Rooting of the Sheeted Dike Complex in the Oman Ophiolite

  • A. Nicolas
  • F. Boudier
Part of the Petrology and Structural Geology book series (PESG, volume 5)

Abstract

The root zone of the sheeted dike complex representing a thin zone (hundred meters thick) of extreme thermal gradient (∼5°C/m) is regarded as a thermal boundary between the convective magma chamber system below, and the main convective hydrothermal circuit which closes above, at the base of this root zone. The root zone of the sheeted dike complex is located at the top of the high level foliated gabbro unit, where the foliation steepens, and where the first diabase dikes appears. It is a complex zone characterized by mutual intrusions of microgabbros dikes (that we call protodikes) with brownish microgranular contacts against the gabbro matrix. Upward, viscous flow in the protodikes and in the reheated enclosing gabbros generate a diffuse transition to the sheeted complex. Protodike margins stretched in the enclosing flowing doleritic gabbros form a complicated network which can be depicted thanks to microstructural analysis. Later diabase dikes cross-cut the section. These relationships are obscured by the hydrothermal circulation which has generated, in particular, isotropic amphibole gabbro veins. These veins tend to propagate horizontally; they may be interpreted as the downward closure of the main hydrothermal convective circuit.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Allen, C.R., 1975. The petrology of a portion of the Troodos plutonic complex, Cyprus. Ph.D., Univ. of Cambridge (unpubl.).Google Scholar
  2. Benn, K. and Allard, B, 1989. Preferred mineral orientations related to magmatic flow in ophiolite layered gabbros. J. Petrology, 30: 925–946.CrossRefGoogle Scholar
  3. Beurrier, M., 1987. Géologie de la nappe ophiolitique de Samail dans les parties orientale et centrale de l’Oman. Thèse Doc. Etat, Paris 6, 406 p.Google Scholar
  4. Browning, P., 1982. The petrology, geochemistry and structure of the plutonic rocks of the Oman ophiolite. Ph.D. The Open University, 404 p.Google Scholar
  5. Delaney, J.R., Mogk, D.W. and Maul, M.J., 1987. Quartz-cemented breccias from the Mid-Atlantic Ridge: samples of a high salinity hydrothermal upflow zone. J. Geophys. Res., 92: 9175–9192.CrossRefGoogle Scholar
  6. Dewey, J.F. and Kidd, W.S.F., 1977. Geometry of plate accretion. Geol. Soc. Amer. Bull., 88: 960–968.CrossRefGoogle Scholar
  7. Gerlach D.C., Ave Lallemant, H.G. and Leeman, W.P., 1981. An island arc origin for the Canyon Mountain Ophiolite Complex, Eastern Oregon, U.S.A. Earth Planet. Sci. Lett., 53: 255–265.CrossRefGoogle Scholar
  8. Gregory, R.T. and Taylor, H.P., 1981. An oxygen isotope profile in a section of Cretaceous oceanic crust, Samail Ophiolite, Oman: evidence for δ180 buffering of the oceans by deep (> 5 km) seawater-hydrothermal circulation at mid-ocean ridges. J. Geophys. Res., 86: 2737–2755.CrossRefGoogle Scholar
  9. Harper, G.D., 1984. The Josephine ophiolite, northwestern California. Geol. Soc. Am. Bull.. 95: 1009–1026.CrossRefGoogle Scholar
  10. Hopson, C.A., Coleman, R.G., Gregory, R.T., Pallister, J.S. and Bailey. E.H., 1981. Geologic section through the Samail ophiolite and associated rocks along a Muscat-Ibra transect. J. Geophys. Res., 86: 2527–2544.CrossRefGoogle Scholar
  11. Juteau, T., Ernewein, E., Reuber, I., Whitechurch H. and Dahl. R., 1988. Duality of magma-tism in the plutonic sequence of the Sumail nappe. Tectonophysics, 151: 107–135.CrossRefGoogle Scholar
  12. Kelly, D.S. and Delaney, J.R., 1987. Two-phase separation and fracturing in mid-ocean ridge gabbros at temperatures greater than 700°C. Earth Planet. Sci. Lett., 83: 53–66.CrossRefGoogle Scholar
