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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. 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.

  4. 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

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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...are investigating the potential correlation between whale tracks, enhanced zooplankton concentrations and hydrothermal vents above the Juan de Fuca...preferentially found above the hydrothermal vent fields where the bio-acoustical data show that the zooplankton concentrations are higher at all depths. 3

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. 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

  2. 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

  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. 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.

  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. 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

  7. Investigating the Relationship between Fin Whales, Zooplankton Concentrations and Hydrothermal Venting on the Juan de Fuca Ridge

    DTIC Science & Technology

    2014-09-30

    1992). Composition of a deep scattering layer overlying a mid - ocean ridge hydrothermal plume, Mar. Biol. 113, 517-526. Croll, D. A., Clark, C. W...Endeavour segment of the Juan de Fuca Ridge (Weekly et al., 2013) that included a network of eight ocean bottom seismometers (OBSs) that operated from... mid -1990s, the Institute of Ocean Sciences in Sidney, BC conducted summer cruises to the Endeavour to collect a series of plankton net tows in

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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.

  19. 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).

  20. 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.

  1. 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.

  2. 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.

  3. 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).

  4. 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...We are investigating the potential correlation between fin whale tracks, enhanced zooplankton concentrations and hydrothermal vents above the Juan de...the location of hydrothermal vents 2. Determine whale call counts for ocean bottom seismometers deployed at mid-plate locations on the Explorer and

  5. 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

    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...concentrations within the water column above the hydrothermal vents . Report Documentation Page Form ApprovedOMB No. 0704-0188 Public reporting burden for

  6. 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

  7. 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

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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.

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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

  4. 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

  5. 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

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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).

  16. 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

  17. 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.

  18. 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

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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

  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. 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

  8. 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.

  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. 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.

  11. 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.

  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. 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.

  14. 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.

  15. 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

  16. 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

  17. 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.

  18. 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).

  19. 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.

  20. 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.

  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. 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.

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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.; 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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

    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. 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.

  16. 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

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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....

  9. 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....

  10. 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....

  11. 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....

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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].

  17. 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...

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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...

  3. 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,...

  4. 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...

  5. 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...

  6. 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...

  7. 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...

  8. 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...

  9. 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,...

  10. 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...

  11. 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...

  12. 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,...

  13. 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...

  14. 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...

  15. 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...

  16. 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...

  17. 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...

  18. 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,...

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Metopic ridge

    MedlinePlus

    ... plates allow for growth of the skull. The places where these plates connect are called sutures or suture lines. They do not fully close until the 2nd or 3rd year of life. A metopic ridge occurs when ...

  4. 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

  5. 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.

  6. 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

  7. 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...

  8. 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...

  9. 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...

  10. 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...

  11. 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...

  12. 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...

  13. 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...

  14. 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...

  15. 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)...

  16. 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)...

  17. 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.

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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...

  12. 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...

  13. 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...

  14. 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...

  15. 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)

  16. 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

  17. 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...

  18. 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...

  19. 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 APPLICABLE TO THE PUBLIC BOUNDARY LINES Pacific Coast § 7.145 Strait of Juan de Fuca, Haro Strait and...

  20. 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...

  1. 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)...

  2. 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)...

  3. 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)...

  4. 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)...

  5. 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)...

  6. 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.

  7. 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.

  8. 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.

  9. 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).

  10. 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.

  11. 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.; 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.

  12. 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

  13. 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.

  14. 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 APPLICABLE TO THE PUBLIC BOUNDARY LINES Pacific Coast § 7.145 Strait of Juan de Fuca, Haro Strait and Strait of Georgia WA. (a) A line drawn from...

  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. 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

  17. An Investigation of Fin and Blue Whales in the NE Pacific Ocean using Data from Cascadia Initiative Ocean Bottom Seismometers

    DTIC Science & Technology

    2014-09-30

    Fuca Ridge . IMPACT/APPLICATIONS There is a movement within the US and global marine seismic communities to expand the number of ocean bottom...network on the Juan de Fuca Ridge , Northeast Pacific Ocean , J. Acoust. Soc. Am., 133, 1751-1761. Stafford K.M., Fox C.G., Clark D.S. (1998) Long... Ocean using Data from Cascadia Initiative Ocean Bottom Seismometers William S. D. Wilcock School of Oceanography University of Washington Box

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

    historical and NEPTUNE Canada ADCP data to understand the relationship between the seasonal migration patterns of zooplankton and their enhanced...continental slope offshore Nootka Sound (Fig. 1). More recently, NEPTUNE Canada has commenced seismic observations at 4 nodes on their cabled observatory...showing the locations of seismometers deployed in the Keck experiment and broadband seismometers on the NEPTUNE Canada cabled observatory. In the

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.…

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. Spatial and temporal distribution of the seismicity along two mid-oceanic ridges with contrasted spreading rates in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Tsang-Hin-Sun, E.; Perrot, J.; Royer, J. Y.

    2015-12-01

    The seismicity of the ultra-slow spreading Southwest (14 mm/y) and intermediate spreading Southeast (60 mm/y) Indian ridges was monitored from February 2012 to March 2013 by the OHASISBIO array of 7 autonomous hydrophones. A total of 1471 events were located with 4 instruments or more, inside the array, with a median location uncertainty < 5 km and a completeness magnitude of mb = 3. Both ridges display similar average rates of seismicity, suggesting that there is no systematic relationship between seismicity and spreading rates. Accretion modes do differ, however, by the along-axis distribution of the seismic events. Along the ultra-slow Southwest Indian Ridge, events are sparse but regularly spaced and scattered up to 50 km off-axis. Along the fast Southeast Indian Ridge, events are irregularly distributed, focusing in narrow regions near the ridge axis at segment ends and along transform faults, whereas ridge-segment centers generally appear as seismic gaps (at the level of completeness of the array). Only two clusters, 6 months apart, are identified in a segment-center at 29°S. From the temporal distribution of the clustered events and comparisons with observations in similar mid-oceanic ridge setting, both clusters seem to have a volcanic origin and to be related to a dike emplacement or a possible eruption on the seafloor. Their onset time and migration rate are comparable to volcanic swarms recorded along the Juan de Fuca Ridge. Overall, the rate of seismicity along the two Indian spreading ridges correlates with the large-scale variations in the bathymetry and shear-wave velocity anomaly in the upper mantle, suggesting that the distribution of the low-magnitude seismicity is mainly controlled by along-axis variations in the lithosphere rheology and temperature.

  8. 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.

  9. Dacite petrogenesis on mid-ocean ridges: Evidence for oceanic crustal melting and assimilation

    USGS Publications Warehouse

    Wanless, V.D.; Perfit, M.R.; Ridley, W.I.; Klein, E.

    2010-01-01

    Whereas the majority of eruptions at oceanic spreading centers produce lavas with relatively homogeneous mid-ocean ridge basalt (MORB) compositions, the formation of tholeiitic andesites and dacites at mid-ocean ridges (MORs) is a petrological enigma. Eruptions of MOR high-silica lavas are typically associated with ridge discontinuities and have produced regionally significant volumes of lava. Andesites and dacites have been observed and sampled at several locations along the global MOR system; these include propagating ridge tips at ridge-transform intersections on the Juan de Fuca Ridge and eastern Gal??pagos spreading center, and at the 9??N overlapping spreading center on the East Pacific Rise. Despite the formation of these lavas at various ridges, MOR dacites show remarkably similar major element trends and incompatible trace element enrichments, suggesting that similar processes are controlling their chemistry. Although most geochemical variability in MOR basalts is consistent with low-pressure fractional crystallization of various mantle-derived parental melts, our geochemical data for MOR dacitic glasses suggest that contamination from a seawater-altered component is important in their petrogenesis. MOR dacites are characterized by elevated U, Th, Zr, and Hf, low Nb and Ta concentrations relative to rare earth elements (REE), and Al2O3, K2O, and Cl concentrations that are higher than expected from low-pressure fractional crystallization alone. Petrological modeling of MOR dacites suggests that partial melting and assimilation are both integral to their petrogenesis. Extensive fractional crystallization of a MORB parent combined with partial melting and assimilation of amphibole-bearing altered crust produces a magma with a geochemical signature similar to a MOR dacite. This supports the hypothesis that crustal assimilation is an important process in the formation of highly evolved MOR lavas and may be significant in the generation of evolved MORB in

  10. Petrogenesis of Near-Ridge Seamounts: AN Investigation of Mantle Source Heterogeneity and Melting Processes

    NASA Astrophysics Data System (ADS)

    Baxter, N. L.; Perfit, M. R.; Lundstrom, C.; Clague, D. A.

    2010-12-01

    Near-ridge (NR) seamounts offer an important opportunity to study lavas that have similar sources to ridge basalts but have been less affected by fractionation and homogenization that takes place at adjacent spreading ridge axes. By studying lavas erupted at these off-axis sites, we have the potential to better understand source heterogeneity and melting and transport processes that can be applied to the ridge system as a whole. One purpose of our study is to investigate the role of dunite conduits in the formation of near-ridge seamount chains. We believe that near-ridge seamounts could form due to focusing of melts in dunite channels located slightly off-axis and that such conduits may be important in the formation and transport of melt both on- and off-axis (Lundstrom et al., 2000). New trace element and isotopic analyses of glasses from Rogue, Hacksaw, and T461 seamounts near the Juan de Fuca Ridge (JdFR), the Lamont Seamounts adjacent to the East Pacific Rise (EPR) ~ 10°N, and the Vance Seamounts next to the JdFR ~45°N provide a better understanding of the petrogenesis of NR seamounts. Our data indicate that lavas from these seamounts have diverse incompatible trace element compositions that range from highly depleted to slightly enriched in comparison to associated ridge basalts. Vance A lavas (the oldest in the Vance chain) have the most enriched signatures and lavas from Rogue seamount on the JdFR plate have the most depleted signatures. Sr-Nd-Pb isotopic ratios indicate that NR seamount lava compositions vary within the chains as well as within individual seamounts, and that there is some mixing between heterogeneous, small-scale mantle sources. Using the program PRIMELT2.XLS (Herzberg and Asimow, 2008), we calculated mantle potential temperatures (Tp) for some of the most primitive basalts erupted at these seamounts. Our data indicate that NR seamount lavas have Tp values that are only slightly higher than that of average ambient mantle. Variations in

  11. Mantle plume capture, anchoring, and outflow during Galápagos plume-ridge interaction

    NASA Astrophysics Data System (ADS)

    Gibson, S. A.; Geist, D. J.; Richards, M. A.

    2015-05-01

    Compositions of basalts erupted between the main zone of Galápagos plume upwelling and adjacent Galápagos Spreading Center (GSC) provide important constraints on dynamic processes involved in transfer of deep-mantle-sourced material to mid-ocean ridges. We examine recent basalts from central and northeast Galápagos including some that have less radiogenic Sr, Nd, and Pb isotopic compositions than plume-influenced basalts (E-MORB) from the nearby ridge. We show that the location of E-MORB, greatest crustal thickness, and elevated topography on the GSC correlates with a confined zone of low-velocity, high-temperature mantle connecting the plume stem and ridge at depths of ˜100 km. At this site on the ridge, plume-driven upwelling involving deep melting of partially dehydrated, recycled ancient oceanic crust, plus plate-limited shallow melting of anhydrous peridotite, generate E-MORB and larger amounts of melt than elsewhere on the GSC. The first-order control on plume stem to ridge flow is rheological rather than gravitational, and strongly influenced by flow regimes initiated when the plume was on axis (>5 Ma). During subsequent northeast ridge migration material upwelling in the plume stem appears to have remained "anchored" to a contact point on the GSC. This deep, confined NE plume stem-to-ridge flow occurs via a network of melt channels, embedded within the normal spreading and advection of plume material beneath the Nazca plate, and coincides with locations of historic volcanism. Our observations require a more dynamically complex model than proposed by most studies, which rely on radial solid-state outflow of heterogeneous plume material to the ridge.

  12. Sub-km HIMU-type Enriched Mantle at a Mid-ocean Ridge Far From a Plume: Endeavour, JdFR

    NASA Astrophysics Data System (ADS)

    Gill, J. B.; Michael, P. J.; Dreyer, B. M.; Clague, D. A.; Ramos, F. C.

    2015-12-01

    The Endeavour segment of the Juan de Fuca Ridge is characterized by abundant enriched (E) MORB since the currently inflated axial ridge formed <105 years ago, and by the full range of depleted (D) to E-MORB during the last 2300 years in the km-wide axial graben. Two different styles of enrichment of moderately incompatible elements are present. The first characterized basalts across the ~5 km-wide ridge from >10,000 to ~4000 years ago, whereas the second characterizes more recent basalts erupted in the axial graben. We attribute the first to a higher proportion of pyroxenite to enriched peridotite in the mantle source during ridge inflation. The more recent style reflects the reduced role of pyroxenite after the axial graben formed. The enriched component for both styles is a HIMU-type because it has low 87Sr/86Sr and 176Hf/177Hf relative to 143Nd/144Nd, lower 3He/4He (~8.1 RA) than in the more depleted basalts, shallow slopes on Pb isotope diagrams, and high Nb/LREE ratios. It is regionally widespread and shared with the West Valley and Explorer segments to the north. At least 14 different samplings of mantle components occurred within <1 km of ridge length and width during a time when <1 km of upwelling occurred, indicating that the scale of mantle heterogeneity is <1 km in this setting that is far from a plume.

  13. Tomography reveals buoyant asthenosphere accumulating beneath the Juan de Fuca plate

    NASA Astrophysics Data System (ADS)

    Hawley, William B.; Allen, Richard M.; Richards, Mark A.

    2016-09-01

    The boundary between Earth’s strong lithospheric plates and the underlying mantle asthenosphere corresponds to an abrupt seismic velocity decrease and electrical conductivity increase with depth, perhaps indicating a thin, weak layer that may strongly influence plate motion dynamics. The behavior of such a layer at subduction zones remains unexplored. We present a tomographic model, derived from on- and offshore seismic experiments, that reveals a strong low-velocity feature beneath the subducting Juan de Fuca slab along the entire Cascadia subduction zone. Through simple geodynamic arguments, we propose that this low-velocity feature is the accumulation of material from a thin, weak, buoyant layer present beneath the entire oceanic lithosphere. The presence of this feature could have major implications for our understanding of the asthenosphere and subduction zone dynamics.

  14. Observations of a summertime reversal in circulation in the Strait of Juan de Fuca

    SciTech Connect

    Frisch, A.S.; Holbrook, J.; Ages, A.B.

    1981-03-20

    While measuring currents in the Strait of Juan de Fuca, we recorded an unusual 3-day reversal in the surface current, from seaward to landward, in apparent response to the southerly winds of a coastal storm. The reversal was mointiored by four surface drifters and three moored current meter arrays that recorded the current at 20- to 130-m depths. Spatial details of the reversal patterns, mapped by an HF current-sensing radar at the boundary between the inward and outward flow, showed a complex surface-circulation pattern with a strong southerly flow toward New Dungeness Split. Although such reversals have been previously recorded in nonsummer months, their appearance in the summer, when coastal cyclonic storms are uncommon and river discharge is high, is unusual.

  15. Tomography reveals buoyant asthenosphere accumulating beneath the Juan de Fuca plate.

    PubMed

    Hawley, William B; Allen, Richard M; Richards, Mark A

    2016-09-23

    The boundary between Earth's strong lithospheric plates and the underlying mantle asthenosphere corresponds to an abrupt seismic velocity decrease and electrical conductivity increase with depth, perhaps indicating a thin, weak layer that may strongly influence plate motion dynamics. The behavior of such a layer at subduction zones remains unexplored. We present a tomographic model, derived from on- and offshore seismic experiments, that reveals a strong low-velocity feature beneath the subducting Juan de Fuca slab along the entire Cascadia subduction zone. Through simple geodynamic arguments, we propose that this low-velocity feature is the accumulation of material from a thin, weak, buoyant layer present beneath the entire oceanic lithosphere. The presence of this feature could have major implications for our understanding of the asthenosphere and subduction zone dynamics.

  16. Polygonal Ridge Networks on Mars

    NASA Astrophysics Data System (ADS)

    Kerber, Laura; Dickson, James; Grosfils, Eric; Head, James W.

    2016-10-01

    Polygonal ridge networks, also known as boxwork or reticulate ridges, are found in numerous locations and geological contexts across Mars. While networks formed from mineralized fractures hint at hot, possibly life-sustaining circulating ground waters, networks formed by impact-driven clasting diking, magmatic dikes, gas escape, or lava flows do not have the same astrobiological implications. Distinguishing the morphologies and geological context of the ridge networks sheds light on their potential as astrobiological and mineral resource sites of interest. The most widespread type of ridge morphology is characteristic of the Nili Fossae and Nilosyrtis region and consists of thin, criss-crossing ridges with a variety of heights, widths, and intersection angles. They are found in ancient Noachian terrains at a variety of altitudes and geographic locations and may be a mixture of clastic dikes, brecciated dikes, and mineral veins. They occur in the same general areas as valley networks and ancient lake basins, but they are not more numerous where these features are concentrated, and can appear in places where they morphologies are absent. Similarly, some of the ridge networks are associated with hydrated mineral detections, but some occur in locations without detections. Smaller, light-toned ridges of variable widths have been found in Gale Crater and other rover sites and are interpreted to be smaller version of the Nili-like ridges, in this case formed by the mineralization of fractures. This type of ridge is likely to be found in many other places on Mars as more high-resolution data becomes available. Hellas Basin is host to a third type of ridge morphology consisting of large, thick, light-toned ridges forming regular polygons at several superimposed scales. While still enigmatic, these are most likely to be the result of sediment-filled fractures. The Eastern Medusae Fossae Formation contains large swaths of a fourth, previously undocumented, ridge network type

  17. Triassic/Jurassic faulting patterns of Conecuh Ridge, southwest Alabama

    SciTech Connect

    Hutley, J.K.

    1985-02-01

    Two major fault systems influenced Jurassic structure and deposition on the Conecuh Ridge, southwest Alabama. Identification and dating of these fault systems are based on seismic-stratigraphic interpretation of a 7-township grid in Monroe and Conecuh Counties. Relative time of faulting is determined by fault geometry and by formation isopachs and isochrons. Smackover and Norphlet Formations, both Late Jurassic in age, are mappable seismic reflectors and are thus reliable for seismicstratigraphic dating. The earlier of the 2 fault systems is a series of horsts and grabens that trends northeast-southwest and is Late Triassic to Early Jurassic in age. The system formed in response to tensional stress associated with the opening of the Atlantic Ocean. The resulting topography was a series of northeast-southwest-trending ridges. Upper Triassic Eagle Mills and Jurassic Werner Formations were deposited in the grabens. The later fault system is also a series of horsts and grabens trending perpendicular to the first. This system was caused by tensional stress related to a pulse in the opening of the Gulf of Mexico. Faulting began in Early Jurassic and continued into Late Jurassic, becoming progressively younger basinward. At the basin margin, faulting produced a very irregular shoreline. Submerged horst blocks became centers for shoaling or carbonate buildups. Today, these blocks are exploration targets in southwest Alabama.

  18. Near-ridge seamount chains in the northeastern Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Clague, David A.; Reynolds, Jennifer R.; Davis, Alicé S.

    2000-07-01

    High-resolution bathymetry and side-scan data of the Vance, President Jackson, and Taney near-ridge seamount chains in the northeast Pacific were collected with a hull-mounted 30-kHz sonar. The central volcanoes in each chain consist of truncated cone-shaped volcanoes with steep sides and nearly flat tops. Several areas are characterized by frequent small eruptions that result in disorganized volcanic regions with numerous small cones and volcanic ridges but no organized truncated conical structure. Several volcanoes are crosscut by ridge-parallel faults, showing that they formed within 30-40 km of the ridge axis where ridge-parallel faulting is still active. Magmas that built the volcanoes were probably transported through the crust along active ridge-parallel faults. The volcanoes range in volume from 11 to 187 km3, and most have one or more multiple craters and calderas that modify their summits and flanks. The craters (<1 km diameter) and calderas (>1 km diameter) range from small pit craters to calderas as large as 6.5×8.5 km, although most are 2-4 km across. Crosscutting relationships commonly show a sequence of calderas stepping toward the ridge axis. The calderas overlie crustal magma chambers at least as large as those that underlie Kilauea and Mauna Loa Volcanoes in Hawaii, perhaps 4-5 km in diameter and ˜1-3 km below the surface. The nearly flat tops of many of the volcanoes have remnants of centrally located summit shields, suggesting that their flat tops did not form from eruptions along circumferential ring faults but instead form by filling and overflowing of earlier large calderas. The lavas retain their primitive character by residing in such chambers for only short time periods prior to eruption. Stored magmas are withdrawn, probably as dikes intruded into the adjacent ocean crust along active ridge-parallel faults, triggering caldera collapse, or solidified before the next batch of magma is intruded into the volcano, probably 1000-10,000 years

  19. Slab stagnation and detachment under northeast China

    NASA Astrophysics Data System (ADS)

    Honda, Satoru

    2016-03-01

    Results of tomography models around the Japanese Islands show the existence of a gap between the horizontally lying (stagnant) slab extending under northeastern China and the fast seismic velocity anomaly in the lower mantle. A simple conversion from the fast velocity anomaly to the low-temperature anomaly shows a similar feature. This feature appears to be inconsistent with the results of numerical simulations on the interaction between the slab and phase transitions with temperature-dependent viscosity. Such numerical models predict a continuous slab throughout the mantle. I extend previous analyses of the tomography model and model calculations to infer the origins of the gap beneath northeastern China. Results of numerical simulations that take the geologic history of the subduction zone into account suggest two possible origins for the gap: (1) the opening of the Japan Sea led to a breaking off of the otherwise continuous subducting slab, or (2) the western edge of the stagnant slab is the previous subducted ridge, which was the plate boundary between the extinct Izanagi and the Pacific plates. Origin (2) suggesting the present horizontally lying slab has accumulated since the ridge subduction, is preferable for explaining the present length of the horizontally lying slab in the upper mantle. Numerical models of origin (1) predict a stagnant slab in the upper mantle that is too short, and a narrow or non-existent gap. Preferred models require rather stronger flow resistance of the 660-km phase change than expected from current estimates of the phase transition property. Future detailed estimates of the amount of the subducted Izanagi plate and the present stagnant slab would be useful to constrain models. A systematic along-arc variation of the slab morphology from the northeast Japan to Kurile arcs is also recognized, and its understanding may constrain the 3D mantle flow there.

  20. SeaVOICE: Sea-going Experiments to Test Potential Linkages among Sea Level Change, Ocean Ridge Volcanism, and Hydrothermal Activity.

    NASA Astrophysics Data System (ADS)

    Langmuir, C. H.; Carbotte, S. M.; Huybers, P. J.; McManus, J. F.; Mukhopadhyay, S.; Winckler, G.; Boulahanis, B.; Costa, K.; Ferguson, D.; Katz, R. F.; Li, Y.; Middleton, J. L.

    2015-12-01

    Changes in sea level influence the pressure of the solid Earth over entire ocean basins. While the absolute changes in sea level caused by glacial cycles are small relative to ocean depths, the temporal variations in sea level can lead to pressure changes of similar order to mantle upwelling rates, with the potential to significantly perturb short term rates of melt production at ocean ridges (Huybers and Langmuir, EPSL, 2009). Such changes could then lead to fluctuations in crustal thickness, magma composition and hydrothermal activity. To investigate possible relationships between glacial cycles and ocean ridge processes, we carried out an 18 day cruise of mapping and sediment coring to the Cleft Segment of the Juan de Fuca ridge. High resolution bathymetry was obtained on the west side of the ridge axis to beyond 1Ma to test whether abyssal hill fabric shows periodicities consistent with glacial cycles. Nine successful piston cores up to 7.6m in length provide a sedimentary record back to more than 600kyr to test for spatial and temporal variations in hydrothermal activity. Oxygen isotope stratigraphy on these cores is systematic and provides good age constraints. Short cores near the ridge axis provide a record of the current trace of hydrothermal activity in youngest sediments. Several of the cores impacted basement and recovered a basement sample. Above basement, basaltic glass shards were recovered in the bottom meter of sediment, raising the possibility of temporal records of basalt chemical compositions using the age constraints the sediments provide. The glass samples provide a unique and new perspective on ridge volcanism, since previous off-axis samples were restricted to dredging old fault scarps. Cores can be taken anywhere, raising the potential for global time series studies of ridge volcanism. The coupled bathymetry, sediment geochemistry and magmatic glass compositions hold the promise of a definitive advance in our understanding of the

  1. A novel microbial habitat in the mid-ocean ridge subseafloor.

    PubMed

    Summit, M; Baross, J A

    2001-02-27

    The subseafloor at the mid-ocean ridge is predicted to be an excellent microbial habitat, because there is abundant space, fluid flow, and geochemical energy in the porous, hydrothermally influenced oceanic crust. These characteristics also make it a good analog for potential subsurface extraterrestrial habitats. Subseafloor environments created by the mixing of hot hydrothermal fluids and seawater are predicted to be particularly energy-rich, and hyperthermophilic microorganisms that broadly reflect such predictions are ejected from these systems in low-temperature ( approximately 15 degrees C), basalt-hosted diffuse effluents. Seven hyperthermophilic heterotrophs isolated from low-temperature diffuse fluids exiting the basaltic crust in and near two hydrothermal vent fields on the Endeavour Segment, Juan de Fuca Ridge, were compared phylogenetically and physiologically to six similarly enriched hyperthermophiles from samples associated with seafloor metal sulfide structures. The 13 organisms fell into four distinct groups: one group of two organisms corresponding to the genus Pyrococcus and three groups corresponding to the genus Thermococcus. Of these three groups, one was composed solely of sulfide-derived organisms, and the other two related groups were composed of subseafloor organisms. There was no evidence of restricted exchange of organisms between sulfide and subseafloor habitats, and therefore this phylogenetic distinction indicates a selective force operating between the two habitats. Hypotheses regarding the habitat differences were generated through comparison of the physiology of the two groups of hyperthermophiles; some potential differences between these habitats include fluid flow stability, metal ion concentrations, and sources of complex organic matter.

