Deep structure of the ocean‐continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: The IAM‐9 transect at 40°20′N

Dean, S. M.; Minshull, T. A.; Whitmarsh, R. B.; Louden, K. E.

doi:10.1029/1999jb900301

Cited by 299 publications

(536 citation statements)

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“…Seismic imaging tentatively suggests that the exhumed mantle is ∼25-100% serpentinized to ∼4 km depth. A deeper section with seismic velocities of 7.3-7.9 km/s can be interpreted as partly (<25%) serpentinized peridotite, with higher extents of serpentinization along deep-reaching fault planes (19). The Mohorovičic discontinuity of the southern Iberia Abyssal Plain is interpreted as a gradual transition from partly serpentinized peridotite to unaltered peridotite with a seismic velocity of 8 km/s (19).…”

Section: Significancementioning

confidence: 99%

“…40-170 km wide and is chiefly composed of altered mantle rocks (18). Serpentinization took place due to seawater influx during rifting along numerous faults that have brecciated the uppermost ∼1 km (19). Seismic imaging tentatively suggests that the exhumed mantle is ∼25-100% serpentinized to ∼4 km depth.…”

Section: Significancementioning

confidence: 99%

“…A deeper section with seismic velocities of 7.3-7.9 km/s can be interpreted as partly (<25%) serpentinized peridotite, with higher extents of serpentinization along deep-reaching fault planes (19). The Mohorovičic discontinuity of the southern Iberia Abyssal Plain is interpreted as a gradual transition from partly serpentinized peridotite to unaltered peridotite with a seismic velocity of 8 km/s (19). Laboratory experiments suggest that serpentinization of such large volumes lasted at least a few million years (20).…”

Section: Significancementioning

confidence: 99%

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Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

Klein

Humphris

Guo

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle (i.e., serpentinite). However, geosphere-biosphere interactions in serpentinite-hosted subseafloor mixing zones remain poorly constrained. Here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a Cretaceous Lost City-type hydrothermal system at the magma-poor passive Iberia Margin (Ocean Drilling Program Leg 149, Hole 897D). Brucite−calcite mineral assemblages precipitated from mixed fluids ca. 65 m below the Cretaceous paleo-seafloor at temperatures of 31.7 ± 4.3°C within steep chemical gradients between weathered, carbonate-rich serpentinite breccia and serpentinite. Mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity. Dense microbial colonies are fossilized in brucite−calcite veins that are strongly enriched in organic carbon (up to 0.5 wt.% of the total carbon) but depleted in 13 C (δ 13 C TOC = −19.4‰). We detected a combination of bacterial diether lipid biomarkers, archaeol, and archaeal tetraethers analogous to those found in carbonate chimneys at the active Lost City hydrothermal field. The exposure of mantle rocks to seawater during the breakup of Pangaea fueled chemolithoautotrophic microbial communities at the Iberia Margin, possibly before the onset of seafloor spreading. Lost City-type serpentinization systems have been discovered at midocean ridges, in forearc settings of subduction zones, and at continental margins. It appears that, wherever they occur, they can support microbial life, even in deep subseafloor environments.serpentinization | microfossils | lipid biomarkers | brucite−calcite | passive margin

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Section: Significancementioning

confidence: 99%

Section: Significancementioning

confidence: 99%

Section: Significancementioning

confidence: 99%

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Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

Klein

Humphris

Guo

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…Dean et al, 2000;Pickup et al, 1996] which is attributed to the extensive serpentinization of brecciated upper mantle peridotite, reducing the seismic velocity [Miller and Christensen, 1997] and hence the impedance contrast to the overlying sediments. The highly reflective and rotated fault-block signature of the upper basement layer near OBS B7 (Figure 6b) contradicts with these observations.…”

Section: Crustal Structure Of the Accommodation Zonementioning

confidence: 99%

East Greenland Ridge in the North Atlantic Ocean: An integrated geophysical study of a continental sliver in a boundary transform fault setting

et al. 2008

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The combined Greenland‐Senja Fracture Zones (GSFZ) represent a first‐order plate tectonic feature in the North Atlantic Ocean. The GSFZ defines an abrupt change in the character of magnetic anomalies with well‐defined seafloor spreading anomalies in the Greenland and Norwegian basins to the south but ambiguous and weak magnetic anomalies in the Boreas Basin to the north. Substantial uncertainty exists concerning the plate tectonic evolution of the latter area, including the role of the East Greenland Ridge, which is situated along the Greenland Fracture Zone. In 2002, a combined ocean‐bottom seismometer and multichannel seismic (MCS) survey acquired two intersecting wide‐angle reflection and coincident MCS profiles across and along the East Greenland Ridge. We present the results of integrated reflection seismic interpretation, first‐arrival tomography, 2D kinematic raytracing, full‐wave amplitude modeling, and gravity modeling of the intersecting profiles. The results show that (1) the Greenland Basin is characterized by a normal oceanic crustal velocity structure, (2) the velocity structure of the East Greenland Ridge is of overall continental type, and (3) a major faulted basin province above highly extended continental crust exists to the NE of the ridge. The results further suggest that a zone of extremely thin and faulted continental crust above partially serpentinized mantle peridotite defines the NW edge of the East Greenland Ridge and the transition to the NE Greenland margin.

