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. [1] 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! 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