Constraints on crustal structure of adjacent OCCs and segment boundaries at 13°N on the Mid-Atlantic Ridge

Peirce, C.; Reveley, Graham; Robinson, A. H.; Funnell, M. J.; Searle, R. C.; Simão, Nuno; Macleod, Christopher; Reston, T. J.

doi:10.1093/gji/ggz074

Cited by 19 publications

(43 citation statements)

References 111 publications

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“…1). The results of P-wave seismic and gravity modelling along Profile R are reported by Peirce et al (2019a). This 2-D profile also traversed the 3-D tomographic seismic grid acquired over the 13°20'N and 13°30'N OCCs (henceforth referred to as the 1320 and 1330 OCCs - Fig.…”

Section: This Studymentioning

confidence: 80%

“…The 13°N segment is bounded to the north by the Fifteen-Twenty FZ, and to the south by the Marathon TF-FZ system, with the Mercurius FZ located ~50 km further south. At the southern ridge-transform intersection, between the 13°N segment and Marathon FZ, there is a prominent inside corner high (Peirce et al, 2019a and references therein). The 1330 OCC lies in the equivalent location of an inside corner with respect to a deviation in trend in ridge axis morphology to its north (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

“…The P-wave velocity-depth and density-depth crustal structures along an ~200 km-long 2-D transect traversing all of these features -Profile R -was described by Peirce et al (2019a). The primary conclusion of that study was that each OCC is structurally distinct and is exhumed along its own detachment fault.…”

Section: Geological Settingmentioning

confidence: 99%

“…The FAST method of Zelt and Barton (1998) was adopted for travel time inversion, using the approach outlined in Peirce et al (2019a) for the P-wave model derived for Profile R. The model was discretized on a 0.25 km by 0.25 km uniform square mesh (forward cell size). The seabed interface, kept fixed throughout inversion, was created by sampling the bathymetry data at 0.25 km intervals along profile, and projecting this and the OBS and shot locations into kilometre distance along profile relative to a model 0,0 located at 11° 56.76'N / 44° 58.2'W ( Fig.…”

Section: Two-dimensional Modellingmentioning

confidence: 99%

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Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Peirce

Robinson

Funnell

et al. 2020

Geophysical Journal International

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SUMMARY A region of oceanic core complexes (OCCs) exists at 13°N on the Mid-Atlantic Ridge that is regarded as a type site. This site includes two OCCs at 13°20′N and 13°30′N, thought to be in the active and dying stages of evolution, and two together called the Ashadze Complex (centred at 13°05′N) that are considered to be relict. Here we describe the results of S-wave seismic modelling along an ∼200-km-long 2-D transect traversing, south-to-north, through both the Mercurius and Marathon fracture zones, the southern outside corner of the 13°N segment, the OCCs, the ridge axis deviation in trend centred at 13°35′N, and the youngest oceanic crust of the eastern ridge flank to the north. Our inversion model, and the corresponding Vp/Vs ratio, show that the majority of the crust beneath the 13°30′N OCC comprises metamorphosed lithologies that have been exhumed to the shallowest subseabed level, while basaltic lithologies underlie the 13°20′N OCC. The transition between these contrasting crustal structures occurs over a distance of <5 km, and extends to at least ∼2 km depth below seafloor. The northern and southern OCCs of the Ashadze Complex have contrasting structures at shallow depth, with the northern OCC having a faster S-wave velocity in the upper crust. A Vp/Vs ratio of >1.9 (and equivalent Poisson's ratio of >0.3) indicates exhumed and/or metamorphosed lithologies beneath the bathymetric depression between them and within the crust beneath the southern OCC. Between the northern and southern flanks of the Marathon fracture zone and northern flank of Mercurius fracture zone, the lower crust has a relatively low Vp/Vs ratio suggesting that the deformation associated with Marathon fracture zone, which facilitates fluid ingress, extends laterally within the lower crust. Marathon fracture zone itself is underlain by a broad zone of low S-wave velocity (∼2.0 km s−1) up to ∼20 km wide from the seabed to at least the mid-crust, that is mirrored in a high Vp/Vs ratio and lower density, particularly deeper than ∼1 km below seabed within its bathymetric footprint. Volcanic domains are highlighted by a low Vp/Vs ratio of <1.6 (and equivalent Poisson's ratio of <0.15). Our combined seismic and density models favour the localized model of OCC evolution. They also show a considerable ridge-parallel variability in the amount and distribution of magmatic versus metamorphosed crust. Our results suggest that the current focus of magmatism lies to the north of the 13°20′N OCC, where the magmatic accretion-type seabed morphology observed is mirrored in the pattern of microseismicity, suggesting that its inward-facing median-valley-wall fault may link to the 13°20′N OCC detachment surface. Magmatism and active faulting behind (to the west) the footwall breakaway of the 13°30′N OCC, and the microseismicity concentrated in a band along its southern flank, suggest a readjustment of ridge geometry along axis is underway. As part of this, a transform offset is forming that will ultimately accommodate the 13°30′N OCC in its inside corner on the eastern flank of the ridge axis to the north.

