A new view of the mid-ocean ridge from the behaviour of ridge-axis discontinuities

Macdonald, Ken C.; Fox, Paul J.; Perram, Laura Jean; Eisen, M. F.; Haymon, Rachel M.; Miller, Stephen; Carbotte, S. M.; Cormier, Marie-Hélène; Shor, Alexander

doi:10.1038/335217a0

Cited by 425 publications

(336 citation statements)

References 32 publications

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“…It is also possible that the degree of communication and separation of the melt delivery systems along strike may vary with depth in the mantle and segregation style, which may themselves be influenced by the thickness, distribution and compositior of heterogeneous veins. A hierarchy of mantle flow and -next delivery systems may aid in the explanation of the hierarchical segmentation that may exist along spreading ridges Macdonald et al, 1988]. The contents of FeO and MgO in mantle melts are constrained by the fact that olivine is always a residual phase.…”

Section: Discussionmentioning

confidence: 99%

Petrological Systematics of Mid-Ocean Ridge Basalts: Constraints on Melt Generation Beneath Ocean Ridges

Langmuir

Klein

Plank

2013

Geophysical Monograph Series

671

390

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Mid-ocean ridge basalts (MORB) are a consequence of pressure-release melting beneath ocean ridges, and contain much information concerning melt formation, melt migration and heterogeneity within the upper mantle. MORB major element chemical systematics can be divided into global and local aspects, once they have been corrected for low pressure fractionation and interlaboratory biases. Regional average compositions for ridges unaffected by hot spots ("normal" ridges) can be used to define the global correlations among normalized Na20, FeO, TiO2 and Si02 contents, CaO/Al203 ratios, axial depth and crustal thickness. Back-arc basins show similar correlations, but are offset to lower FeO and TiO2 contents. Some hot spots, such as the Azores and Galapagos, disrupt the systematics of nearby ridges and have the opposite relationships between FeO, Na 20 and depth over distances of 1000 km.Local variations in basalt chemistry from slow-and fast-spreading ridges are distinct from one another. On slow-spreading ridges, correlations among the elements cross the global vector of variability at a high angle. On the fast-spreading East Pacific Rise (EPR), correlations among the elements are distinct from both global and slow-spreading compositional vectors, and involve two components of variation. Spreading rate does not control the global correlations, but influences the standard deviations of axial depth, crustal thickness, and MgO contents of basalts.Global correlations are not found in very incompatible trace elements, even for samples far from hot spots. Moderately compatible trace elements for normal ridges, however, correlate with the major elements. Trace element systematics are significantly different for the EPR and the mid-Atlantic Ridge (MAR). Normal portions of the MAR are very depleted in REE, with little variability; hot spots cause large long wavelength variations in REE abundances. Normal EPR basalts are significantly more enriched than MAR basalts from normal ridges, and still more enriched basalts can erupt sporadically along the entire length of the EPR. This leads to very different histograms of distribution for the data sets as a whole, and a very different distribution of chemistry along strike for the two ridges. Despite these differences, the mean Ce/Sm ratios from the two ridges are identical.Existing methods for calculating the major element compositions of mantle melts [Klein and Langmuir, 1987;McKenzie and Bickle, 1988;Niu and Batiza, 1991] are critically examined. New quantitative methods for mantle melting and high pressure fractionation are developed to evaluate the chemical consequences of melting and fractionation processes and mantle heterogeneity. The new methods rely on new equations for partition coefficients for the major elements between mantle minerals and melts. The melting calculations can be used to investigate the chemical compositions produced by small extents of melting or high pressures of melting that cannot yet be determined experimentally. Application of the new models to the ...

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Section: Discussionmentioning

confidence: 99%

Petrological Systematics of Mid-Ocean Ridge Basalts: Constraints on Melt Generation Beneath Ocean Ridges

Langmuir

Klein

Plank

2013

Geophysical Monograph Series

671

390

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“…Ultimately discontinuities, with the exception of transforms have a common origin linked to upwelling and segregation of mantle melt beneath the mid-ocean ridge which leads to propagation of magmatic pulses along the ridge [1]. The morphotectonic variability displayed by non-transform offsets however, suggests that discontinuities are influenced by a variety of factors including stress fields and lithospheric rheology [3].…”

Section: Introductionmentioning

confidence: 99%

“…Ocean ridge discontinuities partition and offset spreading centres into spatially and temporally independent segments at a range of scales, which are observed to www.elsevier.com/locate/epsl migrate, lengthen or shorten over time [1,2]. Large scale and structurally organised discontinuities are synonymous with first-order transform faults which can offset a ridge by 10's-100's km.…”

