Development and evolution of detachment faulting along 50 km of the Mid-Atlantic Ridge near 16.5N

This is the accepted manuscript. An edited version of this paper was published by AGU. Copyright 2014 American Geophysical Union.A multifaceted study of the slow-spreading Mid-Atlantic Ridge (MAR) at 16.5ºN provides new insights into detachment faulting and its evolution through time. The survey included regional multibeam bathymetry mapping, high-resolution mapping using AUV Sentry, seafloor imaging using the TowCam system, and an extensive rock-dredging program. At different times, detachment faulting was active along ~50 km of the western flank of the study area, and may have dominated spreading on that flank for the last 5 Ma. Detachment morphologies vary and include a classic corrugated massif, non-corrugated massifs, and back-tilted ridges marking detachment breakaways. High-resolution Sentry data reveal one other detachment morphology; a low-angle, irregular surface in the regional bathymetry is shown to be a finely corrugated detachment surface (corrugation wavelength of only tens of meters and relief of just a few meters). Multi-scale corrugations are observed 2-3 km from the detachment breakaway suggesting that they formed in the brittle layer, perhaps by anastomosing faults. The thin wedge of hanging wall lavas that covers a low-angle (6º) detachment footwall near its termination are intensely faulted and fissured; this deformation may be enhanced by the low-angle of the emerging footwall. Active detachment faulting currently is limited to the western side of the rift valley. Nonetheless, detachment fault morphologies also are present over a large portion of the eastern flank on crust > 2 Ma indicating that within the last 5 Ma parts of the ridge axis have experienced periods of two-sided detachment faulting.This work was supported by the National Science Foundation grant number OCE-1155650

Percutaneous septal ablation for left mid-ventricular obstructive hypertrophic cardiomyopathy: a case report

BACKGROUND: Mid-ventricular obstructive hypertrophic cardiomyopathy (MVOHC) is a rare type of cardiomyopathy. The diagnosis is based on the hourglass appearance on the left ventriculogram and the presence of pressure gradient between apical and basal chamber of the ventriculum on the hemodynamic assessment. CASE PRESENTATION: The present case represents successful percutaneous treatment with septal ablation to patient with MVOHC associated with systolic anterior motion of the mitral valve and obstruction at both the mid-ventricular and outflow levels. CONCLUSION: Alcohol septal ablation has been proposed as less invasive alternatives to surgery in patients with MVOHC

The largest deep-ocean silicic volcanic eruption of the past century

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 4 (2018): e1701121, doi:10.1126/sciadv.1701121.The 2012 submarine eruption of Havre volcano in the Kermadec arc, New Zealand, is the largest deep-ocean eruption in history and one of very few recorded submarine eruptions involving rhyolite magma. It was recognized from a gigantic 400-km2 pumice raft seen in satellite imagery, but the complexity of this event was concealed beneath the sea surface. Mapping, observations, and sampling by submersibles have provided an exceptionally high fidelity record of the seafloor products, which included lava sourced from 14 vents at water depths of 900 to 1220 m, and fragmental deposits including giant pumice clasts up to 9 m in diameter. Most (>75%) of the total erupted volume was partitioned into the pumice raft and transported far from the volcano. The geological record on submarine volcanic edifices in volcanic arcs does not faithfully archive eruption size or magma production.This research was funded by Australian Research Council Postdoctoral fellowships (DP110102196 and DE150101190 to R. Carey), a short-term postdoctoral fellowship grant from the Japan Society for the Promotion of Science (to R. Carey), National Science Foundation grants (OCE1357443 to B.H., OCE1357216 to S.A.S., and EAR1447559 to J.D.L.W.), and a New Zealand Marsden grant (U001616 to J.D.L.W.). J.D.L.W. and A.M. were supported by a research grant and PhD scholarship from the University of Otago. R.W. was supported by NIWA grant COPR1802. J.D.L.W. and F.C.-T. were supported by GNS Science grants CSA-GHZ and CSA-EEZ. M.J. was supported by the U.S. Department of Defense (DoD) through the National Defense Science and Engineering Graduate Fellowship (NDSEG) Program