  2. Hydrothermal recharge and discharge across 50 km guided by seamounts on a young ridge flank.

    PubMed

    Fisher, A T; Davis, E E; Hutnak, M; Spiess, V; Zühlsdorff, L; Cherkaoui, A; Christiansen, L; Edwards, K; Macdonald, R; Villinger, H; Mottl, M J; Wheat, C G; Becker, K

    2003-02-06

    Hydrothermal circulation within the sea floor, through lithosphere older than one million years (Myr), is responsible for 30% of the energy released from plate cooling, and for 70% of the global heat flow anomaly (the difference between observed thermal output and that predicted by conductive cooling models). Hydrothermal fluids remove significant amounts of heat from the oceanic lithosphere for plates typically up to about 65 Myr old. But in view of the relatively impermeable sediments that cover most ridge flanks, it has been difficult to explain how these fluids transport heat from the crust to the ocean. Here we present results of swath mapping, heat flow, geochemistry and seismic surveys from the young eastern flank of the Juan de Fuca ridge, which show that isolated basement outcrops penetrating through thick sediments guide hydrothermal discharge and recharge between sites separated by more than 50 km. Our analyses reveal distinct thermal patterns at the sea floor adjacent to recharging and discharging outcrops. We find that such a circulation through basement outcrops can be sustained in a setting of pressure differences and crustal properties as reported in independent observations and modelling studies.

  3. Microbial community in black rust exposed to hot ridge flank crustal fluids.

    PubMed

    Nakagawa, Satoshi; Inagaki, Fumio; Suzuki, Yohey; Steinsbu, Bjørn Olav; Lever, Mark Alexander; Takai, Ken; Engelen, Bert; Sako, Yoshihiko; Wheat, Charles Geoffrey; Horikoshi, Koki

    2006-10-01

    During Integrated Ocean Drilling Program Expedition 301, we obtained a sample of black rust from a circulation obviation retrofit kit (CORK) observatory at a borehole on the eastern flank of Juan de Fuca Ridge. Due to overpressure, the CORK had failed to seal the borehole. Hot fluids from oceanic crust had discharged to the overlying bottom seawater and resulted in the formation of black rust analogous to a hydrothermal chimney deposit. Both culture-dependent and culture-independent analyses indicated that the black-rust-associated community differed from communities reported from other microbial habitats, including hydrothermal vents at seafloor spreading centers, while it shared phylotypes with communities previously detected in crustal fluids from the same borehole. The most frequently retrieved sequences of bacterial and archaeal 16S rRNA genes were related to the genera Ammonifex and Methanothermococcus, respectively. Most phylotypes, including phylotypes previously detected in crustal fluids, were isolated in pure culture, and their metabolic traits were determined. Quantification of the dissimilatory sulfite reductase (dsrAB) genes, together with stable sulfur isotopic and electron microscopic analyses, strongly suggested the prevalence of sulfate reduction, potentially by the Ammonifex group of bacteria. Stable carbon isotopic analyses suggested that the bulk of the microbial community was trophically reliant upon photosynthesis-derived organic matter. This report provides important insights into the phylogenetic, physiological, and trophic characteristics of subseafloor microbial ecosystems in warm ridge flank crusts.

  4. Remedial Investigation Report on Chestnut Ridge Operable Unit 2 (Filled Coal Ash Pond/Upper McCoy Branch) at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee. Volume 1. Main Text

    SciTech Connect

    Not Available

    1994-08-01

    This document is a report on the remedial investigation (RI) of Chestnut Ridge Operable Unit (OU) 2 at the Oak Ridge Y-12 Plant. Chestnut Ridge OU 2 consists of Upper McCoy Branch (UMB), the Filled Coal Ash Pond (FCAP), and the area surrounding the Sluice Channel formerly associated with coal ash disposal in the FCAP. Chestnut Ridge OU 2 is located within the U.S. Department of Energy`s (DOE`s) Oak Ridge Reservation in Anderson County, Tennessee, approximately 24 miles west of Knoxville. The pond is an 8.5-acre area on the southern slope of Chestnut Ridge, 0.5 mile south of the main Y-12 Plant and geographically separated from the Y-12 Plant by Chestnut Ridge. The elevation of the FCAP is {approximately} 950 ft above mean sea level (msl), and it is relatively flat and largely vegetated. Two small ponds are usually present at the northeast and northwest comers of the FCAP. The Sluice Channel Area extends {approximately}1000 ft from the northern margin of the FCAP to the crest of Chestnut Ridge, which has an elevation of {approximately}1100 ft above msl. The Sluice Channel Area is largely vegetated also. McCoy Branch runs from the top of Chestnut Ridge across the FCAP into Rogers Quarry and out of the quarry where it runs a short distance into Milton Hill Lake at McCoy Embayment, termed UMB. The portion south of Rogers Quarry, within Chestnut Ridge OU 4, is termed Lower McCoy Branch. The DOE Oak Ridge Y-12 Plant disposed of coal ash from its steam plant operations as a slurry that was discharged into an ash retention impoundment; this impoundment is the FCAP. The FCAP was built in 1955 to serve as a settling basin after coal ash slurried over Chestnut Ridge from the Y-12 Plant. The FCAP was constructed by building an earthen dam across the northern tributary of McCoy Branch. The dam was designed to hold 20 years of Y-12 steam plant ash. By July 1967, ash had filled up the impoundment storage behind the dam to within 4 ft of the top.

  5. Ridge 2000 Data Management System

    NASA Astrophysics Data System (ADS)

    Goodwillie, A. M.; Carbotte, S. M.; Arko, R. A.; Haxby, W. F.; Ryan, W. B.; Chayes, D. N.; Lehnert, K. A.; Shank, T. M.

    2005-12-01

    Hosted at Lamont by the marine geoscience Data Management group, mgDMS, the NSF-funded Ridge 2000 electronic database, http://www.marine-geo.org/ridge2000/, is a key component of the Ridge 2000 multi-disciplinary program. The database covers each of the three Ridge 2000 Integrated Study Sites: Endeavour Segment, Lau Basin, and 8-11N Segment. It promotes the sharing of information to the broader community, facilitates integration of the suite of information collected at each study site, and enables comparisons between sites. The Ridge 2000 data system provides easy web access to a relational database that is built around a catalogue of cruise metadata. Any web browser can be used to perform a versatile text-based search which returns basic cruise and submersible dive information, sample and data inventories, navigation, and other relevant metadata such as shipboard personnel and links to NSF program awards. In addition, non-proprietary data files, images, and derived products which are hosted locally or in national repositories, as well as science and technical reports, can be freely downloaded. On the Ridge 2000 database page, our Data Link allows users to search the database using a broad range of parameters including data type, cruise ID, chief scientist, geographical location. The first Ridge 2000 field programs sailed in 2004 and, in addition to numerous data sets collected prior to the Ridge 2000 program, the database currently contains information on fifteen Ridge 2000-funded cruises and almost sixty Alvin dives. Track lines can be viewed using a recently- implemented Web Map Service button labelled Map View. The Ridge 2000 database is fully integrated with databases hosted by the mgDMS group for MARGINS and the Antarctic multibeam and seismic reflection data initiatives. Links are provided to partner databases including PetDB, SIOExplorer, and the ODP Janus system. Improved inter-operability with existing and new partner repositories continues to be

  6. Oak Ridge fault, Ventura fold belt, and the Sisar decollement, Ventura basin, California

    SciTech Connect

    Yeats, R.S.; Huftile, G.J.; Grigsby, F.B. )

    1988-12-01

    The rootless Ventura Avenue, San Miguelito, and Rincon anticlines (Ventura fold belt) in Pliocene -Pleistocene turbidites are fault-propagation folds related to south-dipping reverse faults rising from a decollement in Miocene shale. To the east, the Sulfur Mountain anticlinorium overlies and is cut by the Sisar, Big Canyon, and Lion south-dipping thrusts that merge downward into the Sisar decollement in lower Miocene shale. Shortening of the Miocene and younger sequence is {approximately} 3 km greater than that of underlying competent Paleogens strata in the Ventura fold belt and {approximately} 7 km greater farther east at Sulfur Mountain. Cross-section balancing requires that this difference be taken up by the Paleogene sequence at the Oak Ridge fault to the south. Convergence is northeast to north-northeast on the base of earthquake focal mechanisms, borehole breakouts, and piercing-point offest of the South Mountain seaknoll by the Oak Ridge fault. A northeast-trending line connecting the west end of Oak Ridge and the east end of Sisar fault separates an eastern domain where late Quaternary displacement is taken up entirely on the Oak Ridge fault and a western domain where displacement is transferred to the Sisar decollement and its overlying rootless folds. This implies that (1) the Oak Ridge fault near the coast presents as much seismic risk as it does farther east, despite negligible near-surface late Quaternary movement; (2) ground-rupture hazard is high for the Sisar fault set in the upper Ojai Valley; and (3) the decollement itself could produce an earthquake analogous to the 1987 Whittier Narrows event in Low Angeles.

  7. Depth to the Juan De Fuca slab beneath the Cascadia subduction margin - a 3-D model for sorting earthquakes

    USGS Publications Warehouse

    McCrory, Patricia A.; Blair, J. Luke; Oppenheimer, David H.; Walter, Stephen R.

    2004-01-01

    We present an updated model of the Juan de Fuca slab beneath southern British Columbia, Washington, Oregon, and northern California, and use this model to separate earthquakes occurring above and below the slab surface. The model is based on depth contours previously published by Fluck and others (1997). Our model attempts to rectify a number of shortcomings in the original model and update it with new work. The most significant improvements include (1) a gridded slab surface in geo-referenced (ArcGIS) format, (2) continuation of the slab surface to its full northern and southern edges, (3) extension of the slab surface from 50-km depth down to 110-km beneath the Cascade arc volcanoes, and (4) revision of the slab shape based on new seismic-reflection and seismic-refraction studies. We have used this surface to sort earthquakes and present some general observations and interpretations of seismicity patterns revealed by our analysis. For example, deep earthquakes within the Juan de Fuca Plate beneath western Washington define a linear trend that may mark a tear within the subducting plate Also earthquakes associated with the northern stands of the San Andreas Fault abruptly terminate at the inferred southern boundary of the Juan de Fuca slab. In addition, we provide files of earthquakes above and below the slab surface and a 3-D animation or fly-through showing a shaded-relief map with plate boundaries, the slab surface, and hypocenters for use as a visualization tool.

  8. Data Sharing Report Characterization of Isotope Row Facilities Oak Ridge National Laboratory Oak Ridge TN

    SciTech Connect

    Weaver, Phyllis C.

    2013-12-12

    The U.S. Department of Energy (DOE) Oak Ridge Office of Environmental Management (EM-OR) requested that Oak Ridge Associated Universities (ORAU), working under the Oak Ridge Institute for Science and Education (ORISE) contract, provide technical and independent waste management planning support using funds provided by the American Recovery and Reinvestment Act (ARRA). Specifically, DOE EM-OR requested ORAU to plan and implement a survey approach, focused on characterizing the Isotope Row Facilities located at the Oak Ridge National Laboratory (ORNL) for future determination of an appropriate disposition pathway for building debris and systems, should the buildings be demolished. The characterization effort was designed to identify and quantify radiological and chemical contamination associated with building structures and process systems. The Isotope Row Facilities discussed in this report include Bldgs. 3030, 3031, 3032, 3033, 3033A, 3034, 3036, 3093, and 3118, and are located in the northeast quadrant of the main ORNL campus area, between Hillside and Central Avenues. Construction of the isotope production facilities was initiated in the late 1940s, with the exception of Bldgs. 3033A and 3118, which were enclosed in the early 1960s. The Isotope Row facilities were intended for the purpose of light industrial use for the processing, assemblage, and storage of radionuclides used for a variety of applications (ORNL 1952 and ORAU 2013). The Isotope Row Facilities provided laboratory and support services as part of the Isotopes Production and Distribution Program until 1989 when DOE mandated their shutdown (ORNL 1990). These facilities performed diverse research and developmental experiments in support of isotopes production. As a result of the many years of operations, various projects, and final cessation of operations, production was followed by inclusion into the surveillance and maintenance (S&M) project for eventual decontamination and decommissioning (D&D). The

  9. Zinc, copper, and lead in mid-ocean ridge basalts and the source rock control on Zn/Pb in ocean-ridge hydrothermal deposits

    USGS Publications Warehouse

    Doe, B.R.

    1994-01-01

    The contents of Zn, Cu, and Pb in mid-ocean ridge basalts (MORB) and the MORB source-rock control on Zn/Pb in ocean-ridge hydrothermal deposits are examined. The values of Zn, Cu, and Pb for submarine mid-ocean ridge basalts (MORB) are, respectively (in ppm): average MORB-75, 75, and 0.7; West Valley, Juan de Fuca Ridge (JFR)-87, 64, and 0.5; southern JFR-120 and 0.5; and 21??N, East Pacific Rise (EPR)-73, 78, and 0.5. Values of Zn/Pb range from about 100-240 and Cu/ Pb from 100-156. In this study, Zn is found to correlate positively with TiO2 + FeO (mean square of weighted deviates, MSWD, of 1.6 for JFR basalt), and inversely with Mg number (MSWD of 3.5). Therefore, contrary to statements in the literature that Zn should be compatible in MORB, Zn is a mildly incompatible element and must be enriched in the glass phase relative to olivine as Zn does not fit into the other major phenocryst phase, plagioclase. In the source of MORB, Zn likely is most enriched in oxides: spinel, magnetite, and titanomagnetite. Copper generally does not correlate well with other elements in most MORB data examined. When differentiation is dominated by olivine, Cu has a tendency to behave incompatibly (e.g., at Mg numbers > 70), but, overall, Cu shows some tendency towards being a compatible element, particularly along the Mid-Atlantic Ridge, a behavior presumably due to separation of sulfides in which Cu (but not Zn) is markedly enriched. Copper thus may be in dispersed sulfides in the source of MORB. Ocean ridges provide important data on source-rock controls for sulfide deposits because, in sediment-starved ridges, much is known about the possible source rocks and mineralization is presently occurring. In contrast to Zn/Pb ~5 in continental hot Cl-rich brines, Zn/Pb in the hottest sediment-starved ridge black smoker hydrothermal fluids at 21 ??N, EPR is about 110, similar to local MORB (145), but Cu/Pb is closer to 30, possibly due to subsurface deposition of Cu. At the JFR, the best

  10. The Mid-Ocean Ridge.

    ERIC Educational Resources Information Center

    Macdonald, Kenneth C.; Fox, Paul J.

    1990-01-01

    Described are concepts involved with the formation and actions of the Mid-Ocean Ridge. Sea-floor spreading, the magma supply model, discontinuities, off-axis structures, overlaps and deviation, and aquatic life are discussed. (CW)

  11. Growth of a tectonic ridge

    SciTech Connect

    Fleming, R.W.; Messerich, J.A.; Johnson, A.M.

    1997-12-31

    The 28 June 1992 Landers, California, earthquake of M 7.6 created an impressive record of surface rupture and ground deformation. Fractures extend over a length of more than 80 km including zones of right-lateral shift, steps in the fault zones, fault intersections and vertical changes. Among the vertical changes was the growth of a tectonic ridge described here. In this paper the authors describe the Emerson fault zone and the Tortoise Hill ridge including the relations between the fault zone and the ridge. They present data on the horizontal deformation at several scales associated with activity within the ridge and belt of shear zones and show the differential vertical uplifts. And, they conclude with a discussion of potential models for the observed deformation.

  12. Repeat ridge jumps associated with plume-ridge interaction, melt transport, and ridge migration

    NASA Astrophysics Data System (ADS)

    Mittelstaedt, Eric; Ito, Garrett; van Hunen, Jeroen

    2011-01-01

    Repeated shifts, or jumps, of mid-ocean ridge segments toward nearby hot spots can produce large, long-term changes to the geometry and location of the tectonic plate boundaries. Ridge jumps associated with hot spot-ridge interaction are likely caused by several processes including shear on the base of the plate due to expanding plume material as well as reheating of lithosphere as magma passes through it to feed off-axis volcanism. To study how these processes influence ridge jumps, we use numerical models to simulate 2-D (in cross section) viscous flow of the mantle, viscoplastic deformation of the lithosphere, and melt migration upward from the asthenospheric melting zone, laterally along the base of the lithosphere, and vertically through the lithosphere. The locations and rates that magma penetrates and heats the lithosphere are controlled by the time-varying accumulation of melt beneath the plate and the depth-averaged lithospheric porosity. We examine the effect of four key parameters: magmatic heating rate of the lithosphere, plate spreading rate, age of the seafloor overlying the plume, and the plume-ridge migration rate. Results indicate that the minimum value of the magmatic heating rate needed to initiate a ridge jump increases with plate age and spreading rate. The time required to complete a ridge jump decreases with larger values of magmatic heating rate, younger plate age, and faster spreading rate. For cases with migrating ridges, models predict a range of behaviors including repeating ridge jumps, much like those exhibited on Earth. Repeating ridge jumps occur at moderate magmatic heating rates and are the result of changes in the hot spot magma flux in response to magma migration along the base of an evolving lithosphere. The tendency of slow spreading to promote ridge jumps could help explain the observed clustering of hot spots near the Mid-Atlantic Ridge. Model results also suggest that magmatic heating may significantly thin the lithosphere

  13. Sinuous Ridges in Peta Crater, Mars

    NASA Astrophysics Data System (ADS)

    Parker, T. J.

    2011-03-01

    Peta Crater (21°S,351°E) contains a system of sinuous ridges similar to, but smaller than, the well-known Dorsa Argyre and Dorsa Argentea ridges. Recent CTX and HiRISE images of the Peta crater ridges is enabling a detailed examination of this confined system of ridges.

  14. Seismicity rates of slow, intermediate, and fast spreading ridges: Insights from long-term hydroacoustic monitoring

    NASA Astrophysics Data System (ADS)

    Dziak, R. P.; Haxel, J. H.; Bohnenstiehl, D. R.; Goslin, J.

    2004-12-01

    Ocean basin earthquakes recorded on NOAA/OSU and U.S. Navy hydrophone arrays are used to evaluate long-term volcano-tectonic seismicity levels from segments of the fast-spreading rate East Pacific Rise (EPR) from 20° S-20° N, intermediate-spreading rate Juan de Fuca Ridge (JdFR) from 39° -52° N and Galapagos Rift (GR) from 90° -103° W, and the slow-spreading northern Mid-Atlantic Ridge (MAR) from 5° -60° N. The hydrophones record the acoustic energy of seafloor earthquakes that propagate along the ocean sound channel with little attenuation over large distances. Frequency-magnitude relationships (Bohnenstiehl et al., 2002; Dziak et al., 2004) indicate the hydrophone catalogs are complete in these regions to body-wave magnitude ˜2.5 (EPR and GR), 2.5 (JdFR), and 3.0 (MAR), an improvement of 1.5 to 2 units over the land-based seismic catalogs for mid-ocean ridge systems. Using the hydrophone earthquake catalog, we will compare seismicity rates of the JdFR (12 years of data), to seismicity rates along the GR (6 years) and EPR (6 years) and MAR (4 years of data from 5° -39° N; 16 months from 39° -60° N). During these monitoring periods, five confirmed seafloor spreading events (four of which were associated with magmatic activity) were recorded on discrete JdFR segments, while 6 possible magmatic events were observed on the EPR, one on the GR, and one on the MAR. Empirical orthogonal functions will be used to elucidate the space-time patterns of seismicity and compare between the various spreading rates ridges, as well as to investigate the recurrence rate of seafloor spreading events present. In addition, single-link cluster analysis (SLC; Frolich and Davis, 1990) will be used to de-cluster the earthquake databases to reduce the effects of aftershock sequences and magmatic swarms, allowing us to evaluate how overall plate motion and changes in spreading rate effect levels of seismicity between ridge segments and different ridge systems. Preliminary

  15. Lower Tertiary laterite on the Iceland-Faeroe Ridge and the Thulean land bridge

    USGS Publications Warehouse

    Nilsen, T.H.

    1978-01-01

    CORES of a lower Tertiary lateritic palaeosol resting on basalt were recovered1 from Deep Sea Drilling Project Site 336 (Leg 38) on the north-east flank of the Iceland-Faeroe Ridge (Fig. 1), a major aseismic oceanic ridge that, together with Iceland, forms the Icelandic transverse ridge 2. The transverse ridge extends from the West European continental margin to the East Greenland continental margin, forming the geographic boundary and a partial barrier to flow of water between the Norwegian-Greenland Sea to the north and the northern North Atlantic Ocean to the south. The palaeosol indicates that at least part of the Iceland-Faeroe Ridge was above sea level during early Tertiary time3. Palaeogeographic and palaeooceanographic reconstructions suggest that it formed the main part of the Thulean land bridge that connected South-east Greenland and the Faeroe islands during the early Tertiary4. This report summarises the subsidence history of the Iceland-Faeroe Ridge relative to early Tertiary seafloor spreading, basaltic volcanism, and the development of the proposed Thulean land bridge. ?? 1978 Nature Publishing Group.

  16. Carpenter Ridge Tuff, CO

    NASA Astrophysics Data System (ADS)

    Bachmann, Olivier; Deering, Chad D.; Lipman, Peter W.; Plummer, Charles

    2014-06-01

    The ~1,000 km3 Carpenter Ridge Tuff (CRT), erupted at 27.55 Ma during the mid-tertiary ignimbrite flare-up in the western USA, is among the largest known strongly zoned ash-flow tuffs. It consists primarily of densely welded crystal-poor rhyolite with a pronounced, highly evolved chemical signature (high Rb/Sr, low Ba, Zr, Eu), but thickly ponded intracaldera CRT is capped by a more crystal-rich, less silicic facies. In the outflow ignimbrite, this upper zone is defined mainly by densely welded crystal-rich juvenile clasts of trachydacite composition, with higher Fe-Ti oxide temperatures, and is characterized by extremely high Ba (to 7,500 ppm), Zr, Sr, and positive Eu anomalies. Rare mafic clasts (51-53 wt% SiO2) with Ba contents to 4,000-5,000 ppm and positive Eu anomalies are also present. Much of the major and trace-element variations in the CRT juvenile clasts can be reproduced via in situ differentiation by interstitial melt extraction from a crystal-rich, upper-crustal mush zone, with the trachydacite, crystal-rich clasts representing the remobilized crystal cumulate left behind by the melt extraction process. Late recharge events, represented by the rare mafic clasts and high-Al amphiboles in some samples, mixed in with parts of the crystal cumulate and generated additional scatter in the whole-rock data. Recharge was important in thermally remobilizing the silicic crystal cumulate by partially melting the near-solidus phases, as supported by: (1) ubiquitous wormy/sieve textures and reverse zoning patterns in feldspars and biotites, (2) absence of quartz in this very silicic unit stored at depths of >4-5 km, and (3) heterogeneous melt compositions in the trachydacite fiamme and mafic clasts, particularly in Ba, indicating local enrichment of this element due mostly to sanidine and biotite melting. The injection of hot, juvenile magma into the upper-crustal cumulate also imparted the observed thermal gradient to the deposits and the mixing overprint that

  17. Bay of Biscay and Northeast Atlantic Bathymetric map

    NASA Astrophysics Data System (ADS)

    Loubrieu, B.; Sibuet, J.; Monti, S.; Maze, J.

    2002-12-01

    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°N 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 addition, two topographic features of similar size, the Armorican and Coruna seamounts are tangential to the fossil trajectories, at about 200 km from the triple junction. They are interpreted as twin

  18. Cascadia Initiative Reveals Accumulation of Buoyant Material Beneath the Subducting Juan de Fuca Plate

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The Cascadia Initiative is a four-year (2011-2015) amphibious seismic deployment that covers the Juan de Fuca plate and the Cascadia Subduction Zone. It is comprised of 70 broadband ocean-bottom seismometers that occupy 120 sites in total, as well as 27 land-based stations. This array offers a unique opportunity to study the 3D structure of a subduction zone in unprecedented detail. We present the results of an inversion using teleseismic body waves recorded by the Cascadia Initiative, EarthScope, and other regional and temporary networks in the Pacific Northwest. A low-velocity feature is visible beneath the subducting slab at shallow depths. Previous studies report ponding of low-viscosity, buoyant material at the top of the asthenosphere, unable to rise through the impermeable lithospheric lid. We show that as the lithospheric lid descends into the mantle, this material is not advected with it; rather, due to its own weakness and buoyancy, it accumulates at the subduction zone. Such material could be partly responsible for the rapid uplift and volcanism in the Coast Range of California, in the wake of the northward migration of the Mendocino Triple Junction. This newly observed feature may play an important role in the structure of subduction zones, but understanding the extent of that role on a global scale will require amphibious seismic deployments in other subduction zones.

  19. Helium as a tracer for fluids released from Juan de Fuca lithosphere beneath the Cascadia forearc

    NASA Astrophysics Data System (ADS)

    McCrory, P. A.; Constantz, J. E.; Hunt, A. G.; Blair, J. L.