  13. Lippard, S.J., Shelton, A.W. and Gass, L.G., 1986. The ophiolite of Northern Oman. Geol.Soc. London Mem., 11,178 p.Google Scholar
  14. Mysen, B.O. and Boettcher, A.L., 1974. Melting of a hydrous mantle. I: Phase relations of natural peridotite at high pressures and temperatures with controlled activities of water. carbon dioxide, and hydrogen. J. Petrol., 16: 520–548.Google Scholar
  15. Nehlig, P., 1989. Etude d’un système hydrothermal océanique fossile: [ophiolite de Semail (Oman). Thèse Doc. Univ. Brest, 308 p.Google Scholar
  16. Nehlig P. and Juteau, T., 1988. Flow porosities, permeabilities and preliminary data on fluid inclusions and fossil thermal gradients in the crustal sequence of the Sumail ophiolite (Oman). Tectonophysics, 151: 199–221.CrossRefGoogle Scholar
  17. Nicolas, A., 1989. Structures of ophiolites and dynamics of oceanic lithosphere. Kluwer Acad. Publ., 367 p.CrossRefGoogle Scholar
  18. Nicolas, A., Reuber, I. and Benn, K., 1988a. A new magma chamber model based on structural studies in the Oman ophiolite. Tectonophysics. 151: 87–105.CrossRefGoogle Scholar
  19. Nicolas, A., Ceuleneer, G. and Boudier, F., 1988b. Mantle flow patterns and magma chambers at ocean ridges: evidence from Oman Ophiolite. Marine Geophys. Res.. 9: 293–310.CrossRefGoogle Scholar
  20. Pallister, J.S., 1981. Structure of the sheeted dike complex of the Samail ophiolite near Ibra. Oman. J. Geophys. Res., 86: 2661–2672.CrossRefGoogle Scholar
  21. Pallister, J.S. and Hopson, C.A., 1981. Samail ophiolite plutonic suite: field relations, phase variation, cryptic variation and layering, and a model of a spreading ridge magma chamber. J. Geophys. Res., 86: 2593–2644.CrossRefGoogle Scholar
  22. Payne J.G. and Strong, D.F., 1979. Origin of Twillingate trondhjemite, North-Central Newfoundland: partial melting in the roots of an island arc. In: ‘Trondhjemites, dacites, and related rocks’, F. Barker ed., Elsevier, Amsterdam, 489–516.Google Scholar
  23. Pedersen, R.B., 1986. The nature and significance of magma chamber margins in ophiolites:examples from the Norwegian Caledonides. Earth Planet. Sci. Lett.. 77: 100–112.CrossRefGoogle Scholar
  24. Pedersen, R.B. and Malpas, J., 1985. The origin of oceanic plagiogranites from the Karmoy ophiolite, Western Norway. Contr. Mineral. Petrol., 88: 36–52.CrossRefGoogle Scholar
  25. Rosencrantz, E., 1983. The structure of sheeted dikes and associated rocks in North Arm Massif, Bay of Islands Ophiolite Complex, and the intrusive process at oceanic spreading centers. Canad. J. Earth. Sci., 20: 787–801.CrossRefGoogle Scholar
  26. Rothery, D.A., 1983. The base of a sheeted dyke complex. Oman ophiolite: implications for magma chambers at oceanic spreading axes. J. Geol. Soc., London, 140: 287–296.CrossRefGoogle Scholar
  27. Smewing, J.D., 1981. Mixing characteristics and compositional differences in mantle-derived melts beneath spreading axes: evidence from cyclically layered rocks in the ophiolite of North Oman. J. Geophys. Res., 86: 2645–2660.CrossRefGoogle Scholar
  28. Stern, C. and Elthon, D., 1979. Vertical variations in the effects of hydrothermal metamorphism in Chilean ophiolites: their implications for ocean floor metamorphism. Tectonophysics. 55: 179–213.CrossRefGoogle Scholar
  29. Wyllie, P.J., 1980. The origin of kimberlite. J. Geophys. Res.. 85: 6902–6919.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 1991

Authors and Affiliations

  • A. Nicolas
    • 1
  • F. Boudier
    • 1
  1. 1.Laboratoire de Tectonophysique, URA 1370 CNRSUniversité Montpellier IIMontpellierFrance

Personalised recommendations