Abstract The Eocene–Miocene Mesohellenic Trough is an elongate sediment-filled tectonic basin trending NW across central Greece and into Albania. Neotethyan oceanic rocks, including Triassic–Jurassic rift-related volcanic rocks and deep-sea sediments, accretionary mélange and ophiolitic complexes, crop out along its margins. These units were tectonically emplaced onto the Pelagonian microcontinent to the east and the Apulian–African continental margin to the west. In northern Greece, the mid-Jurassic Vourinos ophiolite on the eastern margin of the trough is geographically separated from the synchronous Pindos ophiolite along the western margin by a minimum c. 20 km distance. The sedimentary fill of the trough obscures their presumed subsurface continuation, although magnetic surveys identify thick ‘ophiolitic’ rocks beneath the basin. We interpret these ophiolites as parts of the same oceanic slab, two parts of a single larger oceanic complex we now term the Mesohellenic ophiolite. Comparable ophiolitic complexes to the south (the Koziakas and Othris) and the ophiolites of the Mirdita complex to the north in Albania are considered as members of this same complex. Geological and petrological data from the Vourinos and Pindos ophiolites define intra-slab heterogeneity. Vourinos essentially is a ‘Penrose-style’ ophiolite with ‘supra-subduction’ compositions; the less continuous Pindos ophiolite shows coexisting mid-ocean ridge basalt and island arc characteristics. Ophiolitic rocks that seem to represent geographical overlap between these characteristic associations crop out along their northern (Dotsikos strip) and southern (Mesovouni) margins. Variations in mantle strain conditions across the ophiolitic slab have been mapped, and demonstrate a single orientation of deformation; this is explained by variable strain kinematics that persisted across the ductile–brittle boundary. A continuity from ductile to brittle emplacement structures spans the Mesohellenic Trough, independent of petrological association, and indicates the original relative positions of these ophiolites within the oceanic slab. These structures illustrate tectonic ‘steps’ of obduction from the ridge crest onto the Pelagonian margin to the east, and can be relatively timed by the overlap of magmatism with ductile deformation in different parts of the slab. Hence, rotations of original horizontality are dated to the period preceding cessation of ductile field deformation, while still in the oceanic environment. The morphology defined by these structures and the horizontal rotation of stratigraphy are analogous to a spoon- or scoop-shaped nappe originating in the ductile field at its base, and crossing into the brittle field rapidly at its leading edge (Vourinos), whereas the mylonitic deformation characterizes the ‘trailing’ end (Pindos). Age relations require that geochemical variation between the two complexes must be explained within a model of synchronous generation, possibly with apparent ‘supra-subduction zone’ rifting of originally heterogeneous mantle, or an overlapping series of diverse processes of magma generation in an initially homogeneous mantle. Indications of the original ridge crest directions suggest the operation of several simultaneous spreading centres, separated by transform faults or ‘pseudofaults’. A palinspastic reconstruction of the slab constrains applicable oceanic models and provides the basis of future research.

Abstract The late Early Permian ( c. 278–270 Ma) supra-subduction zone (SSZ) Dun Mountain ophiolite is bordered to the east by the Pataki Melange and to the NE by the Croisilles Melange. In the south, the ophiolite passes into a dismembered incipient oceanic arc (Otama Complex). The above units represent an oceanic forearc generated above a west-dipping subduction zone. Terrigenous sediment reached the subduction trench after the Mid-Permian(?) docking of the oceanic forearc with the long-lived SE Gondwana active continental margin. Mixed terrigenous–volcaniclastic turbidites accumulated in the trench prior to and during melange accretion. Fragments of the overriding oceanic forearc (and incipient arc, locally) detached and mixed to form melange and broken formation. Despite some individual features (e.g. of the basalt chemistry), the Patuki and Croisilles melanges are interpreted as originally representing a single Permian trench–accretionary complex. The more distal (easterly) part was sliced into the adjacent accretionary complex of the Caples Terrane to form the Croisilles Melange (and equivalent Greenstone Melange) probably after the Triassic. The South Island melanges exemplify accretionary processes in which igneous and sedimentary rocks were detached from the overriding plate by subduction–erosion, together with accretion, including seamount material from the subducting oceanic plate, with implications for melanges elsewhere.

