia A.; Wilson, Douglas S.; Stanley, Richard G.

    2009-01-01

    Many subduction margins that rim the Pacific Ocean contain complex records of Cenozoic slab-window volcanism combined with tectonic disruption of the continental margin. The series of slab windows that opened beneath California and Mexico starting about 28.5 Ma resulted from the death of a series of spreading ridge segments and led to piecewise destruction of a subduction regime. The timing and areal extent of the resultant slab-window volcanism provide constraints on models that depict the subsequent fragmentation and dispersal of the overlying continental margin. The initial Pioneer slab window thermally weakened the overlying western Transverse Ranges and California Borderlands region starting about 28.5 Ma. A second thermal pulse occurred in the same region starting about 19 Ma during growth of the Monterey slab window. This additional heating, combined with the capture of a partially subducted Monterey plate fragment by the Cocos plate, initiated the pulling apart and rotation of the adjacent continental margin. Similarly, the capture of Guadalupe and Magdalena plate fragments by the Pacific plate and initiation of the Guadalupe-Magdalena slab window about 12.5 Ma are coeval with Baja California pulling away from the Mexico continental margin, with the break along the Comondú arc, in crust already thermally weakened by about 10 My of volcanism. In coastal California, distributed crustal extension and subsidence accompanied the new transform plate boundary, and continued until the slab windows cooled and plate motion coalesced along a through-going system of strike-slip faults. The transform boundary continues to evolve, and forward modeling predicts an instability with the current configuration as a result of convergence between the Sierra Nevada and Peninsular Ranges batholiths, starting about 2 My in the future. The instability may be resolved by a shift in the locus of transform motion from the San Andreas fault to the eastern California shear zone, or by

  11. Time-series geochemical and tracer injection recovery data from the deep (basaltic) crustal fluids from IODP Holes 1301A/1362B on the eastern flank of Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Cowen, J. P.; Hsieh, C.; Guss, J.; Fisher, A. T.; Lin, H.; Clark, J. F.; Wheat, C. G.

    2012-12-01

    Integrated Ocean Drilling Program borehole CORK (Circulation Obviation Retrofit Kit) observatories provide invaluable opportunities to study the deep biosphere. In order to draw large volumes of fluids from crustal aquifers to seafloor, we developed an autonomous sensor and fluid sampling system, GeoMICROBE (Cowen et al., 2012). GeoMICROBE's Major components include a positive displacement primary pump, a primary valve manifold system, sensors (e.g., fluid flow rate, temperature, dissolved O2, electrochemistry-voltammrtry analyzer), 24-48 port in situ filtration and fluid collection system, computerized controller, six 24V-40A batteries and wet-mateable (ODI) communications with submersibles. This sampling system has been successfully deployed at IODP Hole 1301A in 2010 on the eastern flank of Juan de Fuca Ridge. The GeoMICROBE was successfully recovered in the summer of 2011. However, due to the narrow inner diameter of the fluid delivery line (1/4''), the batteries were exhausted and only half of the preprogrammed sampling procedures were accomplished. After quick turn-around the GeoMICROBE was redeployed at nearby CORK 1362B for Summer, 2012 recovery. CORKs 1301A and 1362B are only ~800 m apart and both penetrate to ~40-50m into the basement. Unlike CORK 1301A, the fluid deliver line installed on CORK 1362B has 1/2'' inner diameter. The much lower resistance allows us to pump the fluids up with reduced power consumption. A conservative power consumption model was made to ensure that enough battery power would be available to complete the twelve monthly samplings. Monthly, following extensive flushing ~3 L of fluid was passed through a 0.2 μm polycarbonate filter. The filter holder was pre-charged with 6% glutaraldehyde. Also, monthly whole fluid samples were collected and stored in an acid-washed 500mL Tedlar bag. The whole fluid will be used for analysis of colloidal (Microspheres) and dissolved tracers injected into the upper crust in August 2010 as well as

  12. Complex Pull-apart Structure Evolving at Northern Explorer Ridge, Northeast Pacific

    NASA Astrophysics Data System (ADS)

    Embley, R.

    2008-12-01

    The Explorer Spreading Center (ESC) bounding the western edge of the Explorer microplate has undergone substantial reorganization over the past few million years as the microplate has rotated in response to increasing resistance to the subduction of its young crust. The northern Explorer ridge (NER) has evolved into a complex compound structure consisting of several rift basins bounded by half-graben and arcuate shaped faults with a superimposed pattern of rhombohedral grabens and horsts. This pattern is similar to structures on rift zones and pull-apart basins formed along major continental transforms and rift zones and contrasts with the ridge-parallel faults formed at seafloor spreading centers. However, initiation of faulting in the NER appears to have occurred along inactive off-axis faults generated by seafloor spreading. The NER region appears to be evolving into a larger pull-apart-like structure. As extension continues, individual basins have widened with some of the larger arcuate boundary faults linking up to form accommodation zones between adjacent depressions. If diffuse rifting continues in the NER the nascent pull- apart structure will grow longer as it accommodates the changing regional strain field induced by the diminishment of the Explorer plate. Alternatively, a strike-slip fault could propagate through the area and join the two master faults. Although there's no well-defined though-going fault with the strike of the Pacific-North American vector (about 340°), there is some indication from that such a structure is beginning to break through.

  13. Explorer deformation zone: Evidence of a large shear zone and reorganization of the Pacific Juan de Fuca North American triple junction

    NASA Astrophysics Data System (ADS)

    Dziak, Robert P.

    2006-03-01

    Recently collected multibeam bathymetry and hydroacoustic earthquake data are used to investigate the recent tectonics of the Explorer Juan de Fuca Ridge systems, the boundaries between the Pacific and northern Juan de Fuca plates. The bathymetric and seismic evidence presented is consistent with a zone of shear extending well south of the Sovanco Fracture Zone to include the Heck and Heckle seamounts, and potentially as far south as the Springfield Seamounts and Cobb offset along the Juan de Fuca Ridge. This indicates that the triple junction between the Pacific Juan de Fuca North American plates may be reorganizing southward to establish at the Cobb offset.

  14. Regional characteristics of land use in Northeast and Southern Blue Ridge Province: Associations with acid rain effects on surface-water chemistry

    NASA Astrophysics Data System (ADS)

    Liegel, Leon; Cassell, David; Stevens, Donald; Shaffer, Paul; Church, Robbins

    1991-03-01

    The Direct/Delayed Response Project (DDRP) is one of several studies being conducted by the United States Environmental Protection Agency to assess risk to surface waters from acidic deposition in the eastern United States. In one phase of DDRP, land use, wetland, and forest cover data were collected for statistical samples of 145 Northeast lake and 35 Southern Blue Ridge Province stream watersheds in the United States. Land-use and other data then were extrapolated from individual to target watershed populations. Project statistical design allows summarization of results for various subsets of the target population. This article discusses results and implications of the land-use and land-cover characterization for both regions. Forest cover was the primary land use in both regions. In the Northeast, developed (agriculture and urban) land was positively associated with surface-water chemistry values for acid neutralizing capacity, Ca plus Mg, pH, and sulfate in the Pocono/Catskill subregion. Extensive wetlands and beaver activity occur in parts of the Northeast region, whereas topography limits wetland and riparian development in the Southern Blue Ridge Province. Northeast soils have low sulfate adsorption capacity, most watersheds are near sulfur steady state, and lake sulfate concentrations are controlled principally by levels of sulfur deposition. Net annual sulfur retention in Northeast watersheds is positively correlated with occurrence of wetlands and beaver impoundments. In contrast, most Southern Blue Ridge Province soils have high sulfate adsorption capacities, resulting in high net watershed sulfur retention. At the present time, stream sulfate concentrations and percent sulfur retention are controlled principally by soil chemical properties related to adsorption rather than atmospheric deposition and land use.

  15. Seafloor Positioning Across Juan De Fuca Ridge

    DTIC Science & Technology

    1994-04-01

    UNIVERSITY DR NW ATIN CODE WRW402 (B SCHUTZ ) 1 CALGARY ALBERTA CANADA T2N 1N4 I CENTER FOR SPACE RESEARCH UNIVERSITY OF TEXAS AT AUSTIN ATIN DR PER HELGE...AUSTIN TX 78713-8029 D 6100 DARMSTADT GERMANY ATIN PROF ALFRED LEICK I ATIN DR KAMIL EREN 1 3 DEPT OF SURVEYING ENGINEERING UNPD UNIVERSITY OF MAINE PO BOX

  16. Biogeochemistry of dissolved methane and hydrogen in basement fluids of the sediment-buried Juan de Fuca Ridge flank at Boreholes (CORKs) 1301A, 1362A and 1362B: methane isotopic compositions

    NASA Astrophysics Data System (ADS)

    Lin, H.; Cowen, J. P.; Olson, E. J.; Lilley, M. D.; Jungbluth, S.; Rappe, M. S.

    2013-12-01

    The ocean crust is the largest aquifer system on Earth. Within the sediment-buried 3.5 Myr basaltic crust of the eastern Juan de Fuca Ridge (JFR) flank, the circulating basement fluids have moderate temperature (~65°C) and potentially harbor a substantial subseafloor biosphere. With dissolved oxygen and nitrate exhausted, sulfate may serve as the major electron acceptor in this environment. This study aims to evaluate the availability and the biogeochemistry of two important electron donors, methane and hydrogen, for the subseafloor biosphere. Basement fluids were collected via stainless steel and ethylene-tetrafluoroethylene fluoropolymer (ETFE) fluid delivery lines associated with Integrated Ocean Drilling Program (IODP) Circulation Obviation Retrofit Kits (CORKs) that extend from basement depths to outlet ports at the seafloor. Three CORKs were visited; 1301A, 1362A and 1362B lie within 200 to 500 m of each other, and their fluid intakes lie at ~30, ~60, and ~50 m below the sediment-basement interface (mbs), respectively. In addition, CORK 1362A contains a second intake at a deep (~200 mbs) horizon. The basement fluids from the three CORKs contained significantly higher concentrations of methane (1.5-13μM) and hydrogen (0.05-1.1 μM) than in bottom seawater (0.002 and 0.0004, respectively), indicating that prevalence and availability of both methane and hydrogen as electron donors for the subseafloor biosphere. Thermodynamic calculations show that sulfate reduction coupled with either methane or hydrogen oxidation is energy yielding in the oceanic basement. The δ13C values of methane ranged from -43×1‰ to -58×0.3‰; the δ2H values of methane in CORKs 1301A, 1362A and 1362B fluids were 57×5‰, -262×2‰, -209×2‰, respectively. The isotopic compositions suggest that methane in the basement fluid is of biogenic origin. Interestingly, the δ2H value of methane in the CORK 1301A fluids is far more positive than that in other marine environments

  17. Microbial life in ridge flank crustal fluids.

    PubMed

    Huber, Julie A; Johnson, H Paul; Butterfield, David A; Baross, John A

    2006-01-01

    To determine the microbial community diversity within old oceanic crust, a novel sampling strategy was used to collect crustal fluids at Baby Bare Seamount, a 3.5 Ma old outcrop located in the north-east Pacific Ocean on the eastern flank of the Juan de Fuca Ridge. Stainless steel probes were driven directly into the igneous ocean crust to obtain samples of ridge flank crustal fluids. Genetic signatures and enrichment cultures of microorganisms demonstrate that these crustal fluids host a microbial community composed of species indigenous to the subseafloor, including anaerobic thermophiles, and species from other deep-sea habitats, such as seawater and sediments. Evidence using molecular techniques indicates the presence of a relatively small but active microbial population, dominated by bacteria. The microbial community diversity found in the crustal fluids may indicate habitat variability in old oceanic crust, with inputs of nutrients from seawater, sediment pore-water fluids and possibly hydrothermal sources. This report further supports the presence of an indigenous microbial community in ridge flank crustal fluids and advances our understanding of the potential physiological and phylogenetic diversity of this community.

  18. Magnetic Anomalies over the Mid-Atlantic Ridge near 27{degrees}N.

    PubMed

    Phillips, J D

    1967-08-25

    Ten magnetic profiles across the mid-Atlantic ridge near 27 degrees N show trends that are parallel to the ridge axis and symmetrical about the ridge axis. The configuration of magnetic bodies that could account for the pattern supports the Vine and Matthews hypothesis for the origin of magnetic anomalies over oceanic ridges. A polarity-reversal time scale inferred from models for sea-floor spreading in the Pacific-Antarctic ridge and radiometrically dated reversals of the geomagnetic field indicates a spreading rate of 1.25 centimeters per year during the last 6 million years and a rate of 1.65 centimeters per year between 6 and 10 million years ago. A similar analysis of more limited data over the mid-Atlantic ridge near 22 degrees N also indicates a change in the spreading rate. Here a rate of 1.4 centimeters per year appears to have been in effect during the last 5 million years; between 5 and 9 million years ago, an increased rate of 1.7 centimeters per year is indicated. The time of occurrence and relative magnitude of these changes in the spreading rate, about 5 to 6 million years ago and 18 to 27 percent, respectively, accords with the spreading rate change implied for the Juan de Fuca ridge in the northeast Pacific.

  19. Segmented Subduction Across the Juan De Fuca Plate: Challenges in Imaging with an Amphibious Array

    NASA Astrophysics Data System (ADS)

    Hawley, W. B.; Allen, R. M.

    2014-12-01

    The Cascadia Initiative (CI) is an amphibious array spanning the Juan de Fuca plate from formation at the ridge to the destruction of the slab in the mantle beneath western North America. This ambitions project has occupied over 300 onshore and offshore sites, providing an unprecedented opportunity to understand the dynamics of oceanic plates. The CI project is now in its fourth and final year of deployment. Here we present constraints on the structure of the Juan de Fuca plate and its interaction with western North America. We identify segmentation along the Cascadia subduction zone that can be traced back onto the Juan de Fuca plate prior to subduction. These results give insight into the life cycle of oceanic plates, from their creation at a mid-ocean ridge to their subduction and subsequent recycling into the mantle.

  20. Sea level Variability and Juan de Fuca Bathymetry

    NASA Astrophysics Data System (ADS)

    Huybers, P. J.; Boulahanis, B.; Proistosescu, C.; Langmuir, C. H.; Carbotte, S. M.; Katz, R. F.

    2015-12-01

    That deglaciation influences mid-ocean ridge volcanism is well established for Iceland, where depressurization associated with melting a ~2 km ice cap led to order of magnitude increases in volcanism during the last deglaciation. The case was also made that the more subtle ~100 m changes in sea level that accompany glacial cycles have identifiable implications for undersea mid-ocean ridge systems using both models and data from the Australian-Antarctic Ridge (Crowley et al., 2015). Sea level rising at ~1 cm/year during deglaciation leads to an expectation of ~10% decreases in melt production at ridges, given mantle upwelling rates of ˜3 cm/yr at intermediate spreading ridges and mantle density being ~3 times that of seawater. The implications of variations in melt production for bathymetry, however, involve numerous considerations, including whether melt signals are cancelled within the melt column, appreciably alter accretionary or fault processes, and have identifiable surface expressions. Further empirical assessment of bathymetry is thus useful for purposes of confirming patterns and constraining processes. Here we report on spectral analyses of bathymetry recently acquired from the Juan de Fuca ridge between 44°30'N and 45°15'N during the SeaVOICE expedition. Multibeam swath sonar data were acquired with an EM122 sonar insonfiying seafloor to crustal ages of ˜2 ma with 35 m spatial resolution. We examine (1.) the statistical significance of concentrations of bathymetric variability at the 100 ky, 41 ky, and 23 ky periods characteristic of late-Pleistocene sea level variability; (2.) whether sea level responses are primarily at 41 ky periods in crust accreted during the early Pleistocene, when global sea level variations were primarily at this period; and (3.) if sea level responses are superimposed on bathymetry variations or, instead, align with fault features. We also note that Juan de Fuca's proximity to the Cordilleran Ice Sheet implies that regional

  1. Seismic Anisotropy below the Juan De Fuca Plate: Results from the Cascadia Initiative

    NASA Astrophysics Data System (ADS)

    Martin-Short, R.; Allen, R. M.; Bastow, I. D.

    2014-12-01

    Investigation of seismic anisotropy using shear wave splitting is typically used to infer information about asthenospheric flow geometry. In order to understand how such flow varies below the Juan de Fuca plate and is affected by its subduction along the Cascadia forearc, stacked splitting results are determined for 90 offshore and 27 onshore broadband seismometers. These instruments were deployed as part of phases one and two of the Cascadia Initiative, which is an ongoing effort to understand tectonic processes in the Pacific Northwest. The onshore results conform to those of previous studies, suggesting a uniformly trench-perpendicular flow field and thus implying a thick layer of material entrained beneath the slab. The offshore results offer suggestions about how the orientation of asthenospheric flow evolves across the width of the Juan de Fuca plate, and are unique in that they document variation in anisotropy from the ridge to the trench. The results indicate ridge-perpendicular flow geometry close to the Juan de Fuca ridge, which appears to rotate towards the direction of absolute plate motion as one moves towards the trench. As suggested by the latest tomographic images the subducting Juan de Fuca plate is segmented, with 'gaps' between the segments. These gaps may act as channels for the flow of mantle material.

  2. Numerical simulation of mean currents and water property anomalies at Endeavour Ridge: Hydrothermal versus topographic forcing

    NASA Astrophysics Data System (ADS)

    Thomson, Richard E.; Subbotina, Marina M.; Anisimov, Mikhail V.

    2009-09-01

    Numerical simulations based on realistic seafloor topography are used to examine near-bottom currents in the region of the Endeavour segment of Juan de Fuca Ridge (Endeavour Ridge) in the northeast Pacific. Results support earlier findings that hydrothermal venting within the ˜2200-m deep axial valley, rather than topographically modified, basin-scale cross-ridge geostrophic flow, is responsible for the near-steady northward currents observed within the confines of the valley. Although it does not generate deep flow within the valley, the basin-scale circulation determines the horizontal redistribution of the hydrothermal plumes once they rise above the ridge crest. Simulations of the near-bottom temperature and salinity fields reveal that model runs that incorporate a deep westward background flow most closely reproduce the observed plume anomaly distributions above the ridge, indicating that bottom currents in the region are predominantly westward, counter to the prevailing southeasterly flow of the wind-driven California Current in the upper half of the water column.

  3. Petrology and geochemistry of Abyssal Peridotites from the Manipur Ophiolite Complex, Indo-Myanmar Orogenic Belt, Northeast India: Implication for melt generation in mid-oceanic ridge environment

    NASA Astrophysics Data System (ADS)

    Krishnakanta Singh, A.

    2013-04-01

    The Manipur Ophiolite Complex (MOC) located in the Indo-Myanmar Orogenic Belt (IMOB) of Northeast India forms a section of the Tethyan Ophiolite Belt of the Alpine-Himalayan orogenic system. Whole rock compositions and mineral chemistry of mantle peridotites from the MOC show an affinity to the abyssal peridotites, characterized by high contents of Al2O3 (1.28-3.30 anhydrous wt.%); low Cr# of Cr-spinel (0.11-0.27); low Mg# of olivine (˜Fo90) and high Al2O3 in pyroxenes (3.71-6.35 wt.%). They have very low REE concentrations (∑REE = 0.48-2.14 ppb). Lherzolites display LREE-depleted patterns (LaN/SmN = 0.14-0.45) with a flat to slightly fractionated HREE segments (SmN/YbN = 0.30-0.65) whereas Cpx-harburgites have flat to upward-inflected LREE patterns (LaN/SmN = 0.13-1.23) with more fractionated HREE patterns (SmN/YbN = 0.13-0.65) than the lherzolite samples. Their platinum group elements (PGE) contents (<50 ppb) and distinct mantle-normalised PGE patterns with the Pd/Ir values (1.8-11.9) and Pt/Pt* values (0.2-1.1) show an affinity to the characteristic of the residual mantle material. Evaluation of mineralogical and petrological characteristics of these peridotites suggests that they represent the residues remaining after low degree of partial melting (˜2-12%) in the spinel stability field of a mid-oceanic ridge environment. The well-preserved mid-oceanic ridge characteristics of these peridotites further suggest that the mantle section was subsequently trapped in the forearc region of the subduction zone without undergoing significant modification in their chemistry by later subduction-related tectonic and petrological processes before its emplacement to the present crustal level.

  4. Bimodal volcanism in northeast Puerto Rico and the Virgin Islands (Greater Antilles Island Arc): Genetic links with Cretaceous subduction of the mid-Atlantic ridge Caribbean spur

    NASA Astrophysics Data System (ADS)

    Jolly, Wayne T.; Lidiak, Edward G.; Dickin, Alan P.

    2008-07-01

    Bimodal extrusive volcanic rocks in the northeast Greater Antilles Arc consist of two interlayered suites, including (1) a predominantly basaltic suite, dominated by island arc basalts with small proportions of andesite, and (2) a silicic suite, similar in composition to small volume intrusive veins of oceanic plagiogranite commonly recognized in oceanic crustal sequences. The basaltic suite is geochemically characterized by variable enrichment in the more incompatible elements and negative chondrite-normalized HFSE anomalies. Trace element melting and mixing models indicate the magnitude of the subducted sediment component in Antilles arc basalts is highly variable and decreases dramatically from east to west along the arc. In the Virgin Islands, the sediment component ranges between< 0.5 to ˜ 1% in Albian rocks, and between ˜ 1 and 2% in succeeding Cenomanian to Campanian strata. In comparison, sediment proportions in central Puerto Rico range between 0.5 to 1.5% in the Albian to 2 to > 4% during the Cenomanian-Campanian interval. The silicic suite, consisting predominantly of rhyolites, is characterized by depleted Al 2O 3 (average < 16%), low Mg-number (molar Mg/Mg + Fe < 0.5), TiO 2 (< 1.0%), and Sr/Y (< 10), oceanic or arc-like Sr, Nd, and Pb isotope signatures, and by the presence of plagioclase. All of these features are consistent with an anatexic origin in gabbroic sources, of both oceanic and arc-related origin, within the sub-arc basement. The abundance of silicic lavas varies widely along the length of the arc platform. In the Virgin Islands on the east, rhyolites comprise up to 80% of Lower Albian strata (112 to 105 Ma), and about 20% in post-Albian strata (105 to 100 Ma). Farther west, in Puerto Rico, more limited proportions (< 20%) of silicic lavas were erupted. The systematic variation of both sediment flux and abundance of crustally derived silicic lavas are consistent with current tectonic models of Caribbean evolution involving approximately

  5. Diversity and Abundance of Ammonia-Oxidizing Archaea in Hydrothermal Vent Chimneys of the Juan de Fuca Ridge▿ †

    PubMed Central

    Wang, Shufang; Xiao, Xiang; Jiang, Lijing; Peng, Xiaotong; Zhou, Huaiyang; Meng, Jun; Wang, Fengping

    2009-01-01

    The abundance and diversity of archaeal ammonia monooxygenase subunit A (amoA) genes from hydrothermal vent chimneys at the Juan de Fuca Ridge were investigated. The majority of the retrieved archaeal amoA sequences exhibited identities of less than 95% to those in the GenBank database. Novel ammonia-oxidizing archaea may exist in the hydrothermal vent environments. PMID:19395559

  6. Magnetic Anomalies over a Young Oceanic Ridge off Vancouver Island.

    PubMed

    Vine, F J; Wilson, J T

    1965-10-22

    The recent speculation that the magnetic anomalies observed over oceanic ridges might be explained in terms of ocean-floor spreading and periodic reversals of the earth's magnetic field may now be reexamined in the light of suggested reversals during the past 4 million years and the newly described Juan de Fuca Ridge.

  7. High-resolution bathymetry as a primary exploration tool for seafloor massive sulfide deposits - lessons learned from exploration on the Mid-Atlantic and Juan de Fuca Ridges, and northern Lau Basin

    NASA Astrophysics Data System (ADS)

    Jamieson, J. W.; Clague, D. A.; Petersen, S.; Yeo, I. A.; Escartin, J.; Kwasnitschka, T.

    2016-12-01

    High-resolution, autonomous underwater vehicle (AUV)-derived multibeam bathymetry is increasingly being used as an exploration tool for delineating the size and extent of hydrothermal vent fields and associated seafloor massive sulfide deposits. However, because of the limited amount of seafloor that can be surveyed during a single dive, and the challenges associated with distinguishing hydrothermal chimneys and mounds from other volcanic and tectonic features using solely bathymetric data, AUV mapping surveys have largely been employed as a secondary exploration tool once hydrothermal sites have been discovered using other exploration methods such as plume, self-potential and TV surveys, or ROV and submersible dives. Visual ground-truthing is often required to attain an acceptable level of confidence in the hydrothermal origin of features identified in AUV-derived bathymetry. Here, we present examples of high-resolution bathymetric surveys of vent fields from a variety of tectonic environments, including slow- and intermediate-rate mid-ocean ridges, oceanic core complexes and back arc basins. Results illustrate the diversity of sulfide deposit morphologies, and the challenges associated with identifying hydrothermal features in different tectonic environments. We present a developing set of criteria that can be used to distinguish hydrothermal deposits in bathymetric data, and how AUV surveys can be used either on their own or in conjunction with other exploration techniques as a primary exploration tool.

