Carton Helene

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  • Article
    Recent advances in multichannel seismic imaging for academic research in deep oceanic environments
    (The Oceanography Society, 2012-03) Canales, J. Pablo ; Carton, Helene ; Mutter, John C. ; Harding, Alistair J. ; Carbotte, Suzanne M. ; Nedimovic, Mladen R.
    Academic research using marine multichannel seismic (MCS) methods to investigate processes related to Earth's oceanic crust has made substantial advances in the last decade. These advances were made possible by access to state-of-the-art MCS acquisition systems, and by development of data processing and modeling techniques that specifically deal with the particularities of oceanic crustal structure and the challenges of subseafloor imaging in the deep ocean. Among these methods, we highlight multistreamer three-dimensional (3D) imaging, streamer refraction tomography, synthetic ocean bottom experiments (SOBE), and time-lapse (4D) studies.
  • Article
    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
    (John Wiley & Sons, 2016-08-14) Horning, Gregory W. ; Canales, J. Pablo ; Carbotte, Suzanne M. ; Han, Shuoshuo ; Carton, Helene ; Nedimovic, Mladen R. ; van Keken, Peter E.
    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.
  • Preprint
    A multi-sill magma plumbing system beneath the axis of the East Pacific Rise
    ( 2014-09) Marjanovic, Milena ; Carbotte, Suzanne M. ; Carton, Helene ; Nedimovic, Mladen R. ; Mutter, John C. ; Canales, J. Pablo
    The mid-crust axial magma lens detected at fast and intermediate spreading mid-ocean ridges is believed to be the primary magma reservoir for formation of upper oceanic crust. However, the mechanism behind formation of the lower crust is a subject of ongoing debate. The sheeted sill model proposed from observations of ophiloites requires the presence of multiple lenses/sills throughout lower crust but only a single lens is imaged directly beneath the innermost axial zone in prior seismic studies . Here, high-fidelity seismic data from the East Pacific Rise reveal series of reflections below the axial magma lens that we interpret as mid-lower crustal lenses. These deeper lenses are present between 9°20-57′N at variable two-way-travel-times, up to 4.6 s (~1.5 km beneath the axial magma lens), providing direct support for the sheeted sill model. From local changes in the amplitude and geometry of the events beneath a zone of recent volcanic eruption, we infer that melt drained from a lower lens contributed to the replenishment of the axial magma lens above and, perhaps, the eruption. The new data indicate that a multi-level sill complex is present beneath the East Pacific Rise that likely contributes to the formation of both the upper and lower crust.
  • Article
    Variations in axial magma lens properties along the East Pacific Rise (9°30′N–10°00′N) from swath 3-D seismic imaging and 1-D waveform inversion
    (John Wiley & Sons, 2014-04-29) Xu, Min ; Canales, J. Pablo ; Carbotte, Suzanne M. ; Carton, Helene ; Nedimovic, Mladen R. ; Mutter, John C.
    We use three-dimensional multistreamer seismic reflection data to investigate variations in axial magma lens (AML) physical properties along the East Pacific Rise between 9°30′N and 10°00′N. Using partial-offset stacks of P- and S-converted waves reflecting off the top of the AML, we image four 2–4 km long melt-rich sections spaced 5–10 km from each other. One-dimensional waveform inversion indicates that the AML in a melt-rich section is best modeled with a low Vp (2.95–3.23 km/s) and Vs (0.3–1.5 km/s), indicating >70% melt fraction. In contrast, the AML in a melt-poor section requires higher Vp (4.52–4.82 km/s) and Vs (2.0–3.0 km/s), which indicates <40% melt fraction. The thicknesses of the AML are constrained to be 8–32 m and 8–120 m at the melt-rich and -poor sites, respectively. Based on the AML melt-mush segmentation imaged in the area around the 2005–2006 eruption, we infer that the main source of this eruption was a 5 km long section of the AML between 9°48′N and 51′N. The eruption drained most of the melt in this section of the AML, leaving behind a large fraction of connected crystals. We estimate that during the 2005–2006 eruption, a total magma volume of 9–83 × 106 m3 was extracted from the AML, with a maximum of 71 × 106 m3 left unerupted in the crust as dikes. From this, we conclude that an eruption of similar dimensions to the 2005–2006, one would be needed with a frequency of years to decades in order to sustain the long-term average seafloor spreading rate at this location.
