High-resolution bathymetry reveals contrasting landslide activity shaping the walls of the Mid-Atlantic Ridge axial valley

Type Article
Date 2013-04
Language English
Author(s) Cannat Mathilde1, Mangeney Anne2, Ondreas Helene3, Fouquet Yves3, Normand Alain3
Affiliation(s) 1 : Inst Phys Globe Paris, PRES Sorbonne, Equipe Geosci Marines, CNRS UMR7154, Paris, France.
2 : Univ Paris Diderot, PRES Sorbonne, Inst Phys Globe Paris, Equipe Sismol,CNRS UMR7154, Paris, France.
3 : Geosci Marines Geochim Met, Brest, France.
Source Geochemistry Geophysics Geosystems (1525-2027) (Amer Geophysical Union), 2013-04 , Vol. 14 , N. 4 , P. 996-1011
DOI 10.1002/ggge.20056
WOS© Times Cited 26
Keyword(s) Landslides, detachment faults, basalts, mid-ocean ridges, serpentinized peridotites
Abstract Axial valleys are found along most slow-spreading mid-ocean ridges and are one of the most prominent topographic features on Earth. In this paper, we present the first deep-tow swath bathymetry for the axial valley walls of the Mid-Atlantic Ridge. These data allow us to analyze axial valley wall morphology with a very high resolution (0.5 to 1 m compared to 50 m for shipboard multibeam bathymetry), revealing the role played by landslides. Slow-spreading ridge axial valleys also commonly expose mantle-derived serpentinized peridotites in the footwalls of large offset normal faults (detachments). In our map of the Ashadze area (lat. 13 degrees N), ultramafic outcrops have an average slope of 18 degrees and behave as sliding deformable rock masses, with little fragmentation. By contrast, the basaltic seafloor in the Krasnov area (lat. 16 degrees 38N) has an average slope of 32 degrees and the erosion of the steep basaltic rock faces leads to extensive fragmentation, forming debris with morphologies consistent with noncohesive granular flow. Comparison with laboratory experiments suggests that the repose angle for this basaltic debris is > 25 degrees. We discuss the interplay between the normal faults that bound the axial valley and the observed mass wasting processes. We propose that, along axial valley walls where serpentinized peridotites are exposed by detachment faults, mass wasting results in average slopes 20 degrees, even in places where the emergence angle of the detachment is larger.
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Cannat Mathilde, Mangeney Anne, Ondreas Helene, Fouquet Yves, Normand Alain (2013). High-resolution bathymetry reveals contrasting landslide activity shaping the walls of the Mid-Atlantic Ridge axial valley. Geochemistry Geophysics Geosystems, 14(4), 996-1011. Publisher's official version : https://doi.org/10.1002/ggge.20056 , Open Access version : https://archimer.ifremer.fr/doc/00284/39516/