    2016-06-01

    Helium isotopic ratios (3He/4He) observed in 25 mineral springs and wells above the Cascadia forearc provide a marker for fluids derived from Juan de Fuca lithosphere. This exploratory study documents a significant component of mantle-derived helium within forearc springs and wells, and in turn, documents variability in helium enrichment across the Cascadia forearc. Sample sites arcward of the forearc mantle corner generally yield significantly higher ratios (˜1.2-4.0 RA) than those seaward of the corner (˜0.03-0.7 RA). 3He detected above the inner forearc mantle wedge may represent a mixture of both oceanic lithosphere and forearc mantle sources, whereas 3He detected seaward of the forearc mantle corner likely has only an oceanic source. The highest ratios in the Cascadia forearc coincide with slab depths (˜40-45 km) where metamorphic dehydration of young oceanic lithosphere is expected to release significant fluid and where tectonic tremor occurs, whereas little fluid is expected to be released from the slab depths (˜25-30 km) beneath sites seaward of the corner. These observations provide independent evidence that tremor is associated with deep fluids, and further suggest that high pore pressures associated with tremor may serve to keep fractures open for 3He migration through the ductile upper mantle and lower crust.

  20. Geodynamics map of northeast Asia

    USGS Publications Warehouse

    Parfenov, Leonid M.; Khanchuk, Alexander I.; Badarch, Gombosuren; Miller, Robert J.; Naumova, Vera V.; Nokleberg, Warren J.; Ogasawara, Masatsugu; Prokopiev, Andrei V.; Yan, Hongquan

    2013-01-01

    This map portrays the geodynamics of Northeast Asia at a scale of 1:5,000,000 using the concepts of plate tectonics and analysis of terranes and overlap assemblages. The map is the result of a detailed compilation and synthesis at 5 million scale and is part of a major international collaborative study of the mineral resources, metallogenesis, and tectonics of northeast Asia conducted from 1997 through 2002 by geologists from earth science agencies and universities in Russia, Mongolia, northeastern China, South Korea, Japan, and the USA.

  1. Comparison of Ridges on Triton and Europa

    NASA Technical Reports Server (NTRS)

    Prockter, L. M.; Pappalardo, R. .

    2003-01-01

    Triton and Europa each display a variety of ridges and associated troughs. The resemblance of double ridges on these two satellites has been previously noted [R. Kirk, pers. comm.], but as yet, the similarities and differences between these feature types have not been examined in any detail. Triton s ridges, and Europa s, exhibit an evolutionary sequence ranging from isolated troughs, through doublet ridges, to complex ridge swaths [1, 2]. Comparison of ridges on Europa to those on Triton may provide insight into their formation on both satellites, and thereby have implications for the satellites' histories.

  2. Xenon isotopic composition of the Mid Ocean Ridge Basalt (MORB) source

    NASA Astrophysics Data System (ADS)

    Peto, M. K.; Mukhopadhyay, S.

    2012-12-01

    Although convection models do not preclude preservation of smaller mantle regions with more pristine composition throughout Earth's history, it has been widely assumed that the moon forming giant impact likely homogenizes the whole mantle following a magma ocean that extended all the way to the bottom of the mantle. Recent findings of tungsten and xenon heterogeneities in the mantle [1,2,3,4], however, imply that i) the moon forming giant impact may not have homogenized the whole mantle and ii) plate tectonics was inefficient in erasing early formed compositional differences, particularly for the xenon isotopes. Therefore, the xenon isotope composition in the present day mantle still preserves a memory of early Earth processes. However, determination of the xenon isotopic composition of the mantle source is still scarce, since the mantle composition is overprinted by post-eruptive atmospheric contamination in basalts erupted at ocean islands and mid ocean ridges. The xenon composition of the depleted upper mantle has been defined by the gas rich sample, 2πD43 (also known as "popping rock"), from the North Atlantic (13° 469`N). However, the composition of a single sample is not likely to define the composition of the upper mantle, especially since popping rock has an "enriched" trace element composition. We will present Ne, Ar and Xe isotope data on MORB glass samples with "normal" helium isotope composition (8±1 Ra) from the Southeast Indian Ridge, the South Atlantic Ridge, the Sojourn Ridge, the Juan de Fuca, the East Pacific Rise, and the Gakkel Ridge. Following the approach of [1], we correct for syn- and post-eruptive atmosphere contamination, and determine the variation of Ar and Xe isotope composition of the "normal" MORB source. We investigate the effect of atmospheric recycling in the variation of MORB mantle 40Ar/36Ar and 129Xe/130Xe ratios, and attempt to constrain the average upper mantle argon and xenon isotopic compositions. [1] Mukhopadhyay, Nature

  3. HIGHLAND RIDGE ROADLESS AREA, NEVADA.

    USGS Publications Warehouse

    Whitebread, Donald H.; Brown, S. Don

    1984-01-01

    The mineral-resource potential of the Highland Ridge Roadless Area, Nevada was evaluated on the basis of results from field investigations. One area along the west border of the Highland Ridge Roadless Area has substantiated mineral-resource potential for tungsten. Several other areas are classed as having probable mineral-resource potential, based mainly upon anomalously high values of tungsten, lead, silver, and zinc in concentrates of stream sediments. Most of the roadless area is underlain by rocks in the upper plate of the Snake Range decollement, and is considered to have little promise for the occurrence of mineral resources. No energy resource potential was identified in the area.

  4. Noble metals in mid-ocean ridge volcanism: A significant fractionation of gold with respect to platinum group metals

    NASA Technical Reports Server (NTRS)

    Crocket, James H.

    1988-01-01

    Hydrothermal precipitates, black smoker particulate, and massive sulphide dredge samples from the Explorer Ridge on the Juan de Fuca Plate and the TAG hydrothermal area on the Mid-Atlantic Ridge were analyzed for selected noble metals including Au, Ir and Pd by radiochemical neutron activation analysis. The preliminary results indicate that gold contents may reach the ppm range although values in the neighborhood of 100 to 200 ppb are more typical. The platinum group elements (PGE) represented by Ir and Pd are typically less than 0.02 ppb and less than 2 ppb respectively. These abundances represent a significant enrichment of gold relative to the PGE in comparison with average noble metal abundances in mid-ocean ridge basalts (MORB). A partial explanation of this distinctive fractionation can be found in the concepts of sulfur-saturation of basic magma in mid-ocean ridge (MOR) settings, and the origin of MOR hydrothermal fluids. Experimental and petrological data suggest that MORBs are sulfur-saturated at the time of magma generation and that an immiscible sulfide component remains in the mantle residue. Hence, MORBs are noble metal-poor, particularly with respect to PGE. Consequently, black smoker fluids can be expected to reflect the low Ir and Pd contents of the rock column. The average Au content of MORB is 1.3 ppb, and so the rock column is not significantly enriched in Au. The generation of fluids which precipitate solids with 200 ppb Au is apparently dependent on highly efficient fluid chemistry to mobilize Au from the rock column, high Au solubility in seawater hydrothermal fluids and efficient precipitation mechanisms to coprecipitate Au on Fe, Zn and Cu sulfides. Significant differences in these parameters appear to be the ultimate cause of the strong Au-PGE fractionation in the MOR setting. It does not appear from the current data base that MOR hydrothermal fluids are significant contributors to the Ir enrichment seen in Cretaceous-Tertiary boundary

  5. A reduced crustal magnetization zone near the first observed active hydrothermal vent field on the Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Zhu, Jian; Lin, Jian; Chen, Yongshun J.; Tao, Chunhui; German, Christopher R.; Yoerger, Dana R.; Tivey, Maurice A.

    2010-09-01

    Inversion of near-bottom magnetic data reveals a well-defined low crustal magnetization zone (LMZ) near a local topographic high (37°47‧S, 49°39‧E) on the ultraslow-spreading Southwest Indian Ridge (SWIR). The magnetic data were collected by the autonomous underwater vehicle ABE on board R/V DaYangYiHao in February-March 2007. The first active hydrothermal vent field observed on the SWIR is located in Area A within and adjacent to the LMZ at the local topographic high, implying that this LMZ may be the result of hydrothermal alteration of magnetic minerals. The maximum reduction in crustal magnetization is 3 A/M. The spatial extent of the LMZ is estimated to be at least 6.7 × 104 m2, which is larger than that of the LMZs at the TAG vent field on the Mid-Atlantic Ridge (MAR), as well as the Relict Field, Bastille, Dante-Grotto, and New Field vent-sites on the Juan de Fuca Ridge (JdF). The calculated magnetic moment, i.e., the product of the spatial extent and amplitude of crustal magnetization reduction is at least -3 × 107 Am2 for the LMZ on the SWIR, while that for the TAG field on the MAR is -8 × 107 Am2 and that for the four individual vent fields on the JdF range from -5 × 107 to -3 × 107 Am2. Together these results indicate that crustal demagnetization is a common feature of basalt-hosted hydrothermal vent fields at mid-ocean ridges of all spreading rates. Furthermore, the crustal demagnetization of the Area A on the ultraslow-spreading SWIR is comparable in strength to that of the TAG area on the slow-spreading MAR.

  6. Underlying fracture zone nature of Astrid Ridge off Antarctica's Queen Maud Land

    NASA Astrophysics Data System (ADS)

    Bergh, Hugh W.

    1987-01-01

    New geophysical data are used to refine the extent and setting of Astrid Ridge, a volcanic edifice lying off the Princess Astrid Coast section (5°E to 20°E) of Queen Maud Land in Antarctica. New findings presented here include a well-defined fracture zone, occurring as a narrow basement ridge which extends northeast from Astrid Ridge, and an adjacent set of Mesozoic magnetic anomalies M0 to M9, which are offset by 120 km from an identical, previously described set. These two sets of anomalies are combined with the conjugate Mozambique Basin anomalies to define an Africa-Antarctica rotation pole at 10°S, 29°W for anomaly M2 time. The northern edge of Astrid Ridge and the sharp southern margin of the Mozambique Ridge on the African plate are probably related to the same cessation of excess volcanic activity near the end of the Cretaceous normal polarity interval. Both features had their eastern and western limits confined by a contiguous pair of fracture zones. A possible major swing in fracture zone trend prior to anomaly M9 is also suggested.

  7. THE EQUATION AT OAK RIDGE.

    ERIC Educational Resources Information Center

    MORRELL, KEN

    THE STEPS TAKEN TO DESEGREGATE THE OAK RIDGE, TENN., SCHOOLS ARE DESCRIBED IN THIS ARTICLE. ONE ELEMENTARY SCHOOL, SEGREGATED BECAUSE OF RESIDENTIAL PATTERNS, WAS CLOSED AND ITS STUDENTS REDISTRIBUTED AMONG OTHER SCHOOLS IN THE CITY. UNDER THE INITIATIVE OF THE SCHOOL BOARD, THIS PLAN WENT INTO EFFECT IN THE FALL OF 1967 AND IS SAID TO HAVE…

  8. Chlorophyll distribution in a temperate estuary: The Strait of Georgia and Juan de Fuca Strait

    NASA Astrophysics Data System (ADS)

    Masson, Diane; Peña, Angelica

    2009-03-01

    Data collected during 7 years of seasonal surveys are used to investigate the distribution of phytoplankton biomass within the estuarine waters of the Strait of Georgia and Juan de Fuca Strait. Variability of the chlorophyll distribution is examined in relation to the density stratification, light availability and nutrient concentration. In the Strait of Georgia, both the horizontal and vertical distribution of chlorophyll are found to be linked to the presence of a near-surface layer of increased density stratification. Despite important year-to-year variability, the seasonal cycle of chlorophyll in the Strait of Georgia is dominated every year by relatively large near-surface concentrations in the spring that are linked to the seasonal increase in solar radiation onto the stratified near-surface layer. In the vertical, a sub-surface peak is observed around 10 m depth, corresponding to the depth of maximum water column stability. Nutrients within the euphotic zone are in general abundant, with the exception of the Strait of Georgia in summer where phytoplankton growth is potentially limited by low nitrate concentration near the surface. The depth of the euphotic zone is estimated along the thalweg of the estuary from transmissometer profiles. It appears to vary relatively little within the estuary from a minimum of 20 m in spring, near the mouth of the Fraser River, to an autumnal maximum of about 30 m in the northern Strait of Georgia. Finally, the estimated self-shading contribution to light attenuation is shown to be generally significant (5-10%) in the surface waters of the Strait of Georgia, during spring and summer, reaching values as high as 35% during the spring bloom.

  9. Crustal structure and evolution of the southern Juan de Fuca plate from wide-angle seismic data: Insights into the hydration state of the incoming plate off Cascadia subduction zone

    NASA Astrophysics Data System (ADS)

    Horning, G.; Canales, J. P.; Carbotte, S. M.; Nedimovic, M. R.; Carton, H. D.

    2014-12-01

    A multi-channel seismic reflection and wide-angle refraction seismic experiment was conducted on the Juan de Fuca (JdF) plate to investigate the evolution of the plate from accretion to its subduction at the Cascadia margin. Hydration of the upper crust (UC) of the JdF Plate is well documented, but the state of hydration of the lower crust (LC) and upper mantle (UM] remains to be investigated. A 2D P-wave velocity model of the plate is derived from a joint reflection-refraction travel-time inversion of wide-angle seismic data. Stacked MCS reflection images together with modeled sedimentary velocities define an increasing thickness of sedimentary cover of up to 2.7km. Evidence for bending-related faulting is identified in coincident MCS images both indirectly as faulting in the sedimentary layer [Gibson, et al., this meeting] and directly as dipping crustal reflectors [Han et al., this meeting]. Three first order features are evident in the patterns of crustal velocity variations along the profile. 1: Crustal velocities at 150-250 km landward of the spreading ridge (~5 Ma age) show reduced velocities up to -0.20 km/s in comparison to velocities in younger crust (~3 Ma) 100-150 km from the ridge. This decrease in velocities is coincident with a propagator wake. 2: Upper crustal velocities begin to increase at 170km from the deformation front (DF), which coincides with the first evidence of faulting from sedimentary offsets. Crustal velocities start a decreasing trend at 80km from the DF where fault throws are seen to begin increasing trend landward. 3: UC velocities in the region of directly imaged crustal faulting (40km from trench) increase ~0.5km/s at the DF, while LC velocities decrease ~0.3km/s. The contrasting behavior in the upper and lower crust may indicate that bending promotes hydrothermal circulation in the outer rise. Circulation may be vigorous enough within the sediments/UC so that any residual shallow porosity is clogged with alteration products

  10. Active Submarine Volcanoes and Electro-Optical Sensor Networks: The Potential of Capturing and Quantifying an Entire Eruptive Sequence at Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Delaney, J. R.; Kelley, D. S.; Proskurowski, G.; Fundis, A. T.; Kawka, O.

    2011-12-01

    The NE Pacific Regional Scale Nodes (RSN) component of the NSF Ocean Observatories Initiative is designed to provide unprecedented electrical power and bandwidth to the base and summit of Axial Seamount. The scientific community is engaged in identifying a host of existing and innovative observation and measurement techniques that utilize the high-power and bandwidth infrastructure and its real-time transmission capabilities. The cable, mooring, and sensor arrays will enable the first quantitative documentation of myriad processes leading up to, during, and following a submarine volcanic event. Currently planned RSN instrument arrays will provide important and concurrent spatial and temporal constraints on earthquake activity, melt migration, hydrothermal venting behavior and chemistry, ambient currents, microbial community structure, high-definition (HD) still images and HD video streaming from the vents, and water-column chemistry in the overlying ocean. Anticipated, but not yet funded, additions will include AUVs and gliders that continually document the spatial-temporal variations in the water column above the volcano and the distal zones. When an eruption appears imminent the frequency of sampling will be increased remotely, and the potential of repurposing the tracking capabilities of the mobile sensing platforms will be adapted to the spatial indicators of likely eruption activity. As the eruption begins mobile platforms will fully define the geometry, temperature, and chemical-microbial character of the volcanic plume as it rises into the thoroughly documented control volume above the volcano. Via the Internet the scientific community will be able to witness and direct adaptive sampling in response to changing conditions of plume formation. A major goal will be to document the eruptive volume and link the eruption duration to the volume of erupted magma. For the first time, it will be possible to begin to quantify the time-integrated output of an underwater volcanic eruption linked to the heat, chemical, and biological fluxes. In the late stages of the event, the dissipation of the "event plume" into the surrounding water column and the plume's migration patterns in the ambient regional flow will be tracked using specifically designed mobile sensor-platforms. The presence of these assets opens the potential for more immediate, coordinated, and thorough event responses than the community has previously been able to mount. Given the relative abundance of information on many variables in a verifiable and archived spatial and temporal context, and the rapidly evolving ability to conduct real-time genomic analyses, our community may be able to secure entirely novel organisms that are released into the overlying ocean only under well-characterized eruptive conditions.

  11. Isolation of Aerobic Anoxygenic Photosynthetic Bacteria from Black Smoker Plume Waters of the Juan de Fuca Ridge in the Pacific Ocean

    PubMed Central

    Yurkov, Vladimir; Beatty, J. Thomas

    1998-01-01

    A strain of the aerobic anoxygenic photosynthetic bacteria was isolated from a deep-ocean hydrothermal vent plume environment. The in vivo absorption spectra of cells indicate the presence of bacteriochlorophyll a incorporated into light-harvesting complex I and a reaction center. The general morphological and physiological characteristics of this new isolate are described. PMID:16349490

  12. Isolation of Tellurite- and Selenite-Resistant Bacteria from Hydrothermal Vents of the Juan de Fuca Ridge in the Pacific Ocean

    PubMed Central

    Rathgeber, Christopher; Yurkova, Natalia; Stackebrandt, Erko; Beatty, J. Thomas; Yurkov, Vladimir

    2002-01-01

    Deep-ocean hydrothermal-vent environments are rich in heavy metals and metalloids and present excellent sites for the isolation of metal-resistant microorganisms. Both metalloid-oxide-resistant and metalloid-oxide-reducing bacteria were found. Tellurite- and selenite-reducing strains were isolated in high numbers from ocean water near hydrothermal vents, bacterial films, and sulfide-rich rocks. Growth of these isolates in media containing K2TeO3 or Na2SeO3 resulted in the accumulation of metallic tellurium or selenium. The MIC of K2TeO3 ranged from 1,500 to greater than 2,500 μg/ml, and the MIC of Na2SeO3 ranged from 6,000 to greater than 7,000 μg/ml for 10 strains. Phylogenetic analysis of 4 of these 10 strains revealed that they form a branch closely related to members of the genus Pseudoalteromonas, within the γ-3 subclass of the Proteobacteria. All 10 strains were found to be salt tolerant, pH tolerant, and thermotolerant. The metalloid resistance and morphological, physiological, and phylogenetic characteristics of newly isolated strains are described. PMID:12200320

  13. Comment on 'Consequences of phase separation on the distribution of hydrothermal fluids at ASHES vent field, axial volcano, Juan de Fuca ridge' by Christopher G. Fox

    NASA Astrophysics Data System (ADS)

    Scholl, M. A.; Ingebritsen, S. E.; Essaid, H. I.

    1993-02-01

    Fox (1990), in order to explain observations during the Axial Seamount Hydrothermal Emissions Study (ASHES), proposed a conceptual model for a two-phase subsea hydrothermal system in which steam controlled flow patterns by blocking liquid flow. An attempt is made here to demonstrate with a very general model that relative permeability contrasts by themselves do not cause spatial isolation of phases in steam/liquid water systems and that density segregation, independent of relative permeability effects, should not be ruled out as an explanation for the observations at the ASHES site. Fox replies that density segregation is probably not the only mechanism at work.

  14. Novel microbial assemblages inhabiting crustal fluids within mid-ocean ridge flank subsurface basalt.

    PubMed

    Jungbluth, Sean P; Bowers, Robert M; Lin, Huei-Ting; Cowen, James P; Rappé, Michael S

    2016-08-01

    Although little is known regarding microbial life within our planet's rock-hosted deep subseafloor biosphere, boreholes drilled through deep ocean sediment and into the underlying basaltic crust provide invaluable windows of access that have been used previously to document the presence of microorganisms within fluids percolating through the deep ocean crust. In this study, the analysis of 1.7 million small subunit ribosomal RNA genes amplified and sequenced from marine sediment, bottom seawater and basalt-hosted deep subseafloor fluids that span multiple years and locations on the Juan de Fuca Ridge flank was used to quantitatively delineate a subseafloor microbiome comprised of distinct bacteria and archaea. Hot, anoxic crustal fluids tapped by newly installed seafloor sampling observatories at boreholes U1362A and U1362B contained abundant bacterial lineages of phylogenetically unique Nitrospirae, Aminicenantes, Calescamantes and Chloroflexi. Although less abundant, the domain Archaea was dominated by unique, uncultivated lineages of marine benthic group E, the Terrestrial Hot Spring Crenarchaeotic Group, the Bathyarchaeota and relatives of cultivated, sulfate-reducing Archaeoglobi. Consistent with recent geochemical measurements and bioenergetic predictions, the potential importance of methane cycling and sulfate reduction were imprinted within the basalt-hosted deep subseafloor crustal fluid microbial community. This unique window of access to the deep ocean subsurface basement reveals a microbial landscape that exhibits previously undetected spatial heterogeneity.

  15. Novel microbial assemblages inhabiting crustal fluids within mid-ocean ridge flank subsurface basalt

    PubMed Central

    Jungbluth, Sean P; Bowers, Robert M; Lin, Huei-Ting; Cowen, James P; Rappé, Michael S

    2016-01-01

    Although little is known regarding microbial life within our planet's rock-hosted deep subseafloor biosphere, boreholes drilled through deep ocean sediment and into the underlying basaltic crust provide invaluable windows of access that have been used previously to document the presence of microorganisms within fluids percolating through the deep ocean crust. In this study, the analysis of 1.7 million small subunit ribosomal RNA genes amplified and sequenced from marine sediment, bottom seawater and basalt-hosted deep subseafloor fluids that span multiple years and locations on the Juan de Fuca Ridge flank was used to quantitatively delineate a subseafloor microbiome comprised of distinct bacteria and archaea. Hot, anoxic crustal fluids tapped by newly installed seafloor sampling observatories at boreholes U1362A and U1362B contained abundant bacterial lineages of phylogenetically unique Nitrospirae, Aminicenantes, Calescamantes and Chloroflexi. Although less abundant, the domain Archaea was dominated by unique, uncultivated lineages of marine benthic group E, the Terrestrial Hot Spring Crenarchaeotic Group, the Bathyarchaeota and relatives of cultivated, sulfate-reducing Archaeoglobi. Consistent with recent geochemical measurements and bioenergetic predictions, the potential importance of methane cycling and sulfate reduction were imprinted within the basalt-hosted deep subseafloor crustal fluid microbial community. This unique window of access to the deep ocean subsurface basement reveals a microbial landscape that exhibits previously undetected spatial heterogeneity. PMID:26872042

  16. Inner-shelf circulation and sediment dynamics on a series of shoreface connected ridges offshore of Fire Island, NY

    USGS Publications Warehouse

    Warner, John C.; List, Jeffrey H.; Schwab, William C.; Voulgaris, George; Armstrong, Brandy N.; Marshall, N

    2014-01-01

    Locations along the inner-continental shelf offshore of Fire Island, NY, are characterized by a series of shoreface connected ridges (SFCRs). These sand ridges have approximate dimensions of 10 km in length, 3 km spacing, up to ~8 m ridge to trough relief, and are oriented obliquely at approximately 30 degrees clockwise from the coastline. Stability analysis from previous studies explains how sand ridges such as these could be formed and maintained by storm-driven flows directed alongshore with a key maintenance mechanism of offshore deflected flows over ridge crests and onshore in the troughs. We examine these processes both with a limited set of idealized numerical simulations and analysis of observational data. Model results confirm that along-shore flows over the SFCRs exhibit offshore veering of currents over the ridge crests and onshore-directed flows in the troughs, and demonstrate the opposite circulation pattern for a reverse wind. To further investigate these maintenance processes, oceanographic instruments were deployed at seven sites on the SFCRs offshore of Fire Island to measure water levels, ocean currents, waves, suspended-sediment concentrations, and bottom stresses from January to April 2012. Data analysis reveals that during storms with winds from the northeast the processes of offshore deflection of currents over ridge crests and onshore in the troughs were observed, and during storm events with winds from the southwest a reverse flow pattern over the ridges occurred. Computations of suspended-sediment fluxes identify periods that are consistent with SFCR maintenance mechanisms. Alongshore winds from the northeast drove fluxes offshore on the ridge crest and onshore in the trough that would tend to promote ridge maintenance. However, alongshore winds from the southwest drove opposite circulations. The wind fields are related to different storm types that occur in the region (low pressure systems, cold fronts, and warm fronts). From the limited

  17. Inner-shelf circulation and sediment dynamics on a series of shoreface-connected ridges offshore of Fire Island, NY

    NASA Astrophysics Data System (ADS)

    Warner, John C.; List, Jeffrey H.; Schwab, William C.; Voulgaris, George; Armstrong, Brandy; Marshall, Nicole

    2014-12-01

    Locations along the inner-continental shelf offshore of Fire Island, NY, are characterized by a series of shoreface-connected ridges (SFCRs). These sand ridges have approximate dimensions of 10 km in length, 3 km spacing, and up to ˜8 m ridge to trough relief and are oriented obliquely at approximately 30° clockwise from the coastline. Stability analysis from previous studies explains how sand ridges such as these could be formed and maintained by storm-driven flows directed alongshore with a key maintenance mechanism of offshore deflected flows over ridge crests and onshore in the troughs. We examine these processes both with a limited set of idealized numerical simulations and analysis of observational data. Model results confirm that alongshore flows over the SFCRs exhibit offshore veering of currents over the ridge crests and onshore-directed flows in the troughs, and demonstrate the opposite circulation pattern for a reverse wind. To further investigate these maintenance processes, oceanographic instruments were deployed at seven sites on the SFCRs offshore of Fire Island to measure water levels, ocean currents, waves, suspended sediment concentrations, and bottom stresses from January to April 2012. Data analysis reveals that during storms with winds from the northeast, the processes of offshore deflection of currents over ridge crests and onshore in the troughs were observed, and during storm events with winds from the southwest, a reverse flow pattern over the ridges occurred. Computations of suspended sediment fluxes identify periods that are consistent with SFCR maintenance mechanisms. Alongshore winds from the northeast drove fluxes offshore on the ridge crest and onshore in the trough that would tend to promote ridge maintenance. However, alongshore winds from the southwest drove opposite circulations. The wind fields are related to different storm types that occur in the region (low-pressure systems, cold fronts, and warm fronts). From the limited

  18. Sea-floor drainage features of Cascadia Basin and the adjacent continental slope, northeast Pacific Ocean

    USGS Publications Warehouse

    Hampton, M.A.; Karl, Herman A.; Kenyon, Neil H.

