Olive, Jean-Arthur , Parnell-Turner, Ross , Escartín, Javier , Smith, Deborah K. and Petersen, Sven (2019) Controls on the seafloor exposure of detachment fault surfaces. Earth and Planetary Science Letters, 506 . pp. 381-387. DOI 10.1016/j.epsl.2018.11.001.

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Abstract

Highlights

• A small fraction of corrugated detachment fault surfaces is eventually exposed at the seafloor.
• Seafloor slopes indicate effective friction of ∼0.2 on shallow part of detachments.
• Moderate-offset detachment faults may be largely blanketed by hanging wall material.
• Seafloor-shaping processes profoundly alter the morphology of oceanic core complexes.

Abstract

While oceanic detachment faults have been proposed to account for the accretion of ∼40% of new seafloor in the North Atlantic ocean, clear exposures of large-offset, often-corrugated fault surfaces remain scarce and spatially limited. To help resolve this paradox, we examine the conditions under which detachment fault growth may or may not lead to extensive exposure of corrugated fault planes at the seafloor. Using high-resolution bathymetry from four detachment faults at the northern Mid-Atlantic Ridge, we investigate the rafting of hanging wall-derived debris over emerging fault scarps, which can lead to covering shallow-dipping corrugated fault surfaces. We model this process using critical taper theory, and infer low effective friction coefficients (∼0.2) on the shallowest portion of detachment faults. A corollary to this result is that detachments emerging from the seafloor at angles <13° are more likely to become blanketed under an apron of hanging wall material. We generalize these findings as a simple model for the progressive exposure and flexural rotation of detachment footwalls, which accounts for the continued action of seafloor-shaping processes. Our model suggests that many moderate-offset, hidden detachment faults may exist along slow mid-ocean ridges, and do not feature an exposed fault surface.

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