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  • 1
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    Book
    Special issue on Ridge 2000 program research (2012)
    Rockville, Md.
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    Keywords: Aufsatzsammlung
    Type of Medium: Book
    Pages: 316 S , Ill., graph. Darst., Kt
    Series Statement: Oceanography 25.2012,1, Spec. issue
    Language: English
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  • 2
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    A record of eruption and intrusion at a fast spreading ridge axis : axial summit trough of the East Pacific Rise at 9–10°N (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q10T07, doi:10.1029/2008GC002354.
    Description: High-resolution side-scan sonar, near-bottom multibeam bathymetry, and deep-sea photo and bathymetry traverses are used to map the axial summit trough (AST) at the East Pacific Rise between 9 and 10°N. We define three ridge axis morphologic types: no AST, narrow AST, and wide AST, which characterize distinct ridge crest domains spanning tens of kilometers along strike. Near-bottom observations, modeling of deformation above intruding dikes, and comparisons to the geologic and geophysical structure of the ridge crest are used to develop a revised model of AST genesis and evolution. This model helps constrain the record of intrusive and extrusive magmatism and styles of lava deposition along the ridge crest at time scales from hundreds to tens of thousands of years. The grabens in the narrow-AST domain (9°43′–53′N) are consistent with deformation above the most recent (〈10) diking events beneath the ridge crest. Frequent high–effusion rate extrusive volcanism in this domain (several eruptions every ∼100 years) overprints near-axis deformation and maintains a consistent AST width. The most recent eruption at the ridge crest occurred in this area and did not significantly modify the physical characteristics of the AST. The grabens in the wide-AST domain (9°23′–43′N) originated with similar dimensions to the narrow AST. Spreading, driven primarily by the intrusion of shallow dikes within a narrow axial zone, causes the initial graben bounding faults to migrate away from the axis. Infrequent extrusive volcanism (several eruptions every ∼1000 years) fills a portion of the subsidence that accumulates over time but does not significantly modify the width of the AST. Outside of these domains, lower–effusion rate constructional volcanism without efficient drain-back fills and erases the signature of the AST. The relative frequency of intrusive versus extrusive magmatic events controls the morphology of the ridge crest and appears to remain constant over millennial time scales within the domains we have identified; however, over longer time scales (∼10–25 ka), domain-specific intrusive-to-extrusive ratios do not appear to be fixed in space, resulting in a fairly consistent volcanic accretion over the length scale of the second-order ridge segment between 9°N and 10°N.
    Description: This work was supported by NSF grants OCE-0525863 to D. Fornari and S. A. Soule; OCE-0732366 to S. A. Soule; and OCE-9819261 to H. Schouten, M. Tivey, and D. Fornari and by CNRS to J. Escartın.
    Keywords: Mid-ocean ridge ; Submarine volcanism ; Diking ; Seafloor morphology ; Magmatism
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Seafloor photo-geology and sonar terrain modeling at the 9°N overlapping spreading center, East Pacific Rise (2014)
    John Wiley & Sons
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 5146–5170, doi:10.1002/2013GC004858.
    Description: A fundamental goal in the study of mid-ocean ridges is to understand the relationship between the distribution of melt at depth and seafloor features. Building on geophysical information on subsurface melt at the 9°N overlapping spreading center on the East Pacific Rise, we use terrain modeling (DSL-120A side scan and bathymetry), photo-geology (Jason II and WHOI TowCam), and geochemical data to explore this relationship. Terrain modeling identified four distinct geomorphic provinces with common seafloor characteristics that correspond well to changes in subsurface melt distribution. Visual observations were used to interpret terrain modeling results and to establish a relative seafloor age scale, calibrated with radiometric age dates, to identify areas of recent volcanism. On the east limb, recent eruptions in the north are localized over the margins of the 4 km wide asymmetric melt sill, forming a prominent off-axis pillow ridge. Along the southern east limb, recent eruptions occur along a neovolcanic ridge that hugs the overlap basin and lies several kilometers west of the plunging melt sill. Our results suggest that long-term southward migration of the east limb occurs through a series of diking events with a net southward propagation direction. Examining sites of recent eruptions in the context of geophysical data on melt distribution in the crust and upper mantle suggests melt may follow complex paths from depth to the surface. Overall, our findings emphasize the value of integrating information obtained from photo-geology, terrain modeling, lava geochemistry and petrography, and geophysics to constrain the nature of melt delivery at mid-ocean ridges.
