Spreading rate dependence of the axial topography and gravity of the Mid‐Atlantic ridge between 22°N and 38°N

Detailed maps of free-air, Bouguer, and residual gravity anomalies for a survey area 250 km wide across the Mid-Atlantic Ridge between 45° and 46 °N have been compiled. The Bouguer anomaly was terrain-corrected to a radius of 40 km. The residual anomaly was computed from the terrain-corrected Bouguer anomaly using an empirical linear relationship between the Bouguer anomaly and the bathymetry to predict a 'regional' Bouguer anomaly from the depth data. North–south and east–west trends in the gravity data are enhanced in the residual anomaly; and it is suggested that at least one short east–west transform fault may offset the ridge in a right-lateral sense. The offset is presumably a response to a change in sea-floor spreading direction from west–northwest/east–southeast to west/east about 10 m.y. ago. A change in spreading rate may have occurred at the same time. A difference in accretion rate on either side of the ridge axis is indicated by asymmetry in the gravity data and by differences in the topographic compensation across the axis. Variations in the relationship of terrain-corrected Bouguer anomaly to bathymetry within the survey area suggest that a density deficiency or buoyant forces in the upper mantle are responsible for the overall elevation of the crestal mountain region but that the topography of the high-fractured plateau may be partially compensated by undulations of the crust–mantle interface.

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Spreading-rate dependence of melt extraction at mid-ocean ridges from mantle seismic refraction data

Nature ◽

10.1038/nature03140 ◽

2004 ◽

Vol 432 (7018) ◽

pp. 744-747 ◽

Cited By ~ 69

Author(s):

Daniel Lizarralde ◽

James B. Gaherty ◽

John A. Collins ◽

Greg Hirth ◽

Sangmyung D. Kim

Keyword(s):

Seismic Refraction ◽

Spreading Rate ◽

Rate Dependence ◽

Melt Extraction ◽

Ocean Ridges ◽

Seismic Refraction Data ◽

Refraction Data

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Mid-Atlantic Ridge at 37° N: Geophysical anomalies in the area of Leg 37 drilling

Canadian Journal of Earth Sciences ◽

10.1139/e77-067 ◽

1977 ◽

Vol 14 (4) ◽

pp. 664-673 ◽

Cited By ~ 1

Author(s):

D. I. Ross ◽

R. K. H. Falconer

Keyword(s):

Magnetic Anomaly ◽

Fracture Zone ◽

Spreading Rate ◽

Geophysical Data ◽

Fracture Zones ◽

Ridge Crest ◽

Layer 2 ◽

Mid Atlantic Ridge ◽

Drilling Site ◽

Geophysical Anomalies

Geophysical data collected as part of Leg 37 are compiled with more recent data collected for new IPOD drilling site surveys. Bathymetric and magnetic maps covering the area of sites 332–335 are presented. On the basis of magnetic anomaly correlations it is suggested that site 334 is on normal crust between fracture zones A and B and not closer than 15 km to either fracture zone. Magnetic anomaly inversion is applied to a composite profile, extending from the ridge crest out to beyond anomaly 5. It shows a definite change in spreading rate at 4.7 ± 0.5 Ma. Average rates for the periods 0–4.7 Ma and 4.7–10 Ma are 10.2 ± 0.9 mm/yr and 14.0 ± 1.9 mm/yr respectively. The inversion results are consistent with a simple magnetic source layer 2 km thick.

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The spreading-rate dependence of anomalous skewness of Pacific plate magnetic anomaly 32: Revisited

Lithosphere ◽

10.1130/l167.1 ◽

2011 ◽

Vol 3 (6) ◽

pp. 371-378 ◽

Cited By ~ 7

Author(s):

Emilia A. Koivisto ◽

Richard G. Gordon ◽

Jérôme Dyment ◽

Jafar Arkani-Hamed

Keyword(s):

Magnetic Anomaly ◽

Spreading Rate ◽

Pacific Plate ◽

Rate Dependence

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Microseismicity and lithosphere thickness at a nearly amagmatic mid-ocean ridge

10.21203/rs.3.rs-1046015/v1 ◽

2021 ◽

Author(s):

Jie Chen ◽

Wayne Crawford ◽

Mathilde Cannat

Keyword(s):

Hanging Wall ◽

Oceanic Lithosphere ◽

Spreading Rate ◽

Southwest Indian Ridge ◽

Flip Flop ◽

Detachment Faults ◽

Ocean Ridges ◽

Tectonic Earthquakes ◽

Mid Atlantic Ridge ◽

Ocean Ridge

Abstract Successive flip-flop detachment faults in a nearly-amagmatic region of the ultraslow-spreading Southwest Indian Ridge (SWIR) at 64°30'E accommodate ~100% of plate divergence, with mostly ultramafic seafloor. As magma is the main heat carrier to the oceanic lithosphere, the nearly-amagmatic SWIR 64°30'E is expected to have a very thick lithosphere. Here, our microseismicity data shows a 15-km thick seismogenic lithosphere, actually thinner than the more magmatic SWIR Dragon Flag detachment with the same spreading rate. This challenges current models of how spreading rate and melt supply control the thermal regime of mid-ocean ridges. Microearthquakes with normal focal mechanisms are colocated with seismically imaged damage zones of the detachment and reveal hanging-wall normal faulting, which is not seen at more magmatic detachments at the SWIR or the Mid-Atlantic Ridge. We also document a two-day seismic swarm, interpret as caused by an upward-migrating melt intrusion in the detachment footwall (6-11 km), triggering a sequence of shallower (~1.5 km) tectonic earthquakes in the detachment fault plane. This points to a possible link between sparse magmatism and tectonic failure at melt-poor ultraslow ridges.

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