Two New Hydrothermal Fields at the Mid-Atlantic Ridge

Cherkashov, Georgy; Bel’tenev, V. E.; Ivanov, V.N.; Lazareva, L. I.; Samovarov, M. L.; Шилов, В. В.; Stepanova, T. V.; Glasby, G. P.; Kuznetsov, V. Yu.

doi:10.1080/10641190802400708

Cited by 34 publications

(31 citation statements)

References 3 publications

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“…A small sulfide mound, 100 × 100 m wide, is located to the north while a larger mound, 300 × 500 m wide, is located to the south. The latter is cut by the previously mentioned major faults near their intersection and results in a residual half mound feature with a steep N‐S trending, west‐facing 70–100 m high fault scarp exposing massive sulfides [ Cherkashov et al ., ]. A horseshoe‐shaped landslide structure below reflects a mechanically weaker zone in the hydrothermal area (Figure a).…”

Section: Geological Settingmentioning

confidence: 99%

“…Simple thermal calculations indicate that the cooling time of a thermal anomaly within the first 500 m of the oceanic crust is a few thousand years. If the hydrothermal activity ceased 5.6 kyr ago, as suggested by the youngest sulfide dated in the area [ Cherkashov et al ., ], the associated thermal anomaly has almost completely disappeared and the temperature at 500 m depth is much lower than the Curie temperature of extrusive basalt titanomagnetite (150–200°C) [ Kent and Gee , ]. The observed magnetic low is therefore unlikely to be the result of thermal demagnetization.…”

Section: Forward Modelingmentioning

confidence: 99%

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What causes low magnetization at basalt-hosted hydrothermal sites? Insights from inactive site Krasnov (MAR 16°38′N)

Szitkar

Dyment

Choi

et al. 2014

Geochem. Geophys. Geosyst.

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High-resolution magnetic surveys acquired near the seafloor show that active basalt-hosted hydrothermal sites are associated with zones of lower magnetization. This observation may reflect the thermal demagnetization of a hot hydrothermal zone, the alteration of basalt affected by hydrothermal circulation, and/or the presence of thick, nonmagnetic hydrothermal deposits. In order to discriminate among these inferences, we acquired vector magnetic data 50 m above inactive hydrothermal site Krasnov using the Remotely Operated Vehicle (ROV) Victor. This deep hydrothermal site, located 7 km east of the Mid-Atlantic Ridge (MAR) axis at 16 38 0 N, is dissected by major normal faults and shows no evidence of recent hydrothermal activity. It is therefore a perfect target for investigating the magnetic signature of an inactive basalt-hosted hydrothermal site. Krasnov exhibits a strong negative magnetic anomaly, which implies that the lower magnetization observed at basalt-hosted hydrothermal sites is not a transient effect associated with hydrothermal activity, but remains after activity ceases. Thermal demagnetization plays only a secondary role, if any, in the observed magnetic low. Forward models suggest that both the nonmagnetic hydrothermal deposits and an altered zone of demagnetized basalt are required to account for the observed magnetic low. The permanence of this magnetic signature makes it a useful tool to explore midocean ridges and detect inactive hydrothermal sites.

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Section: Geological Settingmentioning

confidence: 99%

Section: Forward Modelingmentioning

confidence: 99%

What causes low magnetization at basalt-hosted hydrothermal sites? Insights from inactive site Krasnov (MAR 16°38′N)

Szitkar

Dyment

Choi

et al. 2014

Geochem. Geophys. Geosyst.