  8. SEISMICITY AND VOLCANISM IN THE PACIFIC NORTHWEST: EVIDENCE FOR THE SEGMENTATION OF THE JUAN DE FUCA PLATE.

    USGS Publications Warehouse

    Weaver, Craig S.; Michaelson, Caryl A.

    1985-01-01

    The distributions of earthquakes and late Cenozoic and Quaternary volcanism in Washington and northern Oregon change markedly across two northeast-striking lines, one near Mount Rainier and one near Mount Hood. On the basis of these observations and a comparison with the Nazoa subduction zone, we propose that the Juan de Fuca subduction zone is divided into two segments. Landward of the coastal thrust zone, we suggest the Juan de Fuca plate dips more steeply beneath the southern segment than beneath the northern segment. Refs.

  9. 33 CFR 80.1385 - Strait of Juan de Fuca.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 1 2013-07-01 2013-07-01 false Strait of Juan de Fuca. 80.1385... NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1385 Strait of Juan de Fuca. The 72 COLREGS shall apply on all waters of the Strait of Juan de Fuca....

  10. 33 CFR 80.1385 - Strait of Juan de Fuca.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 33 Navigation and Navigable Waters 1 2014-07-01 2014-07-01 false Strait of Juan de Fuca. 80.1385... NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1385 Strait of Juan de Fuca. The 72 COLREGS shall apply on all waters of the Strait of Juan de Fuca....

  11. 33 CFR 80.1385 - Strait of Juan de Fuca.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 1 2012-07-01 2012-07-01 false Strait of Juan de Fuca. 80.1385... NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1385 Strait of Juan de Fuca. The 72 COLREGS shall apply on all waters of the Strait of Juan de Fuca....

  12. 33 CFR 80.1385 - Strait of Juan de Fuca.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 1 2011-07-01 2011-07-01 false Strait of Juan de Fuca. 80.1385... NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1385 Strait of Juan de Fuca. The 72 COLREGS shall apply on all waters of the Strait of Juan de Fuca....

  13. Tidal triggering of earthquakes in the Northeast Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Wilcock, William S. D.

    2009-11-01

    There have been many searches for evidence of tidal triggering in earthquake catalogues. With the exception of volcanically active regions, the more rigorous studies in continental settings tend to find no correlation or only a very weak correlation. In the oceans, the effect of loading by the ocean tides can increase tidal stresses by about an order of magnitude over continental settings. In recent years, several studies have reported evidence of tidal triggering in oceanic regions and such observations can represent a useful constraint on models of earthquake rupture. In this paper, I systematically search for a link between ocean tide height and the incidence of earthquakes in the Northeast Pacific Ocean, a region of high-amplitude open ocean tides. The focal mechanisms of most of the earthquakes in these catalogues are unknown but it can be shown that tidal stresses will in most instances promote failure at low tides. I investigate three declustered data sets comprising (1) earthquakes from 1980 to 2007 on the Juan de Fuca plate and in the Queen Charlotte Fault region from land based catalogues; (2) earthquakes from 1992 to 2001 on the Juan de Fuca plate located with the US Navy's Sound Surveillance System (SOSUS) hydrophone array and (3) earthquakes from 1980 to 2001 south of Alaska and the Aleutians located with land based networks. I look at the distributions of earthquakes with ocean tide phase, height, and tidal range and apply Schuster and binomial tests and Monte Carlo simulations to determine if they deviate significantly from random. The results show no evidence of triggering during intervals of increased tidal range but all three data sets show a significant increase in earthquake incidence at low tides. The signal is particularly strong in the land-based catalogue for the Juan de Fuca Plate and Queen Charlotte Fault regions where there is a 15 per cent increase in the rate of seismicity within 15° of the lowest tides. The signal is weakest in the

  14. Directional dispersal between mid-ocean ridges: deep-ocean circulation and gene flow in Ridgeia piscesae.

    PubMed

    Young, C R; Fujio, S; Vrijenhoek, R C

    2008-04-01

    This study examined relationships between bathymetrically induced deep-ocean currents and the dispersal of the hydrothermal vent tubeworm Ridgeia piscesae along the northeast Pacific ridge system. A robust diagnostic model of deep-ocean circulation in this region predicted strong southeasterly currents following contours of the Blanco Transform Fault, a 450-km lateral offset that separates the Gorda and Juan de Fuca ridge systems. Such currents should facilitate the southward dispersal of R. piscesae larvae. Immigration rates for populations north and south of the Blanco Transform Fault were estimated from molecular population genetic data. Mitochondrial DNA evidence revealed population subdivision across the Blanco Transform Fault, and a strong directional bias in gene flow that was consistent with predictions of the circulation model. The distribution of mitochondrial diversity between the northern and southern populations of R. piscesae suggests that the Gorda Ridge tubeworms have maintained larger effective population sizes than the northern populations, a pattern that also exists in co-occurring limpets. Together, these data suggest that the northern vent fields may experience a higher frequency of habitat turnover and consequently more rapid losses of genetic diversity.

  15. Long-term Seismicity Comparisons from Oceanic Transforms Bounded by Slow, Intermediate, and Fast Mid-ocean Ridge Spreading Segments

    NASA Astrophysics Data System (ADS)

    Haxel, J. H.; Dziak, R. P.; Matsumoto, H.; Fowler, M. J.; Lau, T. K.

    2007-12-01

    Long-term observations of seismicity along oceanic transform faults have traditionally been difficult due to limited coverage provided by land based seismic networks. More recently, hydroacoustically recorded earthquakes have been catalogued along the East Pacific Rise (EPR), Mid Atlantic Ridge (MAR), and in the northeast Pacific by the NOAA/PMEL and Oregon State University Acoustic Monitoring Program. These catalogs reduce earthquake detection thresholds by nearly 2 orders of magnitude for the slow spreading MAR, the intermediate spreading Juan de Fuca system, and the fast spreading EPR allowing for a more complete long-term time series of seismic activity along the associated transforms in each spreading regime. Using these hydroacoustically derived earthquake catalogs from 1996-2005, this study examines the long-term temporal and spatial seismicity rate patterns of oceanic transform faults bounded by slow, intermediate, and fast mid-ocean ridge spreading. Our analysis includes 5 MAR transforms, 1 northeast Pacific, and 7 EPR tranform faults. Using standard time series analysis techniques in addition to empirical orthogonal functions (EOF), we describe time space patterns along each transform, characterize seismic behavior between transforms within each spreading regime, and finally compare seismicity time series between transforms bounded by different spreading rates. Through our analysis we anticipate the development of an oceanic tranform fault index parameterized by background seismicity rate, seismicity rate variability during seismic events, fault length, degree of tranform segmentation, and rate of spreading along bounding ridge segments. Utilizing a more complete hydroacoustically derived earthquake catalog provides an unprecedented and comprehensive approach for examining long-term seismicity patterns in transform faulting within these 3 mid-ocean ridge settings.

  16. Analysis of Pn Anisotropy Beneath the Juan de Fuca Plate

    NASA Astrophysics Data System (ADS)

    VanderBeek, B. P.; Toomey, D. R.

    2016-12-01

    We use Pn phases from 40 earthquakes located along the Blanco Transform Fault and the northern Juan de Fuca (JdF) Ridge to constrain the magnitude and orientation of shallow mantle anisotropy beneath the JdF plate. Data are recorded on the year 3 deployment of Cascadia Initiative ocean bottom seismometers (OBSs) and a complimentary array of OBSs located along the Blanco Transform Fault. Nearly 1000 hand-picked Pn arrivals provide complete coverage of the JdF plate. Using a subset of our Pn dataset, we relocated the Blanco events used in this study. Mantle velocities are computed from Pn delay times using the updated source parameters. We find that the best-fit fast-axis azimuth of shallow mantle anisotropy is 92 ± 1°, with a magnitude of 4 ± 1% and a mean velocity of 7.8 km/s (Fig. 1). The observed orientation of anisotropy is rotated 11° counterclockwise to the mean paleo-spreading direction sampled by our dataset. Our results compliment previous measurements of shallow mantle anisotropy beneath the JdF Ridge [VanderBeek et al., 2016] and asthenospheric anisotropy beneath the JdF plate [Bodmer et al., 2015]. Together, these observations provide constraints on mantle deformation across multiple scales and depths. Surprisingly, the seismically inferred orientations of mantle divergence beneath the JdF Ridge and the direction of asthenospheric flow beneath the plate interior from SKS splitting are rotated ahead of recent clockwise changes in JdF plate motion. In comparison, Pn anisotropy averaged across the JdF plate trends between the inferred directions of mantle flow at the ridge and beneath the plate interior. Our results indicate that shallow mantle anisotropy continues to evolve off-axis as the mantle flow field transitions from divergence near the ridge to simple shear that is more closely aligned with absolute plate motion. Moreover, all measurements of anisotropy across the JdF plate indicate that asthenospheric flow is driven by more than plate motion.

  17. 48. Axial Parkway alignment along ridge top. Note the open ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    48. Axial Parkway alignment along ridge top. Note the open vistas to either side of the roadway and the wood guardrail. View is to the northeast. - Blue Ridge Parkway, Between Shenandoah National Park & Great Smoky Mountains, Asheville, Buncombe County, NC

  18. Near-inertial motions over a mid-ocean ridge: Effects of topography and hydrothermal plumes

    SciTech Connect

    Thomson, R.E. ); Roth, S.E.; Dymond, J. )

    1990-05-15

    The authors investigate the spatial structure of near-inertial motions in the vicinity of the Endeavour segment of Juan de Fuca Ridge (approximately 48{degree}N, 129{degree}W) in the northeast Pacific Ocean. Within the lower 1,000 m of the water column where most of the observations were obtained, near-inertial oscillations have rms current speeds of O(1 cm/s) and vertical isotherm displacements of O(10 m). The fluctuations are confined to the frequency band 0.966-1.079 f (f is the local Coriolos parameter) and have characteristic event durations of 1 week. Marked alteration of the near-inertial current amplitudes occurs over two well-defined depth zones within the study region. Within the 200-m zone immediately above the 2,100-m ridge crest, current amplitudes are amplified by a factor of 1.2-1.7 because of bottom reflection and/or scattering of the downward propagating energy. Evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross-slope rotation of the near-inertial current ellipses with increased proximity to the top of the ridge. Near-inertial motions are estimated to have vertical coherence scales of the order of 10-100 m, while horizontal coherence scales exceed the 50-km separation between the mooring locations. Minimum vertical and horizontal coherences are found for the depth zone 1,600-1,800 m, while maximum correlation occurs for near-bottom motions immediately above the crest of the ridge. Weak near-inertial motions are observed within the 100-m-deep axial valley.

  19. Vacuolate-attached filaments: highly productive Ridgeia piscesae epibionts at the Juan de Fuca hydrothermal vents.

    PubMed

    Kalanetra, Karen M; Nelson, Douglas C

    2010-01-01

    Vacuolate sulfur bacteria with high morphological similarity to vacuolate-attached filaments previously described from shallow hydrothermal vents (White Point, CA) were found at deep-sea hydrothermal vents. These filamentous bacteria grow in dense mats that cover surfaces and potentially provide a significant source of organic carbon where they occur. Vacuolate-attached filaments were collected near vents at the Clam Bed site of the Endeavour Segment of the Juan de Fuca Ridge and from the sediment surface at Escanaba Trough on the Gorda Ridge. A phylogenetic analysis comparing their 16S rRNA gene sequences to those collected from the shallow White Point site showed that all vacuolate-attached filament sequences form a monophyletic group within the vacuolate sulfur-oxidizing bacteria clade in the gamma proteobacteria. Abundance of the attached filaments was quantified over the length of the exterior surface of the tubes of Ridgeia piscesae worms collected from the Clam Bed site at Juan de Fuca yielding a per worm average of 0.070 ± 0.018 cm(3) (n = 4). In agreement with previous results for White Point filaments, anion measurements by ion chromatography showed no detectable internal nitrate concentrations above ambient seawater (n = 9). For one R. piscesae tube worm "bush" at the Easter Island vent site, potential gross epibiont productivity is estimated to be 15 to 45× the net productivity of the worms.

  20. Anisotropy of the Juan de Fuca plate: Slab gaps and asthenospheric entrainment

    NASA Astrophysics Data System (ADS)

    Martin-Short, R.; Allen, R. M.

    2013-12-01

    Stacked splitting results are determined for 43 offshore and 27 onshore seismic instruments, which were deployed across the Juan de Fuca plate and the forearc of the Cascadia subduction zone. The onshore results suggest a uniformly trench-perpendicular flow field, indicative of a thick layer of mantle material entrained beneath the slab. The offshore results indicate ridge-perpendicular flow geometry close to the Juan de Fuca ridge, which is superimposed by a radial pattern close to Cobb Hotspot. Towards the trench, flow rotates towards the direction of absolute plate motion, but it also appears to be affected by the presence of a hole or ';gap' in the subducting slab lithosphere beneath central and northern Oregon. This gap is seen in the latest tomographic images and appears to act as a channel for mantle material. Map of the study region showing the oceanic crust magnetic anomaly pattern [Maus et al., 2009] in addition to all available splitting measurements. Offshore measurements obtained by this study are shown in purple, while onshore measurements are shown in red. Results published by previous studies are shown in black [Zandt & Humphreys, 2008; Long et al., 2009; West et al., 2009; Eakin et al., 2010]. The red onshore results are almost entirely trench-perpendicular. The offshore results are sub-perpendicular to the magnetic striping pattern within about 150km of the ridge axis, but then appear to be affected by the presence of the subduction zone. There is also indication of a superposition of ridge perpendicular and radial splitting close to Cobb Hotspot, whose position is shown by the orange dot [Johnson & Embley, 1990].

  1. 33 CFR 80.1385 - Strait of Juan de Fuca.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Strait of Juan de Fuca. 80.1385 Section 80.1385 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1385 Strait of Juan de Fuca. The 72 COLREGS shall apply on all waters of...

  2. Hydrothermal plumes over spreading ridges and related deposits in the northeast Pacific Ocean: The East Pacific Rise near 11 degrees north and 21 degrees north, Explorer Ridge and J. Tuzo Wilson Seamounts

    SciTech Connect

    McConachy, T.F.

    1988-01-01

    Hydrothermal plumes emanating from hot springs over spreading ridges in the north east Pacific Ocean have been mapped and sampled using the submersible ALVIN and equipment deployed from surface ships. The geologic setting and polymetallic sulfides of the vent field producing the hydrothermal plume at 11{degree}N have also been examined. At 11{degree}N, two distinct metalliferous components are delivered to the intermediate to far-field from high temperature black smoker discharge as a result of the physical and chemical processes that occur in the lower 32 m of the plume. About 60 volume % of this material is estimated to settle within a 6-km-radius of the vent field, based on the results of SEM-IPS grain-size analyses and their application to a published particle settling model. The second component delivered to the far-field consists of the remaining 40 volume % of fine-grained sulfides and non-sulfides, 10% of dissolved Fe which will eventually precipitate as oxyhydroxides, and {>=} 80% of the hydrothermally injected Mn, Si, and probably Ba. At 21{degree} N by contrast, only 20 volume % of the smoke particles is conservatively estimated to settle within a 8-km-radius of the NGS vent due to their finer grain size and a higher terminal height of the buoyant hydrothermal plume.

  3. Shallow structure and surface wave propagation characteristics of the Juan de Fuca plate from seismic ambient noise

    NASA Astrophysics Data System (ADS)

    Tian, Y.; Shen, W.; Ritzwoller, M. H.

    2013-12-01

    Ambient noise cross-correlation analysis has been widely used to investigate the continental lithosphere, but the method has been applied much less to study the oceanic lithosphere due to the relative shortage of continuous ocean bottom seismic measurements. The Cascadia Initiative experiment possesses a total of 62 ocean bottom seismometers that spans much of the Juan de Fuca plate and provides data to investigate both the structure and evolution of the oceanic lithosphere near the Juan De Fuca ridge and the characteristics of surface waves and overtones propagating within the oceanic lithosphere. We produce ambient noise cross correlations for the first year of Cascadia OBS data for both the vertical and the horizontal components. The observed empirical Green's functions are first used to test the hypothesis that the near-ridge phase speeds can be described by a simple age-dependent formula, which we invert for an age-dependent shear wave speed model (Figure 1a). A shallow low shear velocity zone with a velocity minimum at about 20km depth is observed in Vsv and the lithosphere thickens with age faster than predicted by a half-space conductive cooling model (Figure 1b). To further understand the oceanic surface waves, we analyze the first higher mode Rayleigh waves that propagate within the Juan De Fuca plate and emerge on the North American continent and investigate the existence of radial anisotropy beneath the ridge by exploring the Rayleigh and Love wave Green's functions. The results of the study are summarized with the age-dependent shear velocity model along with some preliminary observations of both Love wave and higher mode Rayleigh waves.

  4. Attenuation in the Upper Mantle Beneath the Juan de Fuca Plate Using Rayleigh Wave Tomography

    NASA Astrophysics Data System (ADS)

    Forsyth, D. W.; Ruan, Y.; Bell, S. W.

    2016-12-01

    We have measured shear attenuation beneath the Juan de Fuca plate using Rayleigh waves from teleseismic earthquakes propagating across the Cascadia Initiative ocean-bottom seismometer (OBS) arrays. We employ the two-plane-wave technique to account for multi-path interference arising from velocity heterogeneities outside the array, the Born approximation to account for focusing and defocusing within the study area, and station corrections to account for site response and errors in instrument corrections. We solve simultaneously for phase velocity variations within the plate and average Rayleigh wave attenuation coefficients across the entire plate. Rayleigh wave attenuation coefficients extend from periods of 20 s to 143 s. The age of the seafloor ranges from 0 to about 10 Ma. The Juan de Fuca area is slightly more attenuating than seafloor of similar age near the East Pacific Rise in the GLIMPSE and MELT experiments, and the broader period range gives better depth resolution in the asthenosphere than in those studies. The minimum shear quality factor Q is found centered at about 80 km, just below the expected dry solidus and coinciding roughly with the minimum in shear velocity. Q averaged over the well-resolved depth range of 70 to 110 km is 45-50. We compare these observations to predictions of thermal models and various attenuation models. Lateral variations in velocity reveal asymmetry across the ridge axis associated with seamount asymmetry and a minimum in velocity in the vicinity of Axial Seamount.

  5. Tracking fin whales in the northeast Pacific Ocean with a seafloor seismic network.

    PubMed

    Wilcock, William S D

    2012-10-01

    Ocean bottom seismometer (OBS) networks represent a tool of opportunity to study fin and blue whales. A small OBS network on the Juan de Fuca Ridge in the northeast Pacific Ocean in ~2.3 km of water recorded an extensive data set of 20-Hz fin whale calls. An automated method has been developed to identify arrival times based on instantaneous frequency and amplitude and to locate calls using a grid search even in the presence of a few bad arrival times. When only one whale is calling near the network, tracks can generally be obtained up to distances of ~15 km from the network. When the calls from multiple whales overlap, user supervision is required to identify tracks. The absolute and relative amplitudes of arrivals and their three-component particle motions provide additional constraints on call location but are not useful for extending the distance to which calls can be located. The double-difference method inverts for changes in relative call locations using differences in residuals for pairs of nearby calls recorded on a common station. The method significantly reduces the unsystematic component of the location error, especially when inconsistencies in arrival time observations are minimized by cross-correlation.

  6. Earthquakes and submarine volcanism in the Northeast Pacific: Exploration in the time domain based on 21-years of hydroacoustic monitoring

    NASA Astrophysics Data System (ADS)

    Hammond, S. R.; Dziak, R. P.; Fox, C. G.

    2012-12-01

    Monitoring of regional seismic activity in the Northeast Pacific has been accomplished for the past 21 years using US Navy's Sound Surveillance System (SOSUS) hydrophone arrays. Seafloor seismic activity in this region occurs along the spreading center and transform boundaries between the Juan de Fuca, Pacific and North American plates. During the time span, from 1991 through 2011, nearly 50,000 earthquakes were detected and located. The majority of these events were associated with these tectonic boundaries but sections of several plate boundaries were largely aseismic during the this time span. While most of the earthquakes were associated with geological structures revealed in bathymetric maps of the region, there were also less easily explained intraplate events including a swarm of events within the interior of the southern portion of the Juan de Fuca plate. The location and sequential timing of events on portions of the plate boundaries also suggests ordered patterns of stress release. Among the most scientifically significant outcomes of acoustic monitoring was the discovery that deep seafloor magmatic activity can be accompanied by intense (> 1000 events/day) earthquake swarms. The first swarm detected by SOSUS, in 1993, was confirmed to have been associated with an extrusive volcanic eruption which occurred along a segment of the Juan de Fuca spreading center. Notably, this was the first deep spreading center eruption detected, located, and studied while it was active. Subsequently, two more swarms were confirmed to have been associated with volcanic eruptions, one on the Gorda spreading center in 1996 and the other at Axial volcano in 1998. One characteristic of these swarm events is migration of their earthquake locations 10s of km along the ridge axis tracking the movement of magma down-rift. The most rapid magma propagation events have been shown to be associated with seafloor eruptions and dramatic, transient changes in hydrothermal circulation as

  7. Hydrothermal activity on the Gorda Ridge

    NASA Astrophysics Data System (ADS)

    Rona, Peter A.

    Near-bottom plumes of materials indicative of discharge of metal-rich hot springs were discovered at sites on the Gorda Ridge by a research team of government and university scientists on a cruise of the National Oceanic and Atmospheric Administration (NOAA) ship Surveyor during May 1985 as part of the NOAA Vents Program. The Gorda Ridge, off northern California and Oregon, is the only seafloor spreading center within the proclaimed 200-mile U.S. Exclusive Economic Zone (370 km wide) of the conterminous United States and is one of the last oceanic ridges to be explored for metal-rich hot springs. One reason for this neglect is that the Gorda Ridge is slow spreading, with half-rates ranging from 1.1 cm/yr in the southern portion to 2.2 cm/yr in the northern portion. Slow spreading centers have not been fully evaluated with regard to hydrothermal activity by many members of the research community, who have concentrated their attention on the faster spreading East Pacific Rise to the south and the Juan de Fuca Ridge to the north of the Gorda Ridge.

  8. 33 CFR 167.1312 - In the Strait of Juan de Fuca: Southern lanes.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 2 2013-07-01 2013-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1312 In the Strait of Juan de Fuca: Southern lanes. In the southern lanes of the Strait of Juan de Fuca, the following...

  9. 33 CFR 167.1300 - In the approaches to the Strait of Juan de Fuca: General.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... of Juan de Fuca: General. 167.1300 Section 167.1300 Navigation and Navigable Waters COAST GUARD... approaches to the Strait of Juan de Fuca: General. The traffic separation scheme for the approaches to the Strait of Juan de Fuca consists of three parts: the western approach, the southwestern approach,...

  10. 33 CFR 167.1314 - In the Strait of Juan de Fuca: Eastern lanes.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 2 2013-07-01 2013-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1314 In the Strait of Juan de Fuca: Eastern lanes. In the eastern lanes of the Strait of Juan de Fuca, the following are...

  11. 33 CFR 167.1311 - In the Strait of Juan de Fuca: Western lanes.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1311 In the Strait of Juan de Fuca: Western lanes. In the western lanes of the Strait of Juan de Fuca, the following are...

  12. 33 CFR 167.1313 - In the Strait of Juan de Fuca: Northern lanes.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1313 In the Strait of Juan de Fuca: Northern lanes. In the northern lanes of the Strait of Juan de Fuca, the following...

  13. 33 CFR 167.1310 - In the Strait of Juan de Fuca: General.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false In the Strait of Juan de Fuca... Separation Schemes and Precautionary Areas Pacific West Coast § 167.1310 In the Strait of Juan de Fuca: General. The traffic separation scheme in the Strait of Juan de Fuca consists of five parts: the...

  14. 33 CFR 167.1314 - In the Strait of Juan de Fuca: Eastern lanes.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1314 In the Strait of Juan de Fuca: Eastern lanes. In the eastern lanes of the Strait of Juan de Fuca, the following are...

  15. 33 CFR 167.1300 - In the approaches to the Strait of Juan de Fuca: General.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... of Juan de Fuca: General. 167.1300 Section 167.1300 Navigation and Navigable Waters COAST GUARD... approaches to the Strait of Juan de Fuca: General. The traffic separation scheme for the approaches to the Strait of Juan de Fuca consists of three parts: the western approach, the southwestern approach,...

  16. 33 CFR 167.1310 - In the Strait of Juan de Fuca: General.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 33 Navigation and Navigable Waters 2 2014-07-01 2014-07-01 false In the Strait of Juan de Fuca... Separation Schemes and Precautionary Areas Pacific West Coast § 167.1310 In the Strait of Juan de Fuca: General. The traffic separation scheme in the Strait of Juan de Fuca consists of five parts: the...

  17. 33 CFR 167.1310 - In the Strait of Juan de Fuca: General.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 2 2012-07-01 2012-07-01 false In the Strait of Juan de Fuca... Separation Schemes and Precautionary Areas Pacific West Coast § 167.1310 In the Strait of Juan de Fuca: General. The traffic separation scheme in the Strait of Juan de Fuca consists of five parts: the...