  • Article
    Constraints on melt content of off-axis magma lenses at the East Pacific Rise from analysis of 3-D seismic amplitude variation with angle of incidence
    (John Wiley & Sons, 2017-06-28) Aghaei, Omid ; Nedimovic, Mladen R. ; Marjanovic, Milena ; Carbotte, Suzanne M. ; Canales, J. Pablo ; Carton, Helene ; Nikić, Nikola
    We use 3-D multichannel seismic data to form partial angle P wave stacks and apply amplitude variation with angle (AVA) crossplotting to assess melt content and melt distribution within two large midcrustal off-axis magma lenses (OAMLs) found along the East Pacific Rise from 9°37.5′N to 9°57′N. The signal envelope of the partial angle stacks suggests that both OAMLs are partially molten with higher average melt content and more uniform melt distribution in the southern OAML than in the northern OAML. For AVA crossplotting, the OAMLs are subdivided into seven ~1 km2 analysis windows. The AVA crossplotting results indicate that the OAMLs contain a smaller amount of melt than the axial magma lens (AML). For both OAMLs, a higher melt fraction is detected within analysis windows located close to the ridge axis than within the most distant windows. The highest average melt concentration is interpreted for the central sections of the OAMLs. The overall low OAML melt content could be indicative of melt lost due to recent off-axis eruptions, drainage to the AML, or limited mantle melt supply. Based on the results of this and earlier bathymetric, morphological, geochemical, and geophysical investigations, we propose that the melt-poor OAML state is largely the result of limited melt supply from the underlying mantle source reservoir with smaller contribution attributed to melt leakage to the AML. We hypothesize that the investigated OAMLs have a longer period of melt replenishment, lower eruption recurrence rates, and lower eruption volumes than the AML, though some could be single intrusion events.
  • Article
    Recent seismic studies at the East Pacific Rise 8°20'–10°10'N and Endeavour Segment : insights into mid-ocean ridge hydrothermal and magmatic processes
    (The Oceanography Society, 2012-03) Carbotte, Suzanne M. ; Canales, J. Pablo ; Nedimovic, Mladen R. ; Carton, Helene ; Mutter, John C.
    As part of the suite of multidisciplinary investigations undertaken by the Ridge 2000 Program, new multichannel seismic studies of crustal structure were conducted at the East Pacific Rise (EPR) 8°20'–10°10'N and Endeavour Segment of the Juan de Fuca Ridge. These studies provide important insights into magmatic systems and hydrothermal flow in these regions, with broader implications for fast- and intermediate-spreading mid-ocean ridges. A mid-crust magma body is imaged beneath Endeavour Segment underlying all known vent fields, suggesting that prior notions of a tectonically driven hydrothermal system at this site can be ruled out. There is evidence at both sites that the axial magma body is segmented on a similar 5–20 km length scale, with implications for the geometry of high-temperature axial hydrothermal flow and for lava geochemistry. The new data provide the first seismic reflection images of magma sills in the crust away from the axial melt lens. These off-axis magma reservoirs are the likely source of more-evolved lavas typically sampled on the ridge flanks and may be associated with off-axis hydrothermal venting, which has recently been discovered within the EPR site. Clusters of seismic reflection events at the base of the crust are observed, and localized regions of thick Moho Transition Zone, with frozen or partially molten gabbro lenses embedded within mantle rocks, are inferred. Studies of the upper crust on the flanks of Endeavour Segment provide new insights into the low-temperature hydrothermal flow that continues long after crustal formation. Precipitation of alteration minerals due to fluid flow leads to changes in P-wave velocities within seismic Layer 2A (the uppermost layer of the oceanic crust) that vary markedly with extent of sediment blanketing the crust. In addition, intermediate-scale variations in the structure of Layers 2A and 2B with local topography are observed that may result from topographically driven fluid upflow and downflow on the ridge flanks.
  • Article
    Crustal thickness and Moho character of the fast-spreading East Pacific Rise from 9°42′N to 9°57′N from poststack-migrated 3-D MCS data
    (John Wiley & Sons, 2014-03-18) Aghaei, Omid ; Nedimovic, Mladen R. ; Carton, Helene ; Carbotte, Suzanne M. ; Canales, J. Pablo ; Mutter, John C.
    We computed crustal thickness (5740 ± 270 m) and mapped Moho reflection character using 3-D seismic data covering 658 km2 of the fast-spreading East Pacific Rise (EPR) from 9°42′N to 9°57′N. Moho reflections are imaged within ∼87% of the study area. Average crustal thickness varies little between large sections of the study area suggesting regionally uniform crustal production in the last ∼180 Ka. However, individual crustal thickness measurements differ by as much as 1.75 km indicating that the mantle melt delivery has not been uniform. Third-order, but not fourth-order ridge discontinuities are associated with changes in the Moho reflection character and/or near-axis crustal thickness. This suggests that the third-order segmentation is governed by melt distribution processes within the uppermost mantle while the fourth-order ridge segmentation arises from midcrustal to upper-crustal processes. In this light, we assign fourth-order ridge discontinuity status to the debated ridge segment boundary at ∼9°45′N and third-order status at ∼9°51.5′N to the ridge segment boundary previously interpreted as a fourth-order discontinuity. Our seismic results also suggest that the mechanism of lower-crustal accretion varies along the investigated section of the EPR but that the volume of melt delivered to the crust is mostly uniform. More efficient mantle melt extraction is inferred within the southern half of our survey area with greater proportion of the lower crust accreted from the axial magma lens than that for the northern half. This south-to-north variation in the crustal accretion style may be caused by interaction between the melt sources for the ridge and the Lamont seamounts.
