Emplacement of deep crustal and mantle rocks on the west median valley wall of the MARK area (MAR, 23°N)

Mével, Catherine; Cannat, Mathilde; Gente, Pascal; Marion, Eva; Auzende, Jean-Marie; Karson, Jeffrey A.

doi:10.1016/0040-1951(91)90353-t

Cited by 150 publications

(136 citation statements)

References 38 publications

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“…The distance between Sites 670 and 920 is about 20 km. These two sites have been drilled in the same extensive outcrop of serpentinized peridotites (Karson et al, 1987;Mével et al, 1991). These serpentinized peridotites are interpreted as residual mantle material that has been unroofed by extensional tectonics, and extensively altered in the process.…”

Section: Site Location and Previous Workmentioning

confidence: 99%

Oxygen-isotope constraints on serpentinization processes in ultramafic rocks from the Mid-Atlantic Ridge (23°N)

Agrinier¹,

Cannat²

1997

Proceedings of the Ocean Drilling Program

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Früh-Green et al. (1996), we calculate serpentinization temperatures ranging between 430° and 590°C. However, a sensitivity analysis shows that large errors affect these temperatures (about ±100°C). Nevertheless, we think we can determine that the serpentinization occurred at temperatures higher than 350°C.Using the mass-balance equation developed by Taylor (1977), and assuming that seawater (δ 18 θ = Woo) or 18 O hydrothermally enriched seawater (δ 18 θ = +2.4%c) is the serpentinizing fluid, we can determine that the wateπrock ratios (in oxygen atom proportions) were, at 400°C, around 0.55 ± 0.1 and 1.05 ± 0.2, respectively, and at 500°C, 0.4 ± 0.1 and 0.8 ±0.1, respectively.The relatively high serpentinization temperatures derived from this study imply that serpentinization has occurred at significant depth in the axial lithosphere. This has potentially important consequences, which we discuss, on the amount of tectonic rotation during the uplift of the ultramafic rocks to the seafloor, on the orientation of principal stresses at depth beneath the axial valley, and on the seismic velocity and density structure of the oceanic lithosphere.All types of serpentine (meshwork and vein) from Site 920 appear to have formed at these relatively high temperatures. However, previous oxygen-isotope studies Hebert et al., 1990) of cores from Site 670 reported ultramafic rocks that were serpentinized at lower temperature (<200°C). This indicates that the ultramafic component of the axial lithosphere in the area did not become entirely serpentinized at depths corresponding to rock temperatures of at least 350°C.

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Section: Site Location and Previous Workmentioning

confidence: 99%

Oxygen-isotope constraints on serpentinization processes in ultramafic rocks from the Mid-Atlantic Ridge (23°N)

Agrinier¹,

Cannat²

1997

Proceedings of the Ocean Drilling Program

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“…The TiO 2 content of melts are generally changed during the fractional crystallization as shown in the chemical variations of clinopyroxene in the 25 S OCC gabbros. Highly evolved gabbroic rocks were reported from both the slow-spreading ridges (Bloomer et al 1989;Mével et al 1991;Cannat et al 1992;Morishita et al 2004) and the fast-spreading ridges (Constantin 1999). Physical conditions under slow-spreading ridges are characterized by a highly attenuated magma supply and a high rock/melt ratio during melt ascending.…”

Section: Effect Of Late Modification Due To Infiltration Of Multiple mentioning

confidence: 99%

Petrology of Peridotites and Related Gabbroic Rocks Around the Kairei Hydrothermal Field in the Central Indian Ridge

Morishita

Nakamura

Shibuya

et al. 2014

Subseafloor Biosphere Linked to Hydrothermal Systems

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Peridotites and related gabbroic rocks are widely exposed in the Central Indian Ridge, where the H 2 -rich-fluid-bearing Kairei hydrothermal field exists. We report on petrological and mineralogical characteristics of peridotites and gabbroic rocks recovered from an oceanic core complex at a latitude of 25 South (25 S OCC) and the Yokoniwa Rise around the Kairei hydrothermal field. Gabbros recovered from the 25 S OCC show a wide range of variations in terms of mineral chemistry and mineral assemblages (olivine-gabbro, gabbronorite to highly evolved oxide gabbro) and are similar to those from the Atlantis Bank of the Southwest Indian Ridge, an ultraslow-spreading ocean ridge. Peridotites recovered from 25 S OCC and the Yokoniwa Rise are generally characterized by moderately to highly depleted melt components. The partial melting of these peridotites is followed by chemical modification through interaction with a wide range of melts from relatively less evolved to highly evolved characteristics. Moderately to highly depleted melt components in the studied peridotites can be explained as being either residue after a relatively high-melt productivity period in intermediate-spreading ridges or a geochemically distinctive domain which has suffered from partial melting in the past rather than partial melting beneath the present mid-ocean ridge systems.