    1989-01-01

    Sea-floor drainage features of Cascadia Basin and the adjacent continental slope include canyons, primary fan valleys, deep-sea valleys, and remnant valley segments. Long-range sidescan sonographs and associated seismic-reflection profiles indicate that the canyons may originate along a mid-slope escarpment and grow upslope by mass wasting and downslope by valley erosion or aggradation. Most canyons are partly filled with sediment, and Quillayute Canyon is almost completely filled. Under normal growth conditions, the larger canyons connect with primary fan valleys or deep-sea valleys in Cascadia Basin, but development of accretionary ridges blocks or re-routes most canyons, forcing abandonment of the associated valleys in the basin. Astoria Fan has a primary fan valley that connects with Astoria Canyon at the fan apex. The fan valley is bordered by parallel levees on the upper fan but becomes obscure on the lower fan, where a few valley segments appear on the sonographs. Apparently, Nitinat Fan does not presently have a primary fan valley; none of the numerous valleys on the fan connect with a canyon. The Willapa-Cascadia-Vancouver-Juan de Fuca deep-sea valley system bypasses the submarine fans and includes deeply incised valleys to broad shallow swales, as well as within-valley terraces and hanging-valley confluences. ?? 1989.

  19. Northeast Regional Biomass Energy Program

    SciTech Connect

    O'Connell, R.A.

    1992-04-01

    The Northeast Regional Biomass Program (NRBP) is entering its ninth year of operation. The management and the objectives have virtually remained unchanged and are stated as follows. The program conducted by NRBP has three basic features: (1) a state grant component that provides funds (with a 50 percent matching requirement) to each of the states in the region to strengthen and integrate the work of state agencies involved in biomass energy; (2) a series of technical reports and studies in areas that have been identified as being of critical importance to the development of biomass energy in the region; and (3) a continuous long range planning component with heavy private sector involvement that helps to identify activities necessary to spur greater development and use of biomass energy in the Northeast.

  20. Northeast Regional Biomass Energy Program

    SciTech Connect

    O'Connell, R.A.

    1992-02-01

    The Northeast Regional Biomass Program (NRBP) is entering its ninth year of operation. The management and the objectives have virtually remained unchanged and are stated as follows. The program conducted by NRBP has three basic features: (1) a state grant component that provides funds (with a 50 percent matching requirement) to each of the states in the region to strengthen and integrate the work of state agencies involved in biomass energy; (2) a series of technical reports and studies in areas that have been identified as being of critical importance to the development of biomass energy in the region; and (3) a continuous long range planning component with heavy private sector involvement that helps to identify activities necessary to spur greater development and use of biomass energy in the Northeast.

  1. The Northeast Climate Science Center

    NASA Astrophysics Data System (ADS)

    Ratnaswamy, M. J.; Palmer, R. N.; Morelli, T.; Staudinger, M.; Holland, A. R.

    2013-12-01

    The Department of Interior Northeast Climate Science Center (NE CSC) is part of a federal network of eight Climate Science Centers created to provide scientific information, tools, and techniques that managers and other parties interested in land, water, wildlife and cultural resources can use to anticipate, monitor, and adapt to climate change. Recognizing the critical threats, unique climate challenges, and expansive and diverse nature of the northeast region, the University of Massachusetts Amherst, College of Menominee Nation, Columbia University, Marine Biological Laboratory, University of Minnesota, University of Missouri Columbia, and University of Wisconsin-Madison have formed a consortium to host the NE CSC. This partnership with the U.S. Geological Survey climate science center network provides wide-reaching expertise, resources, and established professional collaborations in both climate science and natural and cultural resources management. This interdisciplinary approach is needed for successfully meeting the regional needs for climate impact assessment, adaptive management, education, and stakeholder outreach throughout the northeast region. Thus, the NE CSC conducts research, both through its general funds and its annual competitive award process, that responds to the needs of natural resource management partners that exist, in part or whole, within the NE CSC bounds. This domain includes the North Atlantic, Upper Midwest and Great Lakes, Eastern Tallgrass and Big Rivers, and Appalachian Landscape Conservation Cooperatives (LCCs), among other management stakeholders. For example, researchers are developing techniques to monitor tree range dynamics as affected by natural disturbances which can enable adaptation of projected climate impacts; conducting a Designing Sustainable Landscapes project to assess the capability of current and potential future landscapes in the Northeast to provide integral ecosystems and suitable habitat for a suite of

  2. 33 CFR 334.1200 - Strait of Juan de Fuca, eastern end; off the westerly shore of Whidbey Island; naval restricted...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... end; off the westerly shore of Whidbey Island; naval restricted areas. 334.1200 Section 334.1200 Navigation and Navigable Waters CORPS OF ENGINEERS, DEPARTMENT OF THE ARMY, DEPARTMENT OF DEFENSE DANGER ZONE AND RESTRICTED AREA REGULATIONS § 334.1200 Strait of Juan de Fuca, eastern end; off the westerly...

  3. Lava Cones and Shields on Intermediate-Rate Mid-Ocean Ridges

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Most eruptions of basalt along mid-ocean ridges produce either sheet flows or pillow mounds and ridges. Rare eruptions on the Juan de Fuca and Gorda Ridges and on the Alarcon Rise (northern East Pacific Rise) produce volcanic cones or shields from point sources. Bathymetric maps at 1-m resolution from an autonomous underwater vehicle enabled classification of these ~circular features. The most common are 290-510m across and <50m tall cones with craters or tumulus-like inflated flows on their summits. There are 8 of these on the upper south rift, caldera floor, and southwest caldera rim on Axial Seamount; one on North Cleft segment near the 1986 pillow mounds; and one in the axial graben on northern Endeavour Segment. Hundreds of smaller pillow mounds lack craters or tumulus-like inflated flows at their summits. Three 660-1300m across circular cones have either a crater or an inflated tumulus-like structure at their flat to slightly domed summits. One in the axial graben on the northern Endeavour Segment is dissected by extensional faulting. Cage Seamount on the Coaxial Segment south of the 1993 pillow ridge is the most voluminous at 1100m across and >200m tall. Two flat-topped cones are located near the center of Alarcon Rise. A low-relief shield volcano on the northern Alarcon Rise is ~1700m across and only ~45m tall, and is cut by numerous faults and fissures. Two other shields, 860m and 1700m across and 50-70m tall, occur south of the 1996 North Gorda pillow mounds. These shields are decorated with small pillow mounds. Five 100-250m across and 15-30m deep pits collapsed on the northern shield. These constructional cones and shields form during eruptions where the initial fissure consolidated to a point, indicative of long duration activity. They are constructed during uncommon eruptions with flux larger than produces pillow mounds and smaller than produces sheet flows. They are a submarine equivalent of subaerial shield-building eruptions.

  4. The seismicity of the equatorial Mid-Atlantic Ridge and its long-offset transforms

    NASA Astrophysics Data System (ADS)

    Smith, D. K.; Dziak, R. P.; Palmiotto, C.; Parnell-Turner, R. E.; Zheleznov, A.

    2012-12-01

    An array of eight hydrophones is monitoring seismicity of the equatorial Atlantic between 20N and 10S. The array is obtaining a two-year, continuous record of seismicity, which will provide an important new view of the spatial and temporal patterns of seismicity at the slow-spreading equatorial Mid-Atlantic Ridge (MAR) and its long-offset transforms. The hydroacoustically-recorded seismicity, which will be in hand in 2014, can be used to address several key questions concerning the modes of spreading along the strongly offset equatorial MAR, the short-term earthquake predictability on some of the longest transform faults in the oceans, and the dynamics of the NA-SA-AF triple junction whose exact location is not known. In addition, seismic patterns of the entire South Atlantic will be obtained (at reduced location accuracy), and will aid in understanding the dynamics of the southern MAR, Walvis Ridge, Rio Grande Rise, and other prominent seafloor features. The hydroacoustic data will also allow characterization of cetacean populations in the region as well as an assessment of the ambient noise levels due to shipping and oil exploration. To provide additional information on the short-term earthquake predictability (retrospective) on oceanic transform faults, we are identifying all magnitude mb >5 earthquakes in our existing hydroacoustic databases and searching for systematic foreshock activity associated with these events. We have multi-year earthquake databases accumulated from past hydrophone experiments along the Central, Southwest and Southeast Indian Ridges, the Juan de Fuca Ridge system, and the northern MAR. Preliminary results are very promising, and there appear to be several examples of clear foreshocks preceding mainshocks by several hours. Also as part of this project, we are compiling a bathymetric map of the equatorial MAR and its transforms between 20N and 10S. There have been several international mapping efforts in this region and the integration of

  5. Status of Blue Ridge Reservoir

    SciTech Connect

    Not Available

    1990-09-01

    This is one in a series of reports prepared by the Tennessee Valley Authority (TVA) for those interested in the conditions of TVA reservoirs. This overview of Blue Ridge Reservoir summarizes reservoir and watershed characteristics, reservoir uses and use impairments, water quality and aquatic biological conditions, and activities of reservoir management agencies. This information was extracted from the most current reports and data available, as well as interview with water resource professionals in various federal, state, and local agencies. Blue Ridge Reservoir is a single-purpose hydropower generating project. When consistent with this primary objective, the reservoir is also operated to benefit secondary objectives including water quality, recreation, fish and aquatic habitat, development of shoreline, aesthetic quality, and other public and private uses that support overall regional economic growth and development. 8 refs., 1 fig.

  6. Structural processes at slow-spreading ridges.

    PubMed

    Mutter, J C; Karson, J A

    1992-07-31

    Slow-spreading (<35 millimeters per year) mid-ocean ridges are dominated by segmented, asymmetric, rifted depressions like continental rifts. Fast-spreading ridges display symmetric, elevated volcanic edifices that vary in shape and size along axis. Deep earthquakes, major normal faults, and exposures of lower crustal rocks are common only along slow-spreading ridges. These contrasting features suggest that mechanical deformation is far more important in crustal formation at slow-spreading ridges than at fast-spreading ridges. New seismic images suggest that the nature and scale of segmentation of slow-spreading ridges is integral to the deformational process and not to magmatic processes that may control segmentation on fast-spreading ridges.

  7. Tectonic evolution of the Resolution Ridge System, New Zealand: insights gained through UNCLOS surveying for natural prolongation

    NASA Astrophysics Data System (ADS)

    Wood, R.; Barker, D.

    2005-12-01

    For coastal States, demonstration of submerged natural prolongation of the land mass is a key element in delimiting the extent of the continental margin under the terms of UNCLOS article 76. Straddling an active plate boundary and with continental margins encompassing most major tectonic settings, the New Zealand (NZ) continent presents numerous, varied examples of natural prolongation of the land mass. The mostly submerged NZ continent covers over 5,000,000 km2. The continent grew by the accretion of basement terranes and the Hikurangi Plateau, a large igneous province, along the eastern margin of Gondwana during the Paleozoic and Mesozoic. Fragmentation of Gondwana initially involved thinning and extension of the continental rocks of New Zealand, and ultimately resulted in the separation of the New Zealand continent from Australia and Antarctica. Renewed tectonic activity in the Cenozoic resulted in the formation of the Resolution Ridge System (RRS) southwest of NZ and several volcanic arcs north of NZ. These volcanic arcs extend onto NZ and are a submerged natural prolongation of the land mass. Geological and geophysical surveys undertaken for the NZ Continental Shelf Project established that most of the RRS was not a prolongation of the NZ land mass, and advanced understanding of NZ's tectonic evolution. The RRS is a series of bathymetric highs extending southwest of Fiordland, NZ, from Resolution Ridge itself, adjacent to the northern limit of the Puysegur Trench, to the southeast termination of the fossil spreading centre in the Tasman Sea (TS; 158°40'E, 48°10'S). A 40° bend at 162°E, 46°30'S divides the ridge system into a northeastern segment, comprising large, en echelon, northeast-southwest-trending basement ridges and basins, and a southwest segment composed of longer, more continuous ridges trending northeast-southwest. The ridge system was formed by rapid reorientation of seafloor spreading directions (through c. 90°) in the TS at ~50 Ma. The

  8. Oak Ridge National Laboratory Review

    SciTech Connect

    Krause, C.; Pearce, J.; Zucker, A.

    1992-01-01

    This report presents brief descriptions of the following programs at Oak Ridge National Laboratory: The effects of pollution and climate change on forests; automation to improve the safety and efficiency of rearming battle tanks; new technologies for DNA sequencing; ORNL probes the human genome; ORNL as a supercomputer research center; paving the way to superconcrete made with polystyrene; a new look at supercritical water used in waste treatment; and small mammals as environmental monitors.

  9. Preliminary northeast Asia geodynamics map

    USGS Publications Warehouse

    Parfenov, Leonid M.; Khanchuk, Alexander I.; Badarch, Gombosuren; Miller, Robert J.; Naumova, Vera V.; Nokleberg, Warren J.; Ogasawara, Masatsugu; Prokopiev, Andrei V.; Yan, Hongquan

    2003-01-01

    This map portrays the geodynamics of Northeast Asia at a scale of 1:5,000,000 using the concepts of plate tectonics and analysis of terranes and overlap assemblages. The map is the result of a detailed compilation and synthesis at 5 million scale and is part of a major international collaborative study of the Mineral Resources, Metallogenesis, and Tectonics of Northeast Asia conducted from 1997 through 2002 by geologists from earth science agencies and universities in Russia, Mongolia, Northeastern China, South Korea, Japan, and the USA. This map is the result of extensive geologic mapping and associated tectonic studies in Northeast Asia in the last few decades and is the first collaborative compilation of the geology of the region at a scale of 1:5,000,000 by geologists from Russia, Mongolia, Northeastern China, South Korea, Japan, and the USA. The map was compiled by a large group of international geologists using the below concepts and definitions during collaborative workshops over a six-year period. The map is a major new compilation and re-interpretation of pre-existing geologic maps of the region. The map is designed to be used for several purposes, including regional tectonic analyses, mineral resource and metallogenic analysis, petroleum resource analysis, neotectonic analysis, and analysis of seismic hazards and volcanic hazards. The map consists of two sheets. Sheet 1 displays the map at a scale of 1:5,000,000, explanation. Sheet 2 displays the introduction, list of map units, and source references. Detailed descriptions of map units and stratigraphic columns are being published separately. This map is one of a series of publications on the mineral resources, metallogenesis, and geodynamics,of Northeast Asia. Companion studies and other articles and maps , and various detailed reports are: (1) a compilation of major mineral deposit models (Rodionov and Nokleberg, 2000; Rodionov and others, 2000; Obolenskiy and others, in press a); (2) a series of

  10. Helium As a Tracer for Fluids Released from Juan De Fuca Lithosphere Beneath the Cascadia Forearc

    NASA Astrophysics Data System (ADS)

    McCrory, P. A.; Constantz, J. E.; Hunt, A. G.; Blair, J. L.

    2014-12-01

    Helium isotope ratios in mineral springs provide an indication of the sources and pathways for magma ascending beneath volcanic arcs and are used as a tracer for fluids associated tectonic processes occurring in subduction systems. We sampled a series of mineral springs to define fluids derived from Juan de Fuca lithosphere beneath the forearc as the subducting slab dehydrates and densifies with increasing depth. Surface springs above the slab depth of 25-30 km have 3He/4He ratios of ~0.3 (R/RA); above the slab at a depth of ~40 km the ratio is ~4.0; and for springs above the slab at depths of 50-55 km the ratio ranges from ~0.7-1.6. The springs situated trenchward of the forearc mantle corner (FMC; varying from 35 to 43 km deep), yield the lowest ratios, thus indicating only a minor component of mantle-derived helium within spring waters. Springs situated arcward of the FMC yield intermediate (0.8-1.2 RC/RA ) to high (>1.2 RC/RA ) ratios, indicating a significant component of mantle-derived helium. Although helium isotopes do not allow us to differentiate between oceanic and forearc mantle sources, the lowest values are situated above the region that lacks forearc mantle, suggesting that either little slab-derived fluid is released at shallow slab depths, or that forearc mantle is the major source of 3He and acquired as the fluids rise to the surface. Sample sites range from 40 km to more than 200 km from the nearest Cascade Arc volcano. For the closer sites, we cannot rule out that 3He may be partially derived from westward migration of arc related fluids. The highest value occurs ~130 km from the nearest arc volcano, thus likely does not reflect arc related fluids. These preliminary observations provide geologic evidence that slab-derived fluids can migrate through the forearc mantle wedge to the surface even though the mantle is typically considered a sink for fluids owing to serpentinization processes. Likely pathways consist of fractures in the forearc mantle

  11. Imaging the Juan de Fuca subduction plate using 3D Kirchoff Prestack Depth Migration

    NASA Astrophysics Data System (ADS)

    Cheng, C.; Bodin, T.; Allen, R. M.; Tauzin, B.

    2014-12-01

    We propose a new Receiver Function migration method to image the subducting plate in the western US that utilizes the US array and regional network data. While the well-developed CCP (common conversion point) poststack migration is commonly used for such imaging; our method applies a 3D prestack depth migration approach. The traditional CCP and post-stack depth mapping approaches implement the ray tracing and moveout correction for the incoming teleseismic plane wave based on a 1D earth reference model and the assumption of horizontal discontinuities. Although this works well in mapping the reflection position of relatively flat discontinuities (such as the Moho or the LAB), CCP is known to give poor results in the presence of lateral volumetric velocity variations and dipping layers. Instead of making the flat layer assumption and 1D moveout correction, seismic rays are traced in a 3D tomographic model with the Fast Marching Method. With travel time information stored, our Kirchoff migration is done where the amplitude of the receiver function at a given time is distributed over all possible conversion points (i.e. along a semi-elipse) on the output migrated depth section. The migrated reflectors will appear where the semicircles constructively interfere, whereas destructive interference will cancel out noise. Synthetic tests show that in the case of a horizontal discontinuity, the prestack Kirchoff migration gives similar results to CCP, but without spurious multiples as this energy is stacked destructively and cancels out. For 45 degree and 60 degree dipping discontinuities, it also performs better in terms of imaging at the right boundary and dip angle. This is especially useful in the Western US case, beneath which the Juan de Fuca plate subducted to ~450km with a dipping angle that may exceed 50 degree. While the traditional CCP method will underestimate the dipping angle, our proposed imaging method will provide an accurate 3D subducting plate image without

  12. Helium as a Tracer for Fluids Released from Juan de Fuca Lithosphere Beneath the Cascadia Forearc

    NASA Astrophysics Data System (ADS)

    McCrory, P. A.; Constantz, J. E.; Hunt, A. G.; Blair, J. L. L.

    2015-12-01

    Helium isotopic ratios (3He/4He) observed in mineral springs above the Cascadia forearc provide a marker for fluids derived from Juan de Fuca lithosphere. Sample sites arcward of the forearc mantle corner generally yield significantly higher ratios (~1.5-4.0 R/RA) than those seaward of the corner (~0.3-0.6 R/RA). 3He detected above the inner forearc mantle wedge may represent a mixture of both oceanic lithosphere and forearc mantle sources, whereas 3He detected seaward of the forearc mantle corner likely has only an oceanic source. The highest ratios in the forearc coincide with slab depths (~40-45 km) where metamorphic dehydration of young, warm oceanic lithosphere is expected to release significant fluid and where tectonic tremor occurs, whereas little fluid is expected to be released from the slab (~ 25-30 km depth) beneath sites seaward of the corner.High helium ratios are also observed in springs and wells in the Nankai and Hikurangi forearcs above the region where tremor and slow slip events are detected. This correlation provides independent evidence that tremor and slow slip are associated with deep fluids, and further suggests that high pore pressures associated with tremor may also serve to keep fractures open for 3He migration through the crust.Even though our preliminary results document mantle-derived helium in surface waters of the Cascadia forearc, these results are based on sparse data from sample locations that are not optimally distributed. We have recently identified additional sample sites to investigate whether specific crustal structures in the Cascadia forearc might serve as conduits to speed the ascent of mantle-derived helium. Finally, the possibility of a 3He source related to westward flow of arc-derived fluids through the forearc mantle cannot be ruled out for some of the sites, nonetheless, the highest ratio (4.0 R/RA) is found >130 km from the nearest Cascade Arc volcano making a magmatic source unlikely.

  13. Directionality of Ambient Noise on the Juan de Fuca Plate: Implications for Source Locations of the Primary and Secondary Microseism

    NASA Astrophysics Data System (ADS)

    Tian, Y.; Ritzwoller, M. H.

    2014-12-01

    Based on cross-correlations computed from 61 ocean bottom seismometers (OBSs) within the Juan de Fuca plate from the Cascadia Initiative experiment and 42 continental stations near the western US coast, we investigate the generation locations of the primary (11-20 sec period) and secondary (5-10 sec period) microseisms in the northern Pacific Ocean by analyzing the directionality of the microseism signals received in this region. (1) Ambient noise observed across the array is much different in the primary and secondary microseism bands, both in its azimuthal content and seasonal variation, indicating different source generation locations. (2) The principal secondary microseism signals propagate toward the east, consistent with source generation in deep water of the North Pacific, perhaps coincident with the region of body wave excitation observed by Gerstoft et al. [2008] and Landès et al. [2010]. (3) Local primary microseism sources within and near the Juan de Fuca plate are implied by observations of the azimuthal dependence of the fundamental mode Rayleigh wave amplitudes as well as observations of precursory arrivals in cross-correlations of ambient noise. The strongest local generation region is observed northwest of the Juan de Fuca plate near the coast of British Columbia perhaps near Graham Island. Weaker local sources appear to be oceanward of Vancouver Island and southern Oregon. (4) High quality Green's functions are derived from cross-correlations between deep water OBSs and continental stations proving that deep water generated signals can efficiently propagate onto the continent and are well recorded by continental seismic stations, at least at periods longer than about 5 sec.In conclusion, the primary and secondary microseisms are generated at different locations, with the secondary microseism dominantly coming from deep-water sources and the source of primary microseism having a significant component in the shallow waters of the eastern Pacific

  14. A new species of Duttaphrynus (Anura:Bufonidae) from Northeast India.

    PubMed

    Das, Abhijit; Chetia, Mitali; Dutta, Sushil Kumar; Sengupta, Saibal

    2013-01-01

    A new species of montane toad Duttaphrynus is described from Nagaland state of Northeast India. The new species is diagnosable based on following combination of characters: absence of preorbital, postorbital and orbitotympanic ridges, elongated and broad parotid gland, first finger longer than second and presence of a mid-dorsal line. The tympanum is hidden under a skin fold (in male) or absent (in female). The species is compared with its congers from India and Indo-China. We propose to consider Duttaphrynus wokhaensis as junior synonym of Duttaphrynus melanostictus.

  15. Comparison of results of two dye-tracer tests at the Chestnut Ridge Security Pits, Y-12 Plant, Oak Ridge, Tennessee

    SciTech Connect

    Goldstrand, P.M.; Haas, J.

    1994-01-01

    Personnel from Martin Marietta Energy Systems, Inc. (Energy Systems) manage a closed hazardous waste disposal unit the Chestnut Ridge Security Pits (CRSP), located on the crest of Chestnut Ridge near the Y-12 Plant, Oak Ridge, Tennessee. To investigate the discharge of groundwater from CRSP to springs and streams located along the flanks and base of Chestnut Ridge, an initial dye-tracer study was conducted during 1990. A hydraulic connection was inferred to exist between the injection well (GW-178) on Chestnut Ridge and several sites to the east-northeast, east, and southeast of CRSP. A second dye-tracer study was conducted in 1992 to verify the results of the initial test and identify additional discharge points that are active during wet-weather conditions. No definitive evidence for the presence of dye was identified at any of the 35 locations monitored during the second dye study. Although interpretations of the initial dye test suggest a hydraulic connection with several sites and CRSP, reevaluation of the spectrofluorescence data from this test suggests that dye may not have been detected during the initial test. A combination of relatively high analytical detection limits during the initial test, and high natural background interference spectral peaks observed during the second test, suggest that high natural background emission spectra near the wavelength of the dye used during the initial test may have caused the apparently high reported concentrations. The results of these two tests do not preclude that a hydraulic connection exists; dye may be present in concentrations below the analytical detection limits or has yet to emerge from the groundwater system. The dye injection well is not completed within any significant karst features. Dye migration therefore, may be within a diffuse, slow-flow portion of the aquifer, at least in the immediate vicinity of the source well.

  16. Mechanisms of Basalt-plains Ridge Formation

    NASA Technical Reports Server (NTRS)

    Watters, T. R.; Maxwell, T. A.

    1985-01-01

    The morphologic similarities between the Columbia Plateau ridges and ridges on the Moon, Mercury and Mars form a strong basis for the interpretation of basalt-plains ridges as compressional folds. The basalt-plains ridges appear to have formed on competent flood basalt units deformed at the surface with essentially no confining pressure. Estimates of compressive strain for planetary ridges range from a few tenths of a percent on the Moon to up to 0.4% on Mars, to as high as 35% for Columbia Plateau folds with associated thrust faults. Such values have strong implications for both deformational mechanisms as well as for the source of stress. Deformational mechanisms that will attempt to account for the morphology, fold geometry, possible associated thrust faulting and regular spacing of the basalt-plains ridges on the terrestrial planets are under investigation.