  • Article
    Heat flow variations on a slowly accreting ridge : constraints on the hydrothermal and conductive cooling for the Lucky Strike segment (Mid-Atlantic Ridge, 37°N)
    (American Geophysical Union, 2006-07-27) Lucazeau, Francis ; Bonneville, Alain ; Escartin, Javier E. ; von Herzen, Richard P. ; Gouze, Philippe ; Carton, Helene ; Cannat, Mathilde ; Vidal, Valerie ; Adam, Claudia
    We report 157 closely spaced heat flow measurements along the Lucky Strike segment in the Mid-Atlantic Ridge (MAR) for ages of the ocean floor between 0 and 11 Ma. On the eastern flank of a volcanic plateau delimiting off-axis and axial domains, the magnitude of heat flow either conforms to the predictions of conductive lithospheric cooling models or is affected by localized anomalies. On the western flank it is uniformly lower than conductive model predictions. We interpret the observed patterns of heat flow by lateral fluid circulation in a highly permeable oceanic basement. The circulation geometries are probably 3-D rather than 2-D and are determined by the configuration of the basement/sediment interface and the distribution of effectively unsedimented seamounts where water recharge can occur. Two major hydrothermal circulation systems can possibly explain the observations off-axis: the first would involve lateral pore water flow from west to east, and the second would have a reverse flow direction. The wavelengths and magnitudes of heat flow anomalies require Darcy velocities of the order of 1–4 m/year, which are similar to those proposed for fast-accreted crust elsewhere. However, a large proportion of this MAR domain remains unaffected by hydrothermal cooling, which is a relatively unusual observation but confirms the validity of conductive thermal models for seafloor ages between 5 and 10 Ma. Closer to the ridge axis (<5 Myr old crust), water circulation affects the overall axial domain, as larger proportions of basement are exposed. As much as 80–90% of the heat flux from the axial domain may be transferred to the Lucky Strike vent field, in agreement with the estimated discharge.
  • Article
    Along-trench structural variations of the subducting Juan de Fuca Plate from multichannel seismic reflection imaging
    (John Wiley & Sons, 2018-04-22) Han, Shuoshuo ; Carbotte, Suzanne M. ; Canales, J. Pablo ; Nedimovic, Mladen R. ; Carton, Helene
    To characterize the along‐strike structural variations of the Juan de Fuca (JdF) Plate as it enters the Cascadia subduction zone, we present prestack time migrated multichannel seismic reflection images of the JdF Plate along a 400‐km‐long trench‐parallel transect extending from 44.3°N to 47.8°N. Beneath the 1.8–3.0‐km‐thick sediment cover, our data reveal basement topographic anomalies associated with a 1.2‐km‐high seamount and in the vicinity of propagator wakes (390–540‐m relief). Weak Moho reflections are imaged beneath the propagator wakes and coincide with reduced Vp in the lower crust and/or uppermost mantle. The inferred locations of propagator wakes in the downgoing plate collocate with some of the boundaries of episodic tremor and slip events. We propose that the structural and hydration heterogeneities associated with these features could lead to anomalous plate interface properties and contribute to episodic tremor and slip segmentation. Intracrustal reflections with apparent dips (20°–30°) consistent with subduction bending normal faults change near 45.8°N, from northward dipping reflections confined to the middle crust in the north to antithetic reflections through the crust in the south, coinciding with a Vp reduction in the lower crust. These observations indicate more extensive faulting deformation and associated hydration of the JdF Plate south of 45.8°N, which likely results from variations of slab dip and resistance to subduction across 46°N. Basement offsets and abrupt depth/amplitude changes in Moho reflections are imaged beneath the four major WNW trending strike‐slip faults that cross the Cascadia deformation front, providing strong evidence of a lower plate origin for these faults.
  • Article
    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
    (John Wiley & Sons, 2016-03-21) Han, Shuoshuo ; Carbotte, Suzanne M. ; Canales, J. Pablo ; Nedimovic, Mladen R. ; Carton, Helene ; Gibson, James C. ; Horning, Gregory W.
    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.
