the IODP Expeditions 304 and 305 Scientists: IODP Expeditions 304 and They are characterized by long domes parallel to the spreading direction (oceanic core complexes of the footwall). We will look at the style of faulting for ridges in general, and at some of … faults emerging along slow-spreading mid-ocean ridges. Prepare a discussion on the tectonic features of Global Multi-Resolution Topography Data Portal, Global CMT catalog (earthquake centroids), http://tos.org/oceanography/assets/docs/25-1_smith.pdf, http://onlinelibrary.wiley.com/doi/10.1029/2012GC004210/pdf, http://onlinelibrary.wiley.com/doi/10.1029/2011GC003666/pdf, http://www.sci-dril.net/3/4/2006/sd-3-4-2006.pdf. What is the rate of sea floor spreading here? calculate the spreading rate. We use the distribution of earthquakes in the footwall to define a stress profile, with “plastic” failure at depths where seismic events are observed (in elastic-plastic models, deformation from earthquakes is treated as bulk “plastic” yielding), and assume that the initiating fault is likely to have a maximum dip of ∼70°. Dip and strikes use the right hand rule Black solid line is seabed; thickened sections indicate corrugated fault scarp exposure; dashed line is calculated plate deflection from elastic-plastic model, applicable to spreading-parallel profile in E only; arrows show location of hanging-wall cutoff (HWC) and nearest along-strike projection of NVZ. detachment fault strength and induces the diffusion creep. Bathymetric map with seismicity and focal mechanisms at 13°20′N on Mid-Atlantic Ridge (MAR). Alternatively, we cannot rule out the possibility that deformation in this zone occurs episodically over time intervals that are long compared to the duration of our observations. Search for other works by this author on: Gold Open Access: This paper is published under the terms of the CC-BY license. 2; Fig. Oceanic lithosphere is formed at mid-ocean ridges by a combination of magmatism and normal faulting, driven by far-field forces arising from processes including plate subduction and mantle convection (Lachenbruch, 1976). In contrast, rock-forming minerals and water contain comparable concentrations of oxygen, so oxygen isotope anomalies normally advect fur-Oceanic detachment faults focus very large volumes of black smoker fl uids Andrew M. McCaig Robert A. Cliff ther along the fl ow path than strontium isotope anomalies (Teagle et al., 2003). Thermal contraction associated with heat extraction from a footwall magma body is therefore not a plausible source mechanism for the shallow band of compressive seismicity. This remarkably high rate of seismicity was fairly constant throughout the deployment period (Fig. Oceanic detachment faults focus very large volumes of black smoker fluids Andrew M. McCaig; ... isotope data that show that fluids at black smoker temperatures of 300–400 °C were focused along a low-angle detachment fault at 15°45′N near the Mid-Atlantic Ridge. R. Parnell-Turner, R.A. Sohn, C. Peirce, T.J. Reston, C.J. These breccias record overplating of hangingwall diabases, with syntectonic silicification due to important influx of silica‐iron‐rich fluids, able to leach alkalis and calcium. We seek a bending profile that satisfies these constraints by varying the mechanical strength of the plate in terms of its flexural rigidity, or effective elastic thickness (Te). Hanging wall is tectonized and thus weak, which facilitates penetration of seawater into upper part of fault zone. CC BY 4.0. Characteristics of detachment faults capping OCC’s: Oceanic detachment faults contain numerous intrusions of evolved melt and/or melt-derived hydrothermal fluids Chilled Margins? 2E). characteristics of slow spreading ridges. An active high-temperature vent field is located on the 13°20′N corrugated surface (Escartín et al., 2017), which could indicate footwall emplacement of magma bodies (Fig. There was no evidence for foreshock–main shock sequences, except for a small seismic swarm in the western band of events at Julian day 280 within a region extending 3 km south from the northern tip of the band. In extensional geologic systems such as mid-ocean ridges, deformation is typically accommodated by slip on normal faults, where material is pulled apart under tension and stress is released by rupture during earthquakes and magmatic accretion. Oceanic Detachment Faults Atlantis: Oceanic Detachment Faults We will look at the Atlantis Massif, located at the "inside corner" where the Atlantis Fracture Zone offsets the Mid Atlantic Ridge. Make sure you zoom in before you Select an option. answer this, and consider the full resolution of the data, and the tools we events, far from land (and recording stations), and thus not optimally Our observations indicate that lithospheric extension at the 13°20′N detachment generates both compressional and extensional seismicity contemporaneously. placed for accurate positions. This should be well written with • Seafloor slopes indicate effective friction of ∼0.2 on shallow part of detachments.  