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Oceanic detachment faults generate compression in extension

Parnell-Turner, R.; Sohn, R.A.; Peirce, C.; Reston, T.J.; MacLeod, C.J.; Searle, R.C.; Simão, N.M.

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Authors

R. Parnell-Turner

R.A. Sohn

T.J. Reston

C.J. MacLeod

R.C. Searle

N.M. Simão



Abstract

In extensional geologic systems such as mid-ocean ridges, deformation is typically accommodated by slip on normal faults, where material is pulled apart under tension and stress is released by rupture during earthquakes and magmatic accretion. However, at slowly spreading mid-ocean ridges where the tectonic plates move apart at rates <80 km m.y.–1, these normal faults may roll over to form long-lived, low-angled detachments that exhume mantle rocks and form corrugated domes on the seabed. Here we present the results of a local micro-earthquake study over an active detachment at 13°20′N on the Mid-Atlantic Ridge to show that these features can give rise to reverse-faulting earthquakes in response to plate bending. During a 6 month survey period, we observed a remarkably high rate of seismic activity, with >244,000 events detected along 25 km of the ridge axis, to depths of ∼10 km below seafloor. Surprisingly, the majority of these were reverse-faulting events. Restricted to depths of 3–7 km below seafloor, these reverse events delineate a band of intense compressional seismicity located adjacent to a zone of deeper extensional events. This deformation pattern is consistent with flexural models of plate bending during lithospheric accretion. Our results indicate that the lower portion of the detachment footwall experiences compressive stresses and deforms internally as the fault rolls over to low angles before emerging at the seafloor. These compressive stresses trigger reverse faulting even though the detachment itself is an extensional system.

Citation

Parnell-Turner, R., Sohn, R., Peirce, C., Reston, T., MacLeod, C., Searle, R., & Simão, N. (2017). Oceanic detachment faults generate compression in extension. Geology, 45(10), 923-926. https://doi.org/10.1130/g39232.1

Journal Article Type Article
Acceptance Date Jun 19, 2017
Online Publication Date Aug 8, 2017
Publication Date Oct 1, 2017
Deposit Date Mar 6, 2017
Publicly Available Date Mar 28, 2024
Journal Geology
Print ISSN 0091-7613
Electronic ISSN 1943-2682
Publisher Geological Society of America
Peer Reviewed Peer Reviewed
Volume 45
Issue 10
Pages 923-926
DOI https://doi.org/10.1130/g39232.1

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Copyright Statement
© 2017 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license.





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