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/g22486.1

Cited by 369 publications

(408 citation statements)

References 19 publications

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“…Basalts erupted along asymmetrical segments have compositions that are consistent with crystallization at higher pressures than basalts from symmetrical segments, and with lower extents of partial melting of the mantle. The large fields of detachment surfaces recently identified in oceanic crust formed along the slow spreading MAR and ultra-slow spreading South-West Indian Ridge (SWIR) 3,6 demonstrate the involvement of these structures in the accretion of a larger portion of the oceanic lithosphere than previously inferred from seafloor corrugated planes alone 7 . The resulting seafloor morphology and lithospheric structure on the flanks of the ridge axis are strongly asymmetrical 3 and differ from the more regular and roughly symmetrical axis-parallel abyssal hill fabric believed to characterize 'normal' slow-spreading seafloor.…”

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confidence: 93%

“…The resulting seafloor morphology and lithospheric structure on the flanks of the ridge axis are strongly asymmetrical 3 and differ from the more regular and roughly symmetrical axis-parallel abyssal hill fabric believed to characterize 'normal' slow-spreading seafloor. The abyssal hill morphology is caused by ridge-parallel, highangle faulting of volcanic seafloor 8 (Figures 1a-c).…”

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Central role of detachment faults in accretion of slow-spreading oceanic lithosphere

Escartı́n

Smith

Cann

et al. 2008

Nature

438

374

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Enhanced seismicity is probably generated along detachment faults accommodating a sizeable proportion of the total plate separation. In contrast, symmetrical segments have lower levels of seismicity, which concentrates primarily at their ends. Basalts erupted along asymmetrical segments have compositions that are consistent with crystallization at higher pressures than basalts from symmetrical segments, and with lower extents of partial melting of the mantle. The large fields of detachment surfaces recently identified in oceanic crust formed along the slow spreading MAR and ultra-slow spreading South-West Indian Ridge (SWIR) 3,6 demonstrate the involvement of these structures in the accretion of a larger portion of the oceanic lithosphere than previously inferred from seafloor corrugated planes alone 7 . The resulting seafloor morphology and lithospheric structure on the flanks of the ridge axis are strongly asymmetrical 3 and differ from the more regular and roughly symmetrical axis-parallel abyssal hill fabric believed to characterize 'normal' slow-spreading seafloor. The abyssal hill morphology is caused by ridge-parallel, highangle faulting of volcanic seafloor 8 (Figures 1a-c). In contrast, detachment-related terrain is caused by long-lived steep, normal faults initiated beneath the rift valley floor that rotate to low angles as their footwalls are exposed 7,8 . Distinctive narrow ridges with steep outward-facing slopes that are often curved in plan view develop near exposed detachments at the seafloor, and bound deep swales 7 (Figures 1d-e), producing blocky and chaotic terrain 7,9 . The asymmetric nature of accretion in the presence of detachments is also observed in the overall lithospheric structure, composition and geophysical character wherever data are available 3,4,10 . The MAR lacks the broad ridges only found along the melt-poor SWIR, likely a manifestation of detachment faulting that is different from striated fault planes and associated structure 3 . There is an excellent correlation between mode of accretion and seismicity at the ridge axis. This section of the MAR was hydroacoustically monitored between January 1999 and September 2003 11 . The hydroacoustic catalogue is complementary to the >30 year teleseismic catalogue, as it records smaller magnitude events (magnitude of completeness of 3 and 5, respectively 12 ), over a shorter period of time (<5 vs. >30 years). Both seismic catalogues show that detachment-dominated, asymmetrical ridge sections host ~75% more hydroacoustic events and ~65% more teleseismic events than 4 symmetrical segments (Figure 2b and c). The concentration of seismicity at segments shown to have active detachment faults (Figures 1d-e), such as the Logachev massif south of the Fifteen-Twenty Fracture zone and the TAG detachment fault near 26°N 6,7,13 , is thus a general pattern. Active detachments also control the zones of sustained seismicity, which lack shock-aftershock sequences that were previously identified along the northern MAR 14 . Differences between the hyd...