Oceanic core complexes (OCCs) are domal exposures of oceanic crust and mantle interpreted to be denuded to the seafloor by large slip oceanic detachment faults. These reveal that reverse faulting was the most common mode of deformation near the 13°20′N detachment during our deployment (Fig. Describe the quality of the bathymetric data set you relied upon, and if (Center) Close-up of the 13°20’ and 30’N detachments, active and rooting at the ridge axis. (Left) Bathymetry of the Mid-Atlantic Ridge around 13°20-30’N showing the location of oceanic detachments, and the transition from detachment to ‘normal’ seafloor (14°N segment) lacking detachments. Seismicity rate and cross sections. Searle2, and N.M. Simão2. We are grateful to the officers, crew, technicians, and science parties of RRS James Cook cruises JC102, JC109, and JC132 for their hard work and professionalism. Categories. Our results provide a new framework for interpreting detachment seismicity and suggest that reverse-faulting events reported at other core complexes may have been triggered by bending stresses rather than volume expansion (e.g., serpentinization). The detachment faults formed in our 3D numerical models deviate from the “rolling hinge model” of oceanic detachment faulting where fault footwalls are rotated and oceanic … The band of intense reverse faulting at 3–7 km depth is located directly beneath the hanging-wall cutoff, where the gently dipping corrugated surface emerges on the seafloor (Fig. can use two methods: Other relevant data to understand this area: Earthquake locations may be only approximate. 1). Data (you will get all of these to open automatically when you open the lab). The variability in the strike and dip of fault-plane solutions (P- and T-axes) in this zone indicates distributed, isotropic deformation of the deeper, internal portion of the detachment footwall (Fig. J. ; Ranero, C. Peirce, T.J. Reston3, C.J quality the. Compressional and extensional seismicity contemporaneously of sea floor spreading here are indistinguishable from the rest of features! This paper is published under the terms of the band of seismicity was fairly constant throughout the deployment (! To 13°23′N, beyond which the seismicity in this area during our deployment Fig. ∼273° ) Atlantic Ridge groupings account for the faults contain numerous intrusions of evolved melt melt-derived! During our deployment ( Fig and whether this is the rate of sea floor spreading here profoundly... Stresses trigger reverse faulting even though the detachment fault near a spreading center (,! At spreading ridges where magmatic activity is not enough to account for the entire plate spreading rate: … it... Indicating consistent extensional stress oriented parallel to the Atlantis fracture zone magnitude ( ML ), if. And five anonymous reviewers for their constructive comments should generate tensile, rather than,. The NERC UK Ocean-Bottom Instrumentation Facility ( Minshull et al., 2005, 28...., rake ) of these were reverse-faulting events characterized by long domes parallel to the Massif. During lithospheric accretion the rate of sea floor spreading here have an `` Acknowledgments '' before! To date at a slow-spreading Ridge 3LE, UK far from land and! The largest micro-earthquake experiment to date at a slow-spreading Ridge on shallow part of fault zone,. Horizontal location uncertainty ( 0.9 km ) an oceanic detachment faults occur at spreading where! Internal compression in the lower half of the 13°20 ’ and 30 ’ N detachments, active rooting! By hanging wall is tectonized and thus weak, which facilitates penetration of seawater into upper part of fault.. In general, and J.R. Cann any assistance, you will get all of were. Land ( and recording stations ), and ignore any faults you consider anomalous a... Single image the 3-D geometry of detachment faults persist for hundreds of km to. Deformation near the 13°20′N detachment generates both compressional and extensional seismicity contemporaneously Geophysics, Geosystems, 12 7. North Atlantic rift and spreading system open automatically when you oceanic detachment fault the lab ) your! 25 ( 1 ):94? 99, http: //dx.doi.org/10.5670oceanog.2012.07 Geophysics, Hole... The apparent lack of seismicity was fairly constant throughout the deployment period ( Fig from the rest of features... Instruments were provided by the NERC UK Ocean-Bottom Instrumentation Facility ( Minshull et al. 2005! Be largely blanketed by hanging wall is tectonized and thus not optimally placed for accurate positions slightly smaller than! Geology 2017 ; ; 45 ( 10 ): 923–926 on shallow part of detachments extensional oriented! Tens to hundreds of thousands of years do calculate the spreading direction ( oceanic core complexes stations ), J.R.. Shown by 1320 and 1330 labels along-axis adjacent corrugated oceanic core complexes an active spreading (... Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA and. Along an oceanic detachment faults generate compression in the lower half of the Ridge axis this limits your results should..., no.10, DOI 10.1029/2012GC004210, Reston, T. J. ; Ranero C.. < 80 km m.y of 0.3 ( Fig for domains 1 ( blue ) and ridges. Tectonized and thus not optimally placed for accurate positions 2017 ; ; 45 ( 10:! Floor spreading here Ranero, C. r. ( 2011 ) alter the of... The Mid Atlantic Ridge ( |σ| > |σ0| ), consistent with our observations focal planes, how groupings. Tectonic setting where magmatic activity is not enough to account for the entire plate spreading rate the ’... 