    Description: The National Science Foundation and the RIDGE2000 program supported this work through grants OCE0526120 to E.M.K., OCE0525872 to S.M.W., OCE0527075 to M.R.P., and OCE 052705300 to K.W.W.S.
    Keywords: Mid-ocean ridge ; Overlapping spreading center ; Melt lens ; Axial magma chamber ; Dike ; Ocean crust
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Central Anomaly Magnetization High documentation of crustal accretion along the East Pacific Rise (9°55′–9°25′N) (2010)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q04015, doi:10.1029/2007GC001611.
    Description: Near-bottom magnetic data collected along the crest of the East Pacific Rise between 9°55′ and 9°25′N identify the Central Anomaly Magnetization High (CAMH), a geomagnetic anomaly modulated by crustal accretionary processes over timescales of ∼104 years. A significant decrease in CAMH amplitude is observed along-axis from north to south, with the steepest gradient between 9°42′ and 9°36′N. The source of this variation is neither a systematic change in geochemistry nor varying paleointensity at the time of lava eruption. Instead, magnetic moment models show that it can be accounted for by an observed ∼50% decrease in seismic Layer 2A thickness along-axis. Layer 2A is assumed to be the extrusive volcanic layer, and we propose that this composes most of the magnetic source layer along the ridge axis. The 9°37′N overlapping spreading center (OSC) is located at the southern end of the steep CAMH gradient, and the 9°42′–9°36′N ridge segment is interpreted to be a transition zone in crustal accretion processes, with robust magmatism north of 9°42′N and relatively low magmatism at present south of 9°36′N. The 9°37′N OSC is also the only bathymetric discontinuity associated with a shift in the CAMH peak, which deviates ∼0.7 km to the west of the axial summit trough, indicating southward migration of the OSC. CAMH boundaries (defined from the maximum gradients) lie within or overlie the neovolcanic zone (NVZ) boundaries throughout our survey area, implying a systematic relationship between recent volcanic activity and CAMH source. Maximum flow distances and minimum lava dip angles are inferred on the basis of the lateral distance between the NVZ and CAMH boundaries. Lava dip angles average ∼14° toward the ridge axis, which agrees well with previous observations and offers a new method for estimating lava dip angles along fast spreading ridges where volcanic sequences are not exposed.
    Description: The research project was funded by National Science Foundation under grants OCE-9819261 and OCE- 0096468.
    Keywords: East Pacific Rise ; Magnetic anomalies ; Mid-ocean ridges ; Volcanic processes ; Magnetic source layer
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Construction of the Galapagos platform by large submarine volcanic terraces (2010)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q03015, doi:10.1029/2007GC001795.
    Description: New multibeam bathymetric and side-scan sonar data from the southwestern edge of the Galápagos platform reveal the presence of ∼60 large, stepped submarine terraces between depths of 800 m and 3500 m. These terraces are unique features, as none are known from any other archipelago that share this geomorphic form or size. The terraces slope seaward at 〈2° and are surrounded by escarpments that average ∼300 m in height with average slopes of 24°. The stepped morphology, fine-scale features, and sinuous planform continuity of terrace edges indicate that each terrace results from a sequence of major submarine volcanic eruptions, similar in extent to young deep-water (〉3000 m) lava flow fields west of Fernandina and Isabela Islands. The terraces are formed of thick sequences of lava flows that coalesce to form the foundation of the Galápagos platform, on which the subaerial central volcanoes are built. The compositions of basalts dredged from the submarine terraces indicate that most lavas are chemically similar to subaerial lavas erupted from Sierra Negra volcano on southern Isabela Island. There are no regular major element, trace element, or isotopic variations in the submarine lavas as a function of depth, relative stratigraphic position, or geographic location along the southwest margin of the platform. We hypothesize that magma supply at the western edge of the Galápagos hot spot, which is influenced by both plume and mid-ocean ridge magmatic processes, leads to episodic eruption of large lava flows. These large lava flows coalesce to form the archipelagic apron upon which the island volcanoes are built.
    Description: This work was supported by the National Science Foundation grants OCE0002818 and EAR0207605 (D.G.), OCE0002461 (D.J.F. and M.K.), OCE05-25864 (M.K.), and EAR0207425 (K.H.).