Abstract The Vardar Zone documents the Mesozoic–Early Cenozoic evolution of several small oceanic basins and a complex history of terrane assembly. Following a Hercynian phase of deformation and granitic intrusion within the Pelagonian Zone to the west, the Vardar Zone rifted in Permian–Triassic time, with the creation of an oceanic basin (Almopias Ocean) during the Late Triassic–Early Jurassic. During the Mid-Jurassic, this ocean subducted northeastwards beneath the Paikon Zone and the Serbo-Macedonian Zone, giving rise to arc volcanism and back-arc rifting. A second ocean basin, the Pindos Ocean, opened to the west of a Pelagonian microcontinent, also during Late Triassic–Early Jurassic time. During the Mid–Late Jurassic, ophiolites were emplaced northeastwards (in present co-ordinates) from the Pindos Ocean onto the Pelagonian microcontinent, forming the Pelagonian ophiolitic mélange within a flexural foredeep. This emplacement is dated at pre-Late Oxfordian–Early Kimmeridgian from the evidence of corals within neritic carbonates that depositionally overlie the emplaced ophiolitic rocks in several areas. Related greenschist- or amphibolite-facies metamorphism is attributed to deep burial following trench–margin collision and the attempted subduction of the Pelagonian continent. An inferred phase of NNW–SSE displacement, also of pre-latest Jurassic age, imparted a regionally persistent stretching lineation and related ductile fabric, apparently related to post-collisional strike-slip. The Pelagonian Zone and its emplaced ophiolitic rocks then underwent extensional exhumation during Late Jurassic–Early Cretaceous time. The western margin of the Vardar Zone experienced extensional (or transtensional) faulting, neritic carbonate and terrigenous clastic deposition, and intermediate–silicic magmatism during Late Jurassic–Early Cretaceous time. Oceanic crust (Meglenitsa Ophiolite) formed further east in the Vardar Zone during Late Jurassic–Early Cretaceous time, possibly above a subduction zone. A near-margin setting is suggested by the presence of a deep-water terrigenous cover, probably derived from the Paikon continental unit to the east. The Vardar Zone as a whole finally closed related to eastward subduction beneath Eurasia, culminating in collision with the Pelagonian microcontinent during latest Cretaceous–Eocene time, as recorded in foreland basin development, HP–LT metamorphism, ophiolite emplacement and large-scale westward thrusting. In contrast to models that suggest closure of the Vardar Ocean in the Mid–Late Jurassic, followed by reopening of a Cretaceous ocean, we believe that the Vardar Ocean remained partly open from Triassic to Late Cretaceous–Early Cenozoic time.

Abstract The Eastern Mediterranean region is characterized by one of the largest concentrations of ophiolites anywhere in the world. Many of these ophiolites are fragmentary or highly deformed, such that their initial mode of tectonic emplacement cannot easily be inferred from the local held relations. The emplacement of many of these ophiolites can usefully be compared with the intact Oman ophiolite, one of the largest and best-studied ophiolites in the world. The Oman ophiolite is commonly believed to have been created in Late Cretaceous time ( c . 95 Ma) above an oceanward-dipping, intra-oceanic subduction zone. This was followed by collision of the subduction zone with the downflexed Arabian passive margin, facilitating the emplacement of the ophiolite onto the continental margin. A less likely alternative is that the Oman ophiolite formed at a mid-ocean ridge that then collapsed, initiating the emplacement of the ophiolite. An Oman-type model is applicable to many of the Mid-Jurassic and the Late Cretaceous ophiolites of the Eastern Mediterranean region that were thrust over former passive continental margins. These ophiolites are again mainly of suprasubductionzone type. Such ophiolites include many of the Jurassic ophiolites of Greece, Albania and former Yugoslavia, and also the Late Cretaceous ophiolites of Turkey and northern Syria. These ophiolites were emplaced from both more northerly and southerly Neotethyan ocean basins. In contrast, the opposing (northerly) margins of these oceanic basins experienced a history of subduction-accretion, marginal arc volcanism and back-arc basin formation (‘Cordilleran-type’ ophiolites). Ophiolites that were emplaced associated with active margin settings range from large accreted thrust sheets to small slices within accretionary prisms and back-arc basins. Examples include the Late Cretaceous ophiolites that are related both to the northern margin of the southern Neotethys and to the northern margin of the northern Neotethys in Turkey. Not all ophiolites were emplaced in response to large-scale horizontal tectonic transport (e.g. Jurassic Guevgueli ophiolite, northern Greece), and several ophiolites experienced dominantly strike-slip or transpression (e.g. the Late Cretaceous Antalya ophiolites, SW Turkey). In general, the mode of ophiolite emplacement, especially the direction of emplacement relative to the orientation of the adjacent continental margin was influenced by the regional palaeogeographical setting.

