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Ophiolites and Oceanic Crust |
1 Department of Geology and Geophysics, University of Edinburgh, Edinburgh EH9 3JW, UK
2 Geological Survey Department, Nicosia, Cyprus
The foundations for study of the Troodos ophiolite and adjacent units in Cyprus were laid down by systematic mapping by the Cyprus Geological Survey Department (1952–1970). Prior to the late 1950s, Cyprus geology was interpreted in classic geosynclinal terms. The first, integrated description of the Troodos was given by Gass & Masson Smith in 1963. Publication of the Vine & Matthew’s (1963) sea-floor spreading hypothesis was followed by Ian Gass’s key interpretation in 1968 of the Troodos as oceanic lithosphere formed by sea-floor spreading. During the early 1970s, the dominant view of the Troodos was of a mid-ocean ridge, formed by spreading at a narrow, linear spreading zone, fed by a single, axial magma chamber. However, early geochemical studies suggested that genesis could have taken place above a subduction zone. During the 1980s, drilling related to the International Cyprus Crustal Study Project stimulated much new field work. By 1990 a popular view of the Troodos was that it had formed above a northward-dipping subduction zone during the earlier stages of convergence within an oceanic basin, similar in some respects to the origin of SW Pacific forearcs. Others favoured an origin as a marginal basin formed by spreading above a southward-dipping subduction zone, either in the vicinity of Cyprus, or located in central Turkey. In whatever scenario, it is generally accepted that the spreading fabric was unstable and was fed by small, multiple magma chambers. The extension outpaced magma supply and this favoured extensional detachment faulting, mainly near the base of the sheeted dykes. The Troodos lithosphere was also bounded by an oceanic fracture zone to the present south. Studies of the Late Cretaceous-Recent sediment cover have documented deep-sea sedimentation and later uplift, related to Africa-Eurasia convergence. In W Cyprus, the adjacent Mamonia Complex was pieced together as a Mesozoic passive margin bordering a small ocean basin, although whether this was a Red Sea-type basin, or a backarc marginal basin is still debated. The Mamonia lavas and sediments were juxtaposed with the Troodos ophiolite by processes, variously interpreted as subduction/accretion, oceanic transform faulting, strike-slip, collision and/or palaeorotation of a Troodos microplate. The Kyrenia Range in N Cyprus also includes remnants of Mesozoic passive margin; it was emplaced in stages apparently by a combination of strike-slip and thrusting. On a regional scale, the Troodos ophiolite preserves part of one of a number of inferred small oceanic basins within the Mesozoic Tethyan area of the Eastern Mediterranean.
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