    Keywords: Submarine volcanism
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Evidence of a recent magma dike intrusion at the slow spreading Lucky Strike segment, Mid-Atlantic Ridge (2010)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): B12102, doi:10.1029/2004JB003141.
    Description: Mid-ocean ridge volcanic activity is the fundamental process for creation of ocean crust, yet the dynamics of magma emplacement along the slow spreading Mid-Atlantic Ridge (MAR) are largely unknown. We present acoustical, seismological, and biological evidence of a magmatic dike intrusion at the Lucky Strike segment, the first detected from the deeper sections (〉1500 m) of the MAR. The dike caused the largest teleseismic earthquake swarm recorded at Lucky Strike in 〉20 years of seismic monitoring, and one of the largest ever recorded on the northern MAR. Hydrophone records indicate that the rate of earthquake activity decays in a nontectonic manner and that the onset of the swarm was accompanied by 30 min of broadband (〉3 Hz) intrusion tremor, suggesting a volcanic origin. Two submersible investigations of high-temperature vents located at the summit of Lucky Strike Seamount 3 months and 1 year after the swarm showed a significant increase in microbial activity and diffuse venting. This magmatic episode may represent one form of volcanism along the MAR, where highly focused pockets of magma are intruded sporadically into the shallow ocean crust beneath long-lived, discrete volcanic structures recharging preexisting seafloor hydrothermal vents and ecosystems.
    Description: This study was made possible through the support of the U.S. National Science Foundation (grants OCE-9811575, OCE- 0137164, and OCE-0201692) and the NOAA Vents Program.
    Keywords: Mid-Atlantic Ridge ; Earthquake ; Hydroacoustic
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Volcanic eruptions in the deep sea (2012)
    The Oceanography Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Oceanography Society, 2012. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 25, no. 1 (2012): 142–157, doi:10.5670/oceanog.2012.12.
    Description: Volcanic eruptions are important events in Earth's cycle of magma generation and crustal construction. Over durations of hours to years, eruptions produce new deposits of lava and/or fragmentary ejecta, transfer heat and magmatic volatiles from Earth's interior to the overlying air or seawater, and significantly modify the landscape and perturb local ecosystems. Today and through most of geological history, the greatest number and volume of volcanic eruptions on Earth have occurred in the deep ocean along mid-ocean ridges, near subduction zones, on oceanic plateaus, and on thousands of mid-plate seamounts. However, deep-sea eruptions (〉 500 m depth) are much more difficult to detect and observe than subaerial eruptions, so comparatively little is known about them. Great strides have been made in eruption detection, response speed, and observational detail since the first recognition of a deep submarine eruption at a mid-ocean ridge 25 years ago. Studies of ongoing or recent deep submarine eruptions reveal information about their sizes, durations, frequencies, styles, and environmental impacts. Ultimately, magma formation and accumulation in the upper mantle and crust, plus local tectonic stress fields, dictate when, where, and how often submarine eruptions occur, whereas eruption depth, magma composition, conditions of volatile segregation, and tectonic setting determine submarine eruption style.
    Description: NSF-OCE 0937409 (KHR), OCE-0525863 and OCE-0732366 (DJF and SAS), 0725605 (WWC), OCE- 0751780 (ETB and RWE), OCE‐0138088 (MRP), OCE-0934278 (DAC), OCE-0623649 (RPD), and a David and Lucile Packard Foundation grant to MBARI (DAC and DWC).
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Formation of submarine lava channel textures : insights from laboratory simulations (2010)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): B03104, doi:10.1029/2005JB003796.
    Description: Laboratory simulations using polyethylene glycol (PEG) extruded at a constant rate and temperature into a tank with a uniform basal slope and filled with a cold sucrose solution generate channels that are defined by stationary levees and mobile flow interiors. These laboratory channels consistently display the following surface textures in the channel: smooth, folded, lineated, and chaotic. In the simulations, we can observe specific local conditions including flow rate, position within the channel, and time that combine to develop each texture. The textures in PEG flows form due to relative differences in shear forces between the PEG crust and the underlying liquid wax. Minimal shear forces form smooth crust, whereas folded crust forms when the shear is sufficiently high to cause ductile deformation. Brittle deformation of solid PEG creates a chaotic texture, and lineated crust results from shear forces along the channel-levee margin. We observe similar textures in submarine lava channels with sources at or near the Axial Summit Trough of the East Pacific Rise between 9° and 10°N. We mapped the surface textures of nine submarine lava channels using high-resolution digital images collected during camera tows. These textural maps, along with observations of the formation of similar features in analog flows, reveal important information about the mechanisms occurring across the channel during emplacement, including relative flow velocity and shear stress.
