Crustal accretion and evolution at slow and ultra-slow spreading mid-ocean ridges

Hosford, Allegra

doi:10.1575/1912/3037

Cited by 7 publications

(3 citation statements)

References 78 publications

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“…Because seismic models in this area show that the entire upper crust (both the extrusive and intrusive components) is only 2–2.5 km thick [ Muller et al , 1997, 2000], the extrusive layer thickness predicted by magnetic modeling is inconsistent with the imaged crustal structure at segment AN‐1. In contrast, the crustal thickness variation required for the gabbroic source model (Figure 11b) agrees well, within error, with both seismic models [ Muller et al , 2000] and crustal thickness predictions from sea‐surface gravity data [ Hosford , 2001]. These results imply that on axis, the extrusive crust contributes a large but near‐constant amplitude to the crustal magnetization, while the lower crust produces the variation in that signal.…”

Section: Discussionsupporting

confidence: 71%

Crustal magnetization and accretion at the Southwest Indian Ridge near the Atlantis II fracture zone, 0–25 Ma

Hosford

Tivey

Matsumoto³

et al. 2003

J. Geophys. Res.

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[1] We analyze geophysical data that extend from 0 to 25-Myr-old seafloor on both flanks of the Southwest Indian Ridge (SWIR). Lineated marine magnetic anomalies are consistent and identifiable within the study area, even over seafloor lacking a basaltic upper crust. The full spreading rate of 14 km/Myr has remained nearly constant since at least 20 Ma, but crustal accretion has been highly asymmetric, with half rates of 8.5 and 5.5 km/Myr on the Antarctic and African flanks, respectively. This asymmetry may be unique to a $400 km wide corridor between large-offset fracture zones of the SWIR. In contrast to the Mid-Atlantic Ridge, crustal magnetization amplitudes correlate directly with seafloor topography along the present-day rift valleys. This pattern appears to be primarily a function of along-axis variations in crustal thickness, rather than magnetic mineralogy. Off-axis, magnetization amplitudes at paleo-segment ends are more positive than at paleo-segment midpoints, suggesting the presence of an induced component of magnetization within the lower crust or serpentinized upper mantle. Alteration of the magnetic source layer at paleo-segment midpoints reduces magnetization amplitudes by 70-80% within 20 Myr of accretion. Magnetic and Ocean Drilling Program (ODP) Hole 735B data suggest that the lower crust cooled quickly enough to lock in a primary thermoremanent magnetization that is in phase with that of the overlying upper crust. Thus magnetic polarity boundaries within the intrusive lower crust may be steeper than envisioned in prior models of ocean crustal magnetization. As the crust ages, the lower crust becomes increasingly important in preserving marine magnetic stripes.

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Section: Discussionsupporting

confidence: 71%

Crustal magnetization and accretion at the Southwest Indian Ridge near the Atlantis II fracture zone, 0–25 Ma

Hosford

Tivey

Matsumoto³

et al. 2003

J. Geophys. Res.

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110

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“…Extreme crustal attenuation during the initial opening of ocean basins (Chian, Keen, Reid, & Louden, 1995;Whitmarsh et al, 1996) and ultra-slow spreading of midocean ridges (Coakley & Cochran, 1998;Hosford, 2001;Louden, Osler, Srivastava, & Keen, 1996), appear to have created unusual crustal structure in many ocean basins. The Cayman Trough in the northwestern Caribbean (Fig.…”