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“…More detailed geological studies followed based on a Nautile submersible cruise in 1992 [ Bougault et al , 1993; Cannat et al , 1997; Cannat and Casey , 1995]. Numerous dredging cruises then led to the collection of more ultramafic samples [ Silantyev , 1998], and to the discovery of the ultramafic‐hosted Logatchev [ Batuev et al , 1994] and Ashadze [ Bel'tenev et al , 2005; Cherkashov et al , 2008] hydrothermal vent fields (Figure 1). More detailed investigations and sampling of these ultramafic outcrops included drilling at ODP Leg 209 Sites 1268, 1270, 1271, and 1272 [ Kelemen et al , 2007] (Figure 1), ROV observations in the Logatchev area [ Augustin et al , 2008; Petersen et al , 2009], and side scan imaging and sampling of the emerging corrugated surfaces at 13°20′N [ MacLeod et al , 2009].…”

Section: Geological Setting and Previous Sampling Of Ultramafic And Gmentioning

confidence: 99%

Deformation associated with the denudation of mantle‐derived rocks at the Mid‐Atlantic Ridge 13°–15°N: The role of magmatic injections and hydrothermal alteration

Picazo

Cannat

Delacour

et al. 2012

Geochem Geophys Geosyst

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[1] Outcrops of deeply derived ultramafic rocks and gabbros are widespread along slow spreading ridges where they are exposed in the footwall of detachment faults. We report on the microstructural and petrological characteristics of a large number of samples from ultramafic exposures in the walls of the Mid-Atlantic Ridge (MAR) axial valley at three distinct locations at lat. 13 N and 14 45′N. One of these locations corresponds to the footwall beneath a corrugated paleo-fault surface. Bearing in mind that dredging and ROV sampling may not preserve the most fragile lithologies (fault gouges), this study allows us to document a sequence of deformation, and the magmatic and hydrothermal history recorded in the footwall within a few hundred meters of the axial detachment fault. At the three sampled locations, we find that tremolitic amphiboles have localized deformation in the ultramafic rocks prior to the onset of serpentinization. We interpret these tremolites as hydrothermal alteration products after evolved gabbroic rocks intruded into the peridotites. We also document two types of brittle deformation in the ultramafic rocks, which we infer could produce the sustained low magnitude seismicity recorded at ridge axis detachment faults. The first type of brittle deformation affects fresh peridotite and is associated with the injection of the evolved gabbroic melts, and the second type affects serpentinized peridotites and is associated with the injection of Si-rich hydrothermal fluids that promote talc crystallization, leading to strain localization in thin talc shear zones. We also observed chlorite + serpentine shear zones but did not identify samples with serpentine-only shear zones. Although the proportion of magmatic injections in the ultramafic rocks is variable, these characteristics are found at each investigated location and are therefore proposed as fundamental components of the deformation in the footwall of the detachment faults associated with denudation of mantle-derived rocks at the MAR.

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“…The MAR western axial valley wall at lat. 16°38′N has only been sampled in the vicinity of the extinct Krasnov vent site, where it exposes basalt and massive sulphides [ Cherkashov et al ., ]. Available shipboard bathymetry in this region has a very low resolution, showing only the broader‐scale features such as the two shelves that form the eastern axial valley wall (Figure a) and the NS trending ridge that sticks out of the lower shelf north of the Krasnov fossil vent site.…”

Section: Introductionmentioning

confidence: 99%

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

Cannat

Mangeney

Ondréas

et al. 2013

Geochem Geophys Geosyst

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[1] 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 N), ultramafic outcrops have an average slope of 18 and behave as sliding deformable rock masses, with little fragmentation. By contrast, the basaltic seafloor in the Krasnov area (lat. 16 38 0 N) has an average slope of 32 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. 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 , even in places where the emergence angle of the detachment is larger.

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Two New Hydrothermal Fields at the Mid-Atlantic Ridge

Cited by 34 publications

References 3 publications

What causes low magnetization at basalt-hosted hydrothermal sites? Insights from inactive site Krasnov (MAR 16°38′N)

What causes low magnetization at basalt-hosted hydrothermal sites? Insights from inactive site Krasnov (MAR 16°38′N)

Deformation associated with the denudation of mantle‐derived rocks at the Mid‐Atlantic Ridge 13°–15°N: The role of magmatic injections and hydrothermal alteration

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

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