Modes of seafloor generation at a melt-poor ultraslow-spreading ridge

Cannat, Mathilde; Sauter, Daniel; Mendel, Véronique; Ruellan, Étienne; Okino, Kyoko; Escartı́n, J.; Combier, Violaine; Baala, Mohamad

doi:10.1130/g22486a.1

Cited by 113 publications

(295 citation statements)

References 19 publications

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“…There are differences in the morphology of the extrusive volcanics in the axial valley between the segments, reflecting changes in magmatic input. On the S. AMAR segment we find a well-defined axial valley, with a large axial volcanic ridge (AVR) as previously observed by Parson et al Exposed fault morphologies include clear fault surfaces and broad areas of smooth seafloor similar to those observed on the Southwest Indian Ridge [Cannat et al, 2006;Sauter et al, 2013]. Faults are characterized by smooth surfaces and dipping slopes, and they are delimited by a sharp ridge (the breakaway ridge) on one side and sometimes a sharp hanging wall cutoff on the other side.…”

Section: Seabed Morphologysupporting

confidence: 86%

Heterogeneous and asymmetric crustal accretion: New constraints from multibeam bathymetry and potential field data from the Rainbow area of the Mid‐Atlantic Ridge (36°15'N)

Paulatto

Canales

Dunn

et al. 2015

Geochem Geophys Geosyst

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At slow-spreading mid-ocean ridges, crustal accretion style can vary significantly along and across ridge segments. In magma-poor regions, seafloor spreading can be accommodated largely by tectonic processes, however, the internal structure and formation mechanism of such highly tectonized crust are not fully understood. We analyze multibeam bathymetry and potential field data from the Rainbow area of the Mid-Atlantic Ridge (35840'N-36840'N), a section of the ridge that shows diverse accretion styles. We identify volcanic, tectonized and sedimented terrain and measure exposed fault area to estimate the tectonic strain, T, and the fraction of magmatic accretion, M. Estimated T values range from 0.2-0.4 on ridge segments to 0.6-0.8 at the Rainbow nontransform discontinuity (NTD). At segment ends T is asymmetric, reflecting asymmetries in accretion rate, topography and faulting between inside and outside offset corners. Detachment faults have formed preferentially at inside corners, where tectonic strain is higher. We identify at least two oceanic core complexes on the fossil trace of the NTD, in addition to the Rainbow massif, which occupies the offset today. A gravity high and low magnetization suggest that the Rainbow massif, which hosts a high-temperature hydrothermal system, was uplifted by a west dipping detachment fault. Asymmetric plate ages indicate localization of tectonic strain at the inside corners and migration of the detachment toward and across the ridge axis, which may have caused emplacement of magma into the footwall. Hydrothermal circulation and heat extraction is possibly favored by increased permeability generated by fracturing of the footwall and deep-penetrating second-generation faults.

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Section: Seabed Morphologysupporting

confidence: 86%

Heterogeneous and asymmetric crustal accretion: New constraints from multibeam bathymetry and potential field data from the Rainbow area of the Mid‐Atlantic Ridge (36°15'N)

Paulatto

Canales

Dunn

et al. 2015

Geochem Geophys Geosyst

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“…Detachment faults are responsible for the exhumation of upper mantle and lower oceanic crust to the ocean floor, and may lead to the formation of uplifted, domal structures known as oceanic core complexes (OCCs) [Cannat et al, 1995;Cann et al, 1997;Tucholke et al, 1998;Blackman et al, 2006;MacLeod et al, 2002MacLeod et al, , 2009Ildefonse et al, 2007]. In addition to unroofing of upper mantle rocks by displacement on oceanic detachment faults, in ultraslow, melt-poor settings (e.g., along the Southwest Indian Ridge) serpentinized mantle peridotites are exposed over large expanses of seafloor, with no evidence for a volcanic upper crustal layer (generating so-called ''smooth seafloor'') [Cannat et al, 2006[Cannat et al, , 2008Sauter et al, 2013]. Exposure of mantle rocks on the seafloor has also been documented in hyper-extended, magma-poor rifted margins (e.g., associated with the opening of the Piemonte-Ligurian ocean) Mohn et al, 2012;Vissers et al, 2013].…”

Section: Introductionmentioning

confidence: 99%

Magnetic properties of variably serpentinized peridotites and their implication for the evolution of oceanic core complexes

Maffione

Morris

Plümper

et al. 2014

Geochem. Geophys. Geosyst.