    Description: The cruise was funded by a grant to WHOI from the National Science Foundation (NSF) OCE-9819261, with additional funding provided by WHOI thorough the Vetlesen Foundation. The PEG experiments were funded by NSF OCE-0425073 in a grant to Tracy Gregg.
    Keywords: East Pacific Rise ; Polyethylene glycol (PEG) ; Lava channels
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Lava geochemistry as a probe into crustal formation at the East Pacific Rise (2012)
    The Oceanography Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Oceanography Society, 2012. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 25, no. 1 (2012): 89–93, doi:10.5670/oceanog.2012.06.
    Description: Basalt lavas comprise the greatest volume of volcanic rocks on Earth, and most of them erupt along the world's mid-ocean ridges (MORs). These MOR basalts (MORBs) are generally thought to be relatively homogeneous in composition over large segments of the global ridge system (e.g., Klein, 2005). However, detailed sampling of two different regions on the northern East Pacific Rise (EPR) and extensive analysis of the samples show that fine-scale mapping and sampling of the ridge axis can reveal significant variations in lava chemistry on both small spatial and short temporal scales. The two most intensely sampled sites within the EPR Integrated Study Site (ISS) lie on and off axis between 9°17'N and 10°N, and from a wide region centered around 9°N where two segments of the EPR overlap (see Fornari et al., 2012, Figure 3, in this issue). The chemical composition of erupted lavas, similar to the genotype of an organism, can be used by igneous petrologists to trace the evolution of magmas from the mantle to the seafloor. The extensive and detailed geochemical studies at the EPR highlight how a thorough understanding of the variability in lava compositions on small spatial scales (i.e., between lava flows) and large spatial scales (i.e., from segment center to segment end and including discontinuities in the ridge crest) can be used in combination with seafloor photography, lava morphology, and bathymetry to provide insights into the magmatic system that drives volcanism and influences hydrothermal chemistry and biology at a fast-spreading MOR.
    Description: Grants that supported EPR ISS field and laboratory studies for our research programs include: MRP: OCE-0138088, OCE-0819469, OCE-825265, OCE-638406, OCE-527077, OCE-535532; DJF: OCE-9819261, OCE-0525863, OCE-0838923, OCE-0096468, OCE-0732366, and OCE-0112737.
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Navigational infrastructure at the East Pacific Rise 9°50′N area following the 2005–2006 eruption : seafloor benchmarks and near-bottom multibeam surveys (2010)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008):Q11T04, doi:10.1029/2008GC002070.
    Description: Four seafloor benchmarks were deployed with ROV Jason2 at frequently visited areas along the northern East Pacific Rise (NEPR) ridge crest near 9°50′N, within the Ridge2000 EPR integrated study site (ISS) bull's eye. When used in concert with established deep-ocean acoustic positioning techniques, these benchmarks provide navigational infrastructure to facilitate the integration of near-bottom data at this site by allowing efficient and quantitative coregistration of data and observations collected on multiple dives and over multiple cruises. High-resolution, near-bottom multibeam bathymetric surveys also were conducted along and across the ridge crest to provide a morphological and geological context for the benchmark areas. We describe the navigation and data processing techniques used to constrain the benchmark positions and outline operational details to effectively use benchmarks at this and other deep-ocean sites where multidisciplinary time series studies are conducted. The well-constrained positions of the benchmarks provide a consistent geospatial framework that can be used to limit navigational uncertainties during seafloor sampling and mapping programs and enable accurate spatial coregistration and integration of observations. These data are important to test a range of multidisciplinary hypotheses that seek to link geological, chemical, and biological processes associated with crustal accretion and energy transfer from the mantle to the hydrosphere at mid-ocean ridges.
    Keywords: Mid-ocean ridge ; Bathymetry ; Navigation ; Acoustic ; Hydrothermal vent
    Repository Name: Woods Hole Open Access Server
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