  17. Constitutive Parameter Measurement Using Double Ridge Waveguide

    DTIC Science & Technology

    2013-03-01

    CONSTITUTIVE PARAMETER MEASUREMENT USING DOUBLE RIDGE WAVEGUIDE THESIS Nathan J. Lehman, Captain, USAF AFIT-ENG-13-M-30 DEPARTMENT OF THE AIR FORCE...copyright protection in the United States. AFIT-ENG-13-M-30 CONSTITUTIVE PARAMETER MEASUREMENT USING DOUBLE RIDGE WAVEGUIDE THESIS Presented to the Faculty...PARAMETER MEASUREMENT USING DOUBLE RIDGE WAVEGUIDE Nathan J. Lehman, B.S.E.E. Captain, USAF Approved: Michael Havrilla, PhD (Chairman) Maj Milo Hyde, PhD

  18. Northeast Texas Workplace Partnership Implementation Program.

    ERIC Educational Resources Information Center

    Northeast Texas Community Coll., Mount Pleasant.

    The Northeast Texas Workplace Partnership Program developed curriculum and training materials based on the literacy requirements of the workplace for two different industries in northeast Texas--Lone Star Steel Company and Pilgrim's Pride Industries. Three advisory committees were established to involve the community, education, and business and…

  19. 11. Exterior detail view of northeast corner, showing stucco finish ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    11. Exterior detail view of northeast corner, showing stucco finish and woodwork details - American Railway Express Company Freight Building, 1060 Northeast Division Street, Bend, Deschutes County, OR

  20. 3. Perspective view of Express Building looking northeast, with Division ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Perspective view of Express Building looking northeast, with Division Street in foreground - American Railway Express Company Freight Building, 1060 Northeast Division Street, Bend, Deschutes County, OR

  1. Geo-Morphological Analyses of the Gakkel Ridge and the Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Dorschel, B.; Schlindwein, V. S. N.; Eagles, G.

    2014-12-01

    The Gakkel Ridge in the Arctic Ocean and the Southwest Indian Ridge in the Southwest Indian Ocean between Africa and Antarctica are ultraslow-spreading (<20 mm yr-1) mid ocean ridges. This type of mid ocean ridge has distinct geo-morphologies that are influenced by the slow rate of plate divergence and by mantle potential temperature, which control the processes (peridotite diapirism and intersticial melt migration) by which material rises to fill the space vacated by plate divergence. These ridges are characterised by non-orthogonal spreading. Transform faults, typical of faster spreading mid ocean ridges, are far less common at ultraslow spreading mid ocean ridges. Thus in return, detailed geo-statistical analyses of the geo-morphology of ultraslow-spreading mid ocean ridges can provide valuable information towards a better understanding of these slowest of spreading ridges. We have generated high resolution bathymetric grids for the Gakkel and Southwest Indian ridges based on high resolution multibeam echosounder data from various expeditions with RV Polarstern. On the basis of these grids, geo-statistical analyses allow for an assessment of the geo-morphological elements of the ridges on various scales. The results of these analyses show that, approximately 200 km long medium-scale sections of the ridges can be characterised by the lengths and orientations of the short-scale (hundreds of meters to tens of kilometres) ridges and troughs. The geomorphologies of short-scale ridges and troughs situated at the junctions between medium scale sections often exhibit a mixture of the geomorphological elements seen in the neighbouring sections. These geo-morphological patterns provide insights into the overall spreading-geometry along the Gakkel Ridge and the Southwest Indian Ridge.

  2. Emergency preparedness at Oak Ridge National Laboratory, Oak Ridge, Tennessee

    SciTech Connect

    Skipper, M.N.

    1990-03-01

    Emergency preparedness for industry was commonly believed to be an essential responsibility on the part of management. Therefore, this study was conducted to research and accumulate information and data on emergency preparedness at Oak Ridge National Laboratory (ORNL). The objective of this study was to conduct a thorough evaluation of emergency preparedness knowledge among employees to determine if they were properly informed or if they needed more training. Also, this study was conducted to provide insight to management as to what their responsibility was concerning this training. To assess employee emergency preparedness knowledge, a questionnaire was developed and administered to 100 employees at ORNL. The data was analyzed using frequencies and percentages of response and was displayed through the use of graphs within the report. 22 refs., 22 figs.

  3. Student Health Services at Orchard Ridge.

    ERIC Educational Resources Information Center

    Nichols, Don D.

    This paper provides a synoptic review of student health services at the community college level while giving a more detailed description of the nature of health services at Orchard Ridge, a campus of Oakland Community College. The present College Health Service program provides for a part-time (24 hrs./wk.) nurse at Orchard Ridge. A variety of…

  4. Ridges and tidal stress on Io

    USGS Publications Warehouse

    Bart, G.D.; Turtle, E.P.; Jaeger, W.L.; Keszthelyi, L.P.; Greenberg, R.

    2004-01-01

    Sets of ridges of uncertain origin are seen in twenty-nine high-resolution Galileo images, which sample seven locales on Io. These ridges are on the order of a few kilometers in length with a spacing of about a kilometer. Within each locale, the ridges have a consistent orientation, but the orientations vary from place to place. We investigate whether these ridges could be a result of tidal flexing of Io by comparing their orientations with the peak tidal stress orientations at the same locations. We find that ridges grouped near the equator are aligned either north-south or east-west, as are the predicted principal stress orientations there. It is not clear why particular groups run north-south and others east-west. The one set of ridges observed far from the equator (52?? S) has an oblique azimuth, as do the tidal stresses at those latitudes. Therefore, all observed ridges have similar orientations to the tidal stress in their region. This correlation is consistent with the hypothesis that tidal flexing of Io plays an important role in ridge formation. ?? 2004 Elsevier Inc. All rights reserved.

  5. Tectonics and magmatism of ultraslow spreading ridges

    NASA Astrophysics Data System (ADS)

    Dubinin, E. P.; Kokhan, A. V.; Sushchevskaya, N. M.

    2013-05-01

    The tectonics, structure-forming processes, and magmatism in rift zones of ultraslow spreading ridges are exemplified in the Reykjanes, Kolbeinsey, Mohns, Knipovich, Gakkel, and Southwest Indian ridges. The thermal state of the mantle, the thickness of the brittle lithospheric layer, and spreading obliquety are the most important factors that control the structural pattern of rift zones. For the Reykjanes and Kolbeinsey ridges, the following are crucial factors: variations in the crust thickness; relationships between the thicknesses of its brittle and ductile layers; width of the rift zone; increase in intensity of magma supply approaching the Iceland thermal anomaly; and spreading obliquety. For the Knipovich Ridge, these are its localization in the transitional zone between the Gakkel and Mohns ridges under conditions of shear and tensile stresses and multiple rearrangements of spreading; nonorthogonal spreading; and structural and compositional barrier of thick continental lithosphere at the Barents Sea shelf and Spitsbergen. The Mohns Ridge is characterized by oblique spreading under conditions of a thick cold lithosphere and narrow stable rift zone. The Gakkel and the Southwest Indian ridges are distinguished by the lowest spreading rate under the settings of the along-strike variations in heating of the mantle and of a variable spreading geometry. The intensity of endogenic structure-forming varies along the strike of the ridges. In addition to the prevalence of tectonic factors in the formation of the topography, magmatism and metamorphism locally play an important role.

  6. Cedar Ridge Camp: Using the Local Environment

    ERIC Educational Resources Information Center

    Burke, Grayson

    2007-01-01

    In 2007 Cedar Ridge Camp opened for its first season as a traditional co-ed summer camp and year-round outdoor education and recreation centre. The mission would centre on creating a program that would encourage personal development and growth through a shared outdoor experience. Cedar Ridge's main goals were to promote the formation of close…

  7. Northeast Regional Planetary Data Center

    NASA Technical Reports Server (NTRS)

    Schultz, Peter H.; Saunders, Stephen (Technical Monitor)

    2005-01-01

    In 1980, the Northeast Planetary Data Center (NEPDC) was established with Tim Mutch as its Director. The Center was originally located in the Sciences Library due to space limitations but moved to the Lincoln Field Building in 1983 where it could serve the Planetary Group and outside visitors more effectively. In 1984 Dr. Peter Schultz moved to Brown University and became its Director after serving in a similar capacity at the Lunar and Planetary Institute since 1976. Debbie Glavin has served as the Data Center Coordinator since 1982. Initially the NEPDC was build around Tim Mutch's research collection of Lunar Orbiter and Mariner 9 images with only partial sets of Apollo and Viking materials. Its collection was broadened and deepened as the Director (PHS) searched for materials to fill in gaps. Two important acquisitions included the transfer of a Viking collection from a previous PI in Tucson and the donation of surplused lunar materials (Apollo) from the USGS/Menlo Park prior to its building being torn down. Later additions included the pipeline of distributed materials such as the Viking photomosaic series and certain Magellan products. Not all materials sent to Brown, however, found their way to the Data Center, e.g., Voyager prints and negatives. In addition to the NEPDC, the planetary research collection is separately maintained in conjunction with past and ongoing mission activities. These materials (e.g., Viking, Magellan, Galileo, MGS mission products) are housed elsewhere and maintained independently from the NEPDC. They are unavailable to other researchers, educators, and general public. Consequently, the NEPDC represents the only generally accessible reference collection for use by researchers, students, faculty, educators, and general public in the Northeast corridor.

  8. Transverse dune trailing ridges and vegetation succession

    NASA Astrophysics Data System (ADS)

    Hesp, Patrick A.; ‘Marisa' Martinez, M. L.

    2008-07-01

    We describe the evolution of, and vegetation succession on, a previously undescribed landform: transverse dune trailing ridges at El Farallón transgressive dunefield in the state of Veracruz, Mexico. Three-dimensional clinometer/compass and tape topographic surveys were conducted in conjunction with 1 m 2 contiguous percent cover and presence/absence vegetation survey transects at eight locations across two adjacent trailing ridges. At the study site, and elsewhere, the transverse dune trailing ridges are formed by vegetation colonization of the lateral margins of active transverse, barchanoidal transverse, and aklé or network dunes. For simplicity, all trailing ridges formed from these dune types are referred to as transverse dune trailing ridges. Because there are several transverse dunes in the dunefield, multiple trailing ridges can be formed at one time. Two adjacent trailing ridges were examined. The shortest length ridge was 70 m long, and evolving from a 2.5 m-high transverse dune, while the longer ridge was 140 m long, and evolving from an 8 m-high dune. Trailing ridge length is a proxy measure of ridge age, since the longer the ridge, the greater the length of time since initial formation. With increasing age or distance upwind, species diversity increased, as well as species horizontal extent and percent cover. In turn, the degree of bare sand decreased. Overall, the data indicate a successional trend in the vegetation presence and cover with increasing age upwind. Those species most tolerant to burial ( Croton and Palafoxia) begin the process of trailing ridge formation. Ipomoea and Canavalia are less tolerant to burial and also are typically the next colonizing species. Trachypogon does not tolerate sand burial or deposition very well and only appears after significant stabilization has taken place. The ridges display a moderately defined successional sequence in plant colonization and percentage cover with time (and upwind distance). They are

  9. Hydroforming Applications at Oak Ridge

    SciTech Connect

    bird, e.l.; ludtka, g.m.

    1999-03-10

    Hydroforming technology is a robust forming process that produces components with high precision and complexity. The goal of this paper is to present a brief description of the sheet hydroforming process with respect to the authors' experience and capabilities. Following the authors' discussion of the sheet-metal forming application, the tubular hydroforming process is described in the context of one of our technology development programs with an automotive industrial partner. After that is a summary of the tubular hydroforming advisor (expert system) development activity, which was a significant part of this overall program based on previous experience in developing a design and manufacturing support hydroforming advisor for the Oak Ridge Y-12 Plant's weapons-component manufacturing needs. Therefore, this paper is divided into three sections: (1) Hydroforming of Stainless Steel Parts, (2) Tubular Hydroforming, and (3) Components of a Tubular Hydroforming Advisor.

  10. Active tectonics of the Devils Mountain Fault and related structures, northern Puget Lowland and eastern Strait of Juan de Fuca region, Pacific Northwest

    USGS Publications Warehouse

    Johnson, Samuel Y.; Dadisman, Shawn V.; Mosher, David C.; Blakely, Richard J.; Childs, Jonathan R.

    2001-01-01

    Information from marine high-resolution and conventional seismic-reflection surveys, aeromagnetic mapping, coastal exposures of Pleistocene strata, and lithologic logs of water wells is used to assess the active tectonics of the northern Puget Lowland and eastern Strait of Juan de Fuca region of the Pacific Northwest. These data indicate that the Devils Mountain Fault and the newly recognized Strawberry Point and Utsalady Point faults are active structures and represent potential earthquake sources.

  11. 1. GENERAL VIEW OF ENTRANCE TO BLUE RIDGE TUNNEL (LEFT) ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. GENERAL VIEW OF ENTRANCE TO BLUE RIDGE TUNNEL (LEFT) FROM SOUTHEAST. ORIGINAL BLUE RIDGE R.R. (CROZET) TUNNEL IS VISIBLE AT RIGHT. - Chesapeake & Ohio Railroad, Blue Ridge Tunnel, Highway 250 at Rockfish Gap, Afton, Nelson County, VA

  12. A shallow high-resolution seismic reflection study of dudley ridge, south-east missouri

    NASA Astrophysics Data System (ADS)

    Shoemaker, M.; Vaughn, J. D.; Anderson, N. L.; Hoffman, D.; Palmer, J. R.

    1997-12-01

    Dudley Ridge is an arcuate, north-trending terrace remnant of Wisconsinan (late Quaternary) outwash in the Western Lowlands of southeast Missouri. The ridge, an elongate topographic bulge, is approximately 12 km long and 2 km wide with up to 5 m of relief. Previous workers have attributed the ridge to fluvial erosion, or to a combination of fluvial erosion and tectonic deformation during the late Quaternary. The Commerce geophysical lineament, which is a major northeast-trending basement feature, is located a few kilometers to the southeast, and swarms of paleoliquefaction and possible neotectonic deformations have been reported in nearby areas of the Western Lowlands. To test the tectonic hypothesis, in 1994 and 1995 we acquired two west-east high-resolution seismic reflection profiles along the crest and western flank of Dudley Ridge to determine whether Paleozoic, Cretaceous and shallow Quaternary strata are faulted or folded. Profile SPB-1 shows several near-vertical faults indicative of at least three periods of movement: Paleozoic to middle Mesozoic; late Cretaceous to Tertiary; and early to late Wisconsinan (late Quaternary). Profile SPB-2 shows three ambiguous fault-like features which cut Cretaceous and Quaternary reflectors, but cannot be interpreted unequivocally to extend down into the Paleozoic section. These new seismic reflection data are interpreted to show that at least three major periods of faulting have disrupted Paleozoic, Cretaceous and Quaternary strata beneath Dudley Ridge, with the most recent faulting being early to late Wisconsinan in age and producing about 6-8 m (8-10 ms) of near-vertical displacement. Because Quaternary reflectors cannot be resolved above about 30-40 ms, the seismic data alone do not reveal whether or not the Wisconsinan deformation affected the surface of Dudley Ridge or whether the faults may have died out as they propagated up through the soft, saturated Wisconsinan outwash. However, the presence of the Farmdale

  13. Probable Causes of the Abnormal Ridge Accompanying the 2013-2014 California Drought: ENSO Precursor and Anthropogenic Warming Footprint

    SciTech Connect

    Wang, S-Y; Hipps, Lawrence; Gillies, Robert R.; Yoon, Jin-Ho

    2014-05-16

    The 2013-14 California drought was accompanied by an anomalous high-amplitude ridge system. The anomalous ridge was investigated using reanalysis data and the Community Earth System Model (CESM). It was found that the ridge emerged from continual sources of Rossby wave energy in the western North Pacific starting in late summer, and subsequently intensified into winter. The ridge generated a surge of wave energy downwind and deepened further the trough over the northeast U.S., forming a dipole. The dipole and associated circulation pattern is not linked directly with either ENSO or Pacific Decadal Oscillation; instead it is correlated with a type of ENSO precursor. The connection between the dipole and ENSO precursor has become stronger since the 1970s, and this is attributed to increased GHG loading as simulated by the CESM. Therefore, there is a traceable anthropogenic warming footprint in the enormous intensity of the anomalous ridge during winter 2013-14, the associated drought and its intensity.

  14. A new look at Northwind Ridge: implications for the history of the Canada Basin

    NASA Astrophysics Data System (ADS)

    Hutchinson, D. R.; Mosher, D. C.; Shimeld, J.; Jackson, R.; Chian, D.; Edwards, B. D.; Hart, P. E.; Mayer, L. A.

    2010-12-01

    ) models of the opening of CB may not require complete closure and therefore (2) NR may not overlap the continental margin of northern Canada, a problem with previous reconstructions. The northeast orientation of NR is subparallel to the inferred orientation of a deeply buried graben complex that is characterized by a northeast-trending negative gravity anomaly and offset ~250 km to the east of NR. Three northeast-trending bathymetric ridges also occur in the Sever Spur area or CB. Although the ages of rifting for either NR or the deeply buried graben complex are not well constrained, their subparallel orientation suggests this northeast direction is a preferred tectonic fabric either inherited prior to or created during the rifting and opening of the basin.

  15. Genome-Wide Analysis Identifies IL-18 and FUCA2 as Novel Genes Associated with Diastolic Function in African Americans with Sickle Cell Disease

    PubMed Central

    Sysol, Justin R.; Abbasi, Taimur; Patel, Amit R.; Lang, Roberto M.; Gupta, Akash; Garcia, Joe G. N.; Gordeuk, Victor R.; Machado, Roberto F.

    2016-01-01

    Background Diastolic dysfunction is common in sickle cell disease (SCD), and is associated with an increased risk of mortality. However, the molecular pathogenesis underlying this development is poorly understood. The aim of this study was to identify a gene expression profile that is associated with diastolic function in SCD, potentially elucidating molecular mechanisms behind diastolic dysfunction development. Methods Diastolic function was measured via echocardiography in 65 patients with SCD from two independent study populations. Gene expression microarray data was compared with diastolic function in both study cohorts. Candidate genes that associated in both analyses were tested for validation in a murine SCD model. Lastly, genotyping array data from the replication cohort was used to derive cis-expression quantitative trait loci (cis-eQTLs) and genetic associations within the candidate gene regions. Results Transcriptome data from both patient cohorts implicated 7 genes associated with diastolic function, and mouse SCD myocardial expression validated 3 of these genes. Genetic associations and eQTLs were detected in 2 of the 3 genes, FUCA2 and IL18. Conclusions FUCA2 and IL18 are associated with diastolic function in SCD patients, and may be involved in the pathogenesis of the disease. Genetic polymorphisms within the FUCA2 and IL18 gene regions are also associated with diastolic function in SCD, likely by affecting expression levels of the genes. PMID:27636371

  16. Plume-ridge interaction: Shaping the geometry of mid-ocean ridges

    NASA Astrophysics Data System (ADS)

    Mittelstaedt, Eric L.

    Manifestations of plume-ridge interaction are found across the ocean basins. Currently there are interactions between at least 21 hot spots and nearby ridges along 15--20% of the global mid-ocean ridge network. These interactions produce a number of anomalies including the presence of elevated topography, negative gravity anomalies, and anomalous crustal production. One form of anomalous crustal production is the formation of volcanic lineaments between hotspots and nearby mid-ocean ridges. In addition, observations indicate that mantle plumes tend to "capture" nearby mid-ocean ridges through asymmetric spreading, increased ridge propagation, and discrete shifts of the ridge axis, or ridge jumps. The initiation of ridge jumps and the formation of off-axis volcanic lineaments likely involve similar processes and may be closely related. In the following work, I use theoretical and numerical models to quantify the processes that control the formation of volcanic lineaments (Chapter 2), the initiation of mid-ocean ridge jumps associated with lithospheric heating due to magma passing through the plate (Chapter 3), and the initiation of jumps due to an upwelling mantle plume and magmatic heating governed by melt migration (Chapter 4). Results indicate that lineaments and ridge jumps associated with plume-ridge interaction are most likely to occur on young lithosphere. The shape of lineaments on the seafloor is predicted to be controlled by the pattern of lithospheric stresses associated with a laterally spreading, near-ridge mantle plume. Ridge jumps are likely to occur due to magmatic heating alone only in lithosphere ˜1Myr old, because the heating rate required to jump increases with spreading rate and plate age. The added effect of an upwelling plume introduces competing effects that both promote and inhibit ridge jumps. For models where magmatic heating is controlled by melt migration, repeat ridge jumps are predicted to occur as the plume and ridge separate, but

  17. The "pressures" of being a ridge

    NASA Astrophysics Data System (ADS)

    Fleeman, K.; Scott, J. L.; Barton, M.

    2015-12-01

    As part of a larger project aimed at understanding the magma plumbing systems and magmatic processes responsible for crust formation at divergent plate margins, we have begun a study of the Galapagos Spreading Center (GSC), an intermediate spreading ridge off the west coast of South America and connected to the East Pacific Rise. This ridge is of interest because it passes close to the Galapagos Islands, allowing the effects of a mantle plume on sub-ridge processes and magma plumbing systems to be examined. In addition, the effects of ridge-ridge intersection, ridge propagation, and ridge offsets by transform faults on magma evolution can be examined. Published compositional data for glasses collected along the ridge were used to calculate pressures of partial crystallization and to examine variations in magma chemistry along the ridge. To aid interpretation of the results, the ridge was divided into 12 segments based on sample distribution and the occurrence of ridge offsets. Calculated pressures for most segments range from 100 and 300 MPa, and indicate depths of partial crystallization of ~3-9 km. This suggests that accretion occurs mostly near the base of the crust. However, the range of pressures for some segments is relatively large with maximum calculated values of 500-750 MPa. For example, near the major transform fault at ~85OW, the calculated maximum pressure is 741 MPa and the average pressure is ~ 300 MPa. We consider it unlikely that the calculated high pressures represent the true pressure of partial crystallization, and suggest that the compositions of some magmas result from processes other than simple crystallization. Correlations between Pressure and MgO, between Na2O and MgO, P2O5 and K2O, and between Na8 and longitude suggest that the processes operating beneath this ridge are complex. Near the transform fault for example, MgO vs Pressure shows a negative correlation with an R2 value of 0.546. Such trends are inconsistent with magma evolution

  18. Enhancing Scientific Literacy in the Northeast Kingdom

    NASA Astrophysics Data System (ADS)

    Blackwell, John; Moss, B.; Wanzer, S.

    2014-01-01

    An observatory in the Northeast Kingdom of Vermont opens to assist surrounding elementary and high schools with science literacy using astronomy as a capstone science, introducing students to advanced instrumentation, scientific method and data manipulation skills.

  19. [Migration and urban poverty in the Northeast].

    PubMed

    Duarte, R

    1983-01-01

    Migration and poverty in Northeast Brazil are studied using data from a survey conducted in 1974-1975 in the barrios of three cities. Information on employment and living conditions of migrants is compared with data for the native population.

  20. SRTM Anaglyph: Wheeler Ridge, California

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Wheeler Ridge and vicinity, California, is a site of major tectonic activity, both historically and over recent geologic time. The epicenter of the 7.5 magnitude Kern County earthquake occurred here on July 21,1952, and numerous geologic and topographic features indicate rapid geologic processes. The ridge itself (upper-right center) is a geologic fold that is growing out of the southern San Joaquin Valley. A prominent 'wind gap,' now used for passage of the California aquaduct (with the aid of a pumping station), is evidence that the ridge grew faster than tranversing streams could erode down. Nearby abrupt and/or landslid mountain fronts similarly indicate a vigorous tectonic setting here, just north of the San Andreas fault. The Interstate 5 freeway can be seen crossing agricultural fields on the right and entering the very rugged and steep Grapevine Canyon toward the bottom.

    This anaglyph was generated by first draping a Landsat satellite image over a preliminary topographic map from the Shuttle Radar Topography Mission (SRTM), then generating two differing perspectives, one for each eye. When viewed through special glasses, the result is a vertically exaggerated view of the Earth's surface in its full three dimensions. Anaglyph glasses cover the left eye with a red filter and cover the right eye with a blue filter. Landsat has been providing visible and infrared views of the Earth since 1972. SRTM elevation data matches the 30 meter resolution of most Landsat images and will substantially help in analyses of the large and growing Landsat image archive.

    The elevation data used in this image was acquired by SRTM aboard the Space Shuttle Endeavour, launched on February 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect three-dimensional measurements of the Earth's surface. To collect

  1. Northeast Clean Energy Application Center

    SciTech Connect

    Bourgeois, Tom

    2013-09-30

    From October 1, 2009 through September 30, 2013 (“contract period”), the Northeast Clean Energy Application Center (“NE-CEAC”) worked in New York and New England (Connecticut, Rhode Island, Vermont, Massachusetts, New Hampshire, and Maine) to create a more robust market for the deployment of clean energy technologies (CETs) including combined heat and power (CHP), district energy systems (DES), and waste heat recovery (WHR) systems through the provision of technical assistance, education and outreach, and strategic market analysis and support for decision-makers. CHP, DES, and WHR can help reduce greenhouse gas emissions, reduce electrical and thermal energy costs, and provide more reliable energy for users throughout the United States. The NE-CEAC’s efforts in the provision of technical assistance, education and outreach, and strategic market analysis and support for decision-makers helped advance the market for CETs in the Northeast thereby helping the region move towards the following outcomes: • Reduction of greenhouse gas emissions and criteria pollutants • Improvements in energy efficiency resulting in lower costs of doing business • Productivity gains in industry and efficiency gains in buildings • Lower regional energy costs • Strengthened energy security • Enhanced consumer choice • Reduced price risks for end-users • Economic development effects keeping more jobs and more income in our regional economy Over the contract period, NE-CEAC provided technical assistance to approximately 56 different potential end-users that were interested in CHP and other CETs for their facility or facilities. Of these 56 potential end-users, five new CHP projects totaling over 60 MW of install capacity became operational during the contract period. The NE-CEAC helped host numerous target market workshops, trainings, and webinars; and NE-CEAC staff delivered presentations at many other workshops and conferences. In total, over 60 different workshops

  2. The structure of mid-ocean ridges

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.; Toomey, Douglas R.