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Serpentinization of ultramafic rocks during hydrothermal alteration at mid-ocean ridges profoundly changes the physical, chemical, rheological, and magnetic properties of the oceanic lithosphere. There is renewed interest in this process following the discovery of widespread exposures of serpentinized mantle on the seafloor in slow spreading oceans. Unroofing of mantle rocks in these settings is achieved by displacement along oceanic detachment faults, which eventually results in structures known as oceanic core complexes (OCCs). However, we have limited understanding of the mechanisms of serpentinization at the seafloor and in particular their relationship with the evolution of OCCs. Since magnetite is a direct product of serpentinization, the magnetic properties of variably serpentinized peridotites can provide unique insights into these mechanisms and their evolution in the oceanic lithosphere. Here we present new results from an integrated, rock magnetic, paleomagnetic, and petrological study of variably serpentinized peridotites from the first fossil OCC recognized in an ophiolite. Integration with existing data from mid-ocean ridge-related abyssal peridotites recovered from several scientific ocean drilling sites yields the first magnetic database from peridotites extending across the complete range (0-100%) of degrees of serpentinization. Variations in a range of magnetic parameters with serpentinization, and associated paleomagnetic data, provide: (i) key constraints on the mechanism(s) of serpentinization at mid-ocean ridges; (ii) insights on the potential for serpentinized peridotites to contribute to marine magnetic anomalies; and (iii) evidence that leads to a new conceptual model for the evolution of serpentinization and related remanence acquisition at OCCs.

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“…Normal faults at slower spreading ridges may have very large offsets (tens of km to greater than a hundred km) and account locally for 60-100% of the plate separation [e.g., Baines et al, 2008;Cannat et al, 2006;Grimes et al, 2008;Ohara et al, 2001;Okino et al, 2004;Searle et al, 2003;Smith et al, 2006Smith et al, , 2008Tucholke et al, 1998]. These long-lived, large-offset faults (commonly referred to as detachment faults) exhume lower crustal and upper mantle rocks.…”

Section: Introductionmentioning

confidence: 99%

“…A number of different morphologies are now associated with oceanic detachment faulting. These include the well-known domed, corrugated detachment surfaces, noncorrugated massifs, highly back-tilted fault breakaways, and broad smooth hills [Cann et al, 1997;Cannat et al, 2006;Dick et al, 2003;MacLeod et al, 2009;Schroeder et al, 2007;Smith et al, 2008;Tucholke et al, 1998]. In addition, detachment fault formation is not restricted to the ends of spreading segments; detachment faults form anywhere along the length of a segment [e.g., Cannat et al, 2006;Smith et al, 2006Smith et al, , 2008, and may link along axis over a significant portion of a ridge segment [e.g., Reston and Ranero, 2011;Smith et al, 2008].…”

Section: Introductionmentioning

confidence: 99%

Development and evolution of detachment faulting along 50 km of the Mid‐Atlantic Ridge near 16.5°N

Smith

Schouten

Dick

et al. 2014

Geochem Geophys Geosyst

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A multifaceted study of the slow spreading Mid-Atlantic Ridge (MAR) at 16.5 N provides new insights into detachment faulting and its evolution through time. The survey included regional multibeam bathymetry mapping, high-resolution mapping using AUV Sentry, seafloor imaging using the TowCam system, and an extensive rock-dredging program. At different times, detachment faulting was active along 50 km of the western flank of the study area, and may have dominated spreading on that flank for the last 5 Ma. Detachment morphologies vary and include a classic corrugated massif, noncorrugated massifs, and back-tilted ridges marking detachment breakaways. High-resolution Sentry data reveal a new detachment morphology; a low-angle, irregular surface in the regional bathymetry is shown to be a finely corrugated detachment surface (corrugation wavelength of only tens of meters and relief of just a few meters). Multiscale corrugations are observed 2-3 km from the detachment breakaway suggesting that they formed in the brittle layer, perhaps by anastomosing faults. The thin wedge of hanging wall lavas that covers a lowangle (6 ) detachment footwall near its termination are intensely faulted and fissured; this deformation may be enhanced by the low angle of the emerging footwall. Active detachment faulting currently is limited to the western side of the rift valley. Nonetheless, detachment fault morphologies also are present over a large portion of the eastern flank on crust >2 Ma, indicating that within the last 5 Ma parts of the ridge axis have experienced periods of two-sided detachment faulting.

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Modes of seafloor generation at a melt-poor ultraslow-spreading ridge

Cited by 113 publications

References 19 publications

Heterogeneous and asymmetric crustal accretion: New constraints from multibeam bathymetry and potential field data from the Rainbow area of the Mid‐Atlantic Ridge (36°15'N)

Heterogeneous and asymmetric crustal accretion: New constraints from multibeam bathymetry and potential field data from the Rainbow area of the Mid‐Atlantic Ridge (36°15'N)

Magnetic properties of variably serpentinized peridotites and their implication for the evolution of oceanic core complexes

Development and evolution of detachment faulting along 50 km of the Mid‐Atlantic Ridge near 16.5°N

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