Abstract Ophiolite assemblages record structural, magmatic, and metamorphic processes that preceded their entrapment in orogenic belts by continental plate collisions. Ophiolite genetic models appealing to ‘oceanic’ or ‘suprasubduction’ provenance are still unable to reconcile several basic problems, including: (1) the association of boninites with oceanic ridge-type structural settings; (2) the diachronous ‘patch-like’ distribution of ophiolites in orogenic belts; (3) disparate ages between and within their mantle and crustal sections; (4) the lack of evidence for ‘obduction’ at modern passive margins. In contrast, the proposal that ophiolite genesis is exclusive to intra-oceanic forearc settings is compelling, given their uniquely shared structural, lithological, and stratigraphic attributes. Forearcs are interpreted to record discrete stages of subduction ‘rollback’ cycles, examples of which begin with subduction nucleation and the formation of boninitic ‘proto-arcs’, followed by arc splitting and concomitant retreat of the evolving arc-forearc complex. Forearc assemblages are likely to resist subduction to become entrapped in orogens, in contrast to denser, recently formed back-arc basin lithosphere, which is reconsumed by subduction following collision of the retreating forearc. As a model for Neo-Tethyan ophiolite genesis, this is predicated on the notion that rollback cycles are driven by ductile asthenosphere mobilized prior to and during collisions of Gondwana fragments with accreting Eurasia. It is also consistent with the apparent correlation of ophiolite ages with collisional events and their conjugate plate kinematic adjustments. Here, we use the slab rollback model as a template for interpreting the structural, magmatic, and metamorphic characteristics of well-studied Tethyan ophiolites, in Albania (Mirdita), Cyprus (Troodos), and Oman (Semail).

Abstract The Middle Unit of the central-northern Argolis Peninsula, in NE Peloponnesus (Greece), is composed of several tectonic slices, locally including intact sequences of mafic volcanic rocks topped by radiolarian cherts. Although some of these sequences are Jurassic in age, many of them display a Triassic age based on biostratigraphical evidence. The petrological studies presented in this paper indicate that the Triassic volcanic rocks were generated in a mid-ocean ridge setting, and that they represent the oldest remnants of the Pindos oceanic crust so far recognized in the Subpelagonian zone. On the basis of immobile trace element analyses, two chemically distinct groups of Triassic lavas can be recognized in the various volcanic sequences. One group is represented by transitional-type mid-ocean ridge basalts (T-MORBs) displaying moderate light rare earth element (LREE) enrichment, and incompatible element abundances very similar to those observed in present-day T-MORBs. The other group exhibits a range of characteristics typical of many normal-type MORBs: that is, variable LREE depletion and flat N-MORB normalized patterns of incompatible element abundance. Moreover, many geochemical characteristics indicate that the various N-MORB type volcanic sequences originated from chemically distinct (heterogeneous) sub-oceanic mantle sources. Analogous to similar basalts from ophiolitic mélanges of the Dinaride-Hellenide belt, the T-MORBs from the Argolis Middle Unit are interpreted as having originated from a primitive mantle source variably enriched by an ocean-island basalt (OIB)-type component. In contrast, the contemporaneous occurrence of N-MORBs implies that, during the Mid-Late Triassic, oceanic spreading of the Pindos basin had already reached, at least in some sectors, a quasi-steady state involving only sub-oceanic mantle sources and their partial melt derivatives. Our model for the Triassic opening of the Pindos oceanic basin and its related tectonomagmatic evolution is largely supported by comparison with the Red Sea embryonic ocean, a modern analogous setting.