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“…A 'volcanic' or magmarich margin is characterized by seaward-dipping reflectors typical of subaerial lava flows which mask the riftrelated extensional structures, whereas a 'non-volcanic' or 'magma-poor' rifted margin lacks these features Dean et al 2000). Hyperextension has been viewed to be a characteristic of magma-poor margins.…”

Section: Introductionmentioning

confidence: 99%

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

Chew

Staal

2014

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A combination of deep seismic imaging and drilling has demonstrated that the ocean-continent transition (OCT) of present-day, magma-poor, rifted continental margins is a zone of hyperextension characterized by extreme thinning of the continental crust that exhumed the lowermost crust and/or serpentinized continental mantle onto the seafloor. The OCT on present-day margins is difficult to sample, and so much of our knowledge on the detailed nature of OCT sequences comes from obducted, magma-poor OCT ophiolites such as those preserved in the upper portions of the Alpine fold-and-thrust belt. Allochthonous, lens-shaped bodies of ultramafic rock are common in many other ancient orogenic belts, such as the Caledonian – Appalachian orogen, yet their origin and tectonic significance remains uncertain. We summarize the occurrences of potential ancient OCTs within this orogen, commencing with Laurentian margin sequences where an OCT has previously been inferred (the Dalradian Supergroup of Scotland and Ireland and the Birchy Complex of Newfoundland). We then speculate on the origin of isolated occurrences of Alpine-type peridotite within Laurentian margin sequences in Quebec – Vermont and Virginia – North Carolina, focusing on rift-related units of Late Neoproterozoic age (so as to eliminate a Taconic ophiolite origin). A combination of poor exposure and pervasive Taconic deformation means that origin and emplacement of many ultramafic bodies in the Appalachians will remain uncertain. Nevertheless, the common occurrence of OCT-like rocks along the whole length of the Appalachian – Caledonian margin of Laurentia suggests that the opening of the Iapetus Ocean may have been accompanied by hyperextension and the formation of magma-poor margins along many segments.SOMMAIREDes travaux d’imagerie sismique et des forages profonds ont montré que la transition océan-continent (OCT) de marges continentales de divergence pauvre en magma exposée de nos jours, correspond à une zone d’hyper-étirement tectonique caractérisée par un amincissement extrême de la croûte continentale, qui a exhumé sur le fond marin, jusqu’à la tranche la plus profonde de la croûte continentale, voire du manteau continental serpentinisé. Parce qu’on peut difficilement échantillonner l’OCT sur les marges actuelles, une grande partie de notre compréhension des détails de la nature de l’OCT provient d’ophiolites pauvres en magma d’une OCT obduite, comme celles préservées dans les portions supérieures de la bande plissée alpine. Des masses lenticulaires de roches ultramafiques allochtones sont communes dans de nombreuses autres bandes orogéniques anciennes, comme l’orogène Calédonienne-Appalaches, mais leur origine et signification tectonique reste incertaine. Nous présentons un sommaire des occurrences d’OCT potentielles anciennes de cet orogène, en commençant par des séquences de la marge laurentienne, où la présence d’OCT a déjà été déduites (le Supergroupe Dalradien d’Écosse et d'Irlande, et le complexe de Birchy de Terre-Neuve). Nous spéculons ensuite sur l'origine de cas isolés de péridotite de type alpin dans des séquences de marge des Laurentides du Québec-Vermont et de la Virginie-Caroline du Nord, en nous concentrant sur les unités de rift d'âge néoprotérozoïque tardif (pour éviter les ophiolites du Taconique). La conjonction d’affleurements de piètre qualité et de la déformation taconique omniprésente, signifie que l'origine et la mise en place de nombreuses masses ultramafiques dans les Appalaches demeureront incertaines. Néanmoins, la présence fréquente de roches de type OCT tout le long de la marge Calédonnienne-Appalaches de Laurentia suggère que l'ouverture de l'océan Iapetus peut avoir été accompagnée d’hyper-étirement et de la formation de marges pauvres en magma le long de nombreux segments.

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Deep structure of the ocean‐continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: The IAM‐9 transect at 40°20′N

Cited by 299 publications

References 71 publications

Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

East Greenland Ridge in the North Atlantic Ocean: An integrated geophysical study of a continental sliver in a boundary transform fault setting

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

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