Diverse styles of submarine venting on the ultraslow spreading Mid-Cayman Rise

Author Posting. © The Authors, 2010. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 107 (2010): 14020-14025, doi:10.1073/pnas.1009205107.Thirty years after the first discovery of high-temperature submarine venting, the vast majority of the global Mid Ocean Ridge remains unexplored for hydrothermal activity. Of particular interest are the world’s ultra-slow spreading ridges which were the last to be demonstrated to host high-temperature venting, but may host systems particularly relevant to pre-biotic chemistry and the origins of life. Here we report first evidence for diverse and very deep hydrothermal vents along the ~110 km long, ultra-slow spreading Mid-Cayman Rise. Our data indicate that the Mid- Cayman Rise hosts at least three discrete hydrothermal sites, each representing a different type of water-rock interaction, including both mafic and ultra-mafic systems and, at ~5000 m, the deepest known hydrothermal vent. Although submarine hydrothermal circulation, in which seawater percolates through and reacts with host lithologies, occurs on all mid-ocean ridges, the diversity of vent-types identified here and their relative geographic isolation make the Mid-Cayman Rise unique in the oceans. These new sites offer prospects for: an expanded range of vent-fluid compositions; varieties of abiotic organic chemical synthesis and extremophile microorganisms; and unparalleled faunal biodiversity - all in close proximity.This research was funded through NASA (ASTEP) and WHOI (Ocean Ridge Initiative)

Globally aligned photomosaic of the Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge, 37°18.5′N) : release of georeferenced data, mosaic construction, and viewing software

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): Q12009, doi:10.1029/2008GC002204.We present a georeferenced photomosaic of the Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge, 37°18′N). The photomosaic was generated from digital photographs acquired using the ARGO II seafloor imaging system during the 1996 LUSTRE cruise, which surveyed a ∼1 km2 zone and provided a coverage of ∼20% of the seafloor. The photomosaic has a pixel resolution of 15 mm and encloses the areas with known active hydrothermal venting. The final mosaic is generated after an optimization that includes the automatic detection of the same benthic features across different images (feature-matching), followed by a global alignment of images based on the vehicle navigation. We also provide software to construct mosaics from large sets of images for which georeferencing information exists (location, attitude, and altitude per image), to visualize them, and to extract data. Georeferencing information can be provided by the raw navigation data (collected during the survey) or result from the optimization obtained from image matching. Mosaics based solely on navigation can be readily generated by any user but the optimization and global alignment of the mosaic requires a case-by-case approach for which no universally software is available. The Lucky Strike photomosaics (optimized and navigated-only) are publicly available through the Marine Geoscience Data System (MGDS, http://www.marine-geo.org). The mosaic-generating and viewing software is available through the Computer Vision and Robotics Group Web page at the University of Girona (http://eia.udg.es/∼rafa/mosaicviewer.html).This work has been supported by the EU Marie Curie RTNs MOMARNet (OD, RG, JE, LN, JF, NG) and FREESUBNet (RG, NG, XC), the Spanish Ministry of Science and Innovation (grant CTM2007–64751; RG, JE), CNRS and ANR (grant ANR NT05–3_42212, JE), ICREA (LN), and by the Generalitat de Catalunya (JE, RG). JF has been funded by MICINN under FPI grant BES-2006-12733 and NG has been supported by MICINN under the ‘‘Ramon y Cajal’’ program

3-D focused inversion of near-seafloor magnetic data with application to the Brothers volcano hydrothermal system, Southern Pacific Ocean, New Zealand

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): B10102, doi:10.1029/2012JB009349.We describe and apply a new inversion method for 3-D modeling of magnetic anomalies designed for general application but which is particularly useful for the interpretation of near-seafloor magnetic anomalies. The crust subsurface is modeled by a set of prismatic cells, each with uniform magnetization, that together reproduce the observed magnetic field. This problem is linear with respect to the magnetization, and the number of cells is normally greater than the amount of available data. Thus, the solution is obtained by solving an under-determined linear problem. A focused solution, exhibiting sharp boundaries between different magnetization domains, is obtained by allowing the amplitudes of magnetization to vary between a pre-determined range and by minimizing the region of the 3-D space where the source shows large variations, i.e., large gradients. A regularization functional based on a depth-weighting function is also introduced in order to counter-act the natural decay of the magnetic field intensity with depth. The inversion method has been used to explore the characteristics of the submarine hydrothermal system of Brothers volcano in the Kermadec arc, by inverting near-bottom magnetic data acquired by Autonomous Underwater Vehicles (AUVs). Different surface expressions of the hydrothermal vent fields show specific vertical structures in their underlying demagnetization regions that we interpret to represent hydrothermal upflow zones. For example, at focused vent sites the demagnetized conduits are vertical, pipe-like structures extending to depths of ~1000 m below the seafloor, whereas at diffuse vent sites the demagnetization regions are characterized by thin and inclined conduits.This contribution was made possible through funding by the New Zealand Foundation for Research, Science and Technology (FRST contract C05X0406) and by the Royal Society of New Zealand by the Marsden Fund (grant GNS1003).2013-04-1

