Overview of the genesis and emplacement of Mesozoic ophiolites in the Eastern Mediterranean Tethyan region

Abstract

The Eastern Mediterranean region exhibits a fascinating diversity of ophiolites and related oceanic magmatic units of mainly Triassic, Jurassic and Cretaceous age. Comparisons with the settings of modern oceanic lithosphere indicate that the various Eastern Mediterranean ophiolites have different origins and formed in a variety of tectonic settings. Some have argued that the largest ophiolites, of Jurassic and Cretaceous age (e.g. Troodos), formed at mid-ocean ridges. However, the widespread occurrence of andesitic extrusives, chemically “depleted” basalts and highly magnesian lavas (boninites), favour formation of most of the large, relatively intact ophiolites in the Eastern Mediterranean region above subduction zones rather than at mid-ocean ridges (MORs). Such ophiolites probably formed by spreading during the initial stages of intra-oceanic subduction, prior to the emergence of any major related oceanic arc. Supra-subduction-type ophiolites typically formed during short-lived periods (<5 Ma) of regional plate re-organisation. By contrast, most MOR-type oceanic crust was subducted, or is preserved only as dismembered thrust sheets or blocks in ophiolitic melange, commonly metamorphosed under high-pressure/low-temperature (HP/LT) conditions. However, MOR-type ophiolites are locally preserved (e.g. Jurassic Western-type Albanian ophiolite). Seamounts were preferentially accreted into melanges and record subduction of large areas of oceanic crust. Volcanic–sedimentary units of mainly Triassic age, including alkaline to MOR-type extrusives and radiolarites record rifting, transitional to spreading of Neotethyan ocean basins. Back-arc, intra-continental marginal basins of Triassic and Late Jurassic age developed within the northerly (Eurasian) continental margin (e.g. Jurassic Guevgueli ophiolite, N Greece). Ophiolites formed in these basins were exposed by uplift, without significant transport. Transform-influenced ophiolites are occasionally preserved (e.g. Late Cretaceous Tekirova ophiolite, SW Turkey). Metamorphic soles reflect tectonic displacement of oceanic lithosphere while still hot, near a spreading centre (whether of mid-ocean ridge or supra-subduction type). The Eastern Mediterranean subduction-type ophiolites, of both Jurassic and Cretaceous age, were rooted in several coeval Neotethyan oceanic basins, separated by microcontinents and cannot be interpreted as vast, far traveled thrust sheets derived (at different times) from a single, palaeogeographically simple Tethyan oceanic basin.