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“…The outcrops are marked by moderately dipping faults and shear zones defining a nearly continuous dip slope. Some fault zones can be followed for several hundred meters upslope and may correspond to major detachment faults (Dick et al, 1981;Karson and Dick, 1983;Karson, 1991;Mével et al, 1991). They dip to the east-northeast along the eastern face of the massif and to the north and northeast along the northern, transform-parallel wall.…”

Section: Leg 153 Preliminary Reportmentioning

confidence: 99%

Mid Atlantic Ridge

Cannat¹,

Karson²,

Miller³

1994

ODP Preliminary Report

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The principal success of Leg 153 was the recovery of extensive sections of ultramafic and mafic rocks from a slow-spreading mid-ocean ridge. Drilling was undertaken at multiple sites along the western flank of the Mid-Atlantic Ridge (MAR), south of the Kane Transform (MARK). The principal objectives of this second in a series of offset drilling legs and subsequent shore-based studies were to investigate the chemical composition and evolution of the lower crust and mantle created at a slow-spreading ridge, the geometry of magmatic and deformation structures preserved in residual peridotite and in lower crustal rocks, and the intensity and diversity of metamorphism attending crustal evolution in this slow-spreading environment.Site 920, located at latitude 23°20.32'N, about 40 km south of the Kane Transform along the western wall of the Mid-Atlantic Ridge median valley, sampled predominantly serpentinized harzburgite, interpreted to represent uplifted and altered suboceanic mantle. Drilling at this site achieved the best penetration and recovery of any drilling efforts to date in massive serpentinized peridotite. Other rock types sampled from this site include serpentinized lherzolite, dunite, clinopyroxenite, and websterite, as well as variably metamorphosed intervals of gabbro, olivine gabbro, oxide mineral-rich gabbro and gabbronorite, and plagioclase-olivine phyric diabase.Despite intense alteration of the primary minerals to serpentine, primary mineralogy and textures are widely preserved in the recovered ultramafic rocks. The dominant texture is coarse grained porphyroclastic with lobate grain boundaries and frequent 120° triple junctions, suggesting efficient grain growth at close to solidus temperature. Most samples also display an anastomosing serpentine foliation that results from the preferred orientation of fine, discontinuous veins of serpentine and iron oxide minerals cutting the background mesh-textured serpentine.Paleomagnetic studies indicate that this anastomosing foliation probably dips moderately to the east, toward the MAR neovolcanic zone. Pyroxenite and gabbroic veins, and gabbroic intervals up to at least a few decimeters thick are ubiquitous in the cored ultramafic rocks, and cover a wide range of compositions from spinel-bearing interstitial melt segregations to altered, oxide mineral-, apatite-, and zircon-bearing gabbro.Sites 921 through 924 are located in outcrops of gabbroic rocks, also along the western wall of the Mid-Atlantic Ridge median valley near its intersection with the Kane Transform. These outcrops occur on the flank of a broad, dome-like uplift, referred to as an inside-corner high or Leg 153 Preliminary Report Page 8 ridge/transform intersection massif. Sites 921, 922, and 923 lie along a north-south-trending ridge axis parallel transect, such that variations in the igneous, metamorphic, and deformational features in the rocks recovered from these sites may reflect along-axis variability in the processes that create and modify lower crustal rocks. Site 924 is offs...

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Emplacement of deep crustal and mantle rocks on the west median valley wall of the MARK area (MAR, 23°N)

Cited by 150 publications

References 38 publications

Oxygen-isotope constraints on serpentinization processes in ultramafic rocks from the Mid-Atlantic Ridge (23°N)

Oxygen-isotope constraints on serpentinization processes in ultramafic rocks from the Mid-Atlantic Ridge (23°N)

Petrology of Peridotites and Related Gabbroic Rocks Around the Kairei Hydrothermal Field in the Central Indian Ridge

Mid Atlantic Ridge

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