Interplay between faults and lava flows in construction of the upper oceanic crust : the East Pacific Rise crest 9°25′–9°58′N

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 8 (2007): Q06005, doi:10.1029/2006GC001399.The distribution of faults and fault characteristics along the East Pacific Rise (EPR) crest between 9°25′N and 9°58′N were studied using high-resolution side-scan sonar data and near-bottom bathymetric profiles. The resulting analysis shows important variations in the density of deformational features and tectonic strain estimates at young seafloor relative to older, sediment-covered seafloor of the same spreading age. We estimate that the expression of tectonic deformation and associated strain on “old” seafloor is ~5 times greater than that on “young” seafloor, owing to the frequent fault burial by recent lava flows. Thus the unseen, volcanically overprinted tectonic deformation may contribute from 30% to 100% of the ~300 m of subsidence required to fully build up the extrusive pile (Layer 2A). Many longer lava flows (greater than ~1 km) dam against inward facing fault scarps. This limits their length at distances of 1–2 km, which are coincident with where the extrusive layer acquires its full thickness. More than 2% of plate separation at the EPR is accommodated by brittle deformation, which consists mainly of inward facing faults (~70%). Faulting at the EPR crest occurs within the narrow, ~4 km wide upper crust that behaves as a brittle lid overlying the axial magma chamber. Deformation at greater distances off axis (up to 40 km) is accommodated by flexure of the lithosphere due to thermal subsidence, resulting in ~50% inward facing faults accommodating ~50% of the strain. On the basis of observed burial of faults by lava flows and damming of flows by fault scarps, we find that the development of Layer 2A is strongly controlled by low-relief growth faults that form at the ridge crest and its upper flanks. In turn, those faults have a profound impact on how lava flows are distributed along and across the ridge crest.The field and laboratory studies were supported by NSF grants OCE-9819261 (to H.S., M.A.T., and D.J.F.), OCE-0525863 (D.J.F. and S.A.S.), OCE-0138088 (M.P.), WHOI Vetlesen Foundation Funds (J.E., D.J.F., and S.A.S.). Additional support by INSU/CNRS to J.E. is also acknowledged

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

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

Young volcanism and related hydrothermal activity at 5°S on the slow-spreading southern Mid-Atlantic Ridge

The effect of volcanic activity on submarine hydrothermal systems has been well documented along fast- and intermediate-spreading centers but not from slow-spreading ridges. Indeed, volcanic eruptions are expected to be rare on slow-spreading axes. Here we report the presence of hydrothermal venting associated with extremely fresh lava flows at an elevated, apparently magmatically robust segment center on the slow-spreading southern Mid-Atlantic Ridge near 5°S. Three high-temperature vent fields have been recognized so far over a strike length of less than 2 km with two fields venting phase-separated, vapor-type fluids. Exit temperatures at one of the fields reach up to 407°C, at conditions of the critical point of seawater, the highest temperatures ever recorded from the seafloor. Fluid and vent field characteristics show a large variability between the vent fields, a variation that is not expected within such a limited area. We conclude from mineralogical investigations of hydrothermal precipitates that vent-fluid compositions have evolved recently from relatively oxidizing to more reducing conditions, a shift that could also be related to renewed magmatic activity in the area. Current high exit temperatures, reducing conditions, low silica contents, and high hydrogen contents in the fluids of two vent sites are consistent with a shallow magmatic source, probably related to a young volcanic eruption event nearby, in which basaltic magma is actively crystallizing. This is the first reported evidence for direct magmatic-hydrothermal interaction on a slow-spreading mid-ocean ridge