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1. Seismicity trends and detachment fault structure at 13°N, Mid-Atlantic Ridge

   https://doi.org/10.1130/G48420.1  

   Parnell-Turner, R.; Sohn, R.A.; Peirce, C.; Reston, T.J.; MacLeod, C.J.; Searle, R.C.; Simão, N.M. (November 2020, Geology)

   null (Ed.)

   At slow-spreading ridges, plate separation is commonly partly accommodated by slip on long-lived detachment faults, exposing upper mantle and lower crustal rocks on the seafloor. However, the mechanics of this process, the subsurface structure, and the interaction of these faults remain largely unknown. We report the results of a network of 56 ocean-bottom seismographs (OBSs), deployed in 2016 at the Mid-Atlantic Ridge near 13°N, that provided dense spatial coverage of two adjacent detachment faults and the intervening ridge axis. Although both detachments exhibited high levels of seismicity, they are separated by an ~8-km-wide aseismic zone, indicating that they are mechanically decoupled. A linear band of seismic activity, possibly indicating magmatism, crosscuts the 13°30′N domed detachment surface, confirming previous evidence for fault abandonment. Farther south, where the 2016 OBS network spatially overlapped with a similar survey done in 2014, significant changes in the patterns of seismicity between these surveys are observed. These changes suggest that oceanic detachments undergo previously unobserved cycles of stress accumulation and release as plate spreading is accommodated. 

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2. Local Seismicity of the Rainbow Massif on the Mid-Atlantic Ridge

   https://doi.org/10.1002/2017JB015288  

   Horning, G.; Sohn, R. A.; Canales, J. P.; Dunn, R. A. (February 2018, Journal of Geophysical Research: Solid Earth)
3. Deep Currents in the Rift Valley of the North Mid-Atlantic Ridge

   https://doi.org/10.3389/fmars.2019.00597  

   Lahaye, Noé; Gula, Jonathan; Thurnherr, Andreas M.; Reverdin, Gilles; Bouruet-Aubertot, Pascale; Roullet, Guillaume (September 2019, Frontiers in Marine Science)
4. Mechanisms Driving the Dispersal of Hydrothermal Iron From the Northern Mid Atlantic Ridge

   https://doi.org/10.1029/2022GL100615  

   Tagliabue, Alessandro; Lough, Alastair J. M.; Vic, Clément; Roussenov, Vassil; Gula, Jonathan; Lohan, Maeve C.; Resing, Joseph A.; Williams, Richard G. (November 2022, Geophysical Research Letters)

   Abstract The dispersal of dissolved iron (DFe) from hydrothermal vents is poorly constrained. Combining field observations and a modeling hierarchy, we find the dispersal of DFe from the Trans‐Atlantic‐Geotraverse vent site occurs predominantly in the colloidal phase and is controlled by multiple physical processes. Enhanced mixing near the seafloor and transport through fracture zones at fine‐scales interacts with the wider ocean circulation to drive predominant westward DFe dispersal away from the Mid‐Atlantic ridge at the 100 km scale. In contrast, diapycnal mixing predominantly drives northward DFe transport within the ridge axial valley. The observed DFe dispersal is not reproduced by the coarse resolution ocean models typically used to assess ocean iron cycling due to their omission of local topography and mixing. Unless biogeochemical models account for fine‐scale physics and colloidal Fe, they will inaccurately represent DFe dispersal from axial valley ridge systems, which make up half of the global ocean ridge crest. 

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5. Uppermost Mantle Velocity beneath the Mid-Atlantic Ridge and Transform Faults in the Equatorial Atlantic Ocean

   https://doi.org/10.1785/0120200248  

   de Melo, Guilherme W.; Parnell-Turner, Ross; Dziak, Robert P.; Smith, Deborah K.; Maia, Marcia; do Nascimento, Aderson F.; Royer, Jean-Yves (December 2020, Bulletin of the Seismological Society of America)

   null (Ed.)

   ABSTRACT Seismic rays traveling just below the Moho provide insights into the thermal and compositional properties of the upper mantle and can be detected as Pn phases from regional earthquakes. Such phases are routinely identified in the continents, but in the oceans, detection of Pn phases is limited by a lack of long-term instrument deployments. We present estimates of upper-mantle velocity in the equatorial Atlantic Ocean from Pn arrivals beneath, and flanking, the Mid-Atlantic Ridge and across several transform faults. We analyzed waveforms from 50 earthquakes with magnitude Mw>3.5, recorded over 12 months in 2012–2013 by five autonomous hydrophones and a broadband seismograph located on the St. Peter and St. Paul archipelago. The resulting catalog of 152 ray paths allows us to resolve spatial variations in upper-mantle velocities, which are consistent with estimates from nearby wide-angle seismic experiments. We find relatively high velocities near the St. Paul transform system (∼8.4  km s−1), compared with lower ridge-parallel velocities (∼7.7  km s−1). Hence, this method is able to resolve ridge-transform scale velocity variations. Ray paths in the lithosphere younger than 10 Ma have mean velocities of 7.9±0.5  km s−1, which is slightly lower than those sampled in the lithosphere older than 20 Ma (8.1  km±0.3  s−1). There is no apparent systematic relationship between velocity and ray azimuth, which could be due to a thickened lithosphere or complex mantle upwelling, although uncertainties in our velocity estimates may obscure such patterns. We also do not find any correlation between Pn velocity and shear-wave speeds from the global SL2013sv model at depths <150  km. Our results demonstrate that data from long-term deployments of autonomous hydrophones can be used to obtain rare and insightful estimates of uppermost mantle velocities over hundreds of kilometers in otherwise inaccessible parts of the deep oceans. 

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