  18. 33 CFR 167.1300 - In the approaches to the Strait of Juan de Fuca: General.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... of Juan de Fuca: General. 167.1300 Section 167.1300 Navigation and Navigable Waters COAST GUARD... approaches to the Strait of Juan de Fuca: General. The traffic separation scheme for the approaches to the Strait of Juan de Fuca consists of three parts: the western approach, the southwestern approach,...

  19. 33 CFR 167.1312 - In the Strait of Juan de Fuca: Southern lanes.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1312 In the Strait of Juan de Fuca: Southern lanes. In the southern lanes of the Strait of Juan de Fuca, the following...

  20. 33 CFR 167.1310 - In the Strait of Juan de Fuca: General.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 2 2013-07-01 2013-07-01 false In the Strait of Juan de Fuca... Separation Schemes and Precautionary Areas Pacific West Coast § 167.1310 In the Strait of Juan de Fuca: General. The traffic separation scheme in the Strait of Juan de Fuca consists of five parts: the...

  1. 33 CFR 167.1313 - In the Strait of Juan de Fuca: Northern lanes.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 2 2013-07-01 2013-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1313 In the Strait of Juan de Fuca: Northern lanes. In the northern lanes of the Strait of Juan de Fuca, the following...

  2. 33 CFR 167.1311 - In the Strait of Juan de Fuca: Western lanes.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 2 2012-07-01 2012-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1311 In the Strait of Juan de Fuca: Western lanes. In the western lanes of the Strait of Juan de Fuca, the following are...

  3. 33 CFR 167.1311 - In the Strait of Juan de Fuca: Western lanes.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 2 2013-07-01 2013-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1311 In the Strait of Juan de Fuca: Western lanes. In the western lanes of the Strait of Juan de Fuca, the following are...

  4. 33 CFR 167.1300 - In the approaches to the Strait of Juan de Fuca: General.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... of Juan de Fuca: General. 167.1300 Section 167.1300 Navigation and Navigable Waters COAST GUARD... approaches to the Strait of Juan de Fuca: General. The traffic separation scheme for the approaches to the Strait of Juan de Fuca consists of three parts: the western approach, the southwestern approach,...

  5. Seismic velocity structure of the Juan de Fuca and Gorda plates revealed by a joint inversion of ambient noise and regional earthquakes

    NASA Astrophysics Data System (ADS)

    Gao, Haiying

    2016-05-01

    The crust and upper mantle seismic structure, spanning from the Juan de Fuca and Gorda spreading centers to the Cascade back arc, is imaged with full-wave propagation simulation and a joint inversion of ambient noise and regional earthquake recordings. The spreading centers have anomalously low shear wave velocity beneath the oceanic lithosphere. Around the Cobb axial seamount, we observe a low-velocity anomaly underlying a relatively thin oceanic lithosphere, indicating its influence on the Juan de Fuca ridge. The oceanic Moho is clearly defined by a P velocity increase from 6.3 km/s to 7.5 km/s at about 6 km depth beneath the seafloor. The thickness of the oceanic plates is less than 40 km prior to subduction, and the structure of the oceanic lithosphere varies both along strike and along dip. Farther landward, very low velocity anomalies are observed above the plate interface along the Cascade fore arc, indicative of subducted sediments.

  6. Honeycomb Ridges

    NASA Image and Video Library

    2006-04-14

    The odd ridges in this image from NASA Mars Odyssey spacecraft are located on the floor of an unnamed impact crater. The ridges probably formed when a resistant material filled in cracks in a less-resistant material that has since been eroded away.

  7. Surface-Wave Imaging of the Juan de Fuca Plate and Cascadia Subduction Zone

    NASA Astrophysics Data System (ADS)

    Janiszewski, H. A.; Gaherty, J. B.; Abers, G. A.

    2015-12-01

    The Juan de Fuca plate over the past four years has been the location of the onshore-offshore Cascadia Initiative (CI) array. These data present a rare opportunity to image the evolution of the crust and mantle of an entire plate from the ridge through the subduction zone. The Cascadia subduction zone is capable of up to a M9 megathrust earthquake; seismic imaging provides a major constraint on the thermal structure and hydration state of the plate, which in turn constrain models of seismogenesis. We utilize a multi-channel cross-correlation analysis to estimate the phase-velocity of Rayleigh waves traversing the CI from teleseismic earthquakes recorded over the first three years of the deployment, to image the structure of the Juan de Fuca plate and the Cascadia arc and forearc. Our initial results are dominated by the transition from high-velocity oceanic to low-velocity continental lithosphere across the margin, high velocities in the region of the subducting slab, and low velocities beneath the arc. All of these areas produce reasonable standard deviation in the velocity estimates. These images confirm the robustness of our methodology, despite the different noise characteristics of the onshore sites and the ocean bottom seismometers (OBS). Among the OBS sites there are additional differences between those deployed in deep water on oceanic crust and those in shallow water on the continental shelf. Compliance and tilt corrections have a significant effect at some stations and are taken into account accordingly. These results will be combined with recent results from offshore receiver functions and estimates of short-period Rayleigh wave dispersion from ambient noise to constrain the crust and mantle structure in a joint inversion.

  8. Offshore finfish mariculture in the Strait of Juan de Fuca

    SciTech Connect

    Rensel, Jack; Kiefer, Dale; Forster, John R.; Woodruff, Dana L.; Evans, Nathan R.

    2007-10-07

    Finfish mariculture has existed in the U.S. Pacific Northwest for over thirty years, but for the past 15 years most effort has focused on culture of Atlantic salmon in protected, inshore cage sites. The Strait of Juan de Fuca (the "Strait") is a large area with relatively sparce shoreline development and several apparent advantages for mariculture using offshore technology.

  9. Northeast Atlantic bathymetric map

    NASA Astrophysics Data System (ADS)

    Loubrieu, B.; Sibuet, J.-C.; Monti, S.; Mazé, J.-P.

    2003-04-01

    The new bathymetric map of the Bay of Biscay and Northeast Atlantic Ocean is based on all available conventional and multibeam data. It extends from the European coast to the mid-Atlantic ridge in longitude and from the Azores-Gibraltar fracture zone to 50^oN in latitude. Grid spacing is one km. The map is in Mercator projection at a 1/2,400,000 scale. With respect to previously published maps, the detailed morphology of Eurasian and Iberian continental margins, a complete picture of the two fossil trajectories of the Bay of Biscay triple junction, which limit the western extension of the Bay of Biscay, and the precise location of the plate boundary between Eurasia and Iberia, which was active during the Tertiary, are now available. The Bay of Biscay and Northeast Atlantic opened simultaneously between chrons M0 (118 Ma) and 33o (80 Ma). A triple junction existed during that period. Fossil triple junctions trajectories on each of the three Eurasia (EU), Iberia (IB) and North America (NA) plates separate oceanic domains which were formed between the three plate pairs: IB/EU for the Bay of Biscay, EU/NA and IB/NA for the northern and southern portions of the Northeast Atlantic respectively. On each side of the fossil trajectories, rift directions formed between different plate pairs present different azimuths. The two eastern branches have been identified on the basis of available bathymetric, magnetic and seismic data. They are generally associated with a basement ridge whose bathymetric expression is clearly shown in their youngest parts. The intersections of these two fossil trajectories with the base of the continental margins are conjugate points before the opening of the Bay of Biscay, giving an independent constraint for plate reconstructions at M0 time. In a companion poster, we have used the constraints deduced from the new bathymetric map to derive the IB/EU kinematic motions and discuss their consequences on the formation of Pyrenees.

  10. Ridge Tectonics, Magma Supply, and Ridge-Hotpot Interaction at the Eastern End of the Australian-Antarctic Ridge

    NASA Astrophysics Data System (ADS)

    Kim, S.; Lin, J.; Park, S.; Choi, H.; Lee, S.

    2013-12-01

    the Balleny hotpot is not dominant in the axial morphology of the AAR super-segment. The axial topography of this super-segment exhibits a sharp transition from axial highs at the western end to rift valleys at the eastern end, with regions of axial highs being associated with more magma supply as indicated by more negative RMBA. The eastern AAR will be further compared with other intermediate fast spreading ridges, such as the Juan de Fuca Ridge, Galápagos Spreading Center, and Southeast Indian Ridge west of the Australian-Antarctic Discordance, to better understand the influence of ridge-hotspot interaction on ridge magma supply and tectonics.

  11. The importance of hydrothermal venting to water-column secondary production in the northeast Pacific

    NASA Astrophysics Data System (ADS)

    Burd, Brenda J.; Thomson, Richard E.

    2015-11-01

    The purpose of this study is to show that seafloor hydrothermal venting in the open northeast Pacific Ocean has a marked impact on secondary biomass and production within the overlying water column. Specifically, we use net tows and concurrently measured acoustic backscatter data collected over six summers to examine the effects of hydrothermal venting from the Endeavour Segment of Juan de Fuca Ridge on macro-zooplankton biomass and production throughout the entire 2000 m depth range. Previous research shows that ontogenetic diapausing migrators and their predators from the upper ocean aggregate above the neutrally buoyant plumes in summer and resume feeding on plume and bottom upwelled particles, resulting in increased zooplankton reproductive output to the upper ocean. Within the limitations of our sampling methodology, net tows reveal a statistically significant exponential decline in total water-column biomass with increasing lateral distance from the vent fields. The acoustic backscatter data show a similar decline, but only below 800 m depth. Near-surface biomass was highly variable throughout the region, but values near vents consistently ranged higher than summer values found elsewhere in the offshore northeast Pacific. Water-column biomass was similar in magnitude above and below 800 m depth throughout the region. Because epiplume biomass can be advected a considerable distance from vent fields, biomass enhancement of the water column from hydrothermal venting may extend considerable distances to the west and northwest of the vent sites, in the prevailing directions of the subsurface flow. Based on the extensive acoustic Doppler current profiler (ADCP) data collected, and the strong correlation between zooplankton production derived from net sample biomass and acoustic backscatter intensity, we estimate that daily macro-zooplankton production in the upper 400 m of the water column within 10 km of the vent fields averages approximately 16% of photosynthetic

  12. 247. Axial Parkway alignment along ridge top. Note the open ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    247. Axial Parkway alignment along ridge top. Note the open vistas to either side of the roadway. These are maintained through vegetation management. The wood guide rail is a primary safety feature. View is to the northeast. - Blue Ridge Parkway, Between Shenandoah National Park & Great Smoky Mountains, Asheville, Buncombe County, NC

  13. Variations in Seismic Structure of the Incoming Juan de Fuca Plate Along the Cascadia Deformation Front

    NASA Astrophysics Data System (ADS)

    Canales, J.; Carton, H. D.; Carbotte, S. M.; Nedimovic, M. R.

    2013-12-01

    The Cascadia subduction zone displays regional-scale variations in its structural characteristics, rupture zones of paleo-earthquakes, intra-slab seismicity and episodic tremor and slip, and submarine morphology. In Summer 2012 we conducted an active-source multichannel seismic (MCS) reflection and wide-angle ocean bottom seismometer (OBS) study of the Juan de Fuca plate to investigate the north-south structural segmentation of the incoming plate and its role in contributing to regional variations in Cascadia subduction zone processes. Here we present traveltime P-wave tomography results from a combined MCS+OBS ~400-km-long seismic profile extending from offshore Northern Washington to offshore Central Oregon, ~10 km seaward from the Cascadia deformation front. Data were acquired with a single 8-km-long, 636-hydrophone streamer (shot spacing of 37.5 m), and with 26 OBSs spaced ~15 km apart (shot spacing of 500 m). Preliminary results from the southern 120-km section of the profile indicate that offshore Oregon, sediment thickness varies between 2.4 and 3.0 km. In this region at latitude 45°N, the profile crosses a 9-m.y.-old pseudofault formed at the paleo Juan de Fuca Ridge. Across the pseudofault, P-wave velocities in the upper ~2 km of the igneous crust are 3-4% lower than average, indicating localized increased porosity and hydration. However there is no evidence for such anomaly extending deeper into the lower crust. Along the examined section of the profile, crustal thickness is relatively homogeneous (6 km) but mantle velocities vary laterally between 7.5 km/s and 8.2 km/s at lateral scales of ~30 km. These results thus suggest along-margin variations in the state of alteration of the sub-oceanic mantle prior to subduction, although further data analysis is needed to asses their spatial correlation with the segmentation inherited from the ridge axis. Results from the complete profile will be presented at the meeting.

  14. Ambient Noise Tomography and Microseism Directionalities across the Juan de Fuca Plate

    NASA Astrophysics Data System (ADS)

    Tian, Ye

    Ambient noise tomography has been well developed over the past decade and proven to be effective in studying the crust and upper mantle structure beneath the Earth’s continents. With new seismic array deployments beginning in the oceans, the application of the tomographic methods based on ambient noise observed at ocean bottom seismometers (OBSs) has become an important topic for research. In this thesis, I investigate the application of ambient noise tomography to oceanic bottom seismic data recorded by the Cascadia Initiative experiment across the Juan de Fuca plate. With higher local noise levels recorded by OBSs, I find that traditional data processing procedures used in ambient noise tomography produce measurable Rayleigh wave Green’s functions between deep ocean stations, whereas the shallow water stations are severely contaminated by both tilt noise and compliance noise and require new methods of processing. Because the local noise level varies across the study region, four semi-independent studies are conducted to both utilize the quieter deep-water stations and to address the problem posed by noisy shallow water stations. First, I construct an age-dependent shear wave speed model of the crust and uppermost mantle with 18 deep-water stations near the Juan de Fuca Ridge. The model possess a shallow low shear velocity zone near the ridge and has its sedimentary thickness, lithospheric thickness, and mantle shear wave speeds increase systematically with age Second, I investigate the locations and mechanisms of microseism generation using ambient noise cross-correlations constructed between 61 OBSs and 42 continental stations near the western US coast and find that the primary and secondary microseisms are generated at different locations and possibly have different physical mechanisms. Third, I show that tilt and compliance noise on the vertical components of the OBSs can be reduced substantially using the horizontal components and the differential

  15. The strontium isotopic composition of basalts from the Gordo and Juan de Fuca Rises, northeastern Pacific Ocean

    USGS Publications Warehouse

    Hedge, C.E.; Peterman, Z.E.

    1970-01-01

    The strontium isotopic compositions have been determined for twelve tholeiitic basalts dredged from the Gordo and Juan de Fuca Rises. Sr87/Sr86 ratios range from 0.7012 to 0.7031 and average 0.7026. These data, combined with other data from the East Pacific Rise indicate that tholeiite basalts being erupted along the active rises, in the Pacific Ocean, contain less radiogenic Sr87 than basalts erupted on the islands. These isotopic differences between the ocean-ridge tholeiite and the more alkali island basalts indicate that variations in Rb/Sr have persisted in the mantle for billions of years. The possible origins and distribution of these heterogeneties are discussed. ?? 1970 Springer-Verlag.

  16. 33 CFR 167.1315 - In the Strait of Juan de Fuca: Precautionary area “PA.”

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 2 2013-07-01 2013-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1315 In the Strait of Juan de Fuca: Precautionary area “PA.” In the Strait of Juan de Fuca, precautionary area “PA” is...

  17. 33 CFR 167.1315 - In the Strait of Juan de Fuca: Precautionary area “PA.”

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 33 Navigation and Navigable Waters 2 2014-07-01 2014-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1315 In the Strait of Juan de Fuca: Precautionary area “PA.” In the Strait of Juan de Fuca, precautionary area “PA” is...

  18. 33 CFR 167.1302 - In the approaches to the Strait of Juan de Fuca: Southwestern approach.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... of Juan de Fuca: Southwestern approach. 167.1302 Section 167.1302 Navigation and Navigable Waters....1302 In the approaches to the Strait of Juan de Fuca: Southwestern approach. In the southwestern approach to the Strait of Juan de Fuca, the following are established: (a) A separation zone bounded by...

  19. 33 CFR 167.1315 - In the Strait of Juan de Fuca: Precautionary area “PA.”

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1315 In the Strait of Juan de Fuca: Precautionary area “PA.” In the Strait of Juan de Fuca, precautionary area “PA” is...

  20. 33 CFR 167.1301 - In the approaches to the Strait of Juan de Fuca: Western approach.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... of Juan de Fuca: Western approach. 167.1301 Section 167.1301 Navigation and Navigable Waters COAST....1301 In the approaches to the Strait of Juan de Fuca: Western approach. In the western approach to the Strait of Juan de Fuca, the following are established: (a) A separation zone bounded by a line...

  1. 33 CFR 167.1302 - In the approaches to the Strait of Juan de Fuca: Southwestern approach.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... of Juan de Fuca: Southwestern approach. 167.1302 Section 167.1302 Navigation and Navigable Waters....1302 In the approaches to the Strait of Juan de Fuca: Southwestern approach. In the southwestern approach to the Strait of Juan de Fuca, the following are established: (a) A separation zone bounded by...

  2. 33 CFR 167.1315 - In the Strait of Juan de Fuca: Precautionary area “PA.”

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 2 2012-07-01 2012-07-01 false In the Strait of Juan de Fuca... Traffic Separation Schemes and Precautionary Areas Pacific West Coast § 167.1315 In the Strait of Juan de Fuca: Precautionary area “PA.” In the Strait of Juan de Fuca, precautionary area “PA” is...

  3. 33 CFR 167.1301 - In the approaches to the Strait of Juan de Fuca: Western approach.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... of Juan de Fuca: Western approach. 167.1301 Section 167.1301 Navigation and Navigable Waters COAST....1301 In the approaches to the Strait of Juan de Fuca: Western approach. In the western approach to the Strait of Juan de Fuca, the following are established: (a) A separation zone bounded by a line...

  4. 33 CFR 110.229 - Straits of Juan de Fuca, Wash.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 1 2011-07-01 2011-07-01 false Straits of Juan de Fuca, Wash. 110.229 Section 110.229 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY ANCHORAGES ANCHORAGE REGULATIONS Anchorage Grounds § 110.229 Straits of Juan de Fuca, Wash. (a)...

  5. 33 CFR 110.229 - Straits of Juan de Fuca, Wash.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 1 2012-07-01 2012-07-01 false Straits of Juan de Fuca, Wash. 110.229 Section 110.229 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY ANCHORAGES ANCHORAGE REGULATIONS Anchorage Grounds § 110.229 Straits of Juan de Fuca, Wash. (a)...

  6. Geologic history of the summit of Axial Seamount, Juan de Fuca Ridge

    USGS Publications Warehouse

    Clague, David A.; Dreyer, Brian M; Paduan, Jennifer B; Martin, Julie F; Chadwick, William W Jr; Caress, David W; Portner, Ryan A; Guilderson, Thomas P.; McGann, Mary; Thomas, Hans; Butterfield, David A; Embley, Robert W

    2013-01-01

    Multibeam (1 m resolution) and side scan data collected from an autonomous underwater vehicle, and lava samples, radiocarbon-dated sediment cores, and observations of flow contacts collected by remotely operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on Axial Seamount's summit and upper rift zones. The maps show 52 post-410 CE lava flows and 20 precaldera lava flows as old as 31.2 kyr, the inferred age of the caldera. Clastic deposits 1–2 m thick accumulated on the rims postcaldera. Between 31 ka and 410 CE, there are no known lava flows near the summit. The oldest postcaldera lava (410 CE) is a pillow cone SE of the caldera. Two flows erupted on the W rim between ∼800 and 1000 CE. From 1220 to 1300 CE, generally small eruptions of plagioclase phyric, depleted, mafic lava occurred in the central caldera and on the east rim. Larger post-1400 CE eruptions produced inflated lobate flows of aphyric, less-depleted, and less mafic lava on the upper rift zones and in the N and S caldera. All caldera floor lava flows, and most uppermost rift zone flows, postdate 1220 CE. Activity shifted from the central caldera to the upper S rift outside the caldera, to the N rift and caldera floor, and then to the S caldera and uppermost S rift, where two historical eruptions occurred in 1998 and 2011. The average recurrence interval deduced from the flows erupted over the last 800 years is statistically identical to the 13 year interval between historical eruptions.

  7. Cabled-observatory Regional Circulation Moorings on the Endeavour segment of the Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Mihaly, S. F.

    2011-12-01

    In September of 2010, one of four moorings was deployed on the Endeavour node of the NEPTUNE Canada cabled-observatory network. The installation included the laying of a 7km cable from the node to the mooring site in the axial valley about 3km north of the Main Endeavour Vent Field over extraordinary bathymetry. This September, three more cables and secondary junction boxes will be deployed to support the three additional moorings that complete the regional circulation array. The cable-laying is facilitated by the Canadian Scientific Submersible Facility's ROV ROPOS and a remotely operated cable-laying system, whereas the actual deployment of the moorings is a two ship operation. The CCGS John P. Tully lowers the mooring anchor first, while the RV Thomas G. Thompson supports the ROV operations which navigate the mooring to underwater mateable cable end. Precise navigation is needed because there are few areas suitable for placement of the junction boxes. Scientifically, the moorings are designed and located to best constrain the hydrothermally driven circulation within the rift valley, the regional circulation can then be used as a proxy measurement for hydrothermal fluxes. Each mooring carries a current meter/ ctd pair at 4, 50, 125, and 200m, with an upward looking ADCP at 250m. The northern moorings are located between the Hi-Rise and Salty Dawg fields about 700m apart in the ~1km wide rift valley and the southern moorings are located south of the Mothra vent field. Here we present initial results from the four mooring array.

  8. High-resolution AUV mapping of the 2015 flows at Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Paduan, J. B.; Chadwick, W. W., Jr.; Clague, D. A.; Le Saout, M.; Caress, D. W.; Thomas, H. J.; Yoerger, D.

    2016-12-01

    Lava flows erupted in April 2015 at Axial Seamount were mapped at 1-m resolution with the AUV Sentry in August 2015 and the MBARI Mapping AUVs in July 2016 and observed and sampled with ROVs on those same expeditions. Thirty percent of terrain covered by new flows had been mapped by the MBARI AUVs prior to the eruption. Differencing of before and after maps (using ship-collected bathymetry where the AUV had not mapped before) allows calculation of extents and volumes of flows and shows new fissures. The maps reveal unexpected fissure patterns and shifts in the style of flow emplacement through a single eruption. There were 11 separate flows totaling 1.48 x 108 m3 of lava erupted from numerous en echelon fissures over 19 km on the NE caldera floor, on the NE flank, and down the N rift zone. Flows in and around the caldera have maximum thicknesses of 5-19 m. Most erupted as sheet flows and spread along intricate channels that terminated in thin margins. Some utilized pre-existing fissures. Some flows erupted from short fissures, while at least two longer new fissures produced little or no lava. A flow on the upper N rift has a spectacular lava channel flanked by narrow lava pillars supporting a thin roof left after the flow drained. A shatter ring still emanating warm fluid is visible in the map as a 15-m wide low cone. Hundreds of exploded pillows were observed but are not discernable in the bathymetry. The northern-most three flows deep on the N rift are similar in area to the others but comprise the bulk of the eruption volume. Differencing of ship-based bathymetry shows only these flows. Near the eruptive fissures they are sheet flows, but as they flowed downslope they built complexes of coalesced pillow mounds up to 67-128 m thick. Changes in flow morphology occurred through the course of the eruption. Large pillow mounds had molten cores that deformed as the eruption progressed. One flow began as a thin, effusive sheet flow but as the eruption rate decreased, a pillow mound built over the fissure. As the eruption waned on the caldera floor, near the fissure a small inflated margin developed on top of channels from an earlier phase of the flow. Several landslides occurred at the caldera wall. One is near where a 2015 fissure on the caldera floor cut through the caldera-bounding fault into the flank of the volcano.

  9. Geophysical Characteristics of the Australian-Antarctic Ridge

    NASA Astrophysics Data System (ADS)

    Kim, S. S.; Lin, J.; Park, S. H.; Choi, H.; Lee, S. M.

    2014-12-01

    Between 2011 and 2013, the Korea Polar Research Institute (KOPRI) conducted three consecutive geologic surveys at the little explored eastern ends of the Australian-Antarctic Ridge (AAR) to characterize the tectonics, geochemistry, and hydrothermal activity of this intermediate spreading system. Using the Korean icebreaker R/V Araon, the multi-disciplinary research team collected bathymetry, gravity, magnetics, and rock and water column samples. In addition, Miniature Autonomous Plume Recorders (MAPRs) were deployed at wax-core rock sampling sites to detect the presence of active hydrothermal vents. Here we present a detailed analysis of a 300-km-long supersegment of the AAR to quantify the spatial variations in ridge morphology and robust axial and off-axis volcanisms. The ridge axis morphology alternates between rift valleys and axial highs within relatively short ridge segments. To obtain a geological proxy for regional variations in magma supply, we calculated residual mantle Bouguer gravity anomalies (RMBA), gravity-derived crustal thickness, and residual topography for seven sub-segments. The results of the analyses revealed that the southern flank of the AAR is associated with shallower seafloor, more negative RMBA, thicker crust, and/or less dense mantle than the conjugate northern flank. Furthermore, this north-south asymmetry becomes more prominent toward the KR1 supersegment of the AAR. The axial topography of the KR1 supersegment exhibits a sharp transition from axial highs at the western end to rift valleys at the eastern end, with regions of axial highs being associated with more magma supply as indicated by more negative RMBA. We also compare and contrast the characteristics of the AAR supersegment with that of other ridges of intermediate spreading rates, including the Juan de Fuca Ridge, Galápagos Spreading Center, and Southeast Indian Ridge west of the Australian-Antarctic Discordance, to investigate the influence of ridge-hotspot interaction on

  10. Historical Gorda Ridge t-phase swarms: relationships to ridge structure and the tectonic and volcanic state of the ridge during 1964 1966

    NASA Astrophysics Data System (ADS)

    Walker, Daniel A.; Hammond, Stephen R.