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Section: This Studymentioning

confidence: 80%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Two-dimensional Modellingmentioning

confidence: 99%

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Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Peirce

Robinson

Funnell

et al. 2020

Geophysical Journal International

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“…An assumption implicit to this model, where the deeper trailing sides reflect the isostatic adjustment of a thinner crustal section, is that fracture zones do not become locked at RTIs immediately upon transform-to-fracture zone transition. This assumption is supported by a recent seismic study that indicates vertical movement occurs across the Marathon fracture zone at least until~1 Myr after transition from transform fault to fracture zone (Peirce et al, 2019). It challenges the common view that fracture zones are locked and differential subsidence across them is accommodated by nonisostatic lithospheric flexure instead of vertical slip (e.g., Sandwell & Schubert, 1982).…”

Section: Discussionmentioning

confidence: 95%

Distinctive Seafloor Fabric Produced Near Western Versus Eastern Ridge‐Transform Intersections of the Northern Mid‐Atlantic Ridge: Possible Influence of Ridge Migration

Cormier

Sloan

2019

Geochem Geophys Geosyst

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Multibeam bathymetry compiled along fracture zones of the northern Atlantic reveals a striking morphological asymmetry. Seafloor fabric produced at western ridge‐transform intersections (RTIs) tends to consist of linear ridges, small in amplitude, and regularly spaced, and oceanic core complexes (OCCs) occur infrequently. In contrast, seafloor fabric produced at eastern RTIs is more irregular and blocky and displays characteristics usually associated with melt‐poor accretion: These include more than double the occurrence of OCCs as well as greater seafloor depths, even where seafloor is younger than that on the opposite side of the fracture zone. We propose that this asymmetry is a consequence of the westward migration of the Mid‐Atlantic Ridge. Such migration is expected to result in an enhanced melt supply at leading (western) RTIs compared to trailing (eastern) RTIs. The morphological asymmetry is observed for ridge offsets of ~40 to ~200 km, a range that may be related to the width of melting regimes that supply ridge segments. At slow spreading ridges, contrasting melt supplies across fracture zones may therefore be best expressed in the distinct seafloor fabrics preserved beyond the dynamically maintained relief of the axial rift valley and walls rather than in the contrasting axial depths documented for faster spreading ridges. Although OCCs appear to form preferentially at spreading rates lower than 30 mm/year, their common occurrence along the northern Mid‐Atlantic Ridge may also reflect the significantly higher rates at which it is migrating compared to the southern Mid‐Atlantic Ridge.

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Seismic structure of the St. Paul Fracture Zone and Late Cretaceous to Mid Eocene oceanic crust in the equatorial Atlantic Ocean near 18°W

Growe

Grevemeyer

Singh

et al. 2021

Preprint

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Constraints on crustal structure of adjacent OCCs and segment boundaries at 13°N on the Mid-Atlantic Ridge

Cited by 19 publications

References 111 publications

Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Distinctive Seafloor Fabric Produced Near Western Versus Eastern Ridge‐Transform Intersections of the Northern Mid‐Atlantic Ridge: Possible Influence of Ridge Migration

Seismic structure of the St. Paul Fracture Zone and Late Cretaceous to Mid Eocene oceanic crust in the equatorial Atlantic Ocean near 18°W

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Constraints on crustal structure of adjacent OCCs and segment boundaries at 13°N on the Mid-Atlantic Ridge

Cited by 19 publications

References 111 publications

Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge

Distinctive Seafloor Fabric Produced Near Western Versus Eastern Ridge‐Transform Intersections of the Northern Mid‐Atlantic Ridge: Possible Influence of Ridge Migration

Seismic structure of the St. Paul Fracture Zone and Late Cretaceous to Mid Eocene oceanic crust in the equatorial Atlantic Ocean near 18&deg;W

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Product

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Seismic structure of the St. Paul Fracture Zone and Late Cretaceous to Mid Eocene oceanic crust in the equatorial Atlantic Ocean near 18°W