    1992-01-01

    Recent research results on the structure of midocean ridges are reviewed. The new view of ridge-axis crustal structure obtained from high-resolution seismology is reviewed, emphasizing the variation of that structure with spreading rate and along-axis at a given spreading rate. Recent results on upper mantle structure beneath ridges are examined, including variations with seafloor age, indications from anisotropy for directions of mantle flow, and long-wavelength along-axis variations in structure and their implications for lateral heterogeneity in mantle temperature and composition.

  3. Geochemical Evidence for Crustal Assimilation at Mid-Ocean Ridges Using Major and Trace Elements, Volatiles and Oxygen Isotopes

    NASA Astrophysics Data System (ADS)

    Wanless, V.; Perfit, M. R.; Ridley, W. I.; Wallace, P. J.; Valley, J. W.; Grimes, C. B.; Klein, E. M.

    2009-12-01

    Geochemical analyses and petrologic modeling of dacites erupted at three spreading centers suggest that crustal melting and assimilation may be an important process in the petrogenesis of high-silica lavas on mid-ocean ridges (MOR). Experimental results and textural observations of ophiolites suggest that assimilation could be important at MOR, but observational and geochemical evidence of this process are obscured at MOR because of lack of exposure and similar wall rock and magma compositions. Although most geochemical variability on MOR is consistent with low-pressure fractional crystallization of various mantle-derived parental melts, our geochemical investigations of MOR dacitic glasses suggest that there is a seawater-altered component involved in their petrogenesis. If assumed to reflect primary magmatic compositions, the measured high Cl, H2O and relatively low oxygen isotope ratios (~5.6 vs. expected values ~7) in MOR dacite glasses can be explained by assimilation of altered ocean crust, which has lower oxygen isotope ratios, and elevated Cl and H2O concentrations due to alteration/metamorphism by hydrothermal fluids. Petrologic modeling of MOR dacites also suggests assimilation of an altered crustal component. During AFC processes, ascending MORB magma undergoes extreme crystal fractionation (Ol+Plag+Cpx+Fe-oxides) coupled with melting and assimilation of altered ocean crust. Crystallization of silicate phases and Fe-oxides causes an increase in delta18O in the residual magma but assimilation of material altered at high temperatures causes a decrease in delta18O. Lower delta18O values have been observed in evolved volcanics at the East Pacific Rise, Juan de Fuca Ridge, and Galapagos Spreading Center, but coexisting refractory minerals have not yet been analyzed. These dacitic glasses support the hypothesis that crustal assimilation is an important process in the formation of highly evolved MOR lavas.

  4. Status report: Low-level waste siting in the northeast

    SciTech Connect

    1995-11-01

    This afternoon, I am going to recapitulate the status of the state and Compact LLRW siting programs in the eight states of the northeastern United States. First, let us review the configuration of the LLRW Compacts and unaligned states of the Northeast. Maine and Vermont have aligned with Texas in the {open_quotes}surf and turf{close_quotes} compact. Lawrence Jacobi gave an update on progress in that siting effort earlier. Pennsylvania is a member of the Appalachian Compact that was reported on by Walter Newcomb just a few moments ago. However, I can`t resist showing you a copy of last week`s Harrisburg Patriot. This article is most significant in that it appeared 2 days after Barnwell opened to the nation once again. Although access to Barnwell may be available for another decade (just about the time that current siting processes are scheduled to be completed), strong leadership by newly-elected Republican Governor Tom Ridge in support of an enhanced voluntary siting process is refreshing.

  5. Northeast-southwest structural transect: Rocky Mountain foreland, Wyoming

    SciTech Connect

    Stone, D.S.

    1987-08-01

    A northeast-southwest structural transect has been constructed across the Rocky Mountain foreland in Wyoming, a distance of about 400 mi. The line of transect begins in the northern Black Hills and traverses the northern Powder River basin, the Bighorn Mountains from Buffalo to Bonanza, the Big Horn basin from Worland to Hamilton dome, the Owl Creek Mountains, the northern Wind River basin at Maverick Springs, the Wind River Mountains to Pinedale in the Green River basin, the Moxa Arch at Big Piney and Riley Ridge, and into the thrust belt, ending at the Idaho border. In terms of a vertical and horizontal scale of 1 in. = 2000 ft, the section is about 90 ft long (i.e., the section is approximately 409 mi long). The data base for the transect includes published geologic maps, commercial photogeologic mapping, well data, and modern seismic data through critical parts of the basin areas. The data base provides an excellent found for analyzing structural relationships on both a regional and a local scale. Regional horizontal shortening of the foreland has occurred primarily through basement-involved displacements on basin-boundary megathrusts, which separate the mountain ranges from sedimentary basins, and on the smaller, intrabasin thrusts, which produced the anticlinal traps for Paleozoic oil accumulations.

  6. Oral Mucosal Lesions in Indians From Northeast Brazil

    PubMed Central

    Cury, Patricia Ramos; Porto, Lia Pontes Arruda; dos Santos, Jean Nunes; e Ribeiro, Livia Silva Figueiredo; de Aquino Xavier, Flavia Caló; Figueiredo, Andreia Leal; Ramalho, Luciana Maria Pedreira

    2014-01-01

    Abstract The aim of this cross-sectional study was to evaluate the prevalence of oral mucosal lesions, and their risk indicators in adult Kiriri Indians from Northeast Brazil. Clinical oral examination was performed on a representative sample of 223 Indians (age ≥19 years). A systematic evaluation of lips, labial mucosa and sulcus, commissures, buccal mucosa and sulcus, gingiva and alveolar ridge, tongue, floor of the mouth, and soft and hard palate was performed. Bivariate analysis was conducted to assess associations between mucosal conditions and age, gender, income, educational level, diabetic status, and smoking status. Mucosal lesions were found in 50 participants (22.4%). The most prevalent lesions were fistulae (6.2%) and traumatic ulcers (4.48%). Oral mucosal was associated with higher age (≥35 years; odds ratio [OR] = 1.99, 95% confidence interval [CI]: 1.05–3.76, P = 0.03) and lower education level (<9 years; OR = 2.13, 95% CI: 0.96–4.71, P = 0.06). Mucosal conditions are prevalent in Kiriri Indians and the presence of mucosal lesions is associated with advanced age and lower education. A public health program aimed at preventing and treating mucosal lesions and targeted toward the high-risk group is vital to improve the oral health status of this population. PMID:25501053

  7. Controls on melting at spreading ridges from correlated abyssal peridotite - mid-ocean ridge basalt compositions

    NASA Astrophysics Data System (ADS)

    Regelous, Marcel; Weinzierl, Christoph G.; Haase, Karsten M.

    2016-09-01

    Variations in the volume and major element composition of basalt erupted along the global mid-ocean ridge system have been attributed to differences in mantle potential temperature, mantle composition, or plate spreading rate and lithosphere thickness. Abyssal peridotites, the residues of mantle melting beneath mid-ocean ridges, provide additional information on the melting process, which could be used to test these hypotheses. We compiled a global database of abyssal peridotite compositions averaged over the same ridge segments defined by Gale et al. (2013). In addition, we calculated the distance of each ridge segment to the nearest hotspots. We show that Cr# in spinel in abyssal peridotites is negatively correlated with Na90 in basalts from the same ridge segments on a global scale. Ridge segments that erupt basalts apparently produced by larger degrees of mantle melting are thus underlain by peridotites from which large amounts of melt have been extracted. We find that near-ridge hotspots have a more widespread influence on mid-ocean ridge basalt (MORB) composition and ridge depth than previously thought. However, when these hotspot-influenced ridge segments are excluded, the remaining segments show clear relationships between MORB composition, peridotite composition, and ridge depth with spreading rate. Very slow-spreading ridges (<20 mm/yr) are deeper, erupt basalts with higher Na90, Al90, K90/Ti90, and lower Fe90, Ca90/Al90, and expose peridotites with lower Cr# than intermediate and fast-spreading ridges. We show that away from hotspots, the spreading-rate dependence of the maximum degree of mantle melting inferred from Cr# in peridotites (FM) and the bulk degree of melting inferred from Na90 in basalts (FB) from the same ridge segments is unlikely to be due to variations in mantle composition. Nor can the effects of dynamic mantle upwelling or incomplete melt extraction at low spreading rates satisfactorily explain the observed compositions of abyssal

  8. Recent geodynamics and evolution of the Moma rift, Northeast Asia.

    NASA Astrophysics Data System (ADS)

    Imaev, V. S.; Imaeva, L. P.; Kozmin, B. M.; Fujita, K. S.; Mackey, K. G.

    2009-04-01

    Eurasia; this geometry also supports the extrusion of the Okhotsk Sea plate. Poles of rotation calculated earlier using magnetic lineation and fracture zone data from the North Atlantic yielded poles further south, about 62°N. This, combined with other evidence for extension in northeast Russia in the Oligocene and the sedimentary record of the basins, supports the origin of the Moma rift system as an extension of the Arctic Mid-Ocean Ridge in the Oligocene and continuing through about Pliocene time, although the complete lack of any evidence of volcanism in the rifts in this time period is mystifying. Sometime in the Quaternary, the pole of rotation shifted north, placing the Moma rift system into compression. The young age for Balagan-Tas would suggest that the change occurred in the not too distant past. Thus, the Moma rift system probably originated as an extension of the Arctic (Gakkel) Mid-Ocean Ridge into the continent in the Early Cenozoic. hi the Quaternary, movement of the Euler pole between North America and Eurasia resulted in the region being placed under compression with the development (or reactivation) of major strike-slip fault systems and the compression of the former rift basins.

  9. The Northeast Stream Quality Assessment

    USGS Publications Warehouse

    Van Metre, Peter C.; Riva-Murray, Karen; Coles, James F.

    2016-04-22

    In 2016, the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) is assessing stream quality in the northeastern United States. The goal of the Northeast Stream Quality Assessment (NESQA) is to assess the quality of streams in the region by characterizing multiple water-quality factors that are stressors to aquatic life and evaluating the relation between these stressors and biological communities. The focus of NESQA in 2016 will be on the effects of urbanization and agriculture on stream quality in all or parts of eight states: Connecticut, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont.Findings will provide the public and policymakers with information about the most critical factors affecting stream quality, thus providing insights about possible approaches to protect the health of streams in the region. The NESQA study will be the fourth regional study conducted as part of NAWQA and will be of similar design and scope to the first three, in the Midwest in 2013, the Southeast in 2014, and the Pacific Northwest in 2015 (http://txpub.usgs.gov/RSQA/).

  10. Rainwater composition in northeast Uruguay

    NASA Astrophysics Data System (ADS)

    Zunckel, M.; Saizar, C.; Zarauz, J.

    The chemical composition of rainfall in northeast Uruguay in 1999 and 2000 and the sources that contribute to the rainwater chemistry are assessed in this study, contributing to a limited knowledge base of rainwater quality in South America. Principal factor analysis and cluster analysis indicate that four main source groups influence the rainfall chemistry over a range of spatial scales. Terrigenous sources (e.g. rock, soil and dust) and agricultural sources (e.g. livestock and crop fertilization) contribute to rainwater chemistry on a local and sub-regional scale. Influx of marine air from the Atlantic Ocean has a regional-scale influence while biomass burning contributes at both a local and sub-regional scale (e.g. fuel wood, and agroindustries) and through long-range transport (forest fires and land clearing). As may be expected in this area dominated by agriculture, the concentrations of ions that are indicative of industrial emissions, NO 3- and SO 42-, are typical of background measurements. The current data are limited, but provide an indication of rain quality and the sources that influence its chemistry in Uruguay. It may be inferred that large-scale biomass burning in the central parts of the continent influence rainwater chemistry on a scale far larger than indicated by the Uruguayan network. Similarly, but to lesser extent, the influx of marine air off the Atlantic Ocean has a greater regional-scale influence than suggested by these data.

  11. [Environmental mesotheliomas in northeast Corsica].

    PubMed

    Rey, F; Viallat, J R; Boutin, C; Farisse, P; Billon-Galland, M A; Hereng, P; Dumortier, P; De Vuyst, P

    1993-01-01

    Since 1980, we have collected fourteen cases of mesothelioma induced by environmental exposure to asbestos, going back to childhood in patients from north-east Corsica, in a region which was remote from the asbestos mine of Canari. There were eight men and six women with a mean age of 69.5 +/- 4 years. Six patients presented with bilateral calcified pleural plaques as evidence of environmental exposure. The mineral analysis carried out on five patients (four had thoracoscopies and one an alveolar lavage), showed a moderate deposit of chrysotile (0.3 to 3.4 x 10(6) fibres per gram of dry tissue), and elevated level of tremolite (1.4 to 62 x 10(6) fibres/g). The ambient dosage of asbestos has confirmed the existence of environmental pollution by chrysotile fibres and above all by tremolite. In addition, the same type of fibres have been identified in the parietal pleural of animals subjected to the same risk. In this region, the risk is estimated, on the basis of our results, as 10 cases of mesothelioma per 100,000 inhabitants per year.

  12. Northeast View From Pathfinder Lander

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This panorama of the region to the northeast of the lander was constructed to support the Sojourner Rover Team's plans to conduct an 'autonomous traverse' to explore the terrain away from the lander after science objectives in the lander vicinity had been met. The large, relatively bright surface in the foreground, about 10 meters (33 feet) from the spacecraft, in this scene is 'Baker's Bench.' The large, elongated rock left of center in the middle distance is 'Zaphod.'

    This view was produced by combining 8 individual 'Superpan' scenes from the left and right eyes of the IMP camera. Each frame consists of 8 individual frames (left eye) and 7 frames (right eye) taken with different color filters that were enlarged by 500% and then co-added using Adobe Photoshop to produce, in effect, a super-resolution panchromatic frame that is sharper than an individual frame would be.

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology (Caltech). The IMP was developed by the University of Arizona Lunar and Planetary Laboratory under contract to JPL. Peter Smith is the Principal Investigator.

  13. West Chestnut Ridge hydrologic studies

    SciTech Connect

    Elmore, J.L.; Huff, D.D.; Jones, J.R.

    1985-08-01

    Preliminary site characterization work for the proposed West Chestnut Ridge Central Waste Disposal Facility included collection and analysis of data on stream flows, watershed areas, precipitation, water levels at piezometer sites, and physiochemical properties of surface water. Seven temporary water-flow-gaging installations were established and used to characterize runoff patterns in the study area. Chip-floating and regression techniques were used to estimate stream flows after some of the temporary structures were destroyed during high flows. Stream flow fluctuations were quantified using coefficients of variation and percent change in total flow between adjacent sampling dates. The difference between precipitation and observed flows (net loss) was calculated for all stations. Two headwater stations (4 and 6) exhibited lower flows per watershed area and channel length, and higher levels of fluctuation in flow than the other stations. These two stations were also similar in watershed area and flow magnitude. Two other headwater stations (5 and 7) with comparable flows had total drainage areas that were similar in size and smaller than those of the other stations. Stations 5 and 7 exhibited high flows per drainage area and section length, especially in the dry period of the year when flows were higher than at all other stations. Fluctuations in flows were lowest at these two stations. Data indicate that these two sections are fed by sources of dependable groundwater. 7 refs., 4 figs., 8 tabs.

  14. Low Sun from 'Low Ridge'

    NASA Technical Reports Server (NTRS)

    2006-01-01

    A spectacular field of Martian sand ripples separates NASA's Mars Exploration Rover Spirit from the slopes of 'Husband Hill.' It has been 200 Martian days, or sols, since the rover started a descent from the top of the peak to the rover's current position on 'Low Ridge.' Looking back to the north on sol 813 (April 17, 2006), Spirit acquired this blue-filter (436-nanometer) view with the right panoramic camera (Pancam) while the Sun was low in the sky late in the afternoon. Because of the low-angle lighting (sunlight is coming from the left), images like this provide superb views of subtle textures in the topography both near and far. Husband Hill, where the rover was perched late last summer, rises prominently just left of center in this view. A 150-meter wide (500 foot) field of curving sand ripples named 'El Dorado' lies at the base of Husband Hill.

    By collecting photos like this at different times of day, when lighting comes from different directions, scientists can distinguish surface properties such as color and reflectivity from topography and roughness. By separating these components they can map more details of the geologic terrain, providing new clues about the geologic history of Gusev Crater.

  15. Influence of ancient thrust faults on the hydrogeology of the Blue Ridge Province.

    PubMed

    Seaton, William J; Burbey, Thomas J

    2005-01-01

    The Blue Ridge Province contains ubiquitous northeast-southwest-trending thrust faults or smaller thrust "slivers" that greatly impact the nature and character of ground water flow in this region. Detailed investigations at a field site in Floyd County, Virginia, indicate that high-permeability zones occur in the brittle crystalline rocks above these thrust faults. Surface and borehole geophysics, aquifer tests, and chlorofluorocarbon and geochemical data reveal that the shallow saprolite aquifer is separated from the deeper fault-zone aquifer by a low-fracture permeability bedrock confining unit, the hydraulic conductivity of which has been estimated to be six orders of magnitude less than the conductivity of the fault zones at the test site. Within the Blue Ridge Province, these fault zones can occur at depths of 300 m or more, can contain a significant amount of storage, and yield significant quantities of water to wells. Furthermore, it is expected that these faults may compartmentalize the deep aquifer system. Recharge to and discharge from the deep aquifer occurs by slow leakage through the confining unit or through localized breach zones that occur where quartz accumulated in high concentrations during metamorphism and later became extensively fractured during episodes of deformation. The results of this investigation stress the importance of thrust faults in this region and suggest that hydrogeologic models for the Blue Ridge Province include these ancient structural features. Faults in crystalline-rock environments may not only influence the hydrology, they may dominate the flow characteristics of a region.

  16. Carlsberg Ridge and Mid-Atlantic Ridge: Comparison of slow spreading centre analogues

    NASA Astrophysics Data System (ADS)

    Murton, Bramley J.; Rona, Peter A.

    2015-11-01

    Eighty per cent of all mid-ocean spreading centres are slow. Using a mixture of global bathymetry data and ship-board multibeam echosounder data, we explore the morphology of global mid-ocean ridges and compare two slow spreading analogues: the Carlsberg Ridge in the north-west Indian Ocean between 57°E and 60°E, and the Kane to Atlantis super-segment of the Mid-Atlantic Ridge between 21°N and 31°N. At a global scale, mid-ocean spreading centres show an inverse correlation between segment length and spreading rate with segmentation frequency. Within this context, both the Mid-Atlantic Ridge super-segment and Carlsberg Ridge are similar: spreading at 22 and 26 mm/yr full rates respectively, being devoid of major transform faults, and being segmented by dextral, non-transform, second-order discontinuities. For these and other slow spreading ridges, we show that segmentation frequency varies inversely with flank height and ridge axis depth. Segments on both the Mid-Atlantic Ridge super-segment and Carlsberg Ridge range in aspect ratio (ridge flank height/axis width), depth and symmetry. Segments with high aspect ratios and deeper axial floors often have asymmetric rift flanks and are associated with indicators of lower degrees of melt flux. Segments with low aspect ratios have shallower axial floors, symmetric rift flanks, and evidence of robust melt supply. The relationship between segmentation, spreading rate, ridge depth and morphology, at both a global and local scale, is evidence that rates of melting of the underlying mantle and melt delivery to the crust play a significant role in determining the structure and morphology of slow spreading mid-ocean ridges.

  17. 27 CFR 9.182 - Ribbon Ridge.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ..., Oregon, 1956, revised 1993. (c) Boundary. The Ribbon Ridge viticultural area is located in northern... Quadrangle map at the intersection of a light-duty road known locally as Albertson Road and Dopp Road...

  18. 27 CFR 9.182 - Ribbon Ridge.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ..., Oregon, 1956, revised 1993. (c) Boundary. The Ribbon Ridge viticultural area is located in northern... Quadrangle map at the intersection of a light-duty road known locally as Albertson Road and Dopp Road...

  19. 27 CFR 9.182 - Ribbon Ridge.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ..., Oregon, 1956, revised 1993. (c) Boundary. The Ribbon Ridge viticultural area is located in northern... Quadrangle map at the intersection of a light-duty road known locally as Albertson Road and Dopp Road...

  20. 27 CFR 9.182 - Ribbon Ridge.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ..., Oregon, 1956, revised 1993. (c) Boundary. The Ribbon Ridge viticultural area is located in northern... Quadrangle map at the intersection of a light-duty road known locally as Albertson Road and Dopp Road...

  1. 27 CFR 9.182 - Ribbon Ridge.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ..., Oregon, 1956, revised 1993. (c) Boundary. The Ribbon Ridge viticultural area is located in northern... Quadrangle map at the intersection of a light-duty road known locally as Albertson Road and Dopp Road...

  2. Dark and Bright Ridges on Europa

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This high-resolution image of Jupiter's moon Europa, taken by NASA's Galileo spacecraft camera, shows dark, relatively smooth region at the lower right hand corner of the image which may be a place where warm ice has welled up from below. The region is approximately 30 square kilometers in area. An isolated bright hill stands within it. The image also shows two prominent ridges which have different characteristics; youngest ridge runs from left to top right and is about 5 kilometers in width (about 3.1 miles). The ridge has two bright, raised rims and a central valley. The rims of the ridge are rough in texture. The inner and outer walls show bright and dark debris streaming downslope, some of it forming broad fans. This ridge overlies and therefore must be younger than a second ridge running from top to bottom on the left side of the image. This dark 2 km wide ridge is relatively flat, and has smaller-scale ridges and troughs along its length.

    North is to the top of the picture, and the sun illuminates the surface from the upper left. This image, centered at approximately 14 degrees south latitude and 194 degrees west longitude, covers an area approximately 15 kilometers by 20 kilometers (9 miles by 12 miles). The resolution is 26 meters (85 feet) per picture element. This image was taken on December 16, 1997 at a range of 1300 kilometers (800 miles) by Galileo's solid state imaging system.

    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/ galileo.

  3. Internal Tide Generation by Tall Ocean Ridges

    DTIC Science & Technology

    2009-09-01

    April 26th, 1996, of the area enclosed by the solid line in the map of the South China Sea (right). The dashed line indicates the location of the Luzon...115 15 4-9 Bathymetry of (a) the ridge at French Frigate Shoals (FFS) and (b) the Keana Ridge (KR) in the Kauai Channel. The...The thick lines in panel (b) indicate the raw bathymetry data (solid) and a smoothed version of the profile (dashed), and the inset presents the local

  4. A Subnational Perspective for Comparative Research: Education and Development in Northeast Brazil and Northeast Thailand.

    ERIC Educational Resources Information Center

    Fry, Gerald; Kempner, Ken

    1996-01-01

    Case studies of northeast Brazil and northeast Thailand highlight the importance of a subnational approach to comparative research. Compares geographic and economic conditions, regional culture, ethnicity and gender issues, migration patterns, religion, literacy, and educational underdevelopment. Points out that neglect of a region and its people…

  5. Assessing the clarity of friction ridge impressions.

    PubMed

    Hicklin, R Austin; Buscaglia, JoAnn; Roberts, Maria Antonia

    2013-03-10

    The ability of friction ridge examiners to correctly discern and make use of the ridges and associated features in finger or palm impressions is limited by clarity. The clarity of an impression relates to the examiner's confidence that the presence, absence, and attributes of features can be correctly discerned. Despite the importance of clarity in the examination process, there have not previously been standard methods for assessing clarity in friction ridge impressions. We introduce a process for annotation, analysis, and interchange of friction ridge clarity information that can be applied to latent or exemplar impressions. This paper: (1) describes a method for evaluating the clarity of friction ridge impressions by using color-coded annotations that can be used by examiners or automated systems; (2) discusses algorithms for overall clarity metrics based on manual or automated clarity annotation; and (3) defines a method of quantifying the correspondence of clarity when comparing a pair of friction ridge images, based on clarity annotation and resulting metrics. Different uses of this approach include examiner interchange of data, quality assurance, metrics, and as an aid in automated fingerprint matching.

  6. Oak Ridge Reservation environmental report for 1989

    SciTech Connect

    Jacobs, V.A.; Wilson, A.R.

    1990-10-01

    This two-volume report, the Oak Ridge Reservation Environmental Report for 1989, is the nineteenth in an annual series that began in 1971. It reports the results of a comprehensive, year-round program to monitor the impact of operations at the three major US Department of Energy (DOE) production and research installations in Oak Ridge on the immediate areas' and surrounding region's groundwater and surface waters, soil, air quality, vegetation and wildlife, and through these multiple and varied pathways, the resident human population. Information is presented for the environmental monitoring Quality Assurance (QA) Program, audits and reviews, waste management activities, land special environmental studies. Data are included for the Oak Ridge Y-12 Plant, Oak Ridge National Laboratory (ORNL), and Oak Ridge Gaseous Diffusion Plant (ORGDP). Volume 1 presents narratives, summaries, and conclusions based on environmental monitoring at the three DOE installations and in the surrounding environs during calendar year (CY) 1989. Volume 1 is intended to be a stand-alone'' report about the Oak Ridge Reservation (ORR) for the reader who does not want an in-depth review of 1989 data. Volume 2 presents the detailed data from which these conclusions have been drawn and should be used in conjunction with Volume 1.