    1998-12-01

    The U.S. Navy's Sound Surveillance System (SOSUS) hydrophone arrays are extemely efficient receptors of a high-frequency earthquake energy phase known as the t(ertiary)-wave, or t-phase (Fox et al., 1994). After a nearly 30-year hiatus in such studies, SOSUS arrays are again being utilized to detect t-phases and to locate seismic and volcanic events occurring along the Gorda seafloor spreading center (Fox et al., 1995; Fox and Dziak, 1998). Earlier, Northrop et al. (1968) also used other military arrays to infer tectonic structure along the Gorda Ridge. From October 1964 through December 1966, over 600 low-magnitude earthquakes occurred along the Gorda Ridge. Nearly all of these events had magnitudes below the detection thresholds of land-based seismic networks. Northrop et al. (1968) interpreted the geographic distribution of these events as evidence for a nascent fracture zone near the midpoint of the ridge. In the present study, the spatial distributions of these older data and, for the first time, their temporal distributions as well, were examined with respect to detailed bathymetry of the ridge that was acquired in the early 1980s. This analysis, of 570 on-axis and 74 off-axis events, led to the following observations: (1) nearly all of the Gorda Ridge t-phase events occurred in discreet swarms centered about the ridge axis, (2) most of the events within each of 8 (of 9) observed swarms occurred mainly along single ridge segments, and, (3) reconfirming the earlier Northrop et al. (1968) conclusion, most of the events originated in the region of a major change in the strike of the ridge axis. During the 27-month interval that the ridge was observed, relatively few t-phase events took place along the northernmost segment of the Gorda Ridge where the 1996 eruption occurred. However, a unique sequence of small events which visually resemble the events associated with a Juan de Fuca Ridge eruption in 1993 (Fox et al., 1995) and a Gorda Ridge eruption in 1996 (Fox

  11. Statistical Features of Deep-ocean Tsunamis Based on 30 Years of Bottom Pressure Observations in the Northeast Pacific

    NASA Astrophysics Data System (ADS)

    Fine, I.; Thomson, R.; Chadwick, W. W., Jr.; Davis, E. E.; Fox, C. G.

    2016-12-01

    We have used a set of high-resolution bottom pressure recorder (BPR) time series collected at Axial Seamount on the Juan de Fuca Ridge beginning in 1986 to examine tsunami waves of seismological origin in the northeast Pacific. These data are a combination of autonomous, internally-recording battery-powered instruments and cabled instruments on the OOI Cabled Array. Of the total of 120 tsunami events catalogued for the coasts of Japan, Alaska, western North America and Hawaii, we found evidence for 38 events in the Axial Seamount BPR records. Many of these tsunamis were not observed along the adjacent west coast of the USA and Canada because of the much higher noise level of coastal locations and the lack of digital tide gauge data prior to 2000. We have also identified several tsunamis of apparent seismological origin that were observed at coastal stations but not at the deep ocean site. Careful analysis of these observations suggests that they were likely of meteorological origin. Analysis of the pressure measurements from Axial Seamount, along with BPR measurements from a nearby ODP CORK (Ocean Drilling Program Circulation Obviation Retrofit Kit) borehole and DART (Deep-ocean Assessment and Reporting of Tsunamis) locations, reveals features of deep-ocean tsunamis that are markedly different from features observed at coastal locations. Results also show that the energy of deep-ocean tsunamis can differ significantly among the three sets of stations despite their close spatial spacing and that this difference is strongly dependent on the direction of the incoming tsunami waves. These deep-ocean observations provide the most comprehensive statistics possible for tsunamis in the Pacific Ocean over the past 30 years. New insight into the distribution of tsunami amplitudes and wave energy derived from the deep-ocean sites should prove useful for long-term tsunami prediction and mitigation for coastal communities along the west coast of the USA and Canada.

  12. Mantle dynamics beneath the discrete and diffuse plate boundaries of the Juan de Fuca plate: Results from Cascadia Initiative body wave tomography

    NASA Astrophysics Data System (ADS)

    Byrnes, Joseph S.; Toomey, Douglas R.; Hooft, Emilie E. E.; Nábělek, John; Braunmiller, Jochen

    2017-08-01

    We use the delay times of teleseismic S phases recorded by ocean bottom seismometers during the plate-scale Cascadia Initiative community experiment to constrain the heterogeneity of seismic velocity structure beneath young oceanic lithosphere. Our study area covers the entire Juan de Fuca (JdF) and Gorda plates, from their creation at the JdF and Gorda Ridges to their subduction beneath the North American continent, and the entire length of the Blanco transform fault. The range of the observed Vs anomalies requires variations in the melt fraction of the asthenosphere. The data require that low Vs anomalies extend to depths of at least 200 km, which is within the carbonatite melting regime. In the upper 200 km of the mantle, Vs increases rapidly to the east of the JdF Ridge, while there is no clear relationship with the age of the lithosphere in the Gorda region. The distribution of melt is asymmetric about both the JdF and Gorda Ridges. Dynamic upwelling - due to the buoyancy of the mantle - and accompanying downwelling can explain the rapid decrease in melt fraction to the east of the JdF Ridge, the asymmetry about the JdF Ridge, and the sinuous pattern of upwelling near the Blanco transform fault. Finally, mantle flow beneath the diffuse Gorda and Explorer plate boundaries is distinct from that beneath the discrete plate boundary of the JdF Ridge. In particular, shear between the Pacific and JdF plates appears to dominate mantle deformation over seafloor spreading beneath the Gorda Ridge.

  13. The Fate of the Juan de Fuca Plate

    NASA Astrophysics Data System (ADS)

    Xue, M.; Allen, R. M.

    2006-12-01

    The Juan de Fuca plate is subducting beneath the northwestern United States and southwestern Canada. Although the slab has been imaged to depths of at least ~{400} km beneath Washington and at least ~{200} to 300 km beneath northern Oregon with a dip of ~60° to the east, there is little evidence for a slab east of High Cascades deeper than ~150 km beneath central and ~200 km beneath southern Oregon. To image the slab beneath Oregon, we apply tomography technique using a dataset consisting of our own OATS deployment and all other available data. For the Vs inversion, a total of 95 events with clear S and SKS phases were recorded at 45 stations and a total number of 2148 rays were used. For the Vp inversion, a total of 74 events with clear direct P phase were recorded at 46 stations, and a total number of 2043 rays were used. Our tomographic images clearly show that the Juan de Fuca plate dives into the mantle beneath Oregon and continues east of the High Cascades with a dip of ~50° reaching a depth of ~400 km. The slab does not dip more vertically than its counterparts to north and south, which have a dip of ~60° and ~65° respectively. Resolution tests suggest there is little or no velocity anomaly associated with a slab below ~400 km.

  14. Magnetic Field Modeling of the Northern Juan De Fuca and Explorer Plates

    DTIC Science & Technology

    1993-07-01

    THE i NORTHERN JUAN DE FUCA AND EXPLORER PLATES I I JOHN M. QUINN DONALD L. SHIEL DTIC "ELECTE 1AU 18 1994U s.I GD SI q •-(494-26093I...concerns a low-level Project MAGNET survey of the northern Juan de Fuca and Explorer Plates , a region of intense scientific interest due to its volcanic...Juan de Fuca and Explorer Plates 5. AUTHOR(S) John H. Quinn Donald L. Shiel 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING

  15. Ridge systems of Mars. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Gifford, A. W.

    1981-01-01

    Mare-type ridges on the Planet Mars were mapped and described based on Viking images. The ridges mapped range from 5 to 400 km long and 1 to 8 km wide. Most ridges on Mars are on plains and plateau units; 4,321 ridges with a total length of 153,835 km were mapped on these unit types. Ridges which resemble lunar mare ridges were also mapped in craters, basins, and several volcanic calderas on Mars. Mapping of ridges on a global scale reveals that they are preferentially developed in older, thinner plains units probably of flood basalt origin. Measuring the trends of ridges in plains units on Mars shows that there is a planetwide predominance of north, northwest and northeast trends. It is proposed that ridges are compressional tectonic features which have formed in response to changes in the planet's rotational equilibrium figure early in its history. In addition, the Tharsis uplift has created a regional stress system which accounts for the trends of ridges in areas near by. Ridges in craters and basins are similarly caused by shortening across the basin in response to regional stresses.

  16. Characteristics of fin whale vocalizations recorded on instruments in the northeast Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Weirathmueller, Maria Michelle Josephine

    seismometers at two locations are used to assess the method: one on the Juan de Fuca Ridge, a bathymetrically complex mid-ocean ridge environment, and the other at a flat sedimented location in the Cascadia Basin. At both sites, the method is reliable up to 4 km range which is sufficient to enable estimates of call density. The third study explores spatial and temporal trends in fin whale calling patterns. The frequency and inter-pulse interval of fin whale 20 Hz vocalizations were observed over 10 years from 2003-2013 on bottom mounted hydrophones and OBSs in the northeast Pacific Ocean. The instrument locations extended from 40°N and 130°W to 125°W with water depths ranging from 1500-4000 m. The inter-pulse interval (IPI) of fin whale song sequences was observed to increase at a rate of 0.59 seconds/year over the decade of observation. During the same time period, peak frequency decreased at a rate of 0.16 Hz/year. Two primary call patterns were observed. During the earlier years, the more commonly observed pattern had a single frequency and single IPI. In later years, a doublet pattern emerged, with two dominant frequencies and two IPIs. Many call sequences in the intervening years appeared to represent a transitional state between the two patterns. The overall trend was consistent across the entire geographical span, although some regional differences exist.

  17. Juan de Fuca plate: Aseismic subduction at 1. 8 cm/yr

    SciTech Connect

    Acharya, H.

    1981-11-01

    Volcanic activity in the Cascades in historic times suggests that the Juan de Fuca plate is underthrusting aseismically at about 1.8 cm/yr. This rate of underthrusting is identical to the rate computed from sediment studies.

  18. Pole of rotating analysis of present-day Juan de Fuca plate motion

    NASA Technical Reports Server (NTRS)

    Nishimura, C.; Wilson, D. S.; Hey, R. N.

    1984-01-01

    Convergence rates between the Juan de Fuca and North American plates are calculated by means of their relative, present-day pole of rotation. A method of calculating the propagation of errors in addition to the instantaneous poles of rotation is also formulated and applied to determine the Euler pole for Pacific-Juan de Fuca. This pole is vectorially added to previously published poles for North America-Pacific and 'hot spot'-Pacific to obtain North America-Juan de Fuca and 'hot spot'-Juan de Fuca, respectively. The errors associated with these resultant poles are determined by propagating the errors of the two summed angular velocity vectors. Under the assumption that hot spots are fixed with respect to a mantle reference frame, the average absolute velocity of the Juan de Puca plate is computed at approximately 15 mm/yr, thereby making it the slowest-moving of the oceanic plates.

  19. Ridge suction drives plume-ridge interactions

    NASA Astrophysics Data System (ADS)

    Niu, Y.; Hékinian, R.

    2003-04-01

    Deep-sourced mantle plumes, if existing, are genetically independent of plate tectonics. When the ascending plumes approach lithospheric plates, interactions between the two occur. Such interactions are most prominent near ocean ridges where the lithosphere is thin and the effect of plumes is best revealed. While ocean ridges are mostly passive features in terms of plate tectonics, they play an active role in the context of plume-ridge interactions. This active role is a ridge suction force that drives asthenospheric mantle flow towards ridges because of material needs to form the ocean crust at ridges and lithospheric mantle in the vicinity of ridges. This ridge suction force increases with increasing plate separation rate because of increased material demand per unit time. As the seismic low-velocity zone atop the asthenosphere has the lowest viscosity that increases rapidly with depth, the ridge-ward asthenospheric flow is largely horizontal beneath the lithosphere. Recognizing that plume materials have two components with easily-melted dikes/veins enriched in volatiles and incompatible elements dispersed in the more refractory and depleted peridotitic matrix, geochemistry of some seafloor volcanics well illustrates that plume-ridge interactions are consequences of ridge-suction-driven flow of plume materials, which melt by decompression because of lithospheric thinning towards ridges. There are excellent examples: 1. The decreasing La/Sm and increasing MgO and CaO/Al_2O_3 in Easter Seamount lavas from Salas-y-Gomez Islands to the Easter Microplate East rift zone result from progressive decompression melting of ridge-ward flowing plume materials. 2. The similar geochemical observations in lavas along the Foundation hotline towards the Pacific-Antarctic Ridge result from the same process. 3. The increasing ridge suction force with increasing spreading rate explains why the Iceland plume has asymmetric effects on its neighboring ridges: both topographic and

  20. Structure of the Juan de Fuca Plate and Washington Forearc from 2D Travel Time Tomography of OBS and Land Seismometer Data along and East-West Transect

    NASA Astrophysics Data System (ADS)

    Carton, H. D.; Canales, J.; Janiszewski, H. A.; Carbotte, S. M.; Abers, G. A.; Trehu, A. M.; Nedimovic, M. R.

    2013-12-01

    In the summer of 2012 an offshore-onshore active source experiment was conducted spanning the Juan de Fuca plate and transecting the Cascadia margin at two locations. Two plate-scale transects offshore Oregon and Washington were designed to characterize the structure and evolution of the oceanic crust and uppermost mantle as the plate ages from formation at the Juan de Fuca Ridge to subduction at the Cascadia trench. They will provide evidence on how and where incorporation of water is taking place, and, further into the subduction zone, they will provide information on forearc structure and the subducting crust as it begins to dewater beneath the megathrust. Along the northern transect, airgun shots from R/V Lanseth's 6600 cu in array were fired at an interval of 500 m from the Endeavour segment on the Juan de Fuca Ridge to the 1000 m water depth contour on the wide accretionary wedge off Grays Harbor. These shots were recorded on 22 Ocean Bottom Seismometers (OBS) at ~15 km spacing along track and 15 land stations deployed in an ~140 km long east-west corridor in Washington. Two other sets of shots, at 37.5 m interval on the oceanic plate, and at 50 m interval on the wedge and shelf ~14-78 km from shore (thus extending shooting landward), were also recorded on the 15 land stations, and provide data that are easier to pick. Arrivals can be identified out of to a maximum of ~100 km on OBSs located on the oceanic plate and accretionary wedge, and a maximum of ~140 km on the land instruments. The two OBSs closest to shore (< 300 m water depth) returned noisy data and/or had issues. So far first arrivals (Psed, Pg and Pn) have been picked on the OBS gathers, which also show clear PmP phases. We will present two-dimensional P-wave travel time tomography results using the onshore-offshore wide-angle data from this northern transect.

  1. Detail of the ridge framing of the clerestory roof, note ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Detail of the ridge framing of the clerestory roof, note the alternating wood and steel beams, view facing northeast - U.S. Marine Corps Base Hawaii, Kaneohe Bay, Warehouse 250, Aviation Storehouse, C Street between Fifth & Sixth Streets, Kaneohe, Honolulu County, HI

  2. Multi-mode conversion imaging of the subducted Gorda and Juan de Fuca plates below the North American continent

    NASA Astrophysics Data System (ADS)

    Tauzin, Benoit; Bodin, Thomas; Debayle, Eric; Perrillat, Jean-Philippe; Reynard, Bruno

    2016-04-01

    Receiver function analysis and seismic tomography show tectonic structures dipping eastward in the mantle below the Cascadia volcanic arc (western US) that have been related to the subduction of the Gorda and Juan de Fuca oceanic micro-plates. Inconsistencies in the dip angle and depth extent of the slab between the two methods undermine the interpretation of the structure and processes at work. Receiver function imaging is biased by multiple reflection phases that interfere with converted phases, and produce spurious discontinuities in images. Here, we correct the interference using a multiple mode conversion imaging technique that efficiently removes artifacts under dipping structures. The method has the advantage of being applicable to large aperture arrays, and can image large-scale structures down to the transition zone. With this approach, the interfaces between the subducting and overriding plates and the oceanic Moho are imaged at shallow depths (<120 km) with a dip angle of ∼20°, consistently with former studies. In addition, several important features are imaged with the present method. Faint converters located between 100 and 400 km depth in the mantle wedge, and strong sub-horizontal seismic scatterers near 160 km depth, may highlight dehydration and metasomatism processes in the Cascadia subduction zone. A discontinuity located at ∼15 km depth in the lithospheric mantle of the subducted plates and associated with a negative impedance contrast is interpreted as the fossil fabric of the plates acquired at the spreading ridges.

  3. Geochemical Diversity of Near-Ridge Seamounts: Insights into Oceanic Magmatic Processes and Sources

    NASA Astrophysics Data System (ADS)

    Baxter, N. L.; Perfit, M. R.; Wendt, R. E.; Lundstrom, C.; Clague, D. A.

    2009-12-01

    Geochemical studies of lavas erupted at seamounts that form in close proximity to active mid-ocean ridges provide an opportunity to better understand the composition of shallow mantle underneath spreading ridges and how it melts in order to form new oceanic crust. This is because while on-axis samples mostly reflect homogenization of melts within the axial magma lens, seamount lavas bypass this process providing a window into the diversity of melts produced in the melting column. We have analyzed lavas from small near-axis seamounts and two larger near-ridge seamount chains for trace elements and Sr-Nd-Pb isotopes: the Lamont Seamounts adjacent to the East Pacific Rise (EPR) ~ 10°N and the Vance Seamounts next to the Juan de Fuca Ridge (JdFR) ~45°N. One purpose of the study is to test the hypothesis that near ridge seamount chains reflect focusing of melts by dunite channels in the upwelling asthenospheric mantle and that such conduits might affect melting in the shallow mantle (Lundstrom et al., 2000). Our results indicate that lavas from these seamounts have incompatible trace element patterns varying from very depleted to moderately enriched (found at the oldest, most distant Vance seamounts) relative to typical mid-ocean ridge basalts (MORB). Trace element compositions and Sr-Nd-Pb isotope data show that lava compositions vary significantly between seamounts in the chain as well as within individual seamounts. Overall, the Vance and Lamont seamount lavas are more primitive and diverse than associated ridge samples. These variations can be explained by multiple sources as well as different extents of melting, and are unlikely to reflect shallow level fractional crystallization. Sr-Nd-Pb isotope data also indicate some mixing between mantle end members. The significant variations in incompatible trace element and isotopic compositions that are somewhat correlated suggest that the mantle underneath the seamounts is heterogeneous on a small scale. The fact that

  4. Incidence of novel and potentially archaeal nitrogenase genes in the deep Northeast Pacific Ocean.

    PubMed

    Mehta, Mausmi P; Huber, Julie A; Baross, John A

    2005-10-01

    Archaea have been detected throughout the oceanic water column and are quantitatively important members of picoplankton in the deep ocean. Two common groups, group I Crenarchaeota and group II Euryarchaeota, are consistently detected in warm hydrothermal fluid and are assumed to have been drawn into the subseafloor, mixed with hydrothermal fluid and then expelled. However, because they remain resistant to cultivation, very little is known about their physiology. Here we show that cold deep-seawater from the axial valley of Endeavour Segment on the Juan de Fuca Ridge contains not only groups I and II archaea as expected, but also unique potentially archaeal nitrogenase (nifH) genes, which are required for nitrogen fixation. These nifH genes are phylogenetically distinct and have dissimilar G+C content compared with those of hydrothermal vent archaea, suggesting that they belong to non-thermophilic deep-sea archaea. Furthermore, this sample did not contain mcrA genes, which are present in methanogens, the only known archaeal nitrogen fixers. These nifH genes were not detected in upper water column samples, or in a deep-seawater sample 100 km away from the spreading axis of the Juan de Fuca Ridge. We propose that these unique nifH genes may be localized to archaea that circulate through the nitrogen-poor subseafloor at the mid-ocean ridge as part of their life cycle.

  5. Grafts for Ridge Preservation

    PubMed Central

    Jamjoom, Amal; Cohen, Robert E.

    2015-01-01

    Alveolar ridge bone resorption is a biologic phenomenon that occurs following tooth extraction and cannot be prevented. This paper reviews the vertical and horizontal ridge dimensional changes that are associated with tooth extraction. It also provides an overview of the advantages of ridge preservation as well as grafting materials. A Medline search among English language papers was performed in March 2015 using alveolar ridge preservation, ridge augmentation, and various graft types as search terms. Additional papers were considered following the preliminary review of the initial search that were relevant to alveolar ridge preservation. The literature suggests that ridge preservation methods and augmentation techniques are available to minimize and restore available bone. Numerous grafting materials, such as autografts, allografts, xenografts, and alloplasts, currently are used for ridge preservation. Other materials, such as growth factors, also can be used to enhance biologic outcome. PMID:26262646

  6. Ridge Regression: A Panacea?

    ERIC Educational Resources Information Center

    Walton, Joseph M.; And Others

    1978-01-01

    Ridge regression is an approach to the problem of large standard errors of regression estimates of intercorrelated regressors. The effect of ridge regression on the estimated squared multiple correlation coefficient is discussed and illustrated. (JKS)

  7. 33 CFR 167.1303 - In the approaches to the Strait of Juan de Fuca: Precautionary area “JF.”

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... of Juan de Fuca: Precautionary area âJF.â 167.1303 Section 167.1303 Navigation and Navigable Waters....1303 In the approaches to the Strait of Juan de Fuca: Precautionary area “JF.” In the approaches to the Strait of Juan de Fuca, precautionary area “JF” is established and is bounded by a line connecting...

  8. 33 CFR 167.1303 - In the approaches to the Strait of Juan de Fuca: Precautionary area “JF.”

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... of Juan de Fuca: Precautionary area âJF.â 167.1303 Section 167.1303 Navigation and Navigable Waters....1303 In the approaches to the Strait of Juan de Fuca: Precautionary area “JF.” In the approaches to the Strait of Juan de Fuca, precautionary area “JF” is established and is bounded by a line connecting...

  9. 33 CFR 167.1303 - In the approaches to the Strait of Juan de Fuca: Precautionary area “JF.”

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... of Juan de Fuca: Precautionary area âJF.â 167.1303 Section 167.1303 Navigation and Navigable Waters....1303 In the approaches to the Strait of Juan de Fuca: Precautionary area “JF.” In the approaches to the Strait of Juan de Fuca, precautionary area “JF” is established and is bounded by a line connecting...

  10. 33 CFR 167.1303 - In the approaches to the Strait of Juan de Fuca: Precautionary area “JF.”

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... of Juan de Fuca: Precautionary area âJF.â 167.1303 Section 167.1303 Navigation and Navigable Waters....1303 In the approaches to the Strait of Juan de Fuca: Precautionary area “JF.” In the approaches to the Strait of Juan de Fuca, precautionary area “JF” is established and is bounded by a line connecting...

  11. Dive report: Alvin dive #1461; September 28, 1984 (JD 272); Plume site, southern Juan de Fuca Rift

    USGS Publications Warehouse

    Holcomb, R.T.; Kappel, Ellen S.; Ross, Stephanie L.

    1987-01-01

    Dive 1461 was the seventh of nine dives during a sea-going field program to investigate hydrothermal activity along the crest of the southern Juan de Fuca Ridge. During this dive on the Plume site, ALVIN crossed the western floor of the axial valley and traversed about 300 ra of the rim and floor of the narrow inner cleft. Hydrotherraal vents were observed only along the east wall of the inner cleft, and venting was concentrated in a single area less than 50 ra long near the base of that wall. The principal vents extended up the wall from the floor of the cleft to a height of about 10 m. Deposits of hydrothermal minerals occur as incrustations and chimneys on the floor and wall of the cleft. Associated with the hydrothermal vents is a community of vent organisms dominated by vestimentiferan worms and fluffy materials of uncertain nature. The inner cleft at the Plume Site is about 60 ra wide and 15-30 m deep. It has a simple U-shaped profile north of the active vent area, but to the south it contains at least one high, narrow ridge which converges with the east wall of the cleft at the site of hydrothermal venting. This area was also the site of a volcanic eruption, which occurred sometime earlier. Like many similar but subaerial examples, this eruption was episodic, but the cause of its interruptions is not yet known. The present hydrotherraal activity appears to be a residual effect of that last eruption, and the rate of hydrothermal deposition will probably decline in this area until another eruption occurs.

  12. 33 CFR 334.1180 - Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 33 Navigation and Navigable Waters 3 2014-07-01 2014-07-01 false Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. 334.1180 Section 334.1180 Navigation and Navigable... REGULATIONS § 334.1180 Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. (a) The...

  13. 33 CFR 334.1180 - Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 3 2011-07-01 2011-07-01 false Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. 334.1180 Section 334.1180 Navigation and Navigable... REGULATIONS § 334.1180 Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. (a) The...

  14. 33 CFR 334.1180 - Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 3 2012-07-01 2012-07-01 false Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. 334.1180 Section 334.1180 Navigation and Navigable... REGULATIONS § 334.1180 Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. (a) The...