  • Article
    Distribution of melt along the East Pacific Rise from 9°30′ to 10°N from an amplitude variation with angle of incidence (AVA) technique
    (Oxford University Press, 2015-06) Marjanovic, Milena ; Carton, Helene ; Carbotte, Suzanne M. ; Nedimovic, Mladen R. ; Mutter, John C. ; Canales, J. Pablo
    We examine along-axis variations in melt content of the axial magma lens (AML) beneath the fast-spreading East Pacific Rise (EPR) using an amplitude variation with angle of incidence (AVA) crossplotting method applied to multichannel seismic data acquired in 2008. The AVA crossplotting method, which has been developed for and, so far, applied for hydrocarbon prospection in sediments, is for the first time applied to a hardrock environment. We focus our analysis on 2-D data collected along the EPR axis from 9°29.8′N to 9°58.4′N, a region which encompasses the sites of two well-documented submarine volcanic eruptions (1991–1992 and 2005–2006). AVA crossplotting is performed for a ∼53 km length of the EPR spanning nine individual AML segments (ranging in length from ∼3.2 to 8.5 km) previously identified from the geometry of the AML and disruptions in continuity. Our detailed analyses conducted at 62.5 m interval show that within most of the analysed segments melt content varies at spatial scales much smaller (a few hundred of metres) than the length of the fine-scale AML segments, suggesting high heterogeneity in melt concentration. At the time of our survey, about 2 yr after the eruption, our results indicate that the three AML segments that directly underlie the 2005–2006 lava flow are on average mostly molten. However, detailed analysis at finer-scale intervals for these three segments reveals AML pockets (from >62.5 to 812.5 m long) with a low melt fraction. The longest such mushy section is centred beneath the main eruption site at ∼9°50.4′N, possibly reflecting a region of primary melt drainage during the 2005–2006 event. The complex geometry of fluid flow pathways within the crust above the AML and the different response times of fluid flow and venting to eruption and magma reservoir replenishment may contribute to the poor spatial correlation between incidence of hydrothermal vents and presence of highly molten AML. The presented results are an important step forward in our ability to resolve small-scale characteristics of the AML and recommend the AVA crossplotting as a tool for examining mid-ocean ridge magma-systems elsewhere.
  • Preprint
    Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone
    ( 2017-09) Canales, J. Pablo ; Carbotte, Suzanne M. ; Nedimovic, Mladen R. ; Carton, Helene
    Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use seismic data to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. Specifically, we analyse these water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the central Cascadia margin. We find that the Juan de Fuca lower crust and mantle are drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Variable but limited bend faulting along the margin limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. The dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust, and that decompression rather than hydrous melting must dominate arc magmatism in central Cascadia. Additionally, dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab.
  • Article
    Crustal magmatic system beneath the east pacific rise (8 degrees 20 to 10 degrees 10N): Implications for tectonomagmatic segmentation and crustal melt transport at fast-spreading ridges
    (American Geophysical Union, 2018-11-06) Marjanovic, Milena ; Carbotte, Suzanne M. ; Carton, Helene ; Nedimovic, Mladen R. ; Canales, J. Pablo ; Mutter, John C.
    Detailed images of the midcrustal magmatic system beneath the East Pacific Rise (8°20′–10°10′N) are obtained from 2‐D and 3‐D‐swath processing of along axis seismic data and are used to characterize properties of the axial crust, cross‐axis variations, and relationships with structural segmentation of the axial zone. Axial magma lens (AML) reflections are imaged beneath much of the ridge axis (mean depth 1,640 ± 185 m), as are deeper sub‐AML (SAML) reflections (brightest events ~100–800 m below AML). Local shallow regions in the AML underlie two regions of shallow seafloor depth from 9°40′–55′N and 8°26′–33′N. Enhanced magma replenishment at present beneath both sites is inferred and may be linked to nearby off‐axis volcanic chains. SAML reflections, which are observed primarily from 9°20′ to 10°05′N, indicate a finely segmented magma reservoir similar to the AML above, composed of subhorizontal, 2‐ to 7 km‐long AML segments, often with stepwise changes in reflector depth from one segment to the next. We infer that these melt bodies are related to short‐lived melt instability zones. In many locations including where seismic constraints are strongest the intermediate scale (~15–40 km) structural segmentation of the ridge axis identified in this region coincides with (1) changes in average thickness of layer 2A (by 10%–15%), (2) changes in average depth of AML (<100 m), and (3) with the spacing of punctuated low velocity zones mapped in the uppermost mantle. The ~6 km dominant length of multiple AML segments within each of the larger structural segments may reflect the spacing of local sites of ascending magma from discrete melt reservoirs pooled beneath the crust.