Section: Introductionmentioning

confidence: 99%

The nature of the crust under Cayman Trough from gravity

Brink

Coleman

Dillon

2002

Marine and Petroleum Geology

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Considerable crustal thickness variations are inferred along Cayman Trough, a slow-spreading ocean basin in the Caribbean Sea, from modeling of the gravity field. The crust to a distance of 50 km from the spreading center is only 2 -3 km thick in agreement with dredge and dive results. Crustal thickness increases to , 5.5 km at distances between 100 and 430 km west of the spreading center and to 3.5-6 km at distances between 60 and 370 km east of the spreading center. The increase in thickness is interpreted to represent serpentinization of the uppermost mantle lithosphere, rather than a true increase in the volume of accreted ocean crust. Serpentinized peridotite rocks have indeed been dredged from the base of escarpments of oceanic crust rocks in Cayman Trough. Laboratory-measured density and P-wave speed of peridotite with 40 -50% serpentine are similar to the observed speed in published refraction results and to the inferred density from the model. Crustal thickness gradually increases to 7 -8 km at the far ends of the trough partially in areas where sea floor magnetic anomalies were identified. Basement depth becomes gradually shallower starting 250 km west of the rise and 340 km east of the rise, in contrast to the predicted trend of increasing depth to basement from cooling models of the oceanic lithosphere. The gradual increase in apparent crustal thickness and the shallowing trend of basement depth are interpreted to indicate that the deep distal parts of Cayman Trough are underlain by highly attenuated crust, not by a continuously accreted oceanic crust. Published by Elsevier Science Ltd.

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“…A seismic refraction experiment across the Atlantis Bank OCC at the western margin of this ridge segment suggests that average crustal thickness is 4 ± 1 km north and south of the OCC (Muller et al., 1997). Gravity modeling assuming a 4 km model crustal thickness indicates that thickness variations of ∼5 km are required to explain the observed range of gravity values in the area (Hosford, 2001). Serpentinized peridotite, gabbro, diabase, and basalt have been extensively recovered by dredging and drilling in the area of Atlantis Bank OCC (Dick et al., 2000, 2019), although no samples exist in the immediate vicinity of the data boxes analyzed here.…”

Section: Discussionmentioning

confidence: 99%

The Global Spectrum of Seafloor Morphology on Mid‐Ocean Ridge Flanks Related to Magma Supply

Tucholke,

Parnell‐Turner,

Smith

2023

JGR Solid Earth

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Magma supply likely exerts primary control on seafloor morphology of oceanic crust, but most studies have related morphology to spreading rate. Here we examine global patterns of morphology on mid‐ocean ridge (MOR) flanks in relation to magma supply derived from residual mantle Bouguer gravity anomaly (proxy for relative crustal thickness) and spreading rate. We use multibeam bathymetry to characterize morphology using both qualitative (descriptive) and quantitative approaches, and we compare results to both magma supply and spreading rate. Morphology becomes more isotropic and abyssal hills are more irregular and discontinuous as magma supply decreases, while roughness, area of steeper slopes, and anomalous fabric orientation increase. We interpret these changes to reflect changing magma distribution along‐axis, from large‐volume and spatially extensive to progressively reduced, increasingly localized, and more irregularly emplaced. Observed relations between crustal thickness and morphology imply that average thickness of purely magmatic crust in the Atlantic and parts of the Indian ridge system is significantly less than average seismically determined crust. Thus seismically defined crustal thickness in those regions likely includes significant non‐magmatic components such as serpentinized mantle. Excepting regions of extensive mantle exposure, most morphologic parameters that we examined are sensitive to estimated magma supply but not necessarily to spreading rate alone. We summarize our results in schematic models that relate morphologic variations to changes in magma supply and mantle serpentinization throughout the global MOR system. Finally, we note that combined qualitative and quantitative results of our study may be useful for developing automated morphologic classification schemes.

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Crustal accretion and evolution at slow and ultra-slow spreading mid-ocean ridges

Cited by 7 publications

References 78 publications

Crustal magnetization and accretion at the Southwest Indian Ridge near the Atlantis II fracture zone, 0–25 Ma

Crustal magnetization and accretion at the Southwest Indian Ridge near the Atlantis II fracture zone, 0–25 Ma

The nature of the crust under Cayman Trough from gravity

The Global Spectrum of Seafloor Morphology on Mid‐Ocean Ridge Flanks Related to Magma Supply

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