  15. 33 CFR 334.1180 - Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 3 2013-07-01 2013-07-01 false Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. 334.1180 Section 334.1180 Navigation and Navigable... REGULATIONS § 334.1180 Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. (a) The...

  16. 46 CFR 7.145 - Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 1 2014-10-01 2014-10-01 false Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA. 7.145 Section 7.145 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY PROCEDURES APPLICABLE TO THE PUBLIC BOUNDARY LINES Pacific Coast § 7.145 Strait of Juan de Fuca, Haro Strait and...

  17. 46 CFR 7.145 - Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 1 2013-10-01 2013-10-01 false Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA. 7.145 Section 7.145 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY PROCEDURES APPLICABLE TO THE PUBLIC BOUNDARY LINES Pacific Coast § 7.145 Strait of Juan de Fuca, Haro Strait and...

  18. 46 CFR 7.145 - Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 1 2012-10-01 2012-10-01 false Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA. 7.145 Section 7.145 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY PROCEDURES APPLICABLE TO THE PUBLIC BOUNDARY LINES Pacific Coast § 7.145 Strait of Juan de Fuca, Haro Strait and...

  19. 33 CFR 334.1180 - Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 3 2010-07-01 2010-07-01 false Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. 334.1180 Section 334.1180 Navigation and Navigable... REGULATIONS § 334.1180 Strait of Juan de Fuca, Wash.; air-to-surface weapon range, restricted area. (a)...

  20. 75 FR 70818 - Traffic Separation Schemes: In the Strait of Juan de Fuca and Its Approaches; in Puget Sound and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-19

    ... sight-obscured, right-angle turn in the presence of strong currents and numerous small craft. 7... Fuca and Its Approaches; in Puget Sound and Its Approaches; and in Haro Strait, Boundary Pass, and the... Strait of Juan de Fuca and its approaches, in Puget Sound and its approaches, and in Haro Strait...

  1. Geophysical Investigation of Australian-Antarctic Ridge Using High-Resolution Gravity and Bathymetry

    NASA Astrophysics Data System (ADS)

    Kim, S. S.; Lin, J.; Park, S. H.; Choi, H.

    2015-12-01

    Much of the Australian-Antarctic Ridge (AAR) has been remained uncharted until 2011 because of its remoteness and harsh weather conditions. From 2011, the multidisciplinary ridge program initiated by the Korea Polar Research Institute (KOPRI) surveyed the little-explored eastern ends of the AAR to characterize the tectonics, geochemistry, and hydrothermal activity of this intermediate spreading system. In this study, we present a detailed analysis of a 300-km-long supersegment of the AAR to quantify the spatial variations in ridge morphology and axial and off-axis volcanisms as constrained by high-resolution shipboard bathymetry and gravity. The ridge axis morphology alternates between rift valleys and axial highs within relatively short ridge segments. To obtain a geological proxy for regional variations in magma supply, we calculated residual mantle Bouguer gravity anomalies (RMBA), gravity-derived crustal thickness, and residual topography for neighboring seven sub-segments. The results of the analyses revealed that the southern flank of the AAR is associated with shallower seafloor, more negative RMBA, thicker crust, and/or less dense mantle in comparison to the conjugate northern flank. Furthermore, this north-south asymmetry becomes more prominent toward the KR1 supersegment of the AAR. The axial topography of the KR1 supersegment exhibits a sharp transition from axial highs at the western end to rift valleys at the eastern end, with regions of axial highs being associated with more robust magma supply as indicated by more negative RMBA. We also compare and contrast the characteristics of the AAR supersegment with that of other ridges of intermediate spreading rates, including the Juan de Fuca Ridge, Galápagos Spreading Center, and Southeast Indian Ridge west of the Australian-Antarctic Discordance, to investigate the influence of ridge-hotspot interaction on ridge magma supply and tectonics.

  2. On the dynamics of current jets trapped to the flanks of mid-ocean ridges

    NASA Astrophysics Data System (ADS)

    Lavelle, J. W.

    2012-07-01

    Time-mean abyssal current observations over the flanks of the East Pacific Rise (EPR) at 9-10°N and at the Juan de Fuca Ridge at 45°N document the occurrence of paired along-ridge current jets that are trapped to the ridge flanks and sheared across the ridge in an anticyclonic sense. A coincident feature, where local hydrothermal discharge effects are not in play, is the upward bowing of isopycnals over ridge crests and isopycnals plunging into ridge flanks. It would be tempting to explain the jets primarily as geostrophic responses to the doming/plunging isopycnal distribution, though that should lead to the question as to how the isopycnal perturbations originate. A numerical model of time-dependent flow on a cross-ridge (x-z) transect, forced in a way to be consistent with a yearlong, hourly sampled record of currents measured at the EPR ridge crest, is used to investigate some of the underlying physics. It will be shown that the jets can arise from oscillatory flows via eddy-momentum, eddy-heat, and eddy-salt fluxes that ultimately cause the isopycnals to dome over the ridge. As the probable offspring of velocity-velocity and velocity-density correlations that depend upon oscillatory motion, the jets are likely examples of stratified topographic flow rectification. An ancillary feature is a slight yearlong-averaged downward current O (0.1-0.5 mm/s) over the EPR ridge crest that crosses the time-mean, upward bowing isopycnals in a counter-intuitive vertical direction.

  3. How simple is the oceanic asthenosphere? Seismological insights for the Juan de Fuca and Gorda plates from Cascadia Initiative and Blanco Experiment data

    NASA Astrophysics Data System (ADS)

    Byrnes, J. S.

    2015-12-01

    'Normal' oceanic asthenosphere is often assumed to be homogeneous unless perturbed by spreading at mid-ocean ridges, and to flow in response to the overriding plate. Here, we show seismological data that reveal a complex asthenosphere beneath the Juan de Fuca (JdF) and Gorda plates. We present mantle tomographic images using teleseismic S phases and shear-wave splitting measurements of SKS phases using OBS data recorded during the Cascadia Initiative (CI) and Blanco Experiment. Beneath the JdF plate, Vs in the upper 200 km of the mantle is ~5% faster beneath ~10 Myr lithosphere than near the ridge. In the Jdf plate interior, fast polarization directions from shear-wave splitting broadly correlate with absolute plate motion. Beneath the Gorda plate, in contrast, Vs varies only weakly with lithospheric age. Fast polarization directions are aligned with JdF-Pacific relative plate motion over a broad region and do not vary near the Gorda ridge. We also show that low Vs regions beneath three mid-ocean ridges (JdF, Gorda, and southern East Pacific Rise) are asymmetric with respect to the ridge axis. These results indicate that the evolution of the asthenosphere differs beneath the JdF and the Gorda plates. The large increase of Vs beneath the JdF plate is much greater than the predicted ~2% change due to conductive cooling of the lithosphere, and we explore possible explanations for this large degree of heterogeneity. The weak variations in Vs near the Gorda ridge are also not well explained by conductive cooling. The broad region of low Vs could be due to melt retention or to grain size reduction in a shear-zone. Finally, models of mantle upwelling suggest that the asymmetries in Vs with respect to the ridge axes likely require an asymmetric region of upwelling in the presence of pre-existing heterogeneity in the asthenosphere. We suggest that interactions with plate boundaries and heterogeneity may create an active and complex asthenosphere.

  4. Evidence for microbial carbon and sulfur cycling in deeply buried ridge flank basalt.

    PubMed

    Lever, Mark A; Rouxel, Olivier; Alt, Jeffrey C; Shimizu, Nobumichi; Ono, Shuhei; Coggon, Rosalind M; Shanks, Wayne C; Lapham, Laura; Elvert, Marcus; Prieto-Mollar, Xavier; Hinrichs, Kai-Uwe; Inagaki, Fumio; Teske, Andreas

    2013-03-15

    Sediment-covered basalt on the flanks of mid-ocean ridges constitutes most of Earth's oceanic crust, but the composition and metabolic function of its microbial ecosystem are largely unknown. By drilling into 3.5-million-year-old subseafloor basalt, we demonstrated the presence of methane- and sulfur-cycling microbes on the eastern flank of the Juan de Fuca Ridge. Depth horizons with functional genes indicative of methane-cycling and sulfate-reducing microorganisms are enriched in solid-phase sulfur and total organic carbon, host δ(13)C- and δ(34)S-isotopic values with a biological imprint, and show clear signs of microbial activity when incubated in the laboratory. Downcore changes in carbon and sulfur cycling show discrete geochemical intervals with chemoautotrophic δ(13)C signatures locally attenuated by heterotrophic metabolism.

  5. Ambient light emission from hydrothermal vents on the Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    White, Sheri N.; Chave, Alan D.; Reynolds, George T.; Van Dover, Cindy L.

    2002-08-01

    A spectral imaging camera was used to observe light emission from high-temperature, deep-sea vents at three hydrothermal sites on the Mid-Atlantic Ridge (MAR): Logatchev, Snake Pit, and Lucky Strike. Ambient light measured at these sites is similar to that observed at sites along the East Pacific Rise and the Juan de Fuca Ridge, with components from both thermal and non-thermal sources. The shrimp species Rimicaris exoculata, which is found on the MAR but not in the Eastern Pacific, possesses a unique photoreceptor capable of detecting low light levels. It is not yet known if R. exoculata ``sees'' vent light. However, since the characteristics of vent light appear to be unrelated to geographical location, the exclusion of R. exoculata from the Eastern Pacific is probably unrelated to differences in ambient light conditions.

  6. Evidence for microbial carbon and sulfur cycling in deeply buried ridge flank basalt

    USGS Publications Warehouse

    Lever, Mark A.; Rouxel, Olivier; Alt, Jeffrey C.; Shimizu, Nobumichi; Ono, Shuhei; Coggon, Rosalind M.; Shanks, Wayne C.; Lapham, Laura; Elvert, Marcus; Prieto-Mollar, Xavier; Hinrichs, Kai-Uwe; Inagaki, Fumio; Teske, Andreas

    2013-01-01

    Sediment-covered basalt on the flanks of mid-ocean ridges constitutes most of Earth's oceanic crust, but the composition and metabolic function of its microbial ecosystem are largely unknown. By drilling into 3.5-million-year-old subseafloor basalt, we demonstrated the presence of methane- and sulfur-cycling microbes on the eastern flank of the Juan de Fuca Ridge. Depth horizons with functional genes indicative of methane-cycling and sulfate-reducing microorganisms are enriched in solid-phase sulfur and total organic carbon, host δ13C- and δ34S-isotopic values with a biological imprint, and show clear signs of microbial activity when incubated in the laboratory. Downcore changes in carbon and sulfur cycling show discrete geochemical intervals with chemoautotrophic δ13C signatures locally attenuated by heterotrophic metabolism.

  7. Beryllium 10 in hydrothermal vent deposits from the East Pacific Ridges: Role of sediments in the hydrothermal processes

    SciTech Connect

    Valette-Silver, J.N.; Tera, F.; Klein, J.; Middleton, R.

    1987-10-10

    Beryllium 10 concentrations were determined for 31 handpicked hydrothermal sulfides, six oxyhydroxides, seven basalts, and five sediments collected from the hydrothermally active areas of the East Pacific ridges. The samples includes specimens from the East Pacific Rise (EPR) at 21 /sup 0/N and 13 /sup 0/N, the Galapagos Rift, the Guaymas Basin, and the Gorda and the Juan de Fuca ridges. Additional samples from massive sulfides associated with the Oman ophiolites were studied. In all samples, we obtained values ranging from 0.04 x 10/sup 6/ atoms/g to 125 x 10/sup 6/ atoms/g, with the lowest values being very close to our blank (0.015 x 10/sup 6/ atoms/g). The data show systematic variations with sample location and type. The /sup 10/Be concentrations measured for the mid-ocean basalts are of the order of 0.3 x 10/sup 6/ atoms/g and reach 3800 x 10/sup 6/ atoms/g for the pelagic deep-sea sediments collected near the EPR 21 /sup 0/N. Based on their /sup 10/Be concentrations, we can clearly distinguish two categories of sulfides: sulfides containing low /sup 10/Be concentration (<10 /sup 6/ atoms/g) sitting directly on the mid-ocean basalt (EPR of Juan de Fuca), and sulfides with high /sup 10/Be concentration (>10/sup 6/ atoms/g) located atop of a thick pile of young sediments (Guaymas Basin or Gorda Ridge).

  8. Segmentation of mid-ocean ridges attributed to oblique mantle divergence

    NASA Astrophysics Data System (ADS)

    Vanderbeek, Brandon P.; Toomey, Douglas R.; Hooft, Emilie E. E.; Wilcock, William S. D.

    2016-08-01

    The origin of mid-ocean ridge segmentation--the systematic along-axis variation in tectonic and magmatic processes--remains controversial. It is commonly assumed that mantle flow is a passive response to plate divergence and that between transform faults magma supply controls segmentation. Using seismic tomography, we constrain the geometry of mantle flow and the distribution of mantle melt beneath the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge. Our results, in combination with prior studies, establish a systematic skew between the mantle-divergence and plate-spreading directions. In all three cases studied, mantle divergence is advanced with respect to recent changes in the plate-spreading direction and the extent to which the flow field is advanced increases with decreasing spreading rate. Furthermore, seismic images show that large-offset, non-transform discontinuities are regions of enhanced mantle melt retention. We propose that oblique mantle flow beneath mid-ocean ridges is a driving force for the reorientation of spreading segments and the formation of ridge-axis discontinuities. The resulting tectonic discontinuities decrease the efficiency of upward melt transport, thus defining segment-scale variations in magmatic processes. We predict that across spreading rates mid-ocean ridge segmentation is controlled by evolving patterns in asthenospheric flow and the dynamics of lithospheric rifting.

  9. A 2-D tomographic model of the Juan de Fuca plate from accretion at axial seamount to subduction at the Cascadia margin from an active source ocean bottom seismometer survey

    NASA Astrophysics Data System (ADS)

    Horning, G.; Canales, J. P.; Carbotte, S. M.; Han, S.; Carton, H.; Nedimović, M. R.; van Keken, P. E.

    2016-08-01

    We report results from a wide-angle controlled source seismic experiment across the Juan de Fuca plate designed to investigate the evolution of the plate from accretion at the Juan de Fuca ridge to subduction at the Cascadia margin. A two-dimensional velocity model of the crust and upper mantle is derived from a joint reflection-refraction traveltime inversion. To interpret our tomography results, we first generate a plausible baseline velocity model, assuming a plate cooling model and realistic oceanic lithologies. We then use an effective medium theory to infer from our tomography results the extent of porosity, alteration, and water content that would be required to explain the departure from the baseline model. In crust of ages >1 Ma and away from propagator wakes and regions of faulting due to plate bending, we obtain estimates of upper crustal hydration of 0.5-2.1 wt % and find mostly dry lower crust and upper mantle. In sections of the crust affected by propagator wakes we find upper estimates of upper crustal, lower crustal, and upper mantle hydration of 3.1, 0.8, and 1.8 wt %, respectively. At the Cascadia deformation front, we find that the amount of water stored at uppermost mantle levels in the downgoing JdF plate is very limited (<0.3 wt %), with most of the water carried into the subduction zone being stored in the oceanic crust.

  10. Crustal Assimilation and the Petrogenesis of Mid-Ocean Ridge Dacites

    NASA Astrophysics Data System (ADS)

    Wanless, V.; Perfit, M. R.; Ridley, W. I.; Klein, E. M.; Grimes, C. B.; Valley, J. W.

    2010-12-01

    The majority of eruptions at spreading centers produce lavas with relatively homogeneous mid-ocean ridge basalt (MORB) compositions, but andesitic and dacitic lavas have been sampled at several different mid-ocean ridges (MOR). Eruption of high-silica lavas are commonly associated with ridge discontinuities, examples being propagating ridge tips at ridge-transform intersections on the Juan de Fuca Ridge and eastern Galápagos spreading center, and at the 9°N overlapping spreading center on the East Pacific Rise. Although these lavas are found at different ridges, the dacites show remarkably similar major element trends and incompatible trace element enrichments, suggesting that similar processes control their formation. Although most geochemical variability in the MOR series basalts -ferrobasalts - FeTi basalts is consistent with low-pressure fractional crystallization, modeling suggests that extreme fractional crystallization accompanied by partial melting and assimilation of amphibole-bearing altered oceanic crust is important in the petrogenesis of high-silica differentiates. Such a complex process is consistent with dacites showing: 1) elevated U, Th, Zr, and Hf; 2) relatively low Nb and Ta; 3) Al2O3, K2O, Cl, H2O concentrations that are higher than expected from fractional crystallization; 4) relatively low δ18O glass values of ~5.6 compared to values ~6.9 ‰ expected from fractional crystallization. This suggests that crustal assimilation is an important process in the formation of highly evolved MOR lavas (i.e., andesites and dacites) and may be significant in formation of MORB in general. Although basaltic material at MOR is much more voluminous than high-silica lavas, the eruption of dacites at numerous ridges, and the seemingly ubiquitous presence of plagiogranite veins in exposed and drilled sections of gabbroic Layer 3 indicate that high-silica lavas are an intrinsic component of the ocean crust, though their petrogenesis may involve various

  11. Structure of the Lithosphere-Asthenosphere System Beneath the Juan de Fuca Plate: Results of Body Wave Imaging Using Cascadia Initiative Data

    NASA Astrophysics Data System (ADS)

    Byrnes, J. S.; Toomey, D. R.; Hooft, E. E. E.

    2014-12-01

    The plate-scale deployment of ocean bottom seismometers (OBS) as part of the Cascadia Initiative (CI) of NSF provides a unique opportunity to study the structure and dynamics of the lithosphere-asthenosphere system beneath an entire oceanic plate, from its birth at a spreading center to its subduction beneath a continent. Here we present tomographic images of the seismic structure of oceanic upper mantle beneath the Juan de Fuca (JdF) and Gorda plates derived from body wave delay times. The results constrain structural anomalies beneath the JdF and Gorda spreading centers, the Blanco and Mendocino transform faults, near ridge hotspots such as Axial Seamount, and the upper mantle structure beneath the subducting oceanic lithosphere. We measured delay times of teleseismic P and S wave phases for the first two years of the CI. Our tomographic analysis assumes both isotropic and anisotropic starting models and accounts for finite-frequency effects and three-dimensional ray bending. Preliminary results indicate that the upper mantle structure beneath the JdF spreading center is asymmetric, with lower shear wave velocities beneath the Pacific plate (also the direction of ridge migration). On a regional scale, regions of lower seismic velocities beneath the JdF and Gorda spreading centers correlate with shallower ridge depths. Beneath the southern Gorda plate a low velocity anomaly is detected, which is absent to the north; this anomaly is bounded to the south by the Mendocino transform. Ongoing work includes analysis of the third year of CI data, which will improve resolution of structure and allow better definition of anomalies in the vicinity of the Blanco transform. In addition, we will combine ocean and continental data to obtain images of the Cascadia subduction zone.

  12. Fine-Branched Ridges

    NASA Image and Video Library

    2015-10-14

    This image from NASA Mars Reconnaissance Orbiter spacecraft shows numerous branching ridges with various degrees of sinuosity. These branching forms resemble tributaries funneling and draining into larger channel trunks towards the upper portion of the scene. The raised relief of these branching ridges suggests that these are ancient channels are inverted due to lithification and cementation of the riverbed sediment, which made it more resistant to erosion than the surrounding material. Wind-blown bedforms are abundant and resemble small ridges that are aligned in an approximately north-south direction. http://photojournal.jpl.nasa.gov/catalog/PIA20006

  13. Geochemistry of manganese in the northeast Pacific Ocean off Washington

    SciTech Connect

    Jones, C.J.; Murray, J.W.

    1985-01-01

    Water collected along a transect normal to the coast of Washington was analyzed for dissolved and total dissolvable manganese (TDM). The vertical profiles exhibit the same general features observed elsewhere in the Pacific, but a horizontal section of the transect shows that concentrations increase markedly toward the continental margin. A surface maximum is probably due to fluvial inputs, especially from the Columbia River. Another possible source is the upwelling of manganese-enriched bottom water over the shelf. Horizontal gradients are also observed in the oxygen minimum as manganese concentrations decrease from the continental slope to open ocean water. Porewater and solid phase data suggest that manganese is being actively remobilized under reducing conditions in the slope sediments and is diffusing into the overlying seawater at a rate sufficient to balance losses by vertical mixing and particulate scavenging. Two stations on opposite sides of the Juan de Fuca Ridge have deep concentration maxima that are almost certainly due to injections of hydrothermal vent fluid along the ridge.

  14. Precise relative locations for earthquakes in the northeast Pacific region

    DOE PAGES

    Cleveland, K. Michael; VanDeMark, Thomas F.; Ammon, Charles J.

    2015-10-09

    We report that double-difference methods applied to cross-correlation measured Rayleigh wave time shifts are an effective tool to improve epicentroid locations and relative origin time shifts in remote regions. We apply these methods to seismicity offshore of southwestern Canada and the U.S. Pacific Northwest, occurring along the boundaries of the Pacific and Juan de Fuca (including the Explorer Plate and Gorda Block) Plates. The Blanco, Mendocino, Revere-Dellwood, Nootka, and Sovanco fracture zones host the majority of this seismicity, largely consisting of strike-slip earthquakes. The Explorer, Juan de Fuca, and Gorda spreading ridges join these fracture zones and host normal faultingmore » earthquakes. Our results show that at least the moderate-magnitude activity clusters along fault strike, supporting suggestions of large variations in seismic coupling along oceanic transform faults. Our improved relative locations corroborate earlier interpretations of the internal deformation in the Explorer and Gorda Plates. North of the Explorer Plate, improved locations support models that propose northern extension of the Revere-Dellwood fault. Relocations also support interpretations that favor multiple parallel active faults along the Blanco Transform Fault Zone. Seismicity of the western half of the Blanco appears more scattered and less collinear than the eastern half, possibly related to fault maturity. We use azimuthal variations in the Rayleigh wave cross-correlation amplitude to detect and model rupture directivity for a moderate size earthquake along the eastern Blanco Fault. Lastly, the observations constrain the seismogenic zone geometry and suggest a relatively narrow seismogenic zone width of 2 to 4 km.« less

  15. Precise relative locations for earthquakes in the northeast Pacific region

    SciTech Connect

    Cleveland, K. Michael; VanDeMark, Thomas F.; Ammon, Charles J.

    2015-10-09

    We report that double-difference methods applied to cross-correlation measured Rayleigh wave time shifts are an effective tool to improve epicentroid locations and relative origin time shifts in remote regions. We apply these methods to seismicity offshore of southwestern Canada and the U.S. Pacific Northwest, occurring along the boundaries of the Pacific and Juan de Fuca (including the Explorer Plate and Gorda Block) Plates. The Blanco, Mendocino, Revere-Dellwood, Nootka, and Sovanco fracture zones host the majority of this seismicity, largely consisting of strike-slip earthquakes. The Explorer, Juan de Fuca, and Gorda spreading ridges join these fracture zones and host normal faulting earthquakes. Our results show that at least the moderate-magnitude activity clusters along fault strike, supporting suggestions of large variations in seismic coupling along oceanic transform faults. Our improved relative locations corroborate earlier interpretations of the internal deformation in the Explorer and Gorda Plates. North of the Explorer Plate, improved locations support models that propose northern extension of the Revere-Dellwood fault. Relocations also support interpretations that favor multiple parallel active faults along the Blanco Transform Fault Zone. Seismicity of the western half of the Blanco appears more scattered and less collinear than the eastern half, possibly related to fault maturity. We use azimuthal variations in the Rayleigh wave cross-correlation amplitude to detect and model rupture directivity for a moderate size earthquake along the eastern Blanco Fault. Lastly, the observations constrain the seismogenic zone geometry and suggest a relatively narrow seismogenic zone width of 2 to 4 km.

  16. Mars Rover Opportunity Panorama of Wharton Ridge

    NASA Image and Video Library

    2016-10-07

    This scene from NASA's Mars Exploration Rover Opportunity shows "Wharton Ridge," which forms part of the southern wall of "Marathon Valley" on the western rim of Endeavour Crater. The full extent of Wharton Ridge is visible, with the floor of Endeavour Crater beyond it and the far wall of the crater in the distant background. Near the right edge of the scene is "Lewis and Clark Gap," through which Opportunity crossed from Marathon Valley to "Bitterroot Valley" in September 2016. Before the rover departed Marathon Valley, its panoramic camera (Pancam) acquired the component images for this scene on Aug. 30, 2016, during the 4,480th Martian day, or sol, of Opportunity's work on Mars. Opportunity's science team chose the ridge's name to honor the memory of Robert A. Wharton (1951-2012), an astrobiologist who was a pioneer in the use of terrestrial analog environments, particularly in Antarctica, to study scientific problems connected to the habitability of Mars. Over the course of his career, he was a visiting senior scientist at NASA Headquarters, vice president for research at the Desert Research Institute, provost at Idaho State University, and president of the South Dakota School of Mines and Technology. The view spans from east-northeast at left to southeast at right. It merges exposures taken through three of the Pancam's color filters, centered on wavelengths of 753 nanometers (near-infrared), 535 nanometers (green) and 432 nanometers (violet). It is presented in approximately true color. http://photojournal.jpl.nasa.gov/catalog/PIA20849

  17. Heat flow in the flanks of the Oceanographer-Hayes segment of the Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Le Gal, V.; Lucazeau, F.; Cannat, M.; Battani, A.; Poort, J.; Guichet, X.; Monnin, C.; Fontaine, F. J.; Leroy, S. D.

