Characteristics and evolution of the segmentation of the Mid-Atlantic Ridge between 20°N and 24°N during the last 10 million years

Gente, Pascal; Pockalny, R. A.; Durand, C.; Deplus, Christine; Maia, Márcia; Ceuleneer, Georges; Mével, Catherine; Cannat, Mathilde; Laverne, Christine

doi:10.1016/0012-821x(94)00233-o

Cited by 128 publications

(145 citation statements)

References 38 publications

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“…Between TFs along slow-spreading ridges, NTOs divide the axis into second-order segments with lengths of 20-100 km ( Fig. 9a, b; Table 1; Sempéré et al 1993;Gente et al 1995;Thibaud et al 1998). NTOs have typical offsets of 15 -30 km (e.g.…”

Section: Geophysical Properties Of Discontinuities and Ridge Segmentsmentioning

confidence: 99%

Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

Carbotte

Smith

Cannat

et al. 2015

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Mid-ocean ridges display tectonic segmentation defined by discontinuities of the axial zone, and geophysical and geochemical observations suggest segmentation of the underlying magmatic plumbing system. Here, observations of tectonic and magmatic segmentation at ridges spreading from fast to ultraslow rates are reviewed in light of influential concepts of ridge segmentation, including the notion of hierarchical segmentation, spreading cells and centralized v. multiple supply of mantle melts. The observations support the concept of quasi-regularly spaced principal magmatic segments, which are 30-50 km long on average at fast-to slow-spreading ridges and fed by melt accumulations in the shallow asthenosphere. Changes in ridge properties approaching or crossing transform faults are often comparable with those observed at smaller offsets, and even very small discontinuities can be major boundaries in ridge properties. Thus, hierarchical segmentation models that suggest large-scale transform fault-bounded segmentation arises from deeper level processes in the asthenosphere than the finer-scale segmentation are not generally supported. The boundaries between some but not all principal magmatic segments defined by ridge axis geophysical properties coincide with geochemical boundaries reflecting changes in source composition or melting processes. Where geochemical boundaries occur, they can coincide with discontinuities of a wide range of scales.Discovery and interpretations of mid-ocean ridge (MOR) segmentation: historical review

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Section: Geophysical Properties Of Discontinuities and Ridge Segmentsmentioning

confidence: 99%

Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

Carbotte

Smith

Cannat

et al. 2015

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“…Two large scale sea surface magnetic surveys were conducted in the region south of the Kane Transform Fault known as the MARK (Mid-Atlantic Ridge at Kane) area and encompass Kane Megamullion (RC2511 Schulz et al, 1988] and Gente et al, 1995;Pockalny et al, 1995;Schulz et al, 1988] ). The magnetic lineations identified in these studies indicate asymmetric spreading in the region, with faster spreading rates to the west for at least the last 10 Ma (-14 km/Ma to the west and 11 km/Ma to the east ).…”

Section: Regional Settingmentioning

confidence: 99%

Oceanic lithosphere magnetization : marine magnetic investigations of crustal accretion and tectonic processes in mid-ocean ridge environments

Williams¹

2007

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The origin of symmetric alternating magnetic polarity stripes on the seafloor is investigated in two marine environments; along the ridge axis of the fast spreading East Pacific Rise (EPR) (90 25'-90 55'N) and at Kane Megamullion (KMM) (230 40'N), near the intersection of the slow-spreading Mid Atlantic Ridge with Kane Transform Fault. Marine magnetic anomalies and magnetic properties of seafloor samples are combined to characterize the magnetic source layer in both locations. The EPR study suggests that along-axis variations in the observed axial magnetic anomaly result from changing source layer thickness alone, consistent with observed changes in seismic Layer 2a. The extrusive basalts of the upper crust therefore constitute the magnetic source layer along the ridge axis and long term crustal accretion patterns are reflected in the appearance of the axial anomaly. At KMM the C2r.2r/C2An. In (-2.581 Ma) polarity reversal boundary cuts through lower crust (gabbro) and upper mantle (serpentinized peridotites) rocks exposed by a detachment fault on the seafloor, indicating that these lithologies can systematically record a magnetic signal. Both lithologies have stable remanent magnetization, capable of contributing to the magnetic source layer. The geometry of the polarity boundary changes from the northern to the central regions of KMM and is believed to be related to changing lithology. In the northern region, interpreted to be a gabbro pluton, the boundary dips away from the ridge axis and is consistent with a rotated conductively cooled isotherm. In the central region the gabbros have been removed and the polarity boundary, which resides in serpentinized peridotite, dips towards the ridge axis and is thought to represent an alteration front. The linear appearance of the polarity boundary across both regions indicates that the two lithologies acquired their magnetic remanence during approximately the same time interval. Seismic events caused by detachment faulting at Kane and Atlantis Transform Faults are investigated using hydroacoustic waves (T-phases) recorded by a hydrophone array. Observations and ray trace models of event propagation show bathymetric blockage along propagation paths, but suggest current models of T-phase excitation and propagation need to be improved to explain observed characteristics of T-phase data. AcknowledgementsA thesis may have your name on the title page, but it is truly the joint effort of many people that gets you through to the end of a Ph.D.. I am very grateful to my main thesis advisor Maurice Tivey, who taught me so much about magnetics and always had time to talk about my research when I knocked on his door. Learning to write a scientific paper has been a long learning curve and I really appreciate Maurice's editing skills and stamina for reading drafts of my papers. I have been lucky enough to be in the right place at the right time to work on some excellent datasets, particularly the Kane Megamullion data that makes up the majority of my thesis, and I thank Mau...

