• What does the Wilson cycle have to do with the Oman ophiolite?
  
• Where in the world picture did the Oman ophiolitic crust form?
  
• Where in the Tethys Ocean itself was the ophiolitic crust produced?
  
• What implications does this location have for emplacement models?
  

Plate Motions: A quick review of the last 400 million years.

• Pangea forms from collision of Laurasia and Gondwana (Devonian into Carboniferous).
  
• Dispersion of continents due to rifting events. Gondwana separates form Eurasia, forming the Tethys Ocean (Triassic).
  
• Reversal of plate motion causes Afro-Arabian plate to head NE, closing the Tethys Ocean (Cretaceous).
  
• Collision of Eurasian/Arabian plates leads to present day configuration of continents (Tertiary thru present).
  

Tethys Ocean: Birthplace of the Oman ophiolite

• Narrow ocean developed by the end of the Triassic--"Oman Tethys" (also referred to as the "Neo-tethys, or Southern Tethys) should not be confused with the vast ocean somewhat to the east.
  
• NE facing passive margin formed with continental shelf, slope and rise deposits, much like the present day US eastern coast.
  
• No established width for the Oman Tethys: widths range from 800-2400 km, depending upon the combination of spreading rates and subduction models used.
  
• ~110ma: closure begins as Afro-Arabian plate swings NE
  
• Tethys consumed until present day configuration reached.
  

Closure/Collision.

• Present configuration (Coleman, 1981)
  • Zagros fold belt formed when northern edge of Arabia collided with Eurasia
    
  • Makran subduction zone dips to NE
    
• Possible locations for subduction zones which closed the Tethys Ocean. (Lippard et al., 1986)
  • Present location--not enough old volcanics
    
  • Other continental margin, SW dipping--also not enough volcanics
    
  • Somewhere in the middle of the ocean
    
    • at a spreading ridge
      
    • at a differential break in strength (density, temperature, thickness) of the oceanic crust
      

Creation of Ophiolitic Crust (while still under water)

• Back-arc spreading above subduction zone
  • Geometrical basis (Lippard et.al., 1986)
    
  • Lava stratigraphy (Pearce et al., 1981)
    
    • Geotimes unit = oceanic crust
      
    • Lasail/Alley units = volcanic ridge above subduction zone
      • Spider diagrams show affiliation with volcanic arc, not with morb
      • Cr-Y covariation diagram shows upper units in different field than morb
        
• Spreading center origin (Coleman, 1981; Boudier, 1982)
  • Volcanic arc signature could be a result of volcanic activity during intra-oceanic thrusting which began at ridge axis
    
  • Metamorphic constraints on timing and emplacement models (see Mark's talk)
    
  • Compares well to present day oceanic crust in terms of thickness, igneous history and seismic velocities
    

References

• Al-Harthy, M.S. et al., 1991. Tertiary basaltic intrusions in the central Oman Mountains, in Peters, T. et al, (eds), Ophiolite Genesis and Evolution of the Oceanic Lithosphere, Ministry of Petroleum and Minerals, Sultanate of Oman, p. 675-682.

• Andrews-Speed, C.P. and Brookfield, M.E., 1983. Comment on "Tectonic Setting of Ophiolite Obduction in Oman" by Robert Coleman. Journal of Geophisical Resaerch, 88:609-611.

• Boudier, F. et al., 1985. Kinematics of oceanic thrusting in the Oman ophiolite: model of plate convergence. Earth and Planetary Science Letters, 75: 215-222.

• Boudier, F. Nicholas, A., and Bouchez, J.L., 1982. Kinematics of oceanic thrusting and subduction from basal sections of ophiolites. Nature, 296: 825- 828.

• Coleman, R.G., 1981. Tectonic setting for ophiolite obduction in Oman. Journal of Geophisical Resaerch, 86: 2497-2508.

• Gnos, E. et al., 1997. Late Cretaceous/early Tertiary convergence between the Indian and Arabian plates recorded in ophiolites and related sediments. Tectonophysics, 271:1-19.

• Rod, Emile. 1982. Comment on "Tectonic Setting of Ophiolite Obduction in Oman" by Robert Coleman. Journal of Geophisical Resaerch, 87: 4759-4760.

• Hacker, B. R., and Gnos, E., 1997. The conundrum of Samail: explaininng the metamorphic history. Tectonophysics, 279: 215-226.

• Hacker, B.R., 1994. Rapid emplacement of young oceanic lithosphere: argon geochronology of the Oman ophiolite. Nature, 265: 1563-1565.

• Irving, E., 1977. Drift of the major continental blocks since the Devonian. Nature, 270: 304-308.

• Lippard, S.J., Shelton, A.W., and Gass, I.G., 1986. The Ophiolite of Northern Oman, Gelogical Society of London Memoirs, 11, 178p.

• Michard, A., Boudier, F. and Goffe , B., 1991. Obduction versus subduction and collision in the Oman case and other Tethyan settings, in Peters, T. et al, (eds), Ophiolite Genesis and Evolution of the Oceanic Lithosphere, Ministry of Petroleum and Minerals, Sultanate of Oman, p. 447-467.

• Pearce, J.A., et al., 1981. The Oman ophiolite as a Cretaceous arc-basin complex: evidence and implications. Philosophical Transactions of the Royal Society of London. A3: 299-317.