All the geological constraints for an exhaustive reconstruction of the Triassic to Tertiary tectonic history of the southern Dinaric-Hellenic belt can be found in Albania and Greece. This article aims to schematically reconstruct this long tectonic evolution primarily based on a detailed analysis of the tectonic setting, the stratigraphy, the geochemistry, and the age of the ophiolites. In contrast to what was previously reported in the literature, we propose a new subdivision on a regional scale of the ophiolite complexes cropping out in Albania and Greece. This new subdivision includes six types of ophiolite occurrences, each corresponding to different tectonic units derived from a single obducted sheet. These units are represented by: (1) subophiolite me ´lange, (2) Triassic ocean-floor ophiolites, (3) metamorphic soles, (4) Jurassic fore-arc ophiolites, (5) Jurassic intra-oceanic-arc ophiolites, and (6) Jurassic backarc basin ophiolites. The overall features of these ophiolites are coherent with the existence of a single, though composite, oceanic basin located east of the Adria/Pelagonian continental margin. This oceanic basin was originated during the Middle Triassic and was subsequently (Early Jurassic) affected by an east-dipping intra-oceanic subduction. This subduction was responsible for the birth of intra-oceanic-arc and back-arc oceanic basins separated by a continental volcanic arc during the Early to Middle Jurassic. From the uppermost Middle Jurassic to the Early Cretaceous, an obduction developed, during which the ophiolites were thrust westwards firstly onto the neighboring oceanic lithosphere and then onto the Adria margin.

The break-up of Pangea began during the Triassic and was preceded by a generalized Permo-Triassic formation of continental rifts along the future margins between Africa and Europe, between Africa and North America, and between North and South America. During the Middle-Late Triassic, an ocean basin cutting the eastern equatorial portion of the Pangea opened as a prograding branch of the Paleotethys or as a new ocean (the Eastern Tethys); westwards, continental rift basins developed. The Western Tethys and Central Atlantic began to open only during the Middle Jurassic. The timing of the break-up can be hypothesized from data from the oceanic remnants of the peri-Mediterranean and peri-Caribbean regions (the Mesozoic ophiolites) and from the Atlantic ocean crust. In the Eastern Tethys, Middle-Late Triassic mid-oceanic ridge basalt (MORB) ophiolites, Middle-Upper Jurassic MORB, island arc tholeiite (IAT) suprasubduction ophiolites and Middle-Upper Jurassic metamorphic soles occur, suggesting that the ocean drifting was active from the Triassic to the Middle Jurassic. The compressive phases, as early as during the Middle Jurassic, were when the drifting was still active and caused the ocean closure at the Jurassic-Cretaceous boundary and, successively, the formation of the orogenic belts. The present scattering of the ophiolites is a consequence of the orogenesis: once the tectonic disturbances are removed, the Eastern Tethys ophiolites constitute a single alignment. In the Western Tethys only Middle-Upper Jurassic MORB ophiolites are present -this was the drifting time. The closure began during the Late Cretaceous and was completed during the Eocene. Along the area linking the Western Tethys to the Central Atlantic, the break-up was realized through left lateral wrench movements. In the Central Atlantic -the link between the Western Tethys and the Caribbean Tethys -the drifting began at the same time and is still continuing. The Caribbean Tethys opened probably during the Late Jurassic-Early Cretaceous. The general picture rising from the previous data suggest a Pangea break-up rejuvenating from east to west, from the Middle-Late Triassic to the Late Jurassic-Early Cretaceous.

Albanian ophiolites are represented by two different coeval belts, each displaying well-exposed, complete ophiolitic sequences that originated in the same oceanic basin and each showing distinct geochemical characteristics. The eastern belt is characterized by suprasubduction zone (SSZ) ophiolitic sequences, including island arc tholeiitic and boninitic volcanic series. The western belt, although composed mainly of mid-ocean ridge-type (MOR-type) ophiolites with high-Ti geochemical affinity, also exhibits alternating sequences showing distinct geochemical affinities referable to MOR-and SSZ-type volcanics. These volcanics can be geochemically subdivided into four groups: (1) group 1 basalts show high field strength element (HFSE) and rare earth element (REE) concentrations similar to those of ocean-floor basalts; (2) group 2 basalts, basaltic andesites, dacites, and rhyolites, characterized by HFSE and light REE depletion similar to those in many low-Ti volcanics from SSZ settings; (3) group 3 basalts exhibit geochemical features intermediate between groups 1 and 2 but also bear SSZ features, being characterized by HFSE depletion with respect to the N-MORBs; (4) group 4 boninitic dikes display very low-Ti contents and typically depleted, U-shaped REE patterns. These different magmatic groups are interpreted as having originated from fractional crystallization from different primary basalts that were generated, in turn, from partial melting of mantle sources progressively depleted by previous melt extractions. Consequently, group 1 basalts may derive from partial melting of a fertile MORB source, while group 3 basalts may derive from 10% partial melting of a mantle that previously experienced MORB extraction. Finally, the group 2 basalts and group 4 boninites may be derived from about 10% partial melting of a mantle peridotite previously depleted by primary melt extraction of group 1 and group 3 primary melts. To explain the coexistence of these geochemically different magma groups, we present a model based on the complexity of the magmatic processes that may take place during the initiation of subduction in proximity to an active MOR. This model implies that the initiation of subduction processes close to such a ridge leads to contemporaneous eruptions in a fore-arc setting of MORBs (group 1) generated from the extinguishing MOR and the initiation of group 3 basalts generated in the SSZ mantle wedge from a moderately depleted mantle source. The development of the subduction in a young, hot lithosphere caused the generation of island arc tholeiitic basalts (group 2) and boninites (group 4) from strongly depleted mantle peridotites in the early stages of subduction, soon after the generation of group 1 and group 3 basaltic rocks.

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In this paper, a summary of the tectonic history of the Mirdita ophiolitic nappe, northern Albania, is proposed by geological and structural data. The Mirdita ophiolitic nappe includes a subophiolite mélange, the Rubik complex, overlain by two ophiolite units, referred to as the Western and Eastern units. Its history started in the Early Triassic with a rifting stage followed by a Middle to Late Triassic oceanic opening between the Adria and Eurasia continental margins. Subsequently, in Early Jurassic time, the oceanic basin was affected by convergence with the development of a subduction zone. The existence of this subduction zone is provided by the occurrence of the supra-subduction-zone-related magmatic sequences found in both the Western and Eastern units of the Mirdita ophiolitic nappe. During the Middle Jurassic, continuous convergence resulted in the obduction of the oceanic lithosphere, in two different stages -the intraoceanic and marginal stages. The intraoceanic stage is characterized by the westward thrusting of a young and still hot section of oceanic lithosphere leading to the development of a metamorphic sole. In the Late Jurassic, the marginal stage developed by the emplacement of the ophiolitic nappe onto the continental margin. During this second stage, the emplacement of the ophiolites resulted in the development of the Rubik complex. In the Early Cretaceous, the final emplacement of the ophiolites was followed by the unconformable sedimentation of the Barremian-Senonian platform carbonate. From the Late Cretaceous to the Middle Miocene, the Mirdita ophiolitic nappe was translated westward during the progressive migration of the deformation front toward the Adria Plate. In the Middle to Late Miocene, a thinning of the whole nappe pile was achieved by extensional tectonics, while the compression was still active in the westernmost areas of the Adria Plate. On the whole, the Miocene deformations resulted in the uplift and exposition of the Mirdita ophiolites as observed today.