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“…General bathymetric maps of (A) the Kane Fracture Zone and (B) Leg 153 sites investigated in this study. Bathymetric data from Gente et al (1995). ODP sites are shown as labeled, solid circles.…”

Section: Methodsmentioning

confidence: 99%

“…This hole demonstrated the drillability of the ultramafic massif (Detrick et al, 1988), as rapid penetration was achieved in only a few days of drilling. During numerous submersible and camera expeditions to the region, these massifs have been extensively mapped and sampled (e.g., Karson and Dick, 1983;Karson et al, 1987;Gente et al, 1989Gente et al, , 1995Cannatetal., 1993).…”

Section: Introductionmentioning

confidence: 99%

Comparison of major- and trace-element geochemistry of abyssal peridotites and mafic plutonic rocks with basalts from the MARK region of the Mid-Atlantic Ridge

Casey¹

1997

Proceedings of the Ocean Drilling Program

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Holes 920B, 920D, 921A, 921B, 921C, 921D, 921E, 922A, 922B, and 923A were drilled into crust of the Mid-Atlantic Ridge near the Kane Fracture Zone (MARK) area during Leg 153 of the Ocean Drilling Program. Holes 920B and 920D were drilled into an ultramafic massif and Sites 921, 922, and 923 were drilled into a gabbroic massif, both of which are located on the western rift valley wall of the Mid-Atlantic Ridge south of the Kane Transform. Bulk-rock major-, trace-, and rare-earth element (REE) analyses of diabasic, gabbroic, and ultramafic rocks recovered from these holes are reported here. These bulk analyses are augmented by the results of mineral chemistry studies on a subset of the same samples.Large ranges in bulk-rock and mineral chemistry are documented from all rock types. Ultramafic rocks in Holes 920B and 920D are interpreted to be dominantly residual mantle, but they include variably fractionated ultramafic and mafic cumulates that have intrusive contacts with the residual mantle harzburgites. Bulk-rock major-and compatible trace-element abundances, as well as petrographic data for residual harzburgites, indicate that a fertile MORB mantle was depleted by -15% to 20% partial melting or 10%-15% if a more depleted mantle source, such as Tinaquillo Lherzolite, is chosen. The mean extent of melting is likely to have been approximately half of the maximum value computed based on the residuum. Incompatible traceelement data show, however, that this residuum may have been part of an open system and refertilized at late stages by melts flowing through a locally porous matrix and later by more channelized melts (veins) as the residuum became part of the mechanical lithosphere. The crystallization products of these late melts include disseminated magmatic clinopyroxene and narrow veins or composite veins of dunite, wehrlite, pyroxenite, and gabbroic rocks. Ultramafic vein samples are variably depleted to enriched in incompatible elements and span a wide range of fractionation extents based on bulk-rock and mineral chemistry. Melts calculated to have been in equilibrium with clinopyroxene in ultramafic and mafic samples from Site 920 vary widely. They are dominantly ultradepleted, but include some samples that are enriched in incompatible elements (Na and Ti) with respect to MARK basalts, glasses, and Leg 153 diabases. The range in composition cannot simply be explained by crystal fractionation of a single parental magma, but requires a broad range of parental melts or their derivatives to be in equilibrium with clinopyroxene. Bulk-rock and mineral chemistry studies of residual and cumulate ultramafic rocks support the notion of an open-system, near-fractional mantle melting column. The residual peridotites were also cut by late-stage, variably altered, highMgO (13-15 wt%) diabase dikes with quenched margins.Gabbroic samples from Sites 921, 922, and 923 drilled within the gabbroic massif likewise cover a broad spectrum of lithologies and compositions, and include troctolites, olivine gabbros, gabbros, oxid...

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Characteristics and evolution of the segmentation of the Mid-Atlantic Ridge between 20°N and 24°N during the last 10 million years

Cited by 128 publications

References 38 publications

Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

Oceanic lithosphere magnetization : marine magnetic investigations of crustal accretion and tectonic processes in mid-ocean ridge environments

Comparison of major- and trace-element geochemistry of abyssal peridotites and mafic plutonic rocks with basalts from the MARK region of the Mid-Atlantic Ridge

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