Structural mapping in the Oman ophiolites: Mantle diapirism along an oceanic ridge

Nicolas, Adolphe; Ceuleneer, Georges; Boudier, Françoise; Misseri, M.

doi:10.1016/0040-1951(88)90239-9

Cited by 125 publications

(70 citation statements)

References 34 publications

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“…The Alpine Tethyan OCT ophiolites described by Manatschal and Müntener (2009) and other workers clearly do not conform to the classical definition of a Penrose-type ophiolite (Penrose conference participants 1972), such as the Semail ophiolite in Oman (Nicolas et al 1988), the Bay of Islands Complex in Newfoundland (Bird et al 1971) and the Troodos ophiolite in Cyprus (Gass 1968). The Alpine Tethyan OCT ophiolites contain only minor amounts of mafic igneous rocks (basaltic lavas, sheeted dyke complexes and gabbros) and are instead characterized by blocks of ancient subcontinental mantle exhumed by top-basement detachment faults and overlain by extensional being re-enriched in basaltic melt components) and therefore continental mantle is the product of at least two major processes: melt depletion followed by refertilization or other major metasomatic enrichment processes such as Si enrichment (Lee et al 2011).…”

Section: Criteria For Identifying An Ocean-continent Transition (Oct)mentioning

confidence: 91%

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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Section: Criteria For Identifying An Ocean-continent Transition (Oct)mentioning

confidence: 91%

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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“…These records are related to the presence of (1) magma chamber tips in the crust [Juteau et al, 1988a[Juteau et al, , 1988bMacLeod and Rothery, 1992], (2) frozen diapirs in the mantle [Ceuleneer, 1986[Ceuleneer, , 1991Ceuleneer et al, 1988;Nicolas et al, 1988aNicolas et al, , 1988bNicolas et al, , 2000aNicolas et al, , 1994 and (3) areas of abundant sheeted dykes [MacLeod and Rothery, 1992;Python and Ceuleneer, 2003]. The fact that these magmatic features, all considered as acquired at an accreting ridge, were preserved in the Oman ophiolite, was a major argument to stress that a paleo-ridge was indeed obducted [Nicolas et al, 2000a].…”

Section: Geological Backgroundmentioning

confidence: 99%

“…All segments have a center marked by high values of spinel Cr# (% F max ) and edges with the lowest values. The large, 50-100 km segments (70 km in average) may correspond to large asthenospheric mantle upwellings between major deep mantle discontinuities, while the smaller ones possibly relate more superficial mantle instabilities similar to the structural diapirs of Nicolas et al (1988a). We consider that the variation in degree of melting in the short-scale instabilities relates fluid/melt flux melting variations.…”

mentioning

confidence: 99%

Along‐ridge petrological segmentation of the mantle in the Oman ophiolite

Monnier

Girardeau

Mée

et al. 2006

Geochem Geophys Geosyst

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[1] Oman ophiolite mantle has been sampled over a distance of about 400 km, all along the paleo-ridge axis. Primary phases have been analyzed in 174 peridotites (mainly harzburgites) and major and trace element contents measured in 90 and 156 samples, respectively. Most samples display depleted characteristics with very low incompatible element bulk rocks and very low HREE contents. On the basis of the spinel Cr# and in agreement with Yb concentrations in the bulk rocks, an average of 16.5% (F max ) of melt extraction is estimated. These rocks show light REE enrichments marked by high LREE/MREE ratios that well correlate with the extent of melting. The light REE were possibly gained during the latest stage of melting in an open-system melting model, or through interaction with influxed fluid after melting. Chemical data have been processed Fourier Transforms to study the along-ridge variations, which gives results similar to those obtained using the seven point running average . When plotted along ridge, spinel Cr# display variations with two types of wavelengths, defining four 50-100 km long segments (70 km in average) and numerous 10-20 km shorter ones making undulations within the longer ones. All segments have a center marked by high values of spinel Cr# (% F max ) and edges with the lowest values. The large, 50-100 km segments (70 km in average) may correspond to large asthenospheric mantle upwellings between major deep mantle discontinuities, while the smaller ones possibly relate more superficial mantle instabilities similar to the structural diapirs of Nicolas et al. (1988a). We consider that the variation in degree of melting in the short-scale instabilities relates fluid/melt flux melting variations. By comparison with mid-oceanic ridge models, the long Oman segments can correspond to second-order segments and the smallest to third-to fourth-order ones. Our data on the geometry of the melting zones will constrain models of the dynamics of the mantle beneath ridges. They provide a new perspective for further characterization of the segments in the Oman ophiolite.

