Segmentation and crustal structure of the western Mid‐Atlantic Ridge flank, 25°25′–27°10′N and 0–29 m.y.

Tucholke, Brian E.; Lin, Jian; Kleinrock, Martin C.; Tivey, Maurice A.; Reed, Thomas B.; Goff, John A.; Jaroslow, Gary E.

doi:10.1029/96jb03896

Cited by 132 publications

(151 citation statements)

References 60 publications

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“…Ma and the increase at 16-24 Ma (Figure 6a). However, the peak in seamount abundance at 20-24 Ma is coeval with a major plate reorientation event [Tucholke et al, 1997a] and we cannot discount the possibility that this event affected seamount production. The decline in seamount population density at 24-28 Ma is not a sedimentation effect and probably reflects a real decrease in seamount production.…”

Section: Modification Of Seamounts During Transport Off Axismentioning

confidence: 99%

“…We To investigate temporal changes in the population and shape parameters, seamounts were assigned the same age as the underlying crust, as dated from magnetic anomalies [Tucholke et al,' 1997a]. Seamounts located on the inner rift valley floor are referred to as axial seamounts and have ages less than or equal to •0.6 Ma; those located outside the inner rift valley floor are considered to be off-axis seamounts and range in age from •0.6-29 Ma.…”

Section: Study Areamentioning

confidence: 99%

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Record of seamount production and off‐axis evolution in the western North Atlantic Ocean, 25°25′–27°10′N

Jaroslow¹,

Smith²,

Tucholke³

2000

J. Geophys. Res.

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Beyond the crest of the rift mountains (>4 Ma crust) faulting is no longer active, and changes in the off-axis seamount population reflect crustal aging processes as well as temporal changes in seamount production that occurred at the ridge axis. Estimates of population density for off-axis seamounts show a positive correlation to crustal thickness inferred from analysis of gravity data, suggesting that increased seamount production accompanies increased magma input at the ridge axis. We find no systematic variations in seamount population density along isochron within individual ridge segments. Possible explanations are that along-axis production of seamounts is uniform or that seamount production is enhanced in some regions (e.g., segment centers), but many seamounts do not meet our counting criteria because they are masked by younger volcanic eruptions and low-relief flows.

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Section: Modification Of Seamounts During Transport Off Axismentioning

confidence: 99%

Section: Study Areamentioning

confidence: 99%

Record of seamount production and off‐axis evolution in the western North Atlantic Ocean, 25°25′–27°10′N

Jaroslow¹,

Smith²,

Tucholke³

2000

J. Geophys. Res.

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“…at 22-24 Ma [Tucholke et al, 1996], which was also recorded by the Kane FZ [Tucholke and Schouten, 1988]. We thus remap the data by rotating crust younger than 20 Ma by 10°t owards the west, and crust older than 20 Ma by 190 to account for the change in plate motion.…”

Section: Bathymetry and Gravity Data Reductionmentioning

confidence: 75%

“…;Pariso et al, 1995;Tucholke et al, 1996]. These changes in seafloor morphology and gravity patterns indicate that the off-axis structure of the crust is both the product of magmatic accretion at the ridge axis, and of tectonic faulting in the rift valley walls that extensively modifies the magmatic crustal structure.…”

Section: Introductionmentioning

confidence: 99%

“…The dataset comprises primarily bathymetry and gravity from along-axis surveys of Purdy et al [1990] and Lin et al [1990], and from the off-axis survey in the ONR Acoustic Reverberations Special Research Program (ARSRP) study area [Tucholke et al, 1996]. We also use data collected in other areas in the same region, including 1) the MAR axis between 240 and 30'N ; 2) the TAG area [Rona and Gray, 1980]; the MAR axis both 3) north [Fujimoto et al, in press] and 4) south of the Kane FZ [Morris and Detrick, 1991].…”

Section: Bathymetry and Gravity Data Reductionmentioning

confidence: 99%

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Ridge segmentation, tectonic evolution and rheology of slow-spreading oceanic crust