    2016-12-01

    It is currently estimated that a third of the oceanic heat loss is due to fluid circulation in the oceanic crust. Besides high and low temperature fluid discharge at ridge axis, off-axis low temperature fluid circulations can affect large volumes of the oceanic crust. Long term investigations of the Eastern Juan de Fuca ridge flank (Hutnak et al.2006) have established a circulation pattern where hydrothermal discharge and recharge occur at basement outcrops and where sediment is mostly impermeable. Here, we present results from the recent Oceanograflu cruise (2013), on the Oceanographer-Hayes segment ridge flanks of the Mid-Atlantic ridge in crust 5 and 12 myrs in age. On both flanks, we obtained 185 temperature gradients and conductivities in-situ, 30 Küllenberg cores (3 to 5 meters long) coupled with temperature gradients in-situ and conductivity measurements onboard. These data are interpreted in terms of heat flow values and are generally lower than the conductive cooling model. Several temperature-depth profiles don't show linear gradients, but rather sigmoid shapes or inverse gradients suggesting superficial circulations through the first meters of sediments. The corresponding heat flow pattern is not similar to the one observed at Juan de Fuca. No systematic links have been observed between basement outcrops and lower or higher heat flow which would point to discharge or recharge sites. Instead, the pattern recalls studies in the North Pond area (Langseth et al.1992), with a clear predominance of low heat flow values over the site. We propose that the North Pond circulation model is applicable to large portions of slow-spreading ridge flanks such as the Atlantic. In this model, seawater cools the uppermost crust below sediments in basins that are typically tens of kms wide, reducing the surface heat flow under cooling model values. Based on subsidence rates, these shallow hydrothermal circulations have a minor impact on the cooling of the diverging plates.

  18. Ridge Regression Signal Processing

    NASA Technical Reports Server (NTRS)

    Kuhl, Mark R.

    1990-01-01

    The introduction of the Global Positioning System (GPS) into the National Airspace System (NAS) necessitates the development of Receiver Autonomous Integrity Monitoring (RAIM) techniques. In order to guarantee a certain level of integrity, a thorough understanding of modern estimation techniques applied to navigational problems is required. The extended Kalman filter (EKF) is derived and analyzed under poor geometry conditions. It was found that the performance of the EKF is difficult to predict, since the EKF is designed for a Gaussian environment. A novel approach is implemented which incorporates ridge regression to explain the behavior of an EKF in the presence of dynamics under poor geometry conditions. The basic principles of ridge regression theory are presented, followed by the derivation of a linearized recursive ridge estimator. Computer simulations are performed to confirm the underlying theory and to provide a comparative analysis of the EKF and the recursive ridge estimator.

  19. Magnetite formation from ferrihydrite by hyperthermophilic archaea from Endeavour Segment, Juan de Fuca Ridge hydrothermal vent chimneys.

    PubMed

    Lin, T Jennifer; Breves, E A; Dyar, M D; Ver Eecke, H C; Jamieson, J W; Holden, J F

    2014-05-01

    Hyperthermophilic iron reducers are common in hydrothermal chimneys found along the Endeavour Segment in the northeastern Pacific Ocean based on culture-dependent estimates. However, information on the availability of Fe(III) (oxyhydr) oxides within these chimneys, the types of Fe(III) (oxyhydr) oxides utilized by the organisms, rates and environmental constraints of hyperthermophilic iron reduction, and mineral end products is needed to determine their biogeochemical significance and are addressed in this study. Thin-section petrography on the interior of a hydrothermal chimney from the Dante edifice at Endeavour showed a thin coat of Fe(III) (oxyhydr) oxide associated with amorphous silica on the exposed outer surfaces of pyrrhotite, sphalerite, and chalcopyrite in pore spaces, along with anhydrite precipitation in the pores that is indicative of seawater ingress. The iron sulfide minerals were likely oxidized to Fe(III) (oxyhydr) oxide with increasing pH and Eh due to cooling and seawater exposure, providing reactants for bioreduction. Culture-dependent estimates of hyperthermophilic iron reducer abundances in this sample were 1740 and 10 cells per gram (dry weight) of material from the outer surface and the marcasite-sphalerite-rich interior, respectively. Two hyperthermophilic iron reducers, Hyperthermus sp. Ro04 and Pyrodictium sp. Su06, were isolated from other active hydrothermal chimneys on the Endeavour Segment. Strain Ro04 is a neutrophilic (pH opt 7-8) heterotroph, while strain Su06 is a mildly acidophilic (pH opt 5), hydrogenotrophic autotroph, both with optimal growth temperatures of 90-92 °C. Mössbauer spectroscopy of the iron oxides before and after growth demonstrated that both organisms form nanophase (<12 nm) magnetite [Fe3 O4 ] from laboratory-synthesized ferrihydrite [Fe10 O14 (OH)2 ] with no detectable mineral intermediates. They produced up to 40 mm Fe(2+) in a growth-dependent manner, while all abiotic and biotic controls produced <3 mm Fe(2+) . Hyperthermophilic iron reducers may have a growth advantage over other hyperthermophiles in hydrothermal systems that are mildly acidic where mineral weathering at increased temperatures occurs. © 2014 John Wiley & Sons Ltd.

  20. Mineralogical studies of sulfide samples and volatile concentrations of basalt glasses from the southern Juan de Fuca Ridge.

    USGS Publications Warehouse

    Brett, R.; Evans, H.T.; Gibson, E.K.; Hedenquist, J.W.; Wandless, M.-V.; Sommer, M.A.

    1987-01-01

    Specifically considers unusual minerals and geothermometric relations not previously covered. Equilibrium, if attained at all, during deposition of most sulfides was a transient event over a few tens of micrometers at most and was perturbed by rapid temperature and compositional changes of the circulating fluid. Two new minerals were found: one, a hydrated Zn, Fe hydroxy-chlorosulfate, and the other, a (Mn, Mg, Fe) hydroxide or hydroxy-hydrate. Both were formed at relatively low temperatures. Lizardite, starkeyite, and anatase were found for the first time in such an environment.-from Authors

  1. Low-molecular weight hydrocarbons in vent fluids from the Main Endeavour Field, northern Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Cruse, Anna M.; Seewald, Jeffrey S.

    2010-11-01

    Despite its location on sediment-free basalt, vent fluids from the Main Endeavour Field (MEF) contain chemical species that indicate fluids have interacted with sediments during circulation. We report on the distribution and isotopic abundances of organic compounds ( C1- C3 alkanes and alkenes, benzene and toluene) in fluids collected from the Main Endeavour Field (MEF) in July, 2000, to understand the processes that regulate their abundances and characterize fluid sources. Aqueous organic compounds are derived from the thermal alteration of sedimentary organic matter and subsequently undergo further oxidation reactions during fluid flow. Fluid:sediment mass ratios calculated using ΣNH 4 concentrations indicate that the sediments are distal to the MEF, resulting in a common reservoir of fluids for all of the vents. Following the generation from sediment alteration, aqueous organic compounds undergo secondary alteration reactions via a stepwise oxidation reaction mechanism. Alkane distributions and isotopic compositions indicate that organic compounds in MEF fluids have undergone a greater extent of alteration as compared to Middle Valley fluids, either due to differences in subsurface redox conditions or the residence time of fluids at subsurface conditions. The distributions of the aromatic compounds benzene and toluene are qualitatively consistent with the subsurface conditions indicated by equilibration of aqueous alkanes and alkanes. However, benzene and toluene do not achieve chemical equilibrium in the subsurface. Methane and CO 2 also do not equilibrate chemically or isotopically at reaction zone temperatures, a likely result of an insufficient reaction time after addition of CO 2 from magmatic sources during upflow. The organic geochemistry supports the assumption that the sediments with which MEF fluids interact has the same composition as sediments present in Middle Valley itself, and highlight differences in subsurface reaction zone conditions and fluid flow pathways at these two sites.

  2. Heat and chemical flux variability within the Main Endeavour Field, Juan de Fuca Ridge, from 2000, 2004

    NASA Astrophysics Data System (ADS)

    Kellogg, J. P.; McDuff, R. E.; Hautala, S. L.; Stahr, F.

    2010-12-01

    The Main Endeavour Field (MEF) has had a split personality since it was discovered. The southern half of the field is regularly observed to be hotter and fresher than the northern half. Differences lessened after the 1999 earthquake event, but the thermal and chemical gradient remains. We examine CTD and MAVS current meter data collected during surveys, designed to intersect the rising hydrothermal plume, conducted with the Autonomous Benthic Explorer (ABE) in 2000 and 2004. By taking subsets of the data over known clusters of structures within the field, we attribute fractional contributions to the whole field heat and salt fluxes. Preliminary findings indicate that North MEF contributes ~90% and ~100% of the heat from MEF in 2000 and 2004 respectively. It is clear from this that the majority of the MEF buoyancy flux is from North MEF even though the source fluids from South MEF are estimated to be initially more buoyant than those from North MEF. Within North MEF, ~2/3 of the heat comes from the Grotto, Dante, Lobo sulfide cluster and ~1/4 from the Hulk and Crypto cluster. These data, for the intra-field spatial scales of heat and salt flux, may allow us to infer mechanisms capable of altering the porous network of the hydrothermal system.

  3. Investigating the Relationship between Fin Whales, Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge

    DTIC Science & Technology

    2014-09-30

    inconsistent with the commonly observed pattern of baleen whale migration in which whales head north in the spring and south in the fall (e.g., Payne and...consistent with whales moving slowly southward over the winter before migrating north silently in the Spring. Fig. 4. Example of a track with the...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Investigating the Relationship between Fin Whales

  4. Contamination of basaltic lava by seawater: Evidence found in a lava pillar from Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Schiffman, Peter; Zierenberg, Robert; Chadwick, William W.; Clague, David A.; Lowenstern, Jacob

    2010-04-01

    A lava pillar formed during the 1998 eruption at Axial Seamount exhibits compositional and textural evidence for contamination by seawater under magmatic conditions. Glass immediately adjacent to anastomosing microfractures within 1 cm of the inner pillar wall is oxidized and significantly enriched in Na and Cl and depleted in Fe and K with respect to that in glassy selvages from the unaffected outer pillar wall. The affected glass contains up to 1 wt % Cl and is enriched by ˜2 wt % Na2O relative to unaffected glass, consistent with a nearly 1:1 (molar) incorporation of NaCl. Glass bordering the Cl-enriched glass in the inner pillar wall is depleted in Na but enriched in K. The presence of tiny (<10 μm) grains of Cu-Fe sulfides and Fe sulfides as well as elemental Ni, Ag, and Au in the Na-depleted, K-enriched glass of the inner pillar wall implies significant reduction of this glass, presumably by hydrogen generated during seawater contamination and oxidation of lava adjacent to microfractures. We interpret the compositional anomalies we see in the glass of the interior pillar wall as caused by rapid incorporation of seawater into the still-molten lava during pillar growth, probably on the time scale of seconds to minutes. Only one of seven examined lava pillars shows this effect, and we interpret that seawater has to be trapped in contact with molten lava (inside the lava pillar, in this case) to produce the effects we see. Thus, under the right conditions, seawater contamination of lavas during submarine eruptions is one means by which the oceanic crust can sequester Cl during its global flux cycle. However, since very few recent lava flows have been examined in similar detail, the global significance of this process in effecting Earth's Cl budget remains uncertain.

  5. Topographic Analysis of Europa's Ridges

    NASA Astrophysics Data System (ADS)

    Bader, C. E.; Kattenhorn, S. A.; Schenk, P. M.

    2008-12-01

    Ridges are the most ubiquitous surface feature on Europa. Here we examine double ridges that have two parallel, raised flanks with a continuous axial trough (referred to as a ridge pair). Characterizing ridge edifices may help us better understand the processes that drive ridge formation and evolution. Because there is no global elevation map for Europa, topography was derived from high resolution (18 to 181 m/pixel) combined stereographic and photoclinometric images to create 265 topographic profiles across 24 features of interest. Ridge topography was examined across 22 ridge pairs (12 with apparent lateral offsets) and 2 ridge complexes, in the Bright Plains, Conamara Chaos, Cilix, Argadnel Regio, Rhadamanthys Linea, and the E17DISSTR01 (northwest of Katreus Linea) areas. Topographic profiles are oriented perpendicular to the strike of each ridge pair to capture height and width variations as well as to highlight asymmetry between adjacent ridges. We characterize ridges using ridge height and width (vertical and horizontal distance from the base of the ridge flank to the ridge peak), average ridge height (average of the individual peaks in a ridge pair), total ridge width (distance between the ridge's outer flanks), and peak-to-peak (PTP) width (distance between peaks in a ridge pair). Height-to-width ratios of 44 individual ridges fall within a wide range that never exceeds 0.53, implying a maximum outer slope of 28 degrees, slightly less than the suggested angle of repose of loose granular ice (~34 degrees). Most slopes are much gentler, between 10 and 20 degrees, which are significantly smaller than those presented in a prior study undertaken early in the Galileo imaging mission. In fact, we have found that ridges can be very wide and low with outer slopes of only a few degrees, implying that very few ridge morphologies are likely to be controlled by granular flow processes down their outer slopes. The ratio of average ridge height to total ridge width has a

  6. Sedimentation Patterns, Forced Folding and Fluid Upflow Above a Buried Basement Ridge: Results From a High Resolution Seismic 3D Survey

    NASA Astrophysics Data System (ADS)

    Zuehlsdorff, L.; Spiess, V.

    2003-12-01

    During the German R/V Sonne Cruise SO 149 (2000), a high resolution 3D seismic data set was collected at the eastern flank of the Juan de Fuca Ridge off the west coast of North America. On the basis of this data set, a consistent layer model could be developed for the unusual complex stratigraphic pattern at and around a sediment buried basement elevation called First Ridge. This basement ridge acted and acts as an obstruction for incoming turbidites, however, the effect exerted by bathymetry on the flow of turbiditic particle clouds decreased as the adjacent sedimentary basins filled up. Subsequent major turbiditic events affected the whole area including the top of First Ridge. Hydrothermally driven fluid upflow above First Ridge appears to be focused by narrow high porosity zones, which are observed above equally narrow pronounced basement peaks. The higher porosity can be explained by forced folds developing an extensional strain field throughout the sediment column. The forced folds may either be the result of fault movement within the basement or related to fault processes within the sediment cover itself. Yet forced folds and high porosity do not necessarily mean detectable fluid flow. 3D seismic data rather provide information about the development and distribution of a potential plumbing system and thus an understanding of the nature of the flow. One implication is that the contribution of fluids discharging at First Ridge does not balance the in-going and out-coming fluid budget at the eastern flank of the Juan de Fuca Ridge.

  7. Interaction of a mantle plume and a segmented mid-ocean ridge: Results from numerical modeling

    NASA Astrophysics Data System (ADS)

    Georgen, Jennifer E.

    2014-04-01

    Previous investigations have proposed that changes in lithospheric thickness across a transform fault, due to the juxtaposition of seafloor of different ages, can impede lateral dispersion of an on-ridge mantle plume. The application of this “transform damming” mechanism has been considered for several plume-ridge systems, including the Reunion hotspot and the Central Indian Ridge, the Amsterdam-St. Paul hotspot and the Southeast Indian Ridge, the Cobb hotspot and the Juan de Fuca Ridge, the Iceland hotspot and the Kolbeinsey Ridge, the Afar plume and the ridges of the Gulf of Aden, and the Marion/Crozet hotspot and the Southwest Indian Ridge. This study explores the geodynamics of the transform damming mechanism using a three-dimensional finite element numerical model. The model solves the coupled steady-state equations for conservation of mass, momentum, and energy, including thermal buoyancy and viscosity that is dependent on pressure and temperature. The plume is introduced as a circular thermal anomaly on the bottom boundary of the numerical domain. The center of the plume conduit is located directly beneath a spreading segment, at a distance of 200 km (measured in the along-axis direction) from a transform offset with length 100 km. Half-spreading rate is 0.5 cm/yr. In a series of numerical experiments, the buoyancy flux of the modeled plume is progressively increased to investigate the effects on the temperature and velocity structure of the upper mantle in the vicinity of the transform. Unlike earlier studies, which suggest that a transform always acts to decrease the along-axis extent of plume signature, these models imply that the effect of a transform on plume dispersion may be complex. Under certain ranges of plume flux modeled in this study, the region of the upper mantle undergoing along-axis flow directed away from the plume could be enhanced by the three-dimensional velocity and temperature structure associated with ridge-transform-ridge

  8. Transform push, oblique subduction resistance, and intraplate stress of the Juan de Fuca plate

    USGS Publications Warehouse

    Wang, K.; He, J.; Davis, E.E.

    1997-01-01

    The Juan de Fuca plate is a small oceanic plate between the Pacific and North America plates. In the southernmost region, referred to as the Gorda deformation zone, the maximum compressive stress a, constrained by earthquake focal mechanisms is N-S. Off Oregon, and possibly off Washington, NW trending left-lateral faults cutting the Juan de Fuca plate indicate a a, in a NE-SW to E-W direction. The magnitude of differential stress increases from north to south; this is inferred from the plastic yielding and distribution of earthquakes throughout the Gorda deformation zone. To understand how tectonic forces determine the stress field of the Juan de Fuca plate, we have modeled the intraplate stress using both elastic and elastic-perfectly plastic plane-stress finite element models. We conclude that the right-lateral shear motion of the Pacific and North America plates is primarily responsible for the stress pattern of the Juan de Fuca plate. The most important roles are played by a compressional force normal to the Mendocino transform fault, a result of the northward push by the Pacific plate and a horizontal resistance operating against the northward, or margin-parallel, component of oblique subduction. Margin-parallel subduction resistance results in large N-S compression in the Gorda deformation zone because the force is integrated over the full length of the Cascadia subduction zone. The Mendocino transform fault serves as a strong buttress that is very weak in shear but capable of transmitting large strike-normal compressive stresses. Internal failure of the Gorda deformation zone potentially places limits on the magnitude of the fault-normal stresses being transmitted and correspondingly on the magnitude of strike-parallel subduction resistance. Transform faults and oblique subduction zones in other parts of the world can be expected to transmit and create stresses in the same manner. Copyright 1997 by the American Geophysical Union.

  9. Seismic evidence for a magma chamber beneath the slow-spreading Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Calvert, A. J.

    1995-10-01

    SEISMIC reflections from magma chambers have been observed along the fast-spreading East Pacific Rise1,2 and the intermediate-spreading Valu Fa Ridge3,4; sub-axial reflections also exist beneath the intermediate-spreading Juan de Fuca Ridge5. But no magma chambers have been identified beneath the slow-spreading Mid-Atlantic Ridge, suggesting that here magma chambers lie unusually deep or are transient features6-11. Seismic reflection profiles acquired in 1989 over the Snake Pit hydrothermal area, in the rift valley of the Mid-Atlantic Ridge ˜25 km south of the Kane fracture zone, showed no evidence of magmatic activity12, although geochemical analyses of hydrothermal vent fluids suggest the existence of magma at depths as shallow as 1-2 km13,14. By suppressing in these data high-amplitude coherent noise generated at the sea floor, I have obtained images, in an otherwise non-reflective crust, of seismic reflections beneath, and just south of, the Snake Pit hydrothermal area. These reflections define a small, 4-km-wide dome whose apex is ˜ 1,200 m beneath the sea floor. As bright reflections from the upper flanks of this dome occur in the depth range suggested by the vent-fluid geochemistry, I interpret the dome to be the seismic expression of a small magma chamber.

  10. Transport of surface waters from the Juan de Fuca eddy region to the Washington coast

    NASA Astrophysics Data System (ADS)

    MacFadyen, Amoreena; Hickey, Barbara M.; Foreman, Michael G. G.

    2005-10-01

    A seasonal cold eddy located off the mouth of the Strait of Juan de Fuca has been implicated as an initiation site for toxic HABs affecting the Washington coast. To investigate the fate of eddy waters, a diagnostic finite element circulation model was developed for this region and the northern Washington shelf. The model was based on hydrographic data from several cruises in the summer of 1998, a year in which record levels of toxin were measured in razor clams at Washington beaches. Additional model forcing included tides and surface wind stress typical of fair weather/upwelling conditions or fall storms. The model showed strong retention in the eddy and a preferred southeastward trajectory for model drifters leaving the eddy. ARGOS-tracked drifters released in the vicinity of the eddy in the summers of 2001 through 2003 were consistent with model results generated with 1998 data demonstrating the robust nature of the large-scale currents in this region. Model and true drifter results show that the Juan de Fuca eddy is an important source region for PNW shelf waters. Furthermore, both model and true drifters moved onshore during storms suggesting that surface waters of the Juan de Fuca eddy can impact the Washington coast.

  11. Juan de Fuca slab geometry and its relation to Wadati-Benioff zone seismicity

    USGS Publications Warehouse

    McCrory, Patricia A.; Blair, J. Luke; Waldhause, Felix; Oppenheimer, David H.

    2012-01-01

    A new model of the subducted Juan de Fuca plate beneath western North America allows first-order correlations between the occurrence of Wadati-Benioff zone earthquakes and slab geometry, temperature, and hydration state. The geo-referenced 3D model, constructed from weighted control points, integrates depth information from earthquake locations and regional seismic velocity studies. We use the model to separate earthquakes that occur in the Cascadia forearc from those that occur within the underlying Juan de Fuca plate and thereby reveal previously obscured details regarding the spatial distribution of earthquakes. Seismicity within the slab is most prevalent where the slab is warped beneath northwestern California and western Washington suggesting that slab flexure, in addition to expected metamorphic dehydration processes, promotes earthquake occurrence within the subducted oceanic plate. Earthquake patterns beneath western Vancouver Island are consistent with slab dehydration processes. Conversely, the lack of slab earthquakes beneath western Oregon is consistent with an anhydrous slab. Double-differenced relocated seismicity resolves a double seismic zone within the slab beneath northwestern California that strongly constrains the location of the plate interface and delineates a cluster of seismicity 10 km above the surface that includes the 1992 M7.1 Mendocino earthquake. We infer that this earthquake ruptured a surface within the Cascadia accretionary margin above the Juan de Fuca plate. We further speculate that this earthquake is associated with a detached fragment of former Farallon plate. Other subsurface tectonic elements within the forearc may have the potential to generate similar damaging earthquakes.

  12. Fingermark ridge drift.

    PubMed

    De Alcaraz-Fossoul, Josep; Roberts, Katherine A; Feixat, Carme Barrot; Hogrebe, Gregory G; Badia, Manel Gené

    2016-01-01

    Distortions of the fingermark topography are usually considered when comparing latent and exemplar fingerprints. These alterations are characterized as caused by an extrinsic action, which affects entire areas of the deposition and alters the overall flow of a series of contiguous ridges. Here we introduce a novel visual phenomenon that does not follow these principles, named fingermark ridge drift. An experiment was designed that included variables such as type of secretion (eccrine and sebaceous), substrate (glass and polystyrene), and degrees of exposure to natural light (darkness, shade, and direct light) indoors. Fingermarks were sequentially visualized with titanium dioxide powder, photographed and analyzed. The comparison between fresh and aged depositions revealed that under certain environmental conditions an individual ridge could randomly change its original position regardless of its unaltered adjacent ridges. The causes of the drift phenomenon are not well understood. We believe it is exclusively associated with intrinsic natural aging processes of latent fingermarks. This discovery will help explain the detection of certain dissimilarities at the minutiae/ridge level; determine more accurate "hits"; identify potentially erroneous corresponding points; and rethink identification protocols, especially the criteria of "no single minutiae discrepancy" for a positive identification. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  13. 5. INTERIOR OF NORTHEAST ROOM AND MEZZANINE, NORTHEAST VIEW OF ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. INTERIOR OF NORTHEAST ROOM AND MEZZANINE, NORTHEAST VIEW OF (HOISTS IN CENTER). - Vanadium Corporation of America (VCA) Naturita Mill, Sampling Building & Ore Receiving Platform, 3 miles Northwest of Naturita, between Highway 141 & San Miguel River, Naturita, Montrose County, CO

  14. VIEW OF NORTHEAST TOWARD MAINTENANCE SHED AT NORTHEAST CORNER OF ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    VIEW OF NORTHEAST TOWARD MAINTENANCE SHED AT NORTHEAST CORNER OF PARK - Candler Park Historic District, Roughly bounded by Moreland, Dekalb, McLendon & Harold Avenues, Matthews Street & Clifton Terrace, Atlanta, Fulton County, GA

  15. OBLIQUE VIEW OF THE NORTHEAST SIDE AND NORTHEAST BACK OF ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    OBLIQUE VIEW OF THE NORTHEAST SIDE AND NORTHEAST BACK OF BUILDING 13, FACING SOUTH. - Southern Branch of the National Home for Disabled Volunteer Soldiers, Building 13, Harris Avenue at its intersection of Black Avenue and Woodfin Street, Hampton, Hampton, VA

  16. Shoreline-Crossing Shear-Velocity Structure of the Juan de Fuca Plate and Cascadia Subduction Zone from Surface Waves and Receiver Functions

    NASA Astrophysics Data System (ADS)

    Janiszewski, H. A.; Gaherty, J. B.; Abers, G. A.; Gao, H.