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“…The Oman ophiolite and the present-day East Pacific Rise are compared at the same scale in figure 1, modified after Nicolas et al [1988a]. Such fast spreading ridges typically display a periodic segmentation, with the segments being separated from one another by a variety of structural and magmatic discontinuities, including faults, overlapping spreading centers, and small nonoverlapping offsets [Batiza and Margolis, 1986; [1988a]).…”

mentioning

confidence: 99%

The Northern Samail Ophiolite: An Oxygen isotope, microprobe, and field study

Stakes¹,

Taylor²

1992

J. Geophys. Res.

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Divi.Jion ofGeologk:alllllll Plondoty Sdenca, California .bulilu# ofT~ PtlStlllma Geological, petrological, and axygcn isotopic data are pn:sentecl for 228 whole rock and mineral samples collected from a 100x20 km area of the nortbem Samail opbiolite in Oman. MOlt of these samples arc from three detailed profiles tluough the pillow IIIYBI, sbeetecl dikes, and .red pbbi'OI of this laterally heterogeneous fratpnent of Cretaceous oceanic crust, down to and 8C1'0I& the petroaop: Moho. The profiles encompass a l'llDF of petrologic and tectonic styles, and each profile cmibit& distinctive llloJ 1 6o variations compared to one another and to mid-ocean ridge basalt&, as a result of ~ seawater-h)'drothermal interaction that varied in intensity along strike in the ophiolite. In general, 1 Bo depletions arc observed in the layered gabbi'OI and 1llo enrichments in most of the sheeted dikes and pillow lavas, similar to results previously observed in the southem part of the ophiolite (Ibra area), where 1 Bo depletions within the gabbroic section arc quantitatively balanced by 1llo enrichments in the sballower parts of the oceanic crust. The Wadi Hilti profile, selected as an example of relatively intact crust, differs from lbra in having more uniform and slightly bigher6 1 Bo in the gabbi'OI ( + S.4 to +6.3), as well as in containing more h)'drous alteration minerals (amphibole, epidote, cblorite, and prcbnite ). The profiles in the Wadi Kanut-Shafan and Wadi Rajmi sections arc much more complex and reveal the impact of off-axis intrusions and deep crustal shearing. Plagiogranitewebrlite intrusions in the Sbafan-Kanut area superimposed a local h)'drothermal aureole on the ophiolite, evident in dikes highly depleted in 1 Bo, quartz-sulfide veins, abundant epidote, thullite, and cblorite in shallower rocks, and low-temperature h)'drous alteration of deeper gabbroic rocks; the latter produced an overall increase in wbole rock 6 1 Bo ( +6.2 to +6.9). Such late stage intrusions arc found throughout the northem half of the Samail ophiolite. The Wadi Rajmi area, which is a possible fossil transform or propagating rift, represent& the most complex of the three profiles; it also contains the most abundant highly deformed and h)'drothermally altered rocks, together with the deepest and largest zone of 1 Bo depletion yet found in any ophiolite (locally61llo < + 2.0). Conduits for large volumes of high-temperature h)'drothermal fluids were provided by fractures now occupied by low-1 Bo gabbro pegmatitcs and Iow-lllo dikes. Material balance estimates for the regional samples and from the various transects through the ophiolite give crustal bulk 6 1 Bo averages ( +S.9 to +6.3) that arc, within sampling error, almost identical to the average MORB basalt value of about + S.8, if both vertical and lateral crustal heterogeneities are integrated into a threedimensional model. This supports and amplifies the conclusion of earlier workers that the 6 1 Bo of seawater is buffered and controned by h)'drothermal interaction with oceanic crust, as lon...

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Structural mapping in the Oman ophiolites: Mantle diapirism along an oceanic ridge

Cited by 125 publications

References 34 publications

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

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

Along‐ridge petrological segmentation of the mantle in the Oman ophiolite

The Northern Samail Ophiolite: An Oxygen isotope, microprobe, and field study

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