Abstract A combination of geophysical studies and deep-sea drilling have in the past suggested that orthogonally rifted margins fall into two end-members: volcanic-rifted margins (e.g. eastern Greenland) and non-volcanic rifted margins (e.g. Iberia–Newfoundland conjugate). This paper explores the rifted margins of the Eastern Tethys stretching from the Eastern Mediterranean, through Oman to the Himalayas. Rifting in these area was typically pulsed, extending over more than 50 Ma. The timing of final continental breakup ranged from Late Permian in the east, in Oman and the Himalayas, to latest Triassic–earliest Jurassic in many parts of the Eastern Mediterranean (e.g. Antalya in SW Turkey; Pindos in Greece). Rifting in the Himalayas and Oman gave rise to a proximal to a distal ramp geometry with scatted seamounts (continental fragments and atolls) located adjacent to the rifted margin. The Eastern Mediterranean was palaeogeographically varied, and was characterized by a number of mainly elongate continental fragments (tens to several hundreds of kilometres long by tens of kilometres wide). These microcontinents subdivided the Eastern Tethys in the Eastern Mediterranean region into several small ocean basins, which rifted at more or less the same time in latest Triassic–earliest Jurassic time. All of the rifted margins of the Eastern Tethys are associated with rift-related volcanic rocks. However, with the exception of the Permian Panjal Traps in the Himalayas, the volumes of magma and corresponding thermal doming were less than for the ideal Volcanic-rifted margin (i.e. eastern Greenland). None of the Eastern Tethyan rifted margins show evidence of features characteristic of Non-volcanic rifted margins (e.g. sea-floor serpentinite exhumation), in contrast to the Iberia–Newfoundland conjugate or the Alps. Most of the Eastern Tethyan rifted margins appear to correspond to an ‘intermediate’ type, characterized by pulsed rifting, limited rift volcanism and a narrow continent–ocean transition zone. Such ‘intermediate-type’ rifted margins may remain to be explored in the modern oceans by deep-sea drilling. There is little evidence to support previous suggestions that the Eastern Tethyan rifts can be considered as back-arc basins above either northward- or southward-dipping subduction zones. Here it is suggested that the Eastern Tethys documents a fundamentally different type of rifting from either the ‘Volcanic-related’ or ‘Non-volcanic’ intracontinental rifts known from the Alps or the North Atlantic region. The dominant controls of rifting are seen as the traction of rising asthenosphere on the base of the lithosphere, related deviatoric tensional stresses, inherited and thermally induced weaknesses in the crust, and slab-pull. Specifically, in the Eastern Tethyan region continental breakup was probably triggered by a combination of long-term asthenosphere flow, slab-pull related to subduction beneath Eurasia and melt-induced crustal weakening associated with pulsed rifting or plume effects. Final continental breakup corresponds to a major (‘Cimmerian’) convergent phase along the opposing Eurasia margin, which further supports the role of plate boundary forces in Eastern Tethyan rifting. The early Mesozoic oceanic basins opened, probably associated with northwestward propagation of a spreading centre through the already weakened periphery of Gondwana, adjacent to less deformable Palaeotethyan oceanic crust. After a lengthy period of passive margin subsidence, locally punctuated by crustal extension and related volcanism, or plume effects, the rifted margins were finally tectonically emplaced during mid-Mesozoic, late Mesozoic or early Cenozoic time in different areas.

Abstract The time span between the Variscan and Alpine cycles is not devoid of any major tectonic activity, and corresponds to the Cimmerian cycle. Between the Early Permian and Late Triassic, the Eocimmerian cycle was marked by the closure of Palaeotethys and opening of Neotethys and of an array of south Eurasian back-arc basins. This was followed by the break-up of Pangaea and the Early Jurassic opening of the central Atlantic and Alpine Tethys. However, in the area of the Eocimmerian collision, the geodynamic evolution is relatively uninfluenced by this event, and a new cycle of Cimmerian deformation affected the Hellenides, Dinarides, Balkans and Pontides in Jurassic-Early Cretaceous times. The anti-clockwise rotation of Africa during the Late Cretaceous heralded the onset of Alpine orogenic processes, characterized first by major east-west shortening, and opening and closure of younger oceanic basins of back-arc type.