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Modes of faulting at mid-ocean ridges

Abstract

Abyssal-hill-bounding faults that pervade the oceanic crust are the most common tectonic feature on the surface of the Earth. The recognition that these faults form at plate spreading centres came with the plate tectonic revolution. Recent observations reveal a large range of fault sizes and orientations; numerical models of plate separation, dyke intrusion and faulting require at least two distinct mechanisms of fault formation at ridges to explain these observations. Plate unbending with distance from the top of an axial high reproduces the observed dip directions and offsets of faults formed at fast-spreading centres. Conversely, plate stretching, with differing amounts of constant-rate magmatic dyke intrusion, can explain the great variety of fault offset seen at slow-spreading ridges. Very-large-offset normal faults only form when about half the plate separation at a ridge is accommodated by dyke intrusion.

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Figure 1: Shaded relief images of bathymetry over three contrasting sections of the mid-ocean ridge system.
Figure 2: Set-up for numerical models.
Figure 3: Results for buoyancy-dominated ridge models.
Figure 4: Illustration of kinematic stretching fault model.
Figure 5: Results for stretching-dominated ridge models.

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Acknowledgements

Work supported by the National Science Foundation. We thank W. Haxby for help with images and J. Karson for comments on the text.

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Correspondence to W. Roger Buck.

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Contains details of the numerical model of dyking and stretching. (DOC 29 kb)

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Buck, W., Lavier, L. & Poliakov, A. Modes of faulting at mid-ocean ridges. Nature 434, 719–723 (2005). https://doi.org/10.1038/nature03358

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