  7. CoopEUS Case Study: Tsunami Modelling and Early Warning Systems for Near Source Areas (Mediterranean, Juan de Fuca).

    NASA Astrophysics Data System (ADS)

    Beranzoli, Laura; Best, Mairi; Chierici, Francesco; Embriaco, Davide; Galbraith, Nan; Heeseman, Martin; Kelley, Deborah; Pirenne, Benoit; Scofield, Oscar; Weller, Robert

    2015-04-01

    There is a need for tsunami modeling and early warning systems for near-source areas. For example this is a common public safety threat in the Mediterranean and Juan de Fuca/NE Pacific Coast of N.A.; Regions covered by the EMSO, OOI, and ONC ocean observatories. Through the CoopEUS international cooperation project, a number of environmental research infrastructures have come together to coordinate efforts on environmental challenges; this tsunami case study tackles one such challenge. There is a mutual need of tsunami event field data and modeling to deepen our experience in testing methodology and developing real-time data processing. Tsunami field data are already available for past events, part of this use case compares these for compatibility, gap analysis, and model groundtruthing. It also reviews sensors needed and harmonizes instrument settings. Sensor metadata and registries are compared, harmonized, and aligned. Data policies and access are also compared and assessed for gap analysis. Modelling algorithms are compared and tested against archived and real-time data. This case study will then be extended to other related tsunami data and model sources globally with similar geographic and seismic scenarios.

  8. Accretion and Subduction of Oceanic Lithosphere: 2D and 3D Seismic Studies of Off-Axis Magma Lenses at East Pacific Rise 9°37-40'N Area and Downgoing Juan de Fuca Plate at Cascadia Subduction Zone

    NASA Astrophysics Data System (ADS)

    Han, Shuoshuo

    Two thirds of the Earth's lithosphere is covered by the ocean. The oceanic lithosphere is formed at mid-ocean ridges, evolves and interacts with the overlying ocean for millions of years, and is eventually consumed at subduction zones. In this thesis, I use 2D and 3D multichannel seismic (MCS) data to investigate the accretionary and hydrothermal process on the ridge flank of the fast-spreading East Pacific Rise (EPR) at 9°37-40'N and the structure of the downgoing Juan de Fuca plate at the Cascadia subduction zone offshore Oregon and Washington. Using 3D multichannel seismic (MCS) data, I image a series of off-axis magma lenses (OAML) in the middle or lower crust, 2-10 km from the ridge axis at EPR 9°37-40'N. The large OAMLs are associated with Moho travel time anomalies and local volcanic edifices above them, indicating off-axis magmatism contributes to crustal accretion though both intrusion and eruption (Chapter 1). To assess the effect of OAMLs on the upper crustal structure, I conduct 2-D travel time tomography on downward continued MCS data along two across-axis lines above a prominent OAML in our study area. I find higher upper crustal velocity in a region ~ 2 km wide above this OAML compared with the surrounding crust. I attribute these local anomalies to enhanced precipitation of alteration minerals in the pore space of upper crust associated with high-temperature off-axis hydrothermal circulation driven by the OAML (Chapter 2). At Cascadia, a young and hot end-member of the global subduction system, the state of hydration of the downgoing Juan de Fuca (JdF) plate is important to a number of subduction processes, yet is poorly known. As local zones of higher porosity and permeability, faults constitute primary conduits for seawater to enter the crust and potentially uppermost mantle. From pre-stack time migrated MCS images, I observe pervasive faulting in the sediment section up to 200 km from the deformation front. Yet faults with large throw and

  9. 77 FR 68818 - Notice of Inventory Completion: U.S. Department of Energy Oak Ridge Office, Oak Ridge, TN

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-11-16

    ... National Park Service Notice of Inventory Completion: U.S. Department of Energy Oak Ridge Office, Oak Ridge... Oak Ridge Office has completed an inventory of human remains and associated funerary object, in... associated funerary object may contact the U.S. Department of Energy Oak Ridge Office. Repatriation of...

  10. 78 FR 2431 - Notice of Inventory Completion: U.S. Department of Energy Oak Ridge Office, Oak Ridge, TN...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-11

    ... National Park Service Notice of Inventory Completion: U.S. Department of Energy Oak Ridge Office, Oak Ridge.... Department of Energy Oak Ridge Office has corrected an inventory of human remains and associated funerary... of Energy Oak Ridge Office. Repatriation of the human remains and associated funerary object to...

  11. Formation and stability of ridge-ridge-ridge triple junctions in rheologically realistic lithosphere model

    NASA Astrophysics Data System (ADS)

    Gerya, Taras; Burov, Evgueni

    2015-04-01

    -branch junction formation and evolution by using high-resolution 3D numerical mechanical experiments that take into account realistic thermo-rheological structure and rheology of the lithosphere. We find that two major types of quadruple and triple junctions are formed under bi-directional or multidirectional far-field stress field: (i) plate rifting junctions are formed by the initial plate fragmentation and can be subsequently re-arranged into (ii) oceanic spreading junctions controlled by the new oceanic crust accretion. In particular, we document initial formation and destabilization of quadruple R-R-R-R junctions as initial plate rifting structures under bi-directional extension. In most cases, quadruple plate rifting junctions rapidly (typically within 1-2 Myr) evolve towards formation of two diverging triple oceanic spreading junctions connected by a linear spreading center lengthening with time. This configuration remains stable over long time scales. However, under certain conditions, quadruple junctions may also remain relatively stable. Asymmetric stretching results in various configurations, for example formation of "T-junctions" with trans-extensional components and combination of fast and slow spreading ridges. Combined with plume impingement, this scenario evolves in realistic patterns closely resembling observed plate dynamics. In particular, opening of the Red Sea and of the Afar rift system find a logical explanation within a single model. Numerical experiments also suggest that several existing oceanic spreading junctions form as the result of plate motions rearrangements after which only one of two plates spreading along the ridge become subjected to bi-directional spreading.

  12. Results from a 14-month hydroacoustic monitoring of the three mid-oceanic ridges in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Royer, J.-Y.; Dziak, R. P.; Delatre, M.; Chateau, R.; Brachet, C.; Haxel, J. H.; Matsumoto, H.; Goslin, J.; Brandon, V.; Bohnenstielh, D. R.

    2009-04-01

    From October 2006 to January 2008, an hydroacoustic experiment in the Indian Ocean was carried out by the CNRS/University of Brest and NOAA/Oregon State University to monitor the low-level seismic activity associated with the three contrasting spreading ridges and deforming zones in the Indian Ocean. Three autonomous hydrophones were moored in the SOFAR channel by R/V Marion Dufresne for 14 months in the Madagascar Basin, and northeast and southwest of Amsterdam Island, complementing the two permanent hydroacoustic stations of the Comprehensive nuclear-Test-Ban Treaty Organization (CTBTO) located near Diego Garcia Island and off Cape Leeuwin. The three instruments successfully collected 14 month of continuous acoustic records. Combined with the records from the permanent stations, the array detected 1780 acoustic events consisting mostly of earthquake generated T-waves, but also of iceberg tremors from Wilkes Land, Antarctica. Within the triangle defined by the temporary array, the three ridges exhibit contrasting seismicity patterns. Along the Southeast Indian ridge (SEIR), the 272 acoustic events (vs 24 events in the NEIC catalog) occur predominantly along the transform faults ; only one ridge segment (76˚E) displays a continuous activity for 10 months. Along the Central Indian Ridge (CIR), seismicity is distributed along fracture zones and ridge segments (269 events vs 45 NEIC events), with two clusters of events near the triple junction (24-25S) and south of Marie-Celeste FZ (18.5S). Along the Southwest Indian Ridge (SWIR), the 222 events (vs 31 NEIC events) are distributed along the ridge segments with a larger number of events west of Melville FZ and a cluster at 58E. The immediate vicinity of the Rodrigues triple junction shows periods of quiescence and of intense activity. Some large earthquakes (Mb>5) near the triple junction (SEIR and CIR) seem to be preceded by several acoustic events that may be precursors. Finally, off-ridge seismicity is mostly

  13. Lava Flow Ages and Geologic Mapping on Mid-ocean Ridges

    NASA Astrophysics Data System (ADS)

    Clague, D. A.; Paduan, J. B.; Dreyer, B. M.; Caress, D. W.

    2010-12-01

    Geologic mapping of mid-ocean ridges has been hindered by a lack of high-resolution bathymetry and age data. Autonomous underwater vehicles (AUV) with multibeam sonars now produce maps with 1-m resolution. MBARI has collected data since 2006 along the Juan de Fuca and Gorda Ridges, including the 1998 eruptions in summit caldera and upper south rift zone on Axial Seamount, the 1993 and 1982-1991 eruptions on the CoAxial segment, the 1986 pillow mounds and “young sheet flow” on the north Cleft segment, the 1996 eruption on the North Gorda segment, and part of the Endeavour Ridge. The 1-m data allows identification of flow internal structure, boundaries, and emplacement sequences using superposition and abundance of fissures. Geologic maps of young volcanoes on land are constructed using the same principles, constrained by observations of flow contacts and 14C age dates on charcoal from beneath flow margins. In the deep sea, we collect sediment on top of the flows that contains planktic and benthic foraminifera that can be dated using AMS 14C dating. We sampled sediment on flows from the Axial, CoAxial, and North Cleft areas using 30-cm long pushcores deployed from remotely operated vehicles (ROVs). The coring is done with collection of flow samples for chemistry and video observations to confirm contact locations and flow superposition. Cores are inserted until they hit the underlying lava and can be recovered between pillow lobes when the sediment is >~10 cm thick. We recover the basal 1 cm of sediment, sieve to recover foraminifera, and hand-pick for 14C dating. The North Gorda neovolcanic zone at ~3150 m lacks carbonate sediment and therefore ages. Ages of planktic foraminifera are marine calibrated in years before present (aBP). Benthic foraminifera are calibrated against planktic foraminifera from 5 samples. 14C ages obtained from basal sediment from over 40 sites represent minimum ages as there is probably a small amount of unrecovered basal sediment. Ages

  14. Remedial Investigation Work Plan for Chestnut Ridge Operable Unit 1 (Chestnut Ridge Security Pits) at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee

    SciTech Connect

    Not Available

    1994-03-01

    This document outlines the activities necessary to conduct a Remedial Investigation (RI) of the Chestnut Ridge Security Pits (CRSP) at the Oak Ridge Y-12 Plant. The CRSP, also designated Chestnut Ridge Operable Unit (OU) 1, is one of four OUs along Chestnut Ridge on the Oak Ridge Reservation (ORR). The purpose of the RI is to collect data to (1) evaluate the nature and extent of known and suspected contaminants, (2) support an Ecological Risk Assessment (ERA) and a Human Health Risk Assessment (HHRA), (3) support the feasibility study in the development and analysis of remedial alternatives, and (4) ultimately, develop a Record of Decision (ROD) for the site. This chapter summarizes the regulatory background of environmental investigation on the ORR and the approach currently being followed and provides an overview of the RI to be conducted at the CRSP. Subsequent chapters provide details on site history, sampling activities, procedures and methods, quality assurance (QA), health and safety, and waste management related to the RI.

  15. Cell migration on ridges and cliffs

    NASA Astrophysics Data System (ADS)

    Driscoll, Meghan; McCann, Colin; Kopace, Rael; Watts, John; Homan, Tess; Losert, Wolfgang

    2009-03-01

    The amoeba Dictyostelium discoideum is a model system for the study of cellular migration, an important physiological process that occurs in embryonic development, wound healing, and cancer metastasis. We study the motion of D. discoideum on surfaces with various topographies, particularly those that affect the direction of cellular migration. Topographical features, such as ridges and cliffs, were fabricated using multiphoton absorption polymerization. As the cells encountered these topographical features, we tracked their overall motions and shapes, as well as the locations and intensities of certain intracellular signals. We found that when cells undergoing chemokinesis, random migration in response to a chemical signal, encounter a ridge, they tend to move along that ridge, even if the ridge is shorter than the cell. When cells undergoing chemotaxis, directed migration in response to a chemical signal, are directed off of a cliff, they do not fall off the cliff. Instead, they search for new attachment points, eventually change direction, and continue moving along the edge of the cliff. Both ridges and cliffs affect more than just the motion of a cell; they also affect its shape.

  16. Vertical Alveolar Ridge Augmentation by Distraction Osteogenesis

    PubMed Central

    Kumar, N. Nanda; Ravindran, C.

    2015-01-01

    Introduction Compromised alveolar ridge in vertical and horizontal dimension is a common finding in patients visiting practitioners for dental prosthesis. Various treatment modalities are available for correction of deficient ridges among which alveolar distraction osteogenesis is one. Aim To study the efficacy of alveolar distraction osteogenesis in augmentation of alveolar ridges deficient in vertical dimension. Materials and Methods Ten patients aged 16 to 46 years with deficient alveolar ridge underwent ridge augmentation in 11 alveolar segments using the distraction osteogenesis method. For each patient a custom made distraction device was fabricated. The device was indigenously manufactured with SS-316 (ISO 3506). Results The vertical bone gain reached more than 10mm without the use of bone transplantation. Certain complications like incorrect vector of distraction, paresthesia, pain and loss of transport segment were encountered during the course of the study. Conclusion Alveolar vertical distraction osteogenesis is a reliable and predictable technique for both hard and soft tissue genesis. Implant placement is feasible with primary stability in neogenerated bone at the level of the distracted areas. PMID:26816991

  17. Arctic Ocean: hydrothermal activity on Gakkel Ridge.

    PubMed

    Jean-Baptiste, Philippe; Fourré, Elise

    2004-03-04

    In the hydrothermal circulation at mid-ocean ridges, sea water penetrates the fractured crust, becomes heated by its proximity to the hot magma, and returns to the sea floor as hot fluids enriched in various chemical elements. In contradiction to earlier results that predict diminishing hydrothermal activity with decreasing spreading rate, a survey of the ultra-slowly spreading Gakkel Ridge (Arctic Ocean) by Edmonds et al. and Michael et al. suggests that, instead of being rare, the hydrothermal activity is abundant--exceeding by at least a factor of two to three what would be expected by extrapolation from observation on faster spreading ridges. Here we use helium-3 (3He), a hydrothermal tracer, to show that this abundance of venting sites does not translate, as would be expected, into an anomalous hydrothermal 3He output from the ridge. Because of the wide implications of the submarine hydrothermal processes for mantle heat and mass fluxes to the ocean, these conflicting results call for clarification of the link between hydrothermal activity and crustal production at mid-ocean ridges.

  18. Cancer mortality near Oak Ridge, Tennessee.

    PubMed

    Mangano, J J

    1994-01-01

    Oak Ridge, Tennessee, is the site of one of the two oldest nuclear facilities in the United States. Although precise records have not been maintained, low levels of radioactive products have been released into the environment since the facility began operation in World War II. Changes in age-adjusted cancer mortality rates for whites between the periods 1950-1952 and 1987-1989 were analyzed to assess whether these radioactive releases have had any adverse effects on the population living near Oak Ridge. Results indicate that the increases in the local area (under 100 miles from Oak Ridge) exceeded regional increases and far exceeded national increases. Within the region, increases were greatest in rural areas, in Anderson County (where Oak Ridge is located), in mountainous counties, and in the region downwind of Oak Ridge. Each of these findings suggest that low levels of radiation, ingested gradually by local residents, were a factor in the increases in local cancer death rates. Results indicate that more studies of this type are called for and that cessation of all future radioactive emissions from nuclear facilities should be considered.

  19. Climate change in the Brazilian northeast

    NASA Astrophysics Data System (ADS)

    Rodrigues, Regina R.; Haarsma, Reindert J.; Hoelzemann, Judith J.

    2012-10-01

    Climate Change, Impacts and Vulnerabilities in Brazil: Preparing the Brazilian Northeast for the Future; Natal, Brazil, 27 May to 01 June 2012 The variability of the semiarid climate of the Brazilian northeast has enormous environmental and social implications. Because most of the population in this area depends on subsistence agriculture, periods of severe drought in the past have caused extreme poverty and subsequent migration to urban centers. From the ecological point of view, frequent and prolonged droughts can lead to the desertification of large areas. Understanding the causes of rainfall variability, in particular periods of severe drought, is crucial for accurate forecasting, mitigation, and adaptation in this important region of Brazil.

  20. Latest Developments in the Installation Planning for Stage 1, NEPTUNE Regional Cabled Observatory, Northeast Pacific

    NASA Astrophysics Data System (ADS)

    Barnes, C. R.

    2004-12-01

    NEPTUNE is a proposed innovative network of over 30 sub-sea observatories linked by over 3300 km of powered, fiber-optic cables covering the Juan de Fuca Plate (200,000 sq km), Northeast Pacific. Each observatory will host and power many scientific instruments on the surrounding seafloor, in boreholes in the seafloor, and buoyed up into the water column. Remotely operated and autonomous vehicles will reside at depth, recharge at observatories, and respond to distant labs. Continuous near-real-time multidisciplinary measurement series will extend over 30 years. Shore stations will be located in Port Alberni, BC and Nedonna Beach, OR. Major research themes include: the structure and seismic behavior of the ocean crust; the dynamics of hot and cold fluids and gas hydrates in the upper ocean crust and overlying sediments; ocean climate change and its effect on the ocean biota at all depths; and the barely known ecosystem dynamics and biodiversity of the deep-sea. All involve interacting processes, long term changes, and non-linear, chaotic, episodic events that are hard to study with traditional means. VENUS, MARS, and NEPTUNE will use many of the same cable and engineering systems with the former two acting as test-beds for the latter. NEPTUNE is an US/Canada (70/30) partnership with the total facility cost of about 250M. Over 40M has already been funded for NEPTUNE design and development and for VENUS and MARS. Funding for NEPTUNE Canada's installation contribution (CAN$62.4M) was announced in October 2003. With US NSF/MREFC funding not anticipated before FY 2006, the Northern Loop (Stage 1) of the Project will be installed by NEPTUNE Canada, which comprises a consortium of 12 Canadian universities, lead by the University of Victoria. Housed in new quarters at UVic, NEPTUNE Canada has hired a dozen staff members, with more of be appointed, and has purchased the former Teleglobe TPC4 Shore Station at Port Alberni. Current activities include: a) issuing an RFQu and RFP

  1. 2. General context view of Express Building, looking northeast, with ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. General context view of Express Building, looking northeast, with Division Street in foreground, showing relationship to the Bend Depot - American Railway Express Company Freight Building, 1060 Northeast Division Street, Bend, Deschutes County, OR

  2. 53. INTERIOR VIEW LOOKING NORTH NORTHEAST SHOWING THE REMAINS OF ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    53. INTERIOR VIEW LOOKING NORTH NORTHEAST SHOWING THE REMAINS OF A WOODEN SETTLING BOX IN THE BACKGROUND RIGHT. AMALGAMATING PANS IN THE FOREGROUND. - Standard Gold Mill, East of Bodie Creek, Northeast of Bodie, Bodie, Mono County, CA

  3. 2. Light tower and keeper's house, view southwest, north northeast ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Light tower and keeper's house, view southwest, north northeast side of tower, northeast and northwest sides of keeper's house - Wood Island Light Station, East end of Wood Island, at mouth of Soo River, Biddeford Pool, York County, ME

  4. 1. BUILDING 522, SOUTH SIDE, OBLIQUE VIEW, FROM NORTHEAST CORNER ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. BUILDING 522, SOUTH SIDE, OBLIQUE VIEW, FROM NORTHEAST CORNER OF BUILDING 431, LOOKING NORTHEAST. - Oakland Naval Supply Center, Aeronautical Materials Storehouses, Between E & G Streets, between Fourth & Sixth Streets, Oakland, Alameda County, CA

  5. 4. HOUSE No. 16. NORTHEAST SIDE. VIEW TO SOUTHWEST. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. HOUSE No. 16. NORTHEAST SIDE. VIEW TO SOUTHWEST. - Rainbow Hydroelectric Facility, House No. 16, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  6. 2. FOREMAN'S HOUSE. SOUTHWEST SIDE. VIEW TO NORTHEAST. Rainbow ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. FOREMAN'S HOUSE. SOUTHWEST SIDE. VIEW TO NORTHEAST. - Rainbow Hydroelectric Facility, Foreman's House, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  7. 1. TWOSTALL GARAGE. FRONT (SOUTHWEST) SIDE. VIEW TO NORTHEAST. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. TWO-STALL GARAGE. FRONT (SOUTHWEST) SIDE. VIEW TO NORTHEAST. - Rainbow Hydroelectric Facility, Two Stall Garage, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  8. 4. FOREMAN'S HOUSE. NORTHEAST SIDE. VIEW TO SOUTHWEST. Rainbow ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. FOREMAN'S HOUSE. NORTHEAST SIDE. VIEW TO SOUTHWEST. - Rainbow Hydroelectric Facility, Foreman's House, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  9. 3. CLUBHOUSE. FRONT (SOUTHEAST) FACADE AND NORTHEAST SIDE. VIEW TO ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. CLUBHOUSE. FRONT (SOUTHEAST) FACADE AND NORTHEAST SIDE. VIEW TO WEST. - Rainbow Hydroelectric Facility, Clubhouse, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  10. 6. CLUBHOUSE. SOUTHWEST SIDE. VIEW TO NORTHEAST. Rainbow Hydroelectric ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. CLUBHOUSE. SOUTHWEST SIDE. VIEW TO NORTHEAST. - Rainbow Hydroelectric Facility, Clubhouse, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  11. 1. TOOL HOUSE. NORTHEAST AND NORTHWEST SIDES. VIEW TO SOUTHEAST. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. TOOL HOUSE. NORTHEAST AND NORTHWEST SIDES. VIEW TO SOUTHEAST. - Rainbow Hydroelectric Facility, Tool House, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  12. 3. TWOSTALL GARAGE SOUTHEAST AND NORTHEAST SIDES. VIEW TO WEST. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. TWO-STALL GARAGE SOUTHEAST AND NORTHEAST SIDES. VIEW TO WEST. - Rainbow Hydroelectric Facility, Two Stall Garage, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  13. 2. THREESTALL GARAGE. NORTHEAST SIDE. VIEW TO SOUTHWEST. Rainbow ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. THREE-STALL GARAGE. NORTHEAST SIDE. VIEW TO SOUTHWEST. - Rainbow Hydroelectric Facility, Three Stall Garage, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  14. 4. CLUBHOUSE. NORTHEAST SIDE. VIEW TO SOUTHWEST. Rainbow Hydroelectric ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. CLUBHOUSE. NORTHEAST SIDE. VIEW TO SOUTHWEST. - Rainbow Hydroelectric Facility, Clubhouse, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  15. 1. THREESTALL GARAGE. SOUTHEAST AND NORTHEAST SIDES. VIEW TO WEST. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. THREE-STALL GARAGE. SOUTHEAST AND NORTHEAST SIDES. VIEW TO WEST. - Rainbow Hydroelectric Facility, Three Stall Garage, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  16. 2. TOOL HOUSE. NORTHEAST AND SOUTHEAST SIDES. VIEW TO WEST. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. TOOL HOUSE. NORTHEAST AND SOUTHEAST SIDES. VIEW TO WEST. - Rainbow Hydroelectric Facility, Tool House, On north bank of Missouri River 2 miles Northeast of Great Falls, & end of Rainbow Dam Road, Great Falls, Cascade County, MT

  17. 10. Lighthouse boathouse and granite wharf, view north northeast, southwest ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    10. Lighthouse boathouse and granite wharf, view north northeast, southwest and southeast sides of boathouse, west and south sides of dock - Whitehead Light Station, Whitehead Island, East northeast of Tenants Harbor, Spruce Head, Knox County, ME

  18. Steam sand dryer in northeast part of sand tower. View ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Steam sand dryer in northeast part of sand tower. View to northeast - Duluth & Iron Range Rail Road Company Shops, Sand Tower, Southwest of downtown Two Harbors, northwest of Agate Bay, Two Harbors, Lake County, MN

  19. 3. Light tower and fog signal house, view northeast, west ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Light tower and fog signal house, view northeast, west and south sides - Great Duck Island Light Station, At southern tip of Great Duck Island southeast of Bass Harbor & northeast of Frenchboro, Frenchboro, Hancock County, ME

  20. 19. GENERAL VIEW, LOOKING SOUTHWEST TO NORTHEAST, SHOWING ENCLOSED OFFICE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    19. GENERAL VIEW, LOOKING SOUTHWEST TO NORTHEAST, SHOWING ENCLOSED OFFICE UNITS FLANKING OVERHEAD PORT AT NORTHEAST END OF BUILDING - Oakland Army Base, Transit Shed, East of Dunkirk Street & South of Burma Road, Oakland, Alameda County, CA

  1. Interior view of northeast unit master bedroom, looking into sleeping ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Interior view of northeast unit master bedroom, looking into sleeping porch, facing northeast - MacDill Air Force Base, Double Non-Commissioned Officers' Quarters, 7418 Hanger Loop Drive, Tampa, Hillsborough County, FL

  2. 19. INTERIOR OF NORTHEAST REAR BEDROOM SHOWING ALUMINUMFRAME SLIDING GLASS ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    19. INTERIOR OF NORTHEAST REAR BEDROOM SHOWING ALUMINUM-FRAME SLIDING GLASS WINDOWS. VIEW TO NORTHEAST. - Bishop Creek Hydroelectric System, Plant 4, Worker Cottage, Bishop Creek, Bishop, Inyo County, CA

  3. 20. DETAIL OF OFFICE FURNITURE IN NORTHEAST CORNER OF SECRETARIES' ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    20. DETAIL OF OFFICE FURNITURE IN NORTHEAST CORNER OF SECRETARIES' OFFICE ALONG NORTH SIDE OF FIRST FLOOR. VIEW TO NORTHEAST. - Boise Project, Boise Project Office, 214 Broadway, Boise, Ada County, ID

  4. OVERALL VIEW OF QUARRY, FACING NORTHEAST, SHOWING SOUTHERN SECTION OF ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    OVERALL VIEW OF QUARRY, FACING NORTHEAST, SHOWING SOUTHERN SECTION OF QUARRY - Granite Hill Plantation, Quarry No. 2, South side of State Route 16, 1.3 miles northeast east of Sparta, Sparta, Hancock County, GA

  5. 7. Oil house, view northeast, west and south sides ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Oil house, view northeast, west and south sides - Great Duck Island Light Station, At southern tip of Great Duck Island southeast of Bass Harbor & northeast of Frenchboro, Frenchboro, Hancock County, ME

  6. Detail of door and gable treatment, looking northeast at intersection ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Detail of door and gable treatment, looking northeast at intersection of East Wing (Wing 1) and central core - Hospital for Sick Children, 1731 Bunker Hill Road, Northeast, Washington, District of Columbia, DC

  7. 11. DETAIL SHOWING ROLLING ENGINE DECK AND NORTHEAST TRUSS OF ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    11. DETAIL SHOWING ROLLING ENGINE DECK AND NORTHEAST TRUSS OF SUPERSTRUCTURE. Looking northeast. - Edwards Air Force Base, Air Force Rocket Propulsion Laboratory, Test Stand 1-A, Test Area 1-120, north end of Jupiter Boulevard, Boron, Kern County, CA

  8. 55. VIEW TO NORTHEAST OF MOTOR AND REDUCTION GEAR NO. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    55. VIEW TO NORTHEAST OF MOTOR AND REDUCTION GEAR NO. 1: View towards the northeast of Motor and Reduction Gear No. 1, installed in 1957. - San Francisco Cable Railway, Washington & Mason Streets, San Francisco, San Francisco County, CA

  9. 8. Detail of northeast inclined endpost, hip vertical, upper chord, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. Detail of northeast inclined endpost, hip vertical, upper chord, and portal bracing; looking north/northeast - Brosseau Road Bridge, County Road 694 spanning Cloquet at River, Burnett, St. Louis County, MN

  10. Potential for Large Transpressional Earthquakes along the Santa Cruz-Catalina Ridge, California Continental Borderland

    NASA Astrophysics Data System (ADS)

    Legg, M.; Kohler, M. D.; Weeraratne, D. S.; Castillo, C. M.