Section: Introductionmentioning

confidence: 99%

“…Although NTDs have small offsets, their influence on the lithosphere can be very important to the structure of an ocean ridge, most notably in the rotation of tectonic fabrics, rotation and control on volcanic construction and off-axis traces, through rifted basins and chevron structures or "wakes". Estimates from magnetic studies [1] suggest that 20% of the seafloor may be affected by the wakes of migrating discontinuities. This disturbance of the lithosphere may be a result of discontinuities occurring away from regions of partial melt and where the magma supply is reduced.…”

Section: Introductionmentioning

confidence: 99%

“…NTDs may initiate by sustained differential, asymmetric spreading occurring between two spatially independent segments [1,2]. Ultimately discontinuities, with the exception of transforms have a common origin linked to upwelling and segregation of mantle melt beneath the mid-ocean ridge which leads to propagation of magmatic pulses along the ridge [1].…”

Section: Introductionmentioning

confidence: 99%

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Numerical modelling of non-transform discontinuity geometry: Implications for ridge structure, volcano-tectonic fabric development and hydrothermal activity at segment ends

Tyler

Bull

Parson

et al. 2007

Earth and Planetary Science Letters

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Ocean ridge discontinuities partition and offset spreading centres at a range of scales. Large scale discontinuities (10's-100's km) are synonymous with first-order transform faults, which have well defined linear fault zone valleys. In contrast, NonTransform Discontinuities (NTDs) are diffuse, smaller scale offsets (0 to b 20 km), characterised by central basins or topographic highs. The geometry of NTD offsets can be categorised by the sense of offset, either right-stepping or left-stepping, and by the relative positions of the segment tips. The segment tip configurations include under-lapping, over-lapping or simple across-axis jumps or stepping in the ridge axis. In this study finite difference software is used to model segment geometry at a slow-spreading ridge under a normal tensile-stress within a homogeneous and isotropic medium. Along-and across-axis segment separations were varied incrementally for left-and right-stepping senses. The results show that the ratio of along-axis to across-axis segment tip separation is a dominant control of stress field rotation within an NTD. Features which most clearly show rotation within an NTD include basins and tectonically controlled constructional ridges. The obliquity of these features along with measurements of the surrounding fault fabrics are used as a way of observing and determining stress rotations within NTDs along the Central Indian Ridge (CIR). These rotations were used to obtain segment geometries from models where the central tensor showed an equivalent rotation. The results show that geometry has a profound effect on stress field rotation under which large-and small-scale volcanotectonic fabrics form. In addition, a shortfall of the predicted model tip relative to interpreted positions, along with morphology and observation of the ridge fabrics at the terminations to some segments, suggests the existence of a zone, broadly analogous to the process zone observed in fracture mechanics, which we call a damage zone. Given the criteria for the promotion of hydrothermal circulation, this damage zone would have a greater potential for hosting hydrothermal activity.

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Seafloor photo‐geology and sonar terrain modeling at the 9°N overlapping spreading center, East Pacific Rise

Klein

White

Nunnery

et al. 2013

Geochem Geophys Geosyst

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[1] A fundamental goal in the study of mid-ocean ridges is to understand the relationship between the distribution of melt at depth and seafloor features. Building on geophysical information on subsurface melt at the 9 N overlapping spreading center on the East Pacific Rise, we use terrain modeling (DSL-120A side scan and bathymetry), photo-geology (Jason II and WHOI TowCam), and geochemical data to explore this relationship. Terrain modeling identified four distinct geomorphic provinces with common seafloor characteristics that correspond well to changes in subsurface melt distribution. Visual observations were used to interpret terrain modeling results and to establish a relative seafloor age scale, calibrated with radiometric age dates, to identify areas of recent volcanism. On the east limb, recent eruptions in the north are localized over the margins of the 4 km wide asymmetric melt sill, forming a prominent off-axis pillow ridge. Along the southern east limb, recent eruptions occur along a neovolcanic ridge that hugs the overlap basin and lies several kilometers west of the plunging melt sill. Our results suggest that long-term southward migration of the east limb occurs through a series of diking events with a net southward propagation direction. Examining sites of recent eruptions in the context of geophysical data on melt distribution in the crust and upper mantle suggests melt may follow complex paths from depth to the surface. Overall, our findings emphasize the value of integrating information obtained from photo-geology, terrain modeling, lava geochemistry and petrography, and geophysics to constrain the nature of melt delivery at mid-ocean ridges.Components: 13,950 words, 12 figures.

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A new view of the mid-ocean ridge from the behaviour of ridge-axis discontinuities

Cited by 425 publications

References 32 publications

Petrological Systematics of Mid-Ocean Ridge Basalts: Constraints on Melt Generation Beneath Ocean Ridges

Petrological Systematics of Mid-Ocean Ridge Basalts: Constraints on Melt Generation Beneath Ocean Ridges

Numerical modelling of non-transform discontinuity geometry: Implications for ridge structure, volcano-tectonic fabric development and hydrothermal activity at segment ends

Seafloor photo‐geology and sonar terrain modeling at the 9°N overlapping spreading center, East Pacific Rise

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