    2016-12-01

    The Cascadia subduction zone (CSZ) is the site of the onshore-offshore Cascadia Initiative, which deployed seismometers extending from the Juan de Fuca ridge to the subduction zone and onshore beyond the volcanic arc. This array allows the unique opportunity to seismically image the evolution and along-strike variation of the crust and mantle of the entire CSZ. We compare teleseismic receiver functions, ambient-noise Rayleigh-wave phase velocities in the 10-20 s period band, and earthquake-source Rayleigh-wave phase velocities from 20-100 s, to determine shear-velocity structure in the upper 200 km. Receiver functions from both onshore and shallow-water offshore sites provide constraints on crustal and plate interface structure. Spectral-domain fitting of ambient-noise empirical Green's functions constrains shear velocity of the crust and shallow mantle. An automated multi-channel cross-correlation analysis of teleseismic Rayleigh waves provides deeper lithosphere and asthenosphere constraints. The amphibious nature of the array means it is essential to examine the effect of noise variability on data quality. Ocean bottom seismometers (OBS) are affected by tilt and compliance noise. Removal of this noise from the vertical components of the OBS is essential for the teleseismic Rayleigh waves; this stabilizes the output phase velocity maps particularly along the coastline where observations are predominately from shallow water OBS. Our noise-corrected phase velocity maps reflect major structures and tectonic transitions including the transition from high-velocity oceanic lithosphere to low-velocity continental lithosphere, high velocities associated with the subducting slab, and low velocities beneath the ridge and arc. We interpret the resulting shear-velocity model in the context of temperature and compositional variation in the incoming plate and along the strike of the CSZ.

  17. Shoreline-crossing shear-velocity structure of the Juan de Fuca plate and Cascadia subduction zone from surface waves and receiver functions

    NASA Astrophysics Data System (ADS)

    Janiszewski, Helen; Gaherty, James; Abers, Geoffrey; Gao, Haiying

    2017-04-01

    The Cascadia subduction zone (CSZ) is the site of the onshore-offshore Cascadia Initiative, which deployed seismometers extending from the Juan de Fuca ridge to the subduction zone and onshore beyond the volcanic arc. This array allows the unique opportunity to seismically image the evolution and along-strike variation of the crust and mantle of the entire CSZ. We compare teleseismic receiver functions, ambient-noise Rayleigh-wave phase velocities in the 10-20 s period band, and earthquake-source Rayleigh-wave phase velocities from 20-100 s, to determine shear-velocity structure in the upper 200 km. Receiver functions from both onshore and shallow-water offshore sites provide constraints on crustal and plate interface structure. Spectral-domain fitting of ambient-noise empirical Green's functions constrains shear velocity of the crust and shallow mantle. An automated multi-channel cross-correlation analysis of teleseismic Rayleigh waves provides deeper lithosphere and asthenosphere constraints. The amphibious nature of the array means it is essential to examine the effect of noise variability on data quality. Ocean bottom seismometers (OBS) are affected by tilt and compliance noise. Removal of this noise from the vertical components of the OBS is essential for the teleseismic Rayleigh waves; this stabilizes the output phase velocity maps particularly along the coastline where observations are predominately from shallow water OBS. Our noise-corrected phase velocity maps reflect major structures and tectonic transitions including the transition from high-velocity oceanic lithosphere to low-velocity continental lithosphere, high velocities associated with the subducting slab, and low velocities beneath the ridge and arc. We interpret the resulting shear-velocity model in the context of temperature and compositional variation in the incoming plate and along the strike of the CSZ.

  18. Massive sulfide deposition and trace element remobilization in the Middle Valley sediment-hosted hydrothermal system, northern Juan de Fuca Rdge

    USGS Publications Warehouse

    Houghton, J.L.; Shanks, Wayne C.; Seyfried, W.E.

    2004-01-01

    The Bent Hill massive sulfide deposit and ODP Mound deposit in Middle Valley at the northernmost end of the Juan de Fuca Ridge are two of the largest modern seafloor hydrothermal deposits yet explored. Trace metal concentrations of sulfide minerals, determined by laser-ablation ICP-MS, were used in conjunction with mineral paragenetic studies and thermodynamic calculations to deduce the history of fluid-mineral reactions during sulfide deposition. Detailed analyses of the distribution of metals in sulfides indicate significant shifts in the physical and chemical conditions responsible for the trace element variability observed in these sulfide deposits. Trace elements (Mn, Co, Ni, As, Se, Ag, Cd, Sb, Pb, and Bi) analyzed in a representative suite of 10 thin sections from these deposits suggest differences in conditions and processes of hydrothermal alteration resulting in mass transfer of metals from the center of the deposits to the margins. Enrichments of some trace metals (Pb, Sb, Cd, Ag) in sphalerite at the margins of the deposits are best explained by dissolution/reprecipitation processes consistent with secondary remineralization. Results of reaction-path models clarify mechanisms of mass transfer during remineralization of sulfide deposits due to mixing of hydrothermal fluids with seawater. Model results are consistent with patterns of observed mineral paragenesis and help to identify conditions (pH, redox, temperature) that may be responsible for variations in trace metal concentrations in primary and secondary minerals. Differences in trace metal distributions throughout a single deposit and between nearby deposits at Middle Valley can be linked to the history of metal mobilization within this active hydrothermal system that may have broad implications for sulfide ore formation in other sedimented and unsedimented ridge systems. ?? 2004 Elsevier Ltd.

  19. Massive sulfide deposition and trace element remobilization in the Middle Valley sediment-hosted hydrothermal system, northern Juan de Fuca Rdge

    NASA Astrophysics Data System (ADS)

    Houghton, J. L.; Shanks, W. C.; Seyfried, W. E.

    2004-07-01

    The Bent Hill massive sulfide deposit and ODP Mound deposit in Middle Valley at the northernmost end of the Juan de Fuca Ridge are two of the largest modern seafloor hydrothermal deposits yet explored. Trace metal concentrations of sulfide minerals, determined by laser-ablation ICP-MS, were used in conjunction with mineral paragenetic studies and thermodynamic calculations to deduce the history of fluid-mineral reactions during sulfide deposition. Detailed analyses of the distribution of metals in sulfides indicate significant shifts in the physical and chemical conditions responsible for the trace element variability observed in these sulfide deposits. Trace elements (Mn, Co, Ni, As, Se, Ag, Cd, Sb, Pb, and Bi) analyzed in a representative suite of 10 thin sections from these deposits suggest differences in conditions and processes of hydrothermal alteration resulting in mass transfer of metals from the center of the deposits to the margins. Enrichments of some trace metals (Pb, Sb, Cd, Ag) in sphalerite at the margins of the deposits are best explained by dissolution/reprecipitation processes consistent with secondary remineralization. Results of reaction-path models clarify mechanisms of mass transfer during remineralization of sulfide deposits due to mixing of hydrothermal fluids with seawater. Model results are consistent with patterns of observed mineral paragenesis and help to identify conditions (pH, redox, temperature) that may be responsible for variations in trace metal concentrations in primary and secondary minerals. Differences in trace metal distributions throughout a single deposit and between nearby deposits at Middle Valley can be linked to the history of metal mobilization within this active hydrothermal system that may have broad implications for sulfide ore formation in other sedimented and unsedimented ridge systems.

  20. FOSSIL RIDGE WILDERNESS STUDY AREA, COLORADO.

    USGS Publications Warehouse

    DeWitt, Ed; Kluender, Steven E.

    1984-01-01

    The Fossil Ridge Wilderness Study Area, approximately 20 mi northeast of Gunnison in central Colorado, was studied and its mineral-resource potential assessed. Portions of the study area have substantiated resource potential for gold, silver, copper, lead, zinc, molybdenum, uranium, thorium, rare-earth elements, and high-calcium limestone. Much of the area has a probable resource potential for the preceeding commodities as well as for tin. Various other elements are found in anomalous concentrations within the study area, but there is likelihood for their occurrence in amounts sufficient to constitute resources. Exploration, especially for molybdenum, gold, and uranium, has been active in the past and is expected to continue in the future. No potential for fossil fuel resources was identified in this study.

  1. Ridge: a computer program for calculating ridge regression estimates

    Treesearch

    Donald E. Hilt; Donald W. Seegrist

    1977-01-01

    Least-squares coefficients for multiple-regression models may be unstable when the independent variables are highly correlated. Ridge regression is a biased estimation procedure that produces stable estimates of the coefficients. Ridge regression is discussed, and a computer program for calculating the ridge coefficients is presented.

  2. [sup 226]Ra-[sup 230]Th disequilibrium in axial and off-axis mid-ocean ridge basalts

    SciTech Connect

    Volpe, A.M.; Goldstein, S.J. Los Alamos National Lab., NM )

    1993-03-01

    The authors describe [sup 226]Ra-[sup 230]Th disequilibrium in mid-ocean ridge basalt (MORB) glasses from the Juan de Fuca, Gorda, and East Pacific ridges. These first mass spectrometric measurements of [sup 226]Ra in MORB glasses at sub-picogram abundance levels confirm the large excesses over [sup 230]Th determined by radon-emanation techniques and alpha spectrometry. All off-axis MORB glasses have [sup 226]Ra-[sup 230]Th and [sup 234]U-[sup 238]U in secular equilibrium. This suggests that magmatic processes, not secondary post-eruption alteration, generate [sup 238]U-series disequilibrium in these MORB. Least evolved, N-MORB from axial valleys have ([sup 226]Ra/[sup 230]Th) between 2.2-2.3. Differentiated and enriched E-type MORB have consistently low ([sup 226]Ra/[sup 230]Th) ratios compared with N-MORB from the same ridge sections. Ra-Th fractionation may be less pronounced, or magma residence-transit periods may be long for differentiated MORB. Also, E-MORB may be generated by different melt extraction volumes and rates. Estimated [sup 226]Ra-[sup 230]Th ages for N-MORB agree with location on and off ridge segments, and with Th-U model ages. These preliminary results show that [sup 226]Ra-[sup 230]Th disequilibrium could be used to quantify volcanic episodicity at ocean ridges. 39 refs., 6 figs., 4 tabs.

  3. The Greenland-Iceland-Faroe Ridge Complex

    NASA Astrophysics Data System (ADS)

    Erlendsson, Ögmundur; Hjartarson, Árni; Blischke, Anett

    2017-04-01

    The Greenland-Iceland-Faroe Ridge Complex GIFRC covers 480.000 km2 of a thick volcanic crust that stretches 1150 km across the central Northeast Atlantic Ocean between the central East Greenland and the Northwest European margins. It incorporates the Iceland plateau, the aseismic Greenland-Iceland ridge, and the Iceland-Faroe ridge. GIFRC has been in development since the opening of the NE-Atlantic around 55 Ma. It appears as a prominent feature in all geological and geophysical data sets. Synclines and anticlines in the area will be summarised and, among others, several new ones that were revealed in seismic reflection data near to Iceland. Specifically, the offshore anticlines and synclines may be related to old rift systems prior the forming of Iceland as an insular shelf region (>24 Ma). Synclines are suggested to be manifestations of former rift axes that have been abandoned by rift jumps. These rift jumps appear to be more common inside the GIFRC region than in the ocean basins south and north of the area. They can be confirmed by the observation of cumulative crustal accretion through time as well. The GIFRC represents a complex region of crustal accretion in 3 dimensions due to overlapping rift systems, complex interlinked rift and transform zones, and several unconformities that suggest a variable uplift and subsidence history for the ridge complex. An excellent example to visualise such processes of vertical crustal accretion and rift jumps is seen in seismic reflection data that extends along the southwestern slope of the Iceland-Faroe Ridge. They clearly display the internal structures of basement blocks, separated by a syncline and younger rift system, and the formation of an anticline across the deeply buried basement blocks that are overlain by seaward dipping reflectors (SDR). We suggest a major hiatus (40 Ma - 24-20 Ma) and a related unconformity at the boundary of the volcanic insular shelf edge of East Iceland and the Faroe Ridge, buried beneath

  4. The Sagatu Ridge dike swarm, Ethiopian rift margin. [tectonic evolution

    NASA Technical Reports Server (NTRS)

    Mohr, P. A.; Potter, E. C.

    1976-01-01

    A swarm of dikes forms the core of the Sagatu Ridge, a 70-km-long topographic feature elevated to more than 4000 m above sea level and 1500 m above the level of the Eastern (Somalian) plateau. The ridge trends NNE and lies about 50 km east of the northeasterly trending rift-valley margin. Intrusion of the dikes and buildup of the flood-lava pile, largely hawaiitic but with trachyte preponderant in the final stages, occurred during the late Pliocene-early Pleistocene and may have been contemporaneous with downwarping of the protorift trough to the west. The ensuing faulting that formed the present rift margin, however, bypassed the ridge. The peculiar situation and orientation of the Sagatu Ridge, and its temporary existence as a line of crustal extension and voluminous magmatism, are considered related to a powerful structural control by a major line of Precambrian crustal weakness, well exposed further south. Transverse rift structures of unknown type appear to have limited the development of the ridge to the north and south.

  5. Calculating a Stepwise Ridge Regression.

    ERIC Educational Resources Information Center

    Morris, John D.

    1986-01-01

    Although methods for using ordinary least squares regression computer programs to calculate a ridge regression are available, the calculation of a stepwise ridge regression requires a special purpose algorithm and computer program. The correct stepwise ridge regression procedure is given, and a parallel FORTRAN computer program is described.…

  6. Coastal geology of northeast Africa and implications for prehistory

    SciTech Connect

    Hassan, F.A.; Higab, O.; Sharat, A.

    1985-01-01

    The coast of northeast Africa is characterized by ridges of disputed origin. The authors investigations clearly demonstrate that the ridges consist of littoral cycles and that they are neither wholly marine nor eolian. For example, Gebel Maryut Ridge in Egypt consists of several cycles, each consisting of beach or lagoonal deposits of a transgressive marine hemicycle followed by a regressive hemicycle represented by eolianite, which may be followed by soil development and colluviation. Paleontologic evidence, morphostratigraphy and correlation with the littoral cycles of Spain suggest that the marine sediments in the Gebel Maryut Ridge at 3, 4, 7 and 9 m asl are of Middle Pleistocene age (about 0.9->.25 my). The next and youngest ridge overlooking the modern beach consist of eolianite overlying supratidal gypseous sand and lagoonal shelly sand dating most probably to the last interglacial transgressive hemicycle. The coast today is erosional and the sea level has risen from -2 or -4 m to the present level since Graeco-Roman times. This suggests that sites that may have been located near the seashore from the last interglacial transgression and the recent transgression may have been destroyed. This is confirmed by a lack of prehistoric remains along the Egyptian Mediterranean Coast.

  7. Improved Epicentral Locations for Earthquakes Near Explorer Ridge

    NASA Astrophysics Data System (ADS)

    Clemens-Sewall, D.; Trehu, A. M.

    2014-12-01

    The tectonics and structure of the Explorer region, which is the northern boundary of the subducting Juan de Fuca plate, help to inform our assessments of the seismic hazard in the Pacific Northwest. Our understanding of this tectonically complex area is largely based on morphology of the seafloor from swath bathymetric data, potential field anomalies, and the calculated locations of contemporary earthquakes in the region. However, the Navy Sound Surveillance System hydrophone network, the Canadian National Seismic Network, the U.S. Advanced National Seismic System, and the Harvard Centroid Moment Tensor Catalog report significantly different epicentral locations for swarms of earthquakes near Explorer Ridge in August and October 2008. We relocated the larger (M>5) earthquakes in the August 2008 swarm using data from both U.S. and Canadian networks to improve azimuthal coverage. Absolute locations were determined for the largest events in the swarm, and the smaller events were relocated relative to the largest using a double difference method. To better understand why the locations from land-based seismic networks differ from those computed from the hydrophone arrays, we also examine T-phases from regional events recorded on Ocean Bottom Seismometers from the COLZA and Cascadia Initiative experiments and evaluate the potential for using T-phases to improve the epicentral locations of submarine earthquakes in the Pacific Northwest region.

  8. Improved Epicentral Locations for Earthquakes Near Explorer Ridge

    NASA Astrophysics Data System (ADS)

    Clemens-Sewall, D.; Trehu, A. M.

    2013-12-01

    The tectonics and structure of the Explorer region, which is the northern boundary of the subducting Juan de Fuca plate, help to inform our assessments of the seismic hazard in the Pacific Northwest. Our understanding of this tectonically complex area is largely based on morphology of the seafloor from swath bathymetric data, potential field anomalies, and the calculated locations of contemporary earthquakes in the region. However, the Navy Sound Surveillance System hydrophone network, the Canadian National Seismic Network, the U.S. Advanced National Seismic System, and the Harvard Centroid Moment Tensor Catalog report significantly different epicentral locations for swarms of earthquakes near Explorer Ridge in August and October 2008. We relocated the larger (M>5) earthquakes in the August 2008 swarm using data from both U.S. and Canadian networks to improve azimuthal coverage. Absolute locations were determined for the largest events in the swarm, and the smaller events were relocated relative to the largest using a double difference method. To better understand why the locations from land-based seismic networks differ from those computed from the hydrophone arrays, we also examine T-phases from regional events recorded on Ocean Bottom Seismometers from the COLZA and Cascadia Initiative experiments and evaluate the potential for using T-phases to improve the epicentral locations of submarine earthquakes in the Pacific Northwest region.

  9. The fate of the Juan de Fuca plate: Implications for a Yellowstone plume head

    NASA Astrophysics Data System (ADS)

    Xue, Mei; Allen, Richard M.

    2007-12-01

    Beneath the Pacific Northwest the Juan de Fuca plate, a remnant of the Farallon plate, continues subducting beneath the North American continent. To the east of the Cascadia subduction zone lies the Yellowstone Hotspot Track. The origins of this track can be traced back to the voluminous basaltic outpourings in the Columbia Plateau around 17 Ma. If these basalts are the result of a large melting anomaly rising through the mantle to the base of the North American continent, such as a mantle plume head, the anomaly would need to punch through the subducting Juan de Fuca slab. Here, we use teleseismic body-wave travel-time tomography to investigate the fate of the subducted slab and its possible interaction with a plume head. Our dataset is derived from the Oregon Array for Teleseismic Study (OATS) deployment in Oregon and all other available seismic data in this region during the same period. In our JdF07 models, we image the subducted Juan de Fuca plate in the mantle east of the Cascades beneath Oregon, where the slab has not been imaged before, to a depth of 400 km but no deeper. The slab dips ˜ 50°E and has a thickness of ˜ 75 km. Immediately beneath the slab, we image a low velocity layer with a similar geometry to the slab and extending down to at least ˜ 575 km depth in the V s model. The total length of the high velocity slab is ˜ 660 km, about 180 km longer than the estimated length of slab subducted since 17 Ma. Assuming similar slab geometry to today, this 180 km length of slab would reach ˜ 60 km depth, comparable to the thickness of continental lithosphere. We propose that the absence of the slab below 400 km today is due to the arrival of the Yellowstone plume head ˜ 17 Ma, which destroyed the Juan de Fuca slab at depths greater than the thickness of the continental lithosphere. Given this scenario, the low velocity anomaly beneath the slab is likely the remnant plume head material which has been pulled down by traction with the subducting plate

  10. Pb isotopes in sulfides from mid-ocean ridge hydrothermal sites

    SciTech Connect

    LeHuray, A.P.; Church, S.E.; Koski, R.A.; Bouse, R.M.

    1988-04-01

    The authors report Pb isotope ratios of sulfides deposited at seven recently active mid-ocean ridge (MOR) hydrothermal vents. Sulfides from three sediment-starved sites on the Juan de Fuca Ridge contain Pb with isotope ratios identical to their local basaltic sources. Lead in two deposits from the sediment-covered Escanaba Trough, Gorda Ridge, is derived from the sediments and does not appear to contain any basaltic component. There is a range of isotope ratios in a Guaymas Basin deposit, consistent with a mixture of sediment and MOR basalt Pb. Lead in a Galapagos deposit differs slightly from known Galapagos basalt Pb isotope values. The faithful record of Pb isotope signatures of local sources in MOR sulfides indicates that isotope ratios from ancient analogues ca be used as accurate reflections of ancient oceanic crustal values in ophiolite-hosted deposits and continental crustal averages in sediment-hosted deposits. The preservation of primary ophiolitic or continental crustal Pb isotope signatures in ancient MOR sulfides provides a powerful tool for investigation of crustal evolution and for fingerprinting ancient terranes.

  11. Major off-axis hydrothermal activity on the northern Gorda Ridge

    SciTech Connect

    Rona, P.A. ); Denlinger, R.P. ); Fisk, M.R.; Howard, K.J.; Taghon, G.L. ); Klitgord, K.D. ); McClain, J.S. ); McMurray, G.R. ); Wiltshire, J.C. )

    1990-06-01

    The first hydrothermal field on the northern Gorda Ridge, the Sea Cliff hydrothermal field, was discovered and geologic controls of hydrothermal activity in the rift valley were investigated on a dive series using the DSV Sea Cliff. The Sea Cliff hydrothermal field was discovered where predicted at the intersection of axis-oblique and axis-parallel faults at the south end of a linear ridge at mid-depth (2700 m) on on the east wall. Preliminary mapping and sampling of the field reveal: a setting nested on nearly sediment-free fault blocks 300 m above the rift valley floor 2.6 km from the axis; a spectrum of venting types from seeps to black smokers; high conductive heat flow estimated to be equivalent to the convective flux of multiple black smokers through areas of the sea floor sealed by a caprock of clastic breccia primarily derived from basalt with siliceous cement and barite pore fillings; and a vent biota with Juan de Fuca Ridge affinities. These findings demonstrate the importance of off-axis hydrothermal activity and the role of the intersection of tectonic lineations in controlling hydrothermal sites at sea-floor spreading centers.

  12. High seismic attenuation at a mid-ocean ridge reveals the distribution of deep melt

    PubMed Central

    Eilon, Zachary C.; Abers, Geoffrey A.

    2017-01-01

    At most mid-ocean ridges, a wide region of decompression melting must be reconciled with a narrow neovolcanic zone and the establishment of full oceanic crustal thickness close to the rift axis. Two competing paradigms have been proposed to explain melt focusing: narrow mantle upwelling due to dynamic effects related to in situ melt or wide mantle upwelling with lateral melt transport in inclined channels. Measurements of seismic attenuation provide a tool for identifying and characterizing the presence of melt and thermal heterogeneity in the upper mantle. We use a unique data set of teleseismic body waves recorded on the Cascadia Initiative’s Amphibious Array to simultaneously measure seismic attenuation and velocity across an entire oceanic microplate. We observe maximal differential attenuation and the largest delays (ΔtS*~1.7 s and δTS ~ 2 s) in a narrow zone <50 km from the Juan de Fuca and Gorda ridge axes, with values that are not consistent with laboratory estimates of temperature or water effects. The implied seismic quality factor (Qs ≤ 25) is among the lowest observed worldwide. Models harnessing experimentally derived anelastic scaling relationships require a 150-km-deep subridge region containing up to 2% in situ melt. The low viscosity and low density associated with this deep, narrow melt column provide the conditions for dynamic mantle upwelling, explaining a suite of geophysical observations at ridges, including electrical conductivity and shear velocity anomalies. PMID:28560338

  13. Major off-axis hydrothermal activity on the northern Gorda Ridge

    USGS Publications Warehouse

    Rona, Peter A.; Denlinger, Roger P.; Fisk, M. R.; Howard, K. J.; Taghon, G. L.; Klitgord, Kim D.; McClain, James S.; McMurray, G. R.; Wiltshire, J. C.

    1990-01-01

    The first hydrothermal field on the northern Gorda Ridge, the Sea Cliff hydrothermal field, was discovered and geologic controls of hydrothermal activity in the rift valley were investigated on a dive series using the DSV Sea Cliff. The Sea Cliff hydrothermal field was discovered where predicted at the intersection of axis-oblique and axis-parallel faults at the south end of a linear ridge at mid-depth (2700 m) on the east wall. Preliminary mapping and smpling of the field reveal: a setting nested on nearly sediment-free fault blocks 300 m above the rift valley floor 2.6 km from the axis; a spectrum of venting types from seeps to black smokers; high conductive heat flow estimated to be equivalent to the convective flux of multiple black smokers through areas of the sea floor sealed by a caprock of elastic breccia primarily derived from basalt with siliceous cement and barite pore fillings; and a vent biota with Juan de Fuca Ridge affinites. These findings demonstrate the importance of off-axis hydrothermal activity and the role of the intersection of tectonic lineations in controlling hydrothermal sites at sea-floor spreading centers.

  14. Detection of and response to mid-ocean ridge magmatic events: Implications for the subsurface biosphere

    NASA Astrophysics Data System (ADS)

    Cowen, James P.; Baker, Edward T.; Embley, Robert W.