    2015-12-01

    Transpressional fault systems comprise networks of high-angle strike-slip and more gently-dipping oblique-slip faults. Large oblique-slip earthquakes may involve complex ruptures of multiple faults with both strike-slip and dip-slip. Geophysical data including high-resolution multibeam bathymetry maps, multichannel seismic reflection (MCS) profiles, and relocated seismicity catalogs enable detailed mapping of the 3-D structure of seismogenic fault systems offshore in the California Continental Borderland. Seafloor morphology along the San Clemente fault system displays numerous features associated with active strike-slip faulting including scarps, linear ridges and valleys, and offset channels. Detailed maps of the seafloor faulting have been produced along more than 400 km of the fault zone. Interpretation of fault geometry has been extended to shallow crustal depths using 2-D MCS profiles and to seismogenic depths using catalogs of relocated southern California seismicity. We examine the 3-D fault character along the transpressional Santa Cruz-Catalina Ridge (SCCR) section of the fault system to investigate the potential for large earthquakes involving multi-fault ruptures. The 1981 Santa Barbara Island (M6.0) earthquake was a right-slip event on a vertical fault zone along the northeast flank of the SCCR. Aftershock hypocenters define at least three sub-parallel high-angle fault surfaces that lie beneath a hillside valley. Mainshock rupture for this moderate earthquake appears to have been bilateral, initiating at a small discontinuity in the fault geometry (~5-km pressure ridge) near Kidney Bank. The rupture terminated to the southeast at a significant releasing step-over or bend and to the northeast within a small (~10-km) restraining bend. An aftershock cluster occurred beyond the southeast asperity along the East San Clemente fault. Active transpression is manifest by reverse-slip earthquakes located in the region adjacent to the principal displacement zone

  11. Petrology and Geochemistry of the Northeast Seamounts of the Galapagos Platform

    NASA Astrophysics Data System (ADS)

    Sinton, C. W.; Harpp, K. S.; Christie, D. M.

    2010-12-01

    One of the best locations to study hotspot-ridge interactions is the Northern Galápagos Province (NGP), the region that lies between the Galapagos Spreading Center (GSC) and the central portion of the Galapagos Archipelago. The Galapagos hotspot is currently located off-axis from the GSC but still has a profound influence on the ridge in terms of axial lava composition and ridge bathymetry. The NGP is characterized by an array of volcanic lineaments that are composed of seamounts and five small islands. The eastern edge of the NGP is defined by a group of at least five seamounts (the Northeast Seamounts), three of which were mapped and dredged in 1990 during Leg 2 of the PLUME expedition of the R/V Thomas Washington. We report petrological and geochemical data from the basalts recovered at six dredge sites. All basalts are tholeiitic with a general MORB-like composition, but with considerable variation within some individual dredge hauls and between seamounts. Previously published isotopic data are limited but 3He/4He ratios (Graham et al. 1993) and Sr-Nd-Pb isotopic data (Harpp and White 2000) are consistent with a depleted mantle source for all three seamounts. Based on geochemistry and petrological observations, the basalts can be divided into at least thirteen distinct groups. The bulk of the analyzed glass samples have compositions more than MORB with MgO content of 8-10% wt., although two of the groups are in the 6-7% range. In addition, the primitive lavas have high CaO and Al2O3 . The mineralogy ranges from aphyric for the more evolved lavas to olivine + plagioclase-phyric or plagioclase ultraphyric for the more primitive basalts. The plagioclase appear to be very calcic (up to An91) xenocrysts that are often hosting aluminous spinel (Al2O3 46-48% wt.) and primitive melt inclusions (Sinton et al., 1993). Initial trace element data show light rare earth (LREE)-depleted signatures, although several samples are slightly enriched in the LREE. Taken together

  12. Global Characterization of the Ocean Ridge System

    NASA Astrophysics Data System (ADS)

    Gale, A.; Langmuir, C. H.; Dalton, C. A.

    2010-12-01

    The mid-ocean ridge system is a window into the upper mantle, producing over 80% of Earth’s volcanism. Fundamental, first-order questions remain debated and require a reliable global perspective. Such questions include the relative roles of mantle temperature, mantle heterogeneity and spreading rate on mid-ocean ridge basalt (MORB) compositions, and the importance of spreading rate to melting and fractionation processes. To address these issues and provide a common reference for geochemists and geophysicists, we have assembled a comprehensive petrological presentation of global MORB. The data are compiled from PetDB as well as unpublished data. Transforming the raw data into a useful catalog poses several challenges. First, to link each sample with a particular ridge segment requires defining the individual segments of the ridge system. Using the highest resolution bathymetry available, we identified 771 global ridge segments with a total length of 60,864km. For each segment we also generated a digital along-strike depth profile, enabling precise characterization of both mean depth and depth range. Second, as noted in earlier work, different laboratories calibrate their analyses to different standards, which can lead to significant, systematic offsets among analyses. It is therefore important to apply correction factors to the data to make them consistent with one another. Erroneous data and mislocated samples were identified and either eliminated or manually corrected, leading to a total dataset of 11,366 glass and 874 whole-rock analyses that have had interlab correction values carefully applied. These results show that the mean depth of the global ridge system is 2981m, calculated by averaging the segment mean depths, weighted by segment length. Of the 771 ridge segments, 476 have at least one basalt sample within 10km of the ridge axis but only 181 segments have samples from three or more unique locations. Using these data, a far more reliable composition can

  13. Directionality of ambient noise on the Juan de Fuca plate: implications for source locations of the primary and secondary microseisms

    NASA Astrophysics Data System (ADS)

    Tian, Ye; Ritzwoller, Michael H.

    2015-04-01

    Based on cross-correlations of ambient seismic noise computed using 61 ocean bottom seismometers (OBSs) within the Juan de Fuca (JdF) plate from the Cascadia Initiative experiment and 42 continental stations near the coast of the western United States, we investigate the locations of generation of the primary (11-20 s period) and secondary (5-10 s period) microseisms in the northern Pacific Ocean by analysing the directionality and seasonality of the microseism (Rayleigh wave) signals received in this region. We conclude that (1) the ambient noise observed across the array is much different in the primary and secondary microseism bands, both in its azimuthal content and seasonal variation. (2) The principal secondary microseism signals propagate towards the east, consistent with their generation in deep waters of the North Pacific, perhaps coincident both with the region of observed body wave excitation and the predicted wave-wave interaction region from recent studies. (3) The primary microseism, as indicated by observations of the azimuthal dependence of the fundamental mode Rayleigh wave as well as observations of precursory arrivals, derives significantly from the shallow waters of the eastern Pacific near to the JdF plate but also has a component generated at greater distance of unknown origin. (4) These observations suggest different physical mechanisms for generating the two microseisms: the secondary microseisms are likely to be generated by non-linear wave-wave interaction over the deep Pacific Ocean, while the primary microseism may couple directly into the solid earth locally in shallow waters from ocean gravity waves. (5) Above 5 s period, high quality empirical Green's functions are observed from cross-correlations between deep water OBSs and continental stations, which illustrates that microseisms propagate efficiently from either deep or shallow water source regions onto the continent and are well recorded by continental seismic stations.

  14. NORTHEAST VIEW OF FOUNDRY FROM TOP OF GREY IRON CUPOLA ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    NORTHEAST VIEW OF FOUNDRY FROM TOP OF GREY IRON CUPOLA SHOWING CORE ROOM ROOF DIRECTLY NORTHEAST, GREY IRON FOUNDRY TO THE RIGHT, MALLEABLE IRON CUPOLAS AND FOUNDRY NORTHEAST OF GREY IRON FOUNDRY WITH THE BRASS FOUNDRY IN THE REAR. - Stockham Pipe & Fittings Company, 4000 Tenth Avenue North, Birmingham, Jefferson County, AL

  15. Distribution of mega fauna on sulfide edifices on the Eastern Lau Spreading Center and Valu Fa Ridge

    NASA Astrophysics Data System (ADS)

    Sen, Arunima; Becker, Erin L.; Podowski, Elizabeth L.; Wickes, Leslie N.; Ma, Shufen; Mullaugh, Katherine M.; Hourdez, Stéphane; Luther, George W.; Fisher, Charles R.

    2013-02-01

    Hydrothermal vent sulfide edifices contain some of the most extreme thermal and chemical conditions in which animals are able to live. As a result, sulfide edifices in the East Pacific Rise, Juan de Fuca Ridge, and Mid Atlantic Ridge vent systems often contain distinct faunal assemblages. In this study, we used high-resolution imagery and in-situ physico-chemical measurements within the context of a Geographic Information System (GIS) to examine community structure and niche differentiation of dominant fauna on sulfide edifices in the Eastern Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR) in the Western Pacific Ocean. Our results show that ELSC and VFR sulfide edifices host two distinct types of communities. One type, that covers the majority of sulfide edifice faces, is overall very similar to nearby lava communities and biomass is dominated by the same chemoautotrophic symbiont-containing molluscs that dominate lava communities, namely the provannid gastropods Alviniconcha spp. and Ifremeria nautilei and the mytilid bivalve Bathymodiolus brevior. The spatial distribution of the dominant molluscs is often a variation of the pattern of concentric rings observed on lavas, with Alviniconcha spp. at the tops of edifices where exposure to vent flow is the highest, and I. nautilei and B. brevior below. Our physico-chemical measurements indicate that because of rapid dispersion of vent fluid, habitable area for symbiont-containing fauna is quite limited on sulfide edifices, and the realized niches of the mollusc groups are narrower on sulfide edifices than on lavas. We suggest that competition plays an important role in determining the realized distributions of the mollusc groups on edifices. The other habitat, present in small patches of presumably hot, new anhydrite, is avoided by the dominant symbiont-containing molluscs and inhabited by crabs, shrimp and polynoids that are likely more heat tolerant. The ratio of sulfide concentration to temperature anomaly of

  16. Physiographic divisions and differential uplift in the Piedmont and Blue Ridge

    USGS Publications Warehouse

    Hack, John Tilton

    1982-01-01

    The Piedmont and Blue Ridge are dynamic landscapes that have undergone substantial change since the orogenies that ended in late Paleozoic or, as some believe, early Mesozoic time. The southern Blue Ridge region south of Roanoke, Va., lies on the crest of a topographic uplift that corresponds to the eastern continental drainage divide. To the north, this uplift and divide cross the Appalachian Valley and form the crest of the Appalachian Plateaus as far north as central Pennsylvania. The northern Blue Ridge Mountains as well as parts of the Piedmont are on the eastern part of the uplift area. The southeastern margin of the uplift corresponds to a line within the Piedmont physiographic province that extends northeastward from the Tallapoosa River at the Fall Zone and crosses the Rappahannock River at the Fall Zone. The differential elevation on either side of this line is sharp in some places, as, for example, northeast of Atlanta, Ga. In other places, the difference in elevation is difficult to detect, and, in effect, the line becomes a broad monoclinal slope. The region as a whole can be divided into at least six broad subregions that have somewhat different histories in late geologic time. The Piedmont Lowlands subprovince, southeast of the uplifted area, is dominated by a monotonous topography of low rounded ridges and ravines largely underlain by saprolite on crystalline rocks. Isolated ranges of hills of greater relief are scattered across the region; those investigated are directly related to the presence of erosionally resistant rocks. Stream patterns as well as broad topographic forms indicate that although the southern part of the Piedmont Lowlands was probably once covered by younger sediments, this area has been exposed to erosion for a long time. In North Carolina, the inner part of the Piedmont Lowlands has strongly trellised stream patterns, which suggest that subaerial erosion was active for an even longer time period, perhaps since the latest

  17. ORLANDO -- Oak Ridge Large Neutrino Detector

    SciTech Connect

    Bugg, W.; Cohn, H.; Efremenko, Yu.; Gabriel, T.; Kamyshkov, Yu.; Plasil, F.; Fazely, A.; Svoboda, R.

    1997-12-01

    The authors discuss a proposal for construction of an Oak Ridge LArge Neutrino DetectOr (ORLANDO) to search for neutrino oscillations at the Spallation Neutron Source (SNS). A 4 MW SNS is proposed to be built at the Oak Ridge National Laboratory with the first stage to be operative around 2006. It will have two target stations, which makes it possible with a single detector to perform a neutrino oscillation search at two different distances. Initial plans for the placement of the detector and the discovery potential of such a detector are discussed.

  18. Fluid venting and seepage at accretionary ridges: the Four Way Closure Ridge offshore SW Taiwan

    NASA Astrophysics Data System (ADS)

    Klaucke, Ingo; Berndt, Christian; Crutchley, Gareth; Chi, Wu-Cheng; Lin, Saulwood; Muff, Sina

    2016-06-01

    Within the accretionary prism offshore SW Taiwan, widespread gas hydrate accumulations are postulated to occur based on the presence of a bottom simulating reflection. Methane seepage, however, is also widespread at accretionary ridges offshore SW Taiwan and may indicate a significant loss of methane bypassing the gas hydrate system. Four Way Closure Ridge, located in 1,500 m water depth, is an anticlinal ridge that would constitute an ideal trap for methane and consequently represents a site with good potential for gas hydrate accumulations. The analysis of high-resolution bathymetry, deep-towed sidescan sonar imagery, high-resolution seismic profiling and towed video observations of the seafloor shows that Four Way Closure Ridge is and has been a site of intensive methane seepage. Continuous seepage is mainly evidenced by large accumulations of authigenic carbonate precipitates, which appear to be controlled by the creation of fluid pathways through faulting. Consequently, Four Way Closure Ridge is not a closed system in terms of fluid migration and seepage. A conceptual model of the evolution of gas hydrates and seepage at accretionary ridges suggests that seepage is common and may be a standard feature during the geological development of ridges in accretionary prisms. The observation of seafloor seepage alone is therefore not a reliable indicator of exploitable gas hydrate accumulations at depth.

  19. The influence of ridge migration on the magmatic segmentation of mid-ocean ridges.

    PubMed

    Carbotte, S M; Small, C; Donnelly, K

    2004-06-17

    The Earth's mid-ocean ridges display systematic changes in depth and shape, which subdivide the ridges into discrete spreading segments bounded by transform faults and smaller non-transform offsets of the axis. These morphological changes have been attributed to spatial variations in the supply of magma from the mantle, although the origin of the variations is poorly understood. Here we show that magmatic segmentation of ridges with fast and intermediate spreading rates is directly related to the migration velocity of the spreading axis over the mantle. For over 9,500 km of mid-ocean ridge examined, leading ridge segments in the 'hotspot' reference frame coincide with the shallow magmatically robust segments across 86 per cent of all transform faults and 73 per cent of all second-order discontinuities. We attribute this relationship to asymmetric mantle upwelling and melt production due to ridge migration, with focusing of melt towards ridge segments across discontinuities. The model is consistent with variations in crustal structure across discontinuities of the East Pacific Rise, and may explain variations in depth of melting and the distribution of enriched lavas.

  20. The quantum event of oceanic crustal accretion: impacts of diking at mid-ocean ridges.

    PubMed

    Delaney, J R; Kelley, D S; Lilley, M D; Butterfield, D A; Baross, J A; Wilcock, W S; Embley, R W; Summit, M

    1998-07-10

    Seafloor diking-eruptive events represent the irreducible, quantum events of upper oceanic crustal accretion. They record events by which a large portion of the oceanic crust has formed through geological history. Since 1993, the U.S. Navy's real-time Sound Surveillance System has allowed location of ongoing acoustic signatures of dike emplacement and basalt eruptions at ridge crests in the northeast Pacific. These diking-eruptive events trigger a sequence of related, rapidly evolving physical, chemical, and biological processes. Magmatic volatiles released during these events may provide nutrients for communities of subsea-floor microorganisms, some of which thrive in high-temperature anaerobic environments. Many of the organisms identified from these systems are Archaea. If microorganisms can thrive in the water-saturated pores and cracks within deep, volcanically active portions of our planet, other hydrothermally active planets may harbor similar life forms.

  1. The Quantum Event of Oceanic Crustal Accretion: Impacts of Diking at Mid-Ocean Ridges

    PubMed

    Delaney; Kelley; Lilley; Butterfield; Baross; Wilcock; Embley; Summit

    1998-07-10

    Seafloor diking-eruptive events represent the irreducible, quantum events of upper oceanic crustal accretion. They record events by which a large portion of the oceanic crust has formed through geological history. Since 1993, the U.S. Navy's real-time Sound Surveillance System has allowed location of ongoing acoustic signatures of dike emplacement and basalt eruptions at ridge crests in the northeast Pacific. These diking-eruptive events trigger a sequence of related, rapidly evolving physical, chemical, and biological processes. Magmatic volatiles released during these events may provide nutrients for communities of subseafloor microorganisms, some of which thrive in high-temperature anaerobic environments. Many of the organisms identified from these systems are Archaea. If microorganisms can thrive in the water-saturated pores and cracks within deep, volcanically active portions of our planet, other hydrothermally active planets may harbor similar life forms.

  2. Teacher Morale in Rural Northeast Tennessee

    ERIC Educational Resources Information Center

    Eggers, Brenda Dishman

    2012-01-01

    The purpose of this quantitative study was to investigate the factors that influence the morale levels of teachers in the public school systems of 3 contiguous counties in rural northeast Tennessee. The level of teacher morale was measured using the Purdue Teacher Opinionaire. Data associated with the Tennessee Value-Added Assessment System…

  3. COASTAL 2000 MONITORING IN THE NORTHEAST

    EPA Science Inventory

    Coastal 2000 is a partnership between the U.S. Environmental Protection Agency and coastal states to develop a national coastal monitoring program. The Northeast portion of Coastal 2000 includes states from Delaware to Maine. This joint effort will provide a nationwide assessment...

  4. Northeast Regional Education Planning Project. Final Report.

    ERIC Educational Resources Information Center

    Northeast Regional Exchange Steering Committee, Boston, MA.

    Created to facilitate the dissemination of information between researchers and the educational community, the Northeast Regional Exchange steering committee has defined needs, determined agency qualifications, identified priorities, undertaken a series of minigrant projects, and developed plans for the extension of these projects and a study of…

  5. Geology of the Cooper Ridge NE Quadrangle, Sweetwater County, Wyoming

    USGS Publications Warehouse

    Roehler, Henry W.

    1979-01-01

    The Cooper Ridge NE 7?-minute quadrangle is 18 miles southeast of Rock Springs, Wyo., on the east flank of the Rock Springs uplift. Upper Cretaceous rocks composing the Rock Springs Formation, Ericson Sandstone, Almond Formation, Lewis Shale, Fox Hills Sandstone, and Lance Formation, Paleocene rocks composing the Fort Union Formation, and Eocene rocks composing the Wasatch Formation are exposed and dip 5?-8? southeast. Outcrops are unfaulted and generally homoclinal, but a minor cross-trending fold, the Jackknife Spring anticline, plunges southeastward and interrupts the northeast strike of beds. Older rocks in the subsurface are faulted and folded, especially near the Brady oil and gas field. Coal beds are present in the Almond, Lance, and Fort Union Formations. Coal resources are estimated to be more than 762 million short tons in 16 beds more than 2.5 feet thick, under less than 3,000 ft of overburden. Nearly 166 million tons are under less than 200 ft of overburden and are recoverable by strip mining. Unknown quantities of oil and gas are present in the Cretaceous Rock Springs, Blair, and Dakota Formations, Jurassic sandstone (Entrada Sandstone of drillers), Jurassic(?) and Triassic(?) Nugget Sandstone, Permian Park City Formation, and Pennsylvanian and Permian Weber Sandstone at the Brady field, part of which is in the southeast corner of the quadrangle, and in the Dakota Sandstone at the Prenalta Corp. Bluewater 33-32 well near the northern edge of the quadrangle. Other minerals include uranium in the Almond Formation and titanium in the Rock Springs Formation.

  6. Wrinkle Ridges and Young Fresh Crater

    NASA Technical Reports Server (NTRS)

    2002-01-01

    (Released 10 May 2002) The Science Wrinkle ridges are a very common landform on Mars, Mercury, Venus, and the Moon. These ridges are linear to arcuate asymmetric topographic highs commonly found on smooth plains. The origin of wrinkle ridges is not certain and two leading hypotheses have been put forth by scientists over the past 40 years. The volcanic model calls for the extrusion of high viscosity lavas along linear conduits. This thick lava accumulated over these conduits and formed the ridges. The other model is tectonic and advocates that the ridges are formed by compressional faulting and folding. Today's THEMIS image is of the ridged plains of Lunae Planum located between Kasei Valles and Valles Marineris in the northern hemisphere of the planet. Wrinkle ridges are found mostly along the eastern side of the image. The broadest wrinkle ridges in this image are up to 2 km wide. A 3 km diameter young fresh crater is located near the bottom of the image. The crater's ejecta blanket is also clearly seen surrounding the sharp well-defined crater rim. These features are indicative of a very young crater that has not been subjected to erosional processes. The Story The great thing about the solar system is that planets are both alike and different. They're all foreign enough to be mysterious and intriguing, and yet familiar enough to be seen as planetary 'cousins.' By comparing them, we can learn a lot about how planets form and then evolve geologically over time. Crinkled over smooth plains, the long, wavy raised landforms seen here are called 'wrinkle ridges,' and they've been found on Mars, Mercury, Venus, and the Moon - that is, on rocky bodies that are a part of our inner solar system. We know from this observation that planets (and large-enough moons) follow similar processes. What we don't know for sure is HOW these processes work. Scientists have been trying to understand how wrinkle ridges form for 40 years, and they still haven't reached a conclusion. That

  7. A 14-year-long Measurement of the Convergence Rate of the Juan de Fuca and North America Plates Offshore Central Oregon using GPS-Acoustics

    NASA Astrophysics Data System (ADS)

    Chadwell, C. D.; Webb, S. C.; Nooner, S. L.

    2015-12-01

    The motion of the sea floor was measured at a 3000-m-deep site approximately 120 km offshore Central Oregon using the GPS-Acoustic technique in 2000, 2001, 2002, 2003 and 2014. The GPS-Acoustic derived motion relative to the interior of North America agrees with the geomagnetically-derived value within their measurement uncertainties. The time series from the early 2000's was resurrected using two new innovations. The first innovation, a permanent benchmark that has locating channels and mating pins, allows reoccupation of an established benchmark at any later date using an ROV to replace the transponder on the benchmark. The second innovation: an autonomous platform based on a Waveglider that carries a GPS navigated acoustic transponder interrogation system that is wave and solar powered. This enables measurements to be obtained over a GPSA site without requiring a large ship, greatly reducing the cost of a GPSA measurement. Combining data at this site with data from two other GPS-Acoustic seafloor sites on the Juan de Fuca plate, makes it possible to determine a present-day Euler Pole for the Juan de Fuca - North America plates using GPS-Acoustics seafloor geodesy.

  8. Feasibility of geothermal applications for greenhousing and space heating on the Pine Ridge Indian Reservation, South Dakota

    SciTech Connect

    Culver, G.

    1985-02-01

    Although little is known about the geothermal resources under the Pine Ridge Reservation, there seem to be good possibilities of a resource hot enough to provide heating for greenhouses, at least in the northeast portion of Shannon County. At the present time, there do not appear to be resources hot enough to provide direct use space heating of residential or commercial buildings near any of the existing population centers. Space heating using water source heat pumps may be economical and should be considered for new construction of larger heat users such as the proposed hospital at Pine Ridge. Further resource investigation is recommended, particularly more surface geology and water chemistry work. Test drilling will be required to confirm