Determining the cooling history of in situ lower oceanic crust—Atlantis Bank, SW Indian Ridge

John, Barbara E.; Foster, David A.; Murphy, Janice M.; Cheadle, M. J.; Baines, A. Graham; Fanning, Christopher; Copeland, Peter

doi:10.1016/j.epsl.2004.02.014

Cited by 91 publications

(88 citation statements)

References 34 publications

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“…A significant reduction in cooling rates off axis may be fast enough so the peridotites were able to move through the temperature interval of serpentinization and acquire the majority of their remanence over a very short time interval, resulting in the coherent polarity reversal we observe. Fast cooling rates due to hydrothermal circulation have been estimated in the gabbros at Atlantis Bank (SWIR) [John et al, 2004]. However, these cooling rates were associated with mantle temperatures that are much higher than the 200-400° C required for serpentinization and is it unlikely that a rapid cooling rate process can explain the initial dip of the polarity boundary.…”

Section: Thermal Modelingmentioning

confidence: 95%

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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Section: Thermal Modelingmentioning

confidence: 95%

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

Williams¹

2007

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“…Rocks from Ocean Drilling Program (ODP) Hole 735B and from submersible dives at Atlantis Bank include olivine gabbro, olivine gabbronorite, and oxide gabbro with minor felsic veins (7). Fractionated rocks, including oxide gabbro, comprise È25% of Atlantis Bank and commonly host trace minerals (e.g., zircon) suitable for U-Pb isotopic dating (17). Pb/U zircon ages from ODP Hole 735B range from 11.3 million years ago (Ma) (18) to 11.93 T 0.14 Ma (17).…”

mentioning

confidence: 99%

“…Fractionated rocks, including oxide gabbro, comprise È25% of Atlantis Bank and commonly host trace minerals (e.g., zircon) suitable for U-Pb isotopic dating (17). Pb/U zircon ages from ODP Hole 735B range from 11.3 million years ago (Ma) (18) to 11.93 T 0.14 Ma (17).…”

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confidence: 99%

Dating the Growth of Oceanic Crust at a Slow-Spreading Ridge

Schwartz

John

Cheadle

et al. 2005

Science

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Nineteen uranium-lead zircon ages of lower crustal gabbros from Atlantis Bank, Southwest Indian Ridge, constrain the growth and construction of oceanic crust at this slow-spreading midocean ridge. Approximately 75% of the gabbros accreted within error of the predicted seafloor magnetic age, whereas È25% are significantly older. These anomalously old samples suggest either spatially varying stochastic intrusion at the ridge axis or, more likely, crystallization of older gabbros at depths of È5 to 18 kilometers below the base of crust in the cold, axial lithosphere, which were uplifted and intruded by shallow-level magmas during the creation of Atlantis Bank.Slow-and ultraslow-spreading ridges with spreading rates of G55 mm/year (1) constitute nearly 60% of the total length of midocean ridges. Results from a variety of studies (2-7) indicate that slow-and ultraslow-spreading oceanic crust is dominantly created by the emplacement of small magma bodies of up to 500 m in thickness (7) into zones of par-

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“…Detailed observations and samplings conducted by drilling (ODP Holes 735B and 1105A), dredging, manned submersible and ROV revealed that Atlantis Bank is a typical oceanic core complex, that is an uplifted block of lower oceanic crust and upper mantle by detachment faulting (e.g., Dick et al, 2000;John et al, 2004;Baines et al, 2008). John et al (2004) estimated a cooling rate of 1600°C/myr for temperatures between 850°C and 350°C by thermochronological approach on the Hole 735B rocks. Coogan et al (2007) determined a cooling rate of the order of 10 3 -10 4°C /myr of the Hole 735B gabbros between 1000°C and 600°C using Ca-in-olivine geospeedmeter.…”

Section: Applicationsmentioning

confidence: 99%

A procedure for calculating a consistent set of closure temperatures and cooling rate using Dodson’s formula

Maeda

Zeniya

Kuramoto

et al. 2011

Jour. Geol. Soc. Japan

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Determining the cooling history of in situ lower oceanic crust—Atlantis Bank, SW Indian Ridge

Cited by 91 publications

References 34 publications

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

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

Dating the Growth of Oceanic Crust at a Slow-Spreading Ridge

A procedure for calculating a consistent set of closure temperatures and cooling rate using Dodson’s formula

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