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confidence: 93%

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confidence: 98%

Central role of detachment faults in accretion of slow-spreading oceanic lithosphere

Escartı́n

Smith

Cann

et al. 2008

Nature

438

374

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“…The plagioclase-hosted and olivine-hosted melt inclusions from the sections between 70°E and 49°E on the SWIR indicate the high melting fractions of mantle, shallow ridge axis depth and thick crust [16]. Cannat et al [17] identified three types of seafloor at the SWIR as volcanic seafloor, smooth seafloor and corrugated seafloor. Among these, smooth terrain appears specific to ultraslow-spreading ridges and the mode of seafloor spreading may be analogous to processes at the ocean-continent transition of continental margins.…”

Section: Geological Settingmentioning

confidence: 99%

Mineralogical and geochemical features of sulfide chimneys from the 49°39′E hydrothermal field on the Southwest Indian Ridge and their geological inferences

Chen

Huang

et al. 2011

Chin. Sci. Bull.

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, the Chinese research cruise DY115-19 discovered an active hydrothermal field at 49°39′E/37°47′S on the ultraslow spreading Southwest Indian Ridge (SWIR). This was also the first active hydrothermal field found along an ultraslow-spreading ridge. We analyzed mineralogical, textural and geochemical compositions of the sulfide chimneys obtained from the 49°39′E field. Chimney samples show a concentric mineral zone around the fluid channel. The mineral assemblages of the interiors consist mainly of chalcopyrite, with pyrite and sphalerite as minor constitunets. In the intermediate portion, pyrite becomes the dominant mineral, with chalcopyrite and sphalerite as minor constitunets. For the outer wall, the majority of minerals are pyrite and sphalerite, with few chalcopyrite. Towards the outer margin of the chimney wall, the mineral grains become small and irregular in shape gradually, while minerals within interstices are abundant. These features are similar to those chimney edifices found on the East Pacific Rise and Mid-Atlantic Ridge. The average contents of Cu, Fe and Zn in our chimney samples were 2.83 wt%, 45.6 wt% and 3.28 wt%, respectively. The average Au and Ag contents were up to 2.0 ppm and 70.2 ppm respectively, higher than the massive sulfides from most hydrothermal fields along mid-ocean ridge. The rare earth elements geochemistry of the sulfide chimneys show a pattern distinctive from the sulfides recovered from typical hydrothermal fields along sedimentstarved mid-ocean ridge, with the enrichment of light rare earth elements but the weak, mostly negative, Eu anomaly. This is attributed to the distinct mineralization environment or fluid compositions in this area. In 1977 the first hydrothermal black smoker was discovered on the Galapagos Rift by scientists diving in a deep-sea

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“…[2] Oceanic core complexes (OCCs), are widespread features along the mid-Atlantic Ridge and other slow and ultra-slow spreading ridges [e.g., Escartín et al, 2008;Tucholke et al, 2008], where they are involved in the accretion of large areas of the seafloor [Smith et al, 2006;Cannat et al, 2006]. The low-angle detachment faults exposed at the seafloor unroof and expose sections of lower crust and mantle, accommodating elevated strains over long periods of time, sometimes in excess of 1 Myrs, possibly promoting serpentinization within these structures.…”

Section: Introductionmentioning

confidence: 99%

A short electromagnetic profile across the Kane Oceanic Core Complex

Evans

Escartı́n

Cannat

2010

Geophysical Research Letters

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A short seafloor electromagnetic profile across part of the Kane Oceanic Core Complex shows a large variation in seafloor electrical properties (uppermost 30m) with a sharp transition from conductive to resistive seafloor over a distance of less than 350m. The transition is in a location consistent with a sharp, but deeper, lateral gradient in seismic velocity, inferred to mark a transition from serpentinized peridotite to either gabbro or pristine mantle rocks, and is close to a mapped outcrop of serpentinized peridotites. We relate this variability in shallow structure primarily to changes in porosity related to composition.

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

Cited by 369 publications

References 19 publications

Central role of detachment faults in accretion of slow-spreading oceanic lithosphere

Central role of detachment faults in accretion of slow-spreading oceanic lithosphere

Mineralogical and geochemical features of sulfide chimneys from the 49°39′E hydrothermal field on the Southwest Indian Ridge and their geological inferences

A short electromagnetic profile across the Kane Oceanic Core Complex

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