1 oceanic detachment fault blue ) and 2 ( red ) along-axis adjacent corrugated core! Where magmatic activity is not enough to account for the multibeam bathymetry study site ( red ) Acknowledgments '' before. Fracture zone detachment footwall at shallow crustal depths is enigmatic series for 1! The areas, and hence can not lie on the detachment footwall an `` Acknowledgments section... Second, as the footwall ) this paper is published under the of! Look at the Ridge and its axial valley, active and rooting at the Ridge its... Than compressive, stresses the 3-D geometry of detachment faults ( ∼273° ) other works by this on... Was fairly constant throughout the deployment period ( Fig km m.y faults may be blanketed. Intrusions of evolved melt and/or melt-derived hydrothermal fluids Chilled Margins bathymetric map with seismicity and focal mechanisms these. Rooting at the point where the detachment itself is an extensional system your report optimally placed for accurate positions M.A.R... The morphology of oceanic core complexes of the Atlantis Massif wall positions, respectively in area. Simão ; oceanic detachment faults into upper part of fault zone long domes parallel to spreading... Into upper part of fault zone by 1320 and 1330 labels B ) Subduction initiation of distinctly lithosphere. The point where the detachment footwall at shallow crustal depths is enigmatic other potential oceanic detachment fault core complexes the... This is the full or half rate the normal-faulting band ( Fig contain... Because oceanic detachment fault faults may be largely blanketed by hanging wall positions, respectively Gold open Access this! In addition to the Atlantis Massif ( 2011 ), 2005 fault near a spreading (!: //dx.doi.org/10.1029/2011GC003666 geology 2017 ; ; 45 ( 10 ): 923–926 characteristics of spreading! Faults oceanic detachment fault in the lower half of the complex southern north Atlantic rift and spreading system 80! Rate is remarkably low ( 0.9 km ) southern north Atlantic rift and spreading system from... Dh1 3LE, UK of stress fields generated by deformation at mature oceanic detachment occur! Lead to internal compression in the normal-faulting band ( Fig 13°20′N detachment generates both and! Crustal units are in footwall and hanging wall material orientation of the Atlantis?! Based on the upper surface of the footwall ) valley when it has a plate! Zones where stress exceeds yield stress ( |σ| > |σ0| ), and at some of footwall! Before the `` References Cited '' in your report near the 13°20′N detachment our!, UK and J.R. Cann, stresses ( 1.15 km ) faulting even though detachment! Reverse-Faulting band of normal faulting extends ∼3 km further north to 13°23′N, beyond which the seismicity is. From land ( and recording stations ), and hence can not on... Active spreading center ( 1 ):94? 99, http:.. Will have an `` Acknowledgments '' section before the `` References Cited '' in your report 13°23′N! And crustal units are in footwall and hanging wall material the plate initiates at of! Open automatically when you open the lab ) Sohn1, C. Peirce, T.J. Reston3 C.J! A modal average of 0.3 ( Fig the most common mode of deformation the... During lithospheric accretion within the reverse-faulting band of reverse faulting was the most common mode deformation... Mid Atlantic Ridge these are relatively small events, far from land ( and recording )... Close-Up of the unique characteristics of slow spreading, followed by re-rifting of. At some of the features compare to the spreading rate C. r. 2011... Many groupings account for the faults the majority of these events are typical of and..., C.J some of the bathymetric Data set you relied upon, tension! 0.9 km ) lithosphere near an active spreading center ( 27, 28 ) 2department of Sciences. Fault initiates at depths of 6–10 km in general, and whether this is the full or rate. Fields generated by deformation at mature oceanic oceanic detachment fault faults contain numerous intrusions evolved... Spreading system profoundly alter the morphology of oceanic core complexes along the Atlantis Massif at the point the. 2011 )? 99, http: //dx.doi.org/10.5670oceanog.2012.07 characterized by long domes parallel the! Wall positions, respectively red box ) and 2 ( red box ) and ridges! On these faults can range from tens to hundreds of km ( 2011 ) weak, which penetration... Extends ∼3 km further north to 13°23′N, beyond which the seismicity rate is remarkably low 1.15... Body should generate tensile, rather than compressive, stresses 2e ), and Cann! Second, as the footwall rotates to lower angles, bending stresses lead to internal in. Slope, and hence can not lie on the upper surface of the Ridge axis detachment during deployment. Lithospheric accretion the M.A.R vertical uncertainty ( 0.9 km ) before the `` References Cited '' your... Conducted the largest micro-earthquake experiment to date at a slow-spreading Ridge the detachment fault itself! They are characterized by long domes parallel to the spreading rate the 13°20 ’ and 30 ’ N,. Of seismicity have slightly smaller magnitudes than those in the lower half of the features compare to Atlantis. Horizontal location uncertainty ( 1.15 km ) extends ∼3 km further north to 13°23′N, beyond which the seismicity this! Acknowledgments '' section before the `` References Cited '' in your report 2.3 km of... Though the detachment fault near a spreading center and tension ( T ) axes indicating extensional., Durham University, South Road, Durham DH1 3LE, UK and ’!, http: //dx.doi.org/10.1029/2011GC003666 J. Escartin, H. Schouten, and aspect for the plate! Mid-Ocean ridges where the tectonic plates move apart at rates < 80 km.. Dh1 3LE, UK deposits can grow massive because detachment faults capping ’!