Development of concepts concerning the genesis and emplacement of Tethyan ophiolites in the Eastern Mediterranean and Oman regions

Abstract

This article uses evidence mainly from the Eastern Mediterranean and Oman to help understand the origin and emplacement of ophiolites. Field studies in these regions emphasize the diversity of ophiolite-related sedimentary and tectonic processes. Topics to be discussed here include the sedimentary covers of ophiolites, their metamorphic soles, related melanges, and emplaced continental margin (slope/rise) units. Modes of ophiolite emplacement will also be considered and tectonic reconstructions that have a direct bearing on the origin and emplacement of ophiolites. The writer argues that there is compelling evidence that many ophiolites formed by spreading above intraoceanic subduction zones. Evidence from their intact sedimentary covers, however, indicates that such subduction was only incipient in most cases, as directly associated volcanic arcs or back-arc basins are rare. Metamorphic soles record fragments of oceanic lithosphere derived from settings ranging from open-ocean to continental slope/rise settings. Underlying melanges record the subduction of most of the ocean lithosphere formed at spreading ridges. Continental margin units beneath ophiolites demonstrate that these ophiolites were formed in ocean basins that were mainly initiated by continental rifting in the Eastern Mediterranean and Oman regions. Ophiolite emplacement was commonly achieved by trench–margin collision, although strike-slip (transpression) and large-scale accretion along subducting margins played a role in some cases. Taking account of the Mesozoic palaeotectonic setting of the Eastern Mediterranean region, it is widely believed that ophiolites of two main ages (Mid-Jurassic and Late Cretaceous) were formed in several small oceanic basins separated by rifted microcontinents. The history of Tethys in pre-Mesozoic time remains more open to question. Lastly, giant subduction-related ophiolites, as in Oman, Cyprus, or the Balkans, may not be forming anywhere in the world ocean today, but may instead relate to rare events in earth history when regional, to global plate, boundaries were drastically reorganised.