An Analysis of the Tectonic Environments Experienced by the Oman Ophiolite

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INTRODUCTION

The Oman ophiolite is the largest ophiolite, extending over 600km in a NW-SE direction with a maximum width of 130 km, and is considered to be a fragment of Cretaceous Tethyan oceanic lithosphere (Tamura & Arai, 2006). The Oman ophiolite is a harzburgite ophiolite and is comprised of 12 separate tectonic blocks [Figure 1] whose internal structures imply inter-plate independence during their tectonic emplacement (Tamura, Arai, 2006). The Oman ophiolite has been thoroughly researched because it is well preserved and, particularly in the north, the entire sequence of ophiolite stratigraphy, from the upper mantle to oceanic sediments, is exposed. Within the ophiolite, there co-exists mid-ocean-ridge basalt (MORB)-type extrusive rocks as well as ‘arc signature’ extrusive rocks suggesting that the entire ophiolite was not formed at a mid ocean ridge (MOR) as was previously thought. The following essay will present evidence to support the theory that the Oman ophiolite formed in a MOR environment and could subsequently have experienced a supra-subduction zone (SSZ) setting as well.

Figure 1: Map of the Oman ophiolite with the twelve tectonic plates labelled in black. (Figure 1 Godard et al 2003)

The Oman Ophiolite consists of various layers that constitute the oceanic crust and upper mantle. From top to bottom, the oceanic crust comprises of lavas, a sheeted dyke complex and gabbros, both non-layered and layered. The uppermost part of the mantle includes gabbroic sills, chromitite and dunite in a large deposit of harzburgite. [Figure 2] For this essay emphasis will be placed on the lavas, gabbros and chromitites.

Figure 2: The crustal layers and up...

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...lite. Earth and Planetary Science Letters, 251, 52-65.

• Godard M, Dautria J, Perrin M. (2003) Geochemical variability of the Oman ophiolite lavas: relationship with spatial distribution and paleomagnetic directions. Geochemistry Geophysics Geosystems an electronic Journal of the Earth Sciences, 4, 1-15

• Tamura A, Arai S. (2006) Harzburgite-dunite-orthopyroxenite suite as a record supra-subduction zone setting for the Oman ophiolite mantle. Lithos, 90, 43-56

• France L, Ildefonse B, Koepke J. (2009) Interactions between magma and hydrothermal system in Oman ophiolite and in IODP Hole 1256D: Fossilization of dynamic melt lens at fast spreading ridge. . Geochemistry Geophysics Geosystems an electronic Journal of the Earth Sciences,10. 1-30

• Nicolas, A. (1989). Structure of Ophiolites and Dynamics of Oceanic Lithosphere. Dordrecht: Kluwer Academic Publishers.

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