Escartı́n¹

1996

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Two-thirds of the Earth's surface is oceanic crust formed by magmatic and tectonic processes along mid-ocean ridges. Slow-spreading ridges, such as the Mid-Atlantic Ridge, are discontinuous and composed of ridge segments. Segments are thus fundamental units of magmatic accretion and tectonic deformation that control the evolution of the crust. The objective of this Thesis is to constrain the tectonic processes that occur at the scale of slowspreading segments, to identify the factors controlling segment propagation, and to provide constraints on lithospheric strength with laboratory deformation experiments.In chapter 2, bathymetry and gravity from various areas along the global mid-ocean ridge system are analyzed to quantify systematic variations at the scale of individual segments. There is a marked asymmetry in bathymetry and gravity in the vicinity of segment offsets. We develop a model of faulting to explain these observations. Low-angle faults appear to accommodate tectonic extension at the inside corners of ridge-offset intersections, and result in substantially uplifted terrain with thin crust with respect to that at the outside corners or centers of segments.Results from Chapter 3 indicate that the crust magmatically emplaced on axis is not maintained off-axis. This transition is revealed by both statistical and spectral analyses of bathymetry and gravity. Tectonic extension varies along the length of a segment, resulting in thinning and uplift of the crust at ridge-offset inside corners, and a decorrelation between bathymetry and gravity patterns. Tectonic deformation substantially reshapes the oceanic crust that is magmatically emplaced on-axis, and strongly controls the crustal structure and seafloor morphology off-axis.Satellite gravity data over the Atlantic shown in Chapter 4 reveal a complex history of ridge segmentation, and provides constraints on the processes driving the propagation of segments. The pattern of segmentation is controlled mainly by the geometry of the ridge axis, and secondarily by hot spots. Segments migrate primarily down regional gradients associated with hot spot swells. However, the lack of correlation between gradients and propagation rate, and the propagation up gradient of some offsets, suggest that additional factors control propagation (e.g., variations in lithospheric strength). Most non-transform offsets are short-lived and migrating, while transform offsets are long-lived and stable.Both the propagation of segments (Chapter 4) tectonism along a segment (Chapters 2 and 3) are controlled by the lithospheric rheology. In Chapter 5 I present results from laboratory deformation experiments on serpentinite. These experiments demonstrate that serpentinites are considerably weaker than peridotites or gabbros, display a non-dilatant style of brittle deformation, and strain is accommodated by shear cracking. Serpentinites may weaken the lithosphere, enhance strain localization along faults, and control the style of faulting. Thesis supervisor:Jian Lin Title:Associate...

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Spatial and temporal variations in crustal production at the Mid‐Atlantic Ridge, 25°N–27°30′N and 0–27 Ma

2015

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We use high-resolution multibeam bathymetry, shipboard gravity, side-scan sonar images, and magnetic anomaly data collected on conjugate flanks of the Mid-Atlantic Ridge at 25°N-27°30′N and out tõ 27 Ma crust to investigate the crustal evolution of the ridge. Substantial variations in crustal structure and thickness are observed both along and across isochrons. Along isochrons within spreading segments, there are distinct differences in seafloor morphology and gravity-derived crustal thickness between inside and outside corners. Inside corners are associated with shallow depths, thin crust, and enhanced normal faulting while outside corners have greater depths, thicker crust, and more limited faulting. Across-isochrons, systematic variations in crustal thickness are observed at two different timescales, one at~2-3 Myr and another at >10 Myr, and these are attributed to temporal changes in melt supply at the ridge axis. The shorter-term variations mostly are in-phase between conjugate ridge flanks, although the actual crustal thickness can be significantly different on the two flanks at any given time. We observe no correlation between crustal thickness and spreading rate. Thus, during periods of low melt supply, tectonic extension must increase to accommodate the full plate separation rate. This extension commonly is concentrated in long-lived faults on only one side of the axial valley, resulting in strong across-axis asymmetries in crustal thickness and seafloor morphology. The thin-crust flank has few volcanic features and exhibits elevated, blocky topography with large-offset, often irregular faults, while the conjugate thicker-crust flank shows shorter-offset, regular faulting, and common volcanic features. The variations in melt supply at the ridge axis most likely are caused either by episodic convection in the subaxial mantle or by variable melting of chemically heterogeneous mantle.

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Segmentation and crustal structure of the western Mid‐Atlantic Ridge flank, 25°25′–27°10′N and 0–29 m.y.

Cited by 132 publications

References 60 publications

Record of seamount production and off‐axis evolution in the western North Atlantic Ocean, 25°25′–27°10′N

Record of seamount production and off‐axis evolution in the western North Atlantic Ocean, 25°25′–27°10′N

Ridge segmentation, tectonic evolution and rheology of slow-spreading oceanic crust

Spatial and temporal variations in crustal production at the Mid‐Atlantic Ridge, 25°N–27°30′N and 0–27 Ma

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