    Magmatic events are unpredictable dynamic processes that are integral to the evolution of mid-ocean ridges. Dikes and lava flows develop rapidly and instantly alter the local hydrothermal flow regime, initiating dramatic changes in hydrothermal discharge at the seafloor, and triggering geochemical and microbiological changes within the shallow crust, at the seafloor and within the overlying water column. Despite considerable logistical difficulties, real-time remote detection capabilities (SOSUS) along limited regions of the MOR system have allowed investigators to rapidly respond to significant seismic events. There have been more than 20 documented examples of seafloor volcanic/tectonic events, at both isolated volcanoes and mid-ocean ridges, but only a few of these have led to significant response efforts. The most rapid and thorough response efforts have been to the 1991 9° N EPR event and several events (1986,1993,1996, 1998,2001) on the Juan de Fuca and Gorda Ridges. Together these "SOSUS directed' responses plus the few serendipitous encounters have led to important discoveries (e.g., event plumes; `snow-blower' vents) and provided basic new constraints on presently immature models of submarine magmatic-hydrothermal systems (e.g., intrusive/extrusive diking; event plume formation; subsurface hydrothermal communities). The event response community has gained valuable experience in learning how to exploit these opportunities for scientific observation and is currently poised to continue such studies with increased speed and efficiency. However, our understanding of these geophysical, chemical and biological processes is only in their infancy.

  15. High seismic attenuation at a mid-ocean ridge reveals the distribution of deep melt.

    PubMed

    Eilon, Zachary C; Abers, Geoffrey A

    2017-05-01

    At most mid-ocean ridges, a wide region of decompression melting must be reconciled with a narrow neovolcanic zone and the establishment of full oceanic crustal thickness close to the rift axis. Two competing paradigms have been proposed to explain melt focusing: narrow mantle upwelling due to dynamic effects related to in situ melt or wide mantle upwelling with lateral melt transport in inclined channels. Measurements of seismic attenuation provide a tool for identifying and characterizing the presence of melt and thermal heterogeneity in the upper mantle. We use a unique data set of teleseismic body waves recorded on the Cascadia Initiative's Amphibious Array to simultaneously measure seismic attenuation and velocity across an entire oceanic microplate. We observe maximal differential attenuation and the largest delays ([Formula: see text] s and δTS ~ 2 s) in a narrow zone <50 km from the Juan de Fuca and Gorda ridge axes, with values that are not consistent with laboratory estimates of temperature or water effects. The implied seismic quality factor (Qs ≤ 25) is among the lowest observed worldwide. Models harnessing experimentally derived anelastic scaling relationships require a 150-km-deep subridge region containing up to 2% in situ melt. The low viscosity and low density associated with this deep, narrow melt column provide the conditions for dynamic mantle upwelling, explaining a suite of geophysical observations at ridges, including electrical conductivity and shear velocity anomalies.

  16. Major off-axis hydrothermal activity on the northern Gorda Ridge

    USGS Publications Warehouse

    Rona, Peter A.; Denlinger, Roger P.; Fisk, M. R.; Howard, K. J.; Taghon, G. L.; Klitgord, Kim D.; McClain, James S.; McMurray, G. R.; Wiltshire, J. C.

    1990-01-01

    The first hydrothermal field on the northern Gorda Ridge, the Sea Cliff hydrothermal field, was discovered and geologic controls of hydrothermal activity in the rift valley were investigated on a dive series using the DSV Sea Cliff. The Sea Cliff hydrothermal field was discovered where predicted at the intersection of axis-oblique and axis-parallel faults at the south end of a linear ridge at mid-depth (2700 m) on the east wall. Preliminary mapping and sampling of the field reveal: a setting nested on nearly sediment-free fault blocks 300 m above the rift valley floor 2.6 km from the axis; a spectrum of venting types from seeps to black smokers; high conductive heat flow estimated to be equivalent to the convective flux of multiple black smokers through areas of the sea floor sealed by a caprock of elastic breccia primarily derived from basalt with siliceous cement and barite pore fillings; and a vent biota with Juan de Fuca Ridge affinites. These findings demonstrate the importance of off-axis hydrothermal activity and the role of the intersection of tectonic lineations in controlling hydrothermal sites at sea-floor spreading centers.

  17. Ridge regression processing

    NASA Technical Reports Server (NTRS)

    Kuhl, Mark R.

    1990-01-01

    Current navigation requirements depend on a geometric dilution of precision (GDOP) criterion. As long as the GDOP stays below a specific value, navigation requirements are met. The GDOP will exceed the specified value when the measurement geometry becomes too collinear. A new signal processing technique, called Ridge Regression Processing, can reduce the effects of nearly collinear measurement geometry; thereby reducing the inflation of the measurement errors. It is shown that the Ridge signal processor gives a consistently better mean squared error (MSE) in position than the Ordinary Least Mean Squares (OLS) estimator. The applicability of this technique is currently being investigated to improve the following areas: receiver autonomous integrity monitoring (RAIM), coverage requirements, availability requirements, and precision approaches.

  18. Reactive Hydrothermal Flow Model for Mid-Oceanic Ridges

    NASA Astrophysics Data System (ADS)

    Starger, J. L.; Garven, G.; Tivey, M. K.

    2016-12-01

    A two-dimensional finite-element code known as RST2D [1] is being used to study the geothermal energy, geohydrology, and geochemistry of fluid convection in seafloor hydrothermal systems such as the Juan de Fuca Ridge, East Pacific Rise, and TAG hydrothermal fields. Relative to black smoker vents and other discharge features, submarine recharge zones are understudied. We are attempting to model both the recharge and discharge limbs of these flow fields as a coupled system by mathematically and physically linking the fluid dynamics, heat flow, and geochemical reactions. Numerical simulations have been made to quantify likely flow rates and relevant geochemical water-rock reactions including mineral precipitation and dissolution using a fully-coupled reactive flow modeling approach. In particular, the reactive flow model is being used to predict the formation, likely spatial-temporal distribution, and preservation of anhydrite in the hydrothermal recharge zone and its feedback influence on permeability, fluid flow, and heat transport in the discharge zone. We are focusing on the geochemical effects and controls of on- and off-ridge geology and geometry, permeability-porosity, vent width and geometry, and thermal boundary conditions on the predicted size and extent of the recharge and discharge zones, and whether hydrothermal recharge is focused along extensional faults or diffused across broad areas of the seafloor. Hydrothermal flow systems of this type are known to represent modern analogs for ancient systems such as those being studied for understanding the origin of life on the planet, but also as modern analogs for the formation of volcanogenic massive sulfide ore deposits. Reactive flow modeling provides a useful tool for developing a better understanding of the physiobiochemistry of these episodic flow systems, and could potentially guide exploration for modern and ancient ore deposits. [1] Raffensperger, J.P.,1996, Advances in Porous Media 3, 185 - 305.

  19. Ridges and Flows

    NASA Image and Video Library

    2015-11-16

    Located southwest of Olympus Mons, this image captured by NASA 2001 Mars Odyssey spacecraft shows part of a complex region that has undergone several geologic processes. The hills have been modified by wind, creating narrow ridges, and then the entire region has been covered with volcanic flows from Olympus Mons. Orbit Number: 60744 Latitude: 13.4267 Longitude: 220.554 Instrument: VIS Captured: 2015-08-24 10:00 http://photojournal.jpl.nasa.gov/catalog/PIA20093

  20. Northeast Coast, Hokkaido, Japan

    NASA Image and Video Library

    1992-04-02

    The northeast coast of Hokkaido and Kunashir Island, Japan (44.0N, 143.0E) are seen bordered by drifting sea ice. The sea ice has formed a complex pattern of eddies in response to surface water currents and winds. Photos of this kind aid researchers in describing local ocean current patterns and the effects of wind speed and direction on the drift of surface material, such as ice floes or oil. Kunashir is the southernmost of the Kuril Islands.

  1. Widespread strombolian eruptions of mid-ocean ridge basalt

    NASA Astrophysics Data System (ADS)

    Clague, David A.; Paduan, Jennifer B.; Davis, Alice S.

    2009-03-01

    Glassy lava fragments were collected in pushcores or using a small suction-sampler from over 450 sites along the Juan de Fuca Ridge, Blanco Transform Fault, Gorda Ridge, northern East Pacific Rise, southern East Pacific Rise, Fiji back-arc basin, and near-ridge seamounts in the Vance, President Jackson, Taney, and a seamount off southern California. The samples consist of angular glass fragments, limu o Pele, Pele's hair, and other fluidal fragments formed during pyroclastic eruptions. Since many of the sites are deeper than the critical point of seawater, fragmentation cannot be hydrovolcanic and caused by expansion of seawater to steam. The glass fragments have a wide range of MORB compositions, ranging from fractionated to primitive and from depleted to enriched. Enriched magmas, which have higher volatile contents, may form more abundant pyroclasts than depleted magmas. Eruptions with high effusion rates produce sheet flows and abundant pyroclasts whereas those with low effusion rates produce pillow ridges and few pyroclasts. This relation suggests that high effusion and conduit rise rates are coupled to high magmatic gas contents. The eruptions are mainly effusive with a minor strombolian bubble burst component. We propose that the gas phase is an added component of variable amounts of magmatic foam from the top of the magma reservoir. As the mixture of resident magma and foam rises in the conduit, the larger bubbles in the foam rise more quickly and sweep up the smaller bubbles nucleating and growing from the resident magma. On eruption, the process of bubble coalescence is more complete for the slower rising, gas-poor lavas that erupt as pillow lavas whereas the limu o Pele associated with sheet flow eruptions commonly contain several percent vesicles that avoided coalescence during ascent. The spatter erupted at the vent is quench granulated in seawater above the vent, reducing the pyroclast grainsize. The granulated spatter and limu o Pele fragments are

  2. Northeast Regional Biomass Program

    SciTech Connect

    Lusk, P.D.

    1992-12-01

    The Northeast Regional Biomass Program has been in operation for a period of nine years. During this time, state managed programs and technical programs have been conducted covering a wide range of activities primarily aim at the use and applications of wood as a fuel. These activities include: assessments of available biomass resources; surveys to determine what industries, businesses, institutions, and utility companies use wood and wood waste for fuel; and workshops, seminars, and demonstrations to provide technical assistance. In the Northeast, an estimated 6.2 million tons of wood are used in the commercial and industrial sector, where 12.5 million cords are used for residential heating annually. Of this useage, 1504.7 mw of power has been generated from biomass. The use of wood energy products has had substantial employment and income benefits in the region. Although wood and woodwaste have received primary emphasis in the regional program, the use of municipal solid waste has received increased emphasis as an energy source. The energy contribution of biomass will increase as potentia users become more familiar with existing feedstocks, technologies, and applications. The Northeast Regional Biomass Program is designed to support region-specific to overcome near-term barriers to biomass energy use.

  3. High seismic attenuation at a mid-ocean ridge reveals the distribution of deep melt

    NASA Astrophysics Data System (ADS)

    Eilon, Z.; Abers, G. A.

    2016-12-01

    Measurements of seismic velocity and attenuation provide complementary constraints on the thermal and compositional character of the Earth's interior. In particular, observations of attenuation hold promise for identifying and characterizing the presence of melt and thermal heterogeneity in the upper mantle. By measuring relative phase and amplitude spectra of teleseismic body waves recorded on three years of Cascadia Initiative ocean-bottom seismometers, we calculate differential attenuation across an entire oceanic plate, exploiting the unprecedented coverage from ridge to trench. This study comprises the most detailed body wave interrogation of mid-ocean ridge attenuation to date. We find a strong age-dependency to the apparent attenuation and travel time: maximal attenuation and delays (Δt*S 1.7 s and δTS 2 s) are observed at stations ≤50 km from the Juan de Fuca and Gorda ridge axes, and lowest attenuation is seen at stations on 4-8 Ma crust. The high attenuation implies quality factor (Q) on the order of 20 beneath the mid-ocean ridge - comparable to the lowest Q previously recorded worldwide, in the Lau back-arc. Observed phase spectra, absolute amplitudes, and travel times are not compatible with extrinsic sources of apparent attenuation (scattering or focusing) and imply anelastic dissipation in shear. The increase in ∆t* between 0-4 Ma of the spreading centers is inconsistent with a purely thermal control on attenuation. Rather, several lines of evidence point to a large, localized contribution from deep (>60 km) melt beneath the spreading centers, while the gradual diminution in attenuation with crustal age hints at ponded sub-lithospheric melt 50-100 km off axis. Simple synthetic models harnessing experimentally-derived anelastic scaling relationships indicate that the observations can be satisfied by a sub-ridge region in which up to 2% in situ melt enhances diffusivity and reduces diffusion creep shear viscosity by three orders of magnitude over

  4. Rapid cooling rates at an active mid-ocean ridge from zircon thermochronology

    USGS Publications Warehouse

    Schmitt, Axel K.; Perfit, Michael R.; Rubin, Kenneth H.; Stockli, Daniel F.; Smith, Matthew C.; Cotsonika, Laurie A.; Zellmer, Georg F.; Ridley, W. Ian

    2011-01-01

    Oceanic spreading ridges are Earth's most productive crust generating environment, but mechanisms and rates of crustal accretion and heat loss are debated. Existing observations on cooling rates are ambiguous regarding the prevalence of conductive vs. convective cooling of lower oceanic crust. Here, we report the discovery and dating of zircon in mid-ocean ridge dacite lavas that constrain magmatic differentiation and cooling rates at an active spreading center. Dacitic lavas erupted on the southern Cleft segment of the Juan de Fuca ridge, an intermediate-rate spreading center, near the intersection with the Blanco transform fault. Their U–Th zircon crystallization ages (29.3-4.6+4.8 ka; 1δ standard error s.e.) overlap with the (U–Th)/He zircon eruption age (32.7 ± 1.6 ka) within uncertainty. Based on similar 238U-230Th disequilibria between southern Cleft dacite glass separates and young mid-ocean ridge basalt (MORB) erupted nearby, differentiation must have occurred rapidly, within ~ 10–20 ka at most. Ti-in-zircon thermometry indicates crystallization at 850–900 °C and pressures > 70–150 MPa are calculated from H2O solubility models. These time-temperature constraints translate into a magma cooling rate of ~ 2 × 10-2 °C/a. This rate is at least one order-of-magnitude faster than those calculated for zircon-bearing plutonic rocks from slow spreading ridges. Such short intervals for differentiation and cooling can only be resolved through uranium-series (238U–230Th) decay in young lavas, and are best explained by dissipating heat convectively at high crustal permeability.

  5. Advanced Seismic Studies of the Endeavour Ridge: Understanding the Interplay among Magmatic, Hydrothermal, and Tectonic Processes at Mid-Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Arnoux, G. M.; VanderBeek, B. P.; Morgan, J. V.; Hooft, E. E. E.; Toomey, D. R.; Wilcock, W. S. D.; Warner, M.

    2014-12-01

    At mid-ocean ridges magmatic, hydrothermal, and tectonic processes are linked. Understanding their interactions requires mapping magmatic systems and tectonic structures, as well as their relationship to hydrothermal circulation. Three-dimensional seismic images of the crust can be used to infer the size, shape, and location of magma reservoirs, in addition to the structure of the thermal boundary layer that connects magmatic and hydrothermal processes. Travel time tomography has often been used to study these processes, however, the spatial resolution of travel time tomography is limited. Three-dimensional full waveform inversion (FWI) is a state-of-the art seismic method developed for use in the oil industry to obtain high-resolution models of the velocity structure. The primary advantage of FWI is that it has the potential to resolve subsurface structures on the order of half the seismic wavelength—a significant improvement on conventional travel time tomography. Here, we apply anisotropic FWI to data collected on the Endeavour segment of the Juan de Fuca Ridge. Starting models for anisotropic P-wave velocity were obtained by travel time tomography [Weekly et al., 2014]. During FWI, the isotropic velocity model is updated and anisotropy is held constant. We have recovered low-velocity zones approximately 2-3 km beneath the ridge axis that likely correspond to a segmented magma-rich body and are in concert with those previously resolved using multi-channel seismic reflection methods. The segmented crustal magma body underlies all five known high-temperature hydrothermal vent fields along the Endeavour segment. A high-velocity zone, shallower than the observed low-velocity zones, underlies the southernmost hydrothermal vent field. This may be indicative of waning hydrothermal activity in which minerals are crystallizing beneath the vent field. Our FWI study of the Endeavour Ridge will provide the most detailed three-dimensional images of the crustal structure to

  6. Sub-Seafloor Carbon Dioxide Storage Potential on the Juan de Fuca Plate, Western North America

    SciTech Connect

    Jerry Fairley; Robert Podgorney

    2012-11-01

    The Juan de Fuca plate, off the western coast of North America, has been suggested as a site for geological sequestration of waste carbon dioxide because of its many attractive characteristics (high permeability, large storage capacity, reactive rock types). Here we model CO2 injection into fractured basalts comprising the upper several hundred meters of the sub-seafloor basalt reservoir, overlain with low-permeability sediments and a large saline water column, to examine the feasibility of this reservoir for CO2 storage. Our simulations indicate that the sub-seafloor basalts of the Juan de Fuca plate may be an excellent CO2 storage candidate, as multiple trapping mechanisms (hydrodynamic, density inversions, and mineralization) act to keep the CO2 isolated from terrestrial environments. Questions remain about the lateral extent and connectivity of the high permeability basalts; however, the lack of wells or boreholes and thick sediment cover maximize storage potential while minimizing potential leakage pathways. Although promising, more study is needed to determine the economic viability of this option.

  7. A Geo-referenced 3D model of the Juan de Fuca Slab and associated seismicity

    USGS Publications Warehouse

    Blair, J.L.; McCrory, P.A.; Oppenheimer, D.H.; Waldhauser, F.

    2011-01-01

    We present a Geographic Information System (GIS) of a new 3-dimensional (3D) model of the subducted Juan de Fuca Plate beneath western North America and associated seismicity of the Cascadia subduction system. The geo-referenced 3D model was constructed from weighted control points that integrate depth information from hypocenter locations and regional seismic velocity studies. We used the 3D model to differentiate earthquakes that occur above the Juan de Fuca Plate surface from earthquakes that occur below the plate surface. This GIS project of the Cascadia subduction system supersedes the one previously published by McCrory and others (2006). Our new slab model updates the model with new constraints. The most significant updates to the model include: (1) weighted control points to incorporate spatial uncertainty, (2) an additional gridded slab surface based on the Generic Mapping Tools (GMT) Surface program which constructs surfaces based on splines in tension (see expanded description below), (3) double-differenced hypocenter locations in northern California to better constrain slab location there, and (4) revised slab shape based on new hypocenter profiles that incorporate routine depth uncertainties as well as data from new seismic-reflection and seismic-refraction studies. We also provide a 3D fly-through animation of the model for use as a visualization tool.

  8. Imaging the Juan de Fuca plate beneath southern Oregon using teleseismic P wave residuals

    USGS Publications Warehouse

    Harris, R.A.; Iyer, H.M.; Dawson, P.B.

    1991-01-01

    Images the Juan de Fuca plate in southern Oregon using seismic tomography. P wave travel time residuals from a 366-km-long seismic array operated in southern Oregon in 1982 are inverted. The southeast striking array extended from the Coast ranges to the Modoc Plateau and crossed the High Cascades at Crater Lake, Oregon. Three features under the array were imaged: one high-velocity zone and two low-velocity zones. The high-velocity zone is 3-4% faster than the surrounding upper mantle. It dips steeply at 65?? to the east beneath the Cascade Range and extends down to at least 200 km. It is proposed that this high-velocity feature is subducted Juan de Fuca plate. Two low-velocity zones were also imaged, both of which are 3-4% slower than the surrounding earth structure. The southeastern low-velocity zone may be caused by partially molten crust underlying the Crater Lake volcano region. -from Authors

  9. Tomographic imaging of the Cascadia subduction zone: Constraints on the Juan de Fuca slab

    NASA Astrophysics Data System (ADS)

    Chen, Chuanxu; Zhao, Dapeng; Wu, Shiguo

    2015-04-01

    We used 40,343 P-wave arrival times from 1883 local earthquakes and 105,455 P-wave arrivals from 6361 teleseismic events to study the detailed structure of the Cascadia subduction zone. We conducted tomographic inversions using a starting velocity model which includes the high-velocity subducting Juan de Fuca slab as a priori information. A number of such slab-constrained inversions are conducted by changing the slab thickness and the velocity contrast between the slab and the surrounding mantle. Our optimal 3-D velocity model fits the data much better than that determined by an inversion with a 1-D homogeneous starting model. Our results show that the subducting Juan de Fuca slab has a thickness of 30-50 km and a P-wave velocity of 1-3% higher than that of the surrounding mantle. Beneath the northern and southern parts of the Cascadia, P-wave velocity is lower in the slab and along the slab interface, which may reflect a more hydrated slab and more active slab dehydration there. The lateral velocity variations may indicate different degrees of slab dehydration and forearc mantle serpentinization. The segmentation in episodic tremor and slip (ETS) is also spatially coincident with the velocity heterogeneities, indicating that the ETS occurrence and recurrence interval are controlled by fluid activity in and around the mantle wedge corner.

  10. 46 CFR 7.145 - Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 1 2010-10-01 2010-10-01 false Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA. 7.145 Section 7.145 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY PROCEDURES... of Georgia WA. (a) A line drawn from the northernmost point of Angeles Point to latitude 48°21.1′ N...

  11. 46 CFR 7.145 - Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 1 2011-10-01 2011-10-01 false Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA. 7.145 Section 7.145 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY PROCEDURES... of Georgia WA. (a) A line drawn from the northernmost point of Angeles Point to latitude 48°21.1′ N...

  12. Blastomycosis in northeast Tennessee.

    PubMed

    Vasquez, J E; Mehta, J B; Agrawal, R; Sarubbi, F A

    1998-08-01

    To study the epidemiologic and clinical features of blastomycosis in northeast Tennessee. Retrospective review of blastomycosis cases in the region from 1980 through 1995. Hospitals located in the Tri-Cities region of northeast Tennessee. Seventy-two patients with confirmed blastomycosis infection. None. During the 1980 to 1995 study period, we documented 72 cases of blastomycosis. The mean age was 52 years (range, 13 to 86 years), most were male (69.4%), and nine were immunocompromised. A possible environmental exposure was noted for 28 patients. Pulmonary involvement represented the most common site of infection (61 cases), but multiorgan involvement was common (17 cases). Most patients with pulmonary blastomycosis (66%) presented with a chronic illness, and radiologic findings usually revealed local consolidation or a mass-like lesion. Nine patients developed ARDS with an associated mortality rate of 89%, compared with a 10% mortality for non-ARDS pulmonary cases. Antifungal treatment regimens varied widely, with amphotericin B often used for sicker patients. An epidemiologic evaluation revealed that the mean yearly incidence rate for blastomycosis quadrupled between 1980 and 1987 (0.31 cases/ 100,000 population) and 1988 to 1995 (1.23 cases/100,000 population) (p=0.00001). Most new blastomycosis cases in the 1988 to 1995 period occurred in three counties in the region where significant new construction projects have been underway. Blastomycosis is endemic in northeast Tennessee and the number of cases is increasing, coinciding with major new construction in the region. Clinicians in the area must be alert to this condition.

  13. 2. SOUTHWEST VIEW OF NORTH SIDE (NORTHEAST CORNER).. THE NORTHEAST ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. SOUTHWEST VIEW OF NORTH SIDE (NORTHEAST CORNER).. THE NORTHEAST SIDE OF THE MINE OFFICE IS IN THE BACKGROUND. - Juniata Mill Complex, Mill Camp Shed, 22.5 miles Southwest of Hawthorne, between Aurora Crater & Aurora Peak, Hawthorne, Mineral County, NV

  14. Remedial investigation work plan for Chestnut Ridge Operable Unit 4 (Rogers Quarry/Lower McCoy Branch) at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee

    SciTech Connect

    Not Available

    1993-09-01

    The Oak Ridge Y-12 Plant includes - 800 acres near the northeast comer of the reservation and adjacent to the city of Oak Ridge (Fig. 1-1). The plant is a manufacturing and developmental engineering facility that produced components for various nuclear weapons systems and provides engineering support to other Energy Systems facilities. More than 200 contaminated sites have been identified at the Y-12 Plant that resulted from past waste management practices. Many of the sites have operable units (OUs) based on priority and on investigative and remediation requirements. This Remedial Investigation RI work plan specifically addresses Chestnut Ridge OU 4. Chestnut Ridge OU 4 consists of Rogers Quarry and Lower McCoy Branch (MCB). Rogers Quarry, which is also known as Old Rogers Quarry or Bethel Valley Quarry was used for quarrying from the late 1940s or early 1950s until about 1960. Since that time, the quarry has been used for disposal of coal ash and materials from Y-12 production operations, including classified materials. Disposal of coal ash ended in July 1993. An RI is being conducted at this site in response to CERCLA regulations. The overall objectives of the RI are to collect data necessary to evaluate the nature and extent of contaminants of concern, support an Ecological Risk Assessment and a Human Health Risk Assessment, support the evaluation of remedial alternatives, and ultimately develop a Record of Decision for the site. The purpose of this work plan is to outline RI activities necessary to define the nature and extent of suspected contaminants at Chestnut Ridge OU 4. Potential migration pathways also will be investigated. Data collected during the RI will be used to evaluate the risk posed to human health and the environment by OU 4.