Alastair H. F. Robertson

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 (

Palaeogeographic and palaeotectonic evolution of the Eastern Mediterranean Neotethys

Abstract Integrated basin-scale field and laboratory studies form the basis of detailed discussions of three important areas of the Eastern Mediterranean Neotethys, here termed the Pindos ocean (Greece), the Antalya ocean (SW Turkey) and the Cyprus ocean. These three areas preserve remnants of interconnected Mesozoic small ocean basins, sited along the north margin of Gondwanaland. The most powerful tools available for basin analysis are biostratigraphy, facies trends, tectonic discrimination of basalts and structural evidence of emplacement directions. It is shown that, despite some important differences in the timing of events, individual oceanic basins went through essentially predictable stages, including rifting, spreading, subduction/accretion, displacement/emplacement and collision. An idealised model of small ocean basin evolution can, thus be envisaged. However, in detail, individual areas show considerable palaeogeographic variety, particularly in the size, distribution and shape of carbonate platforms, margins and seamounts and no one area exemplifies Neoethyan evolution as a whole. Rifting in each of the three areas took place in Late Permian? to Mid Triassic time, followed by continental break-up in the Late Triassic. The Pindos ocean developed into a significantly wide small ocean basin (ca. 1000 km) by the Early Jurassic, while the Antalya ocean remained narrower (less than 500 km). The rifted continental fragments subsided and were capped by carbonate platforms that were fringed by slope and deep-water basinal sediments. Intra-oceanic carbonate platforms were present in both the Pindos and Antalya oceans. Ophiolites formed above an inferred west-dipping subduction zone in Greece in the Mid Jurassic, followed by displacement and metamorphic sole formation, then regional emplacement onto a microcontinent, the Pelagonian Zone, in the Late Jurassic. Above-subduction zone spreading took place in the Late Cretaceous in the Cyprus ocean and, probably also in the Antalya ocean basin. Diachronous collisions closed both the Pindos and Antalya oceans by the Early Tertiary, while the Cyprus ocean basin survived as an oceanic remnant until Quaternary-Recent time. Finally, an attempt is made to position the Pindos, Antalya and Cyprus oceanic units in the context of our understanding of the Eastern Mediterranean Neotethys.

Processes of Late Cretaceous to Late Miocene episodic thrust-sheet translation in the Lycian Taurides, SW Turkey

The Lycian Taurides of SW Turkey consist of an allochthonous Mesozoic passive margin succession that was episodically detached from its autochthon and translated southeastwards between latest Cretaceous to Late Miocene times. A combination of structural analysis, sedimentology, palaeontology and geochemistry allows subdivision of this orogenic event into: (1) latest Cretaceous trench–passive margin collision causing ophiolite obduction and detachment of the Köyceđiz Thrust Sheet; (2) Mid–Late Eocene continent–continent collision renewing southeastwards thrusting and causing detachment of the Teke Dere Thrust Sheet and Yavus Thrust Sheets; (3) Miocene extensional collapse of the orogen with southeastwards translation of the allochthon coeval with rift-basin formation in the hinterland.

Mesozoic-Tertiary Tectonic-Sedimentary Evolution of a South Tethyan Oceanic Basin and its Margins in Southern Turkey

This paper focuses on the Mesozoic-Tertiary tectonic evolution of southern Turkey and offshore areas of the easternmost Mediterranean. The area is discussed and interpreted utilizing three segments from west to east. In the far west, the Lycian Nappes represent emplaced remnants of mainly Mesozoic rift, passive margin and oceanic units that formed within a northerly strand of the Mesozoic (i.e. Neotethyan) ocean. Further east, the Hoyran-Beyşehir-Hadim Nappes, likewise encompass sedimentary and igneous units that formed within a northerly Neotethyan oceanic basin, although lithologies, structure and timing of emplacement differ from the Lycian Nappes. Further east (Adana region), ophiolites and ophiolitic mélange also formed in a northerly oceanic basin and were thrust southwards over the regionally extensive Tauride carbonate platform initially in latest Cretaceous time (e.g. Pozanti-Karsanti Ophiolite). By contrast, further south the regionally important Antalya Complex records northerly areas of a separate, contrasting southerly Neotethyan oceanic basin. This comprised a mosaic of carbonate platforms and interconnecting seaways, similar to the Caribbean region today. In particular, an ocean strand separated Tauride carbonate platforms to the west (Bey Dağlari) and east (e.g. Akseki Platform) within the Isparta Angle area. In the centre of southern coastal Turkey, the metamorphic Alanya Massif is interpreted as a Triassic rift basin bordered by two small platform units that was located along the northern margin of the southerly Neotethys which collapsed in latest Cretaceous and was finally emplaced in Early Tertiary time. Remnants of the southerly Neotethyan oceanic basin remain today in the non-emplaced continental margin of the Levant and North Africa, and neighbouring seafloor areas (e.g. Levant and Herodotus Basins). In southern Turkey, emplaced Neotethyan units are unconformably overlain by a complex of mainly Miocene basins. These largely reflect the effects of southward directed crustal loading as convergence of Africa and Eurasia continued, although the basins were also influenced by an inferred more southerly subduction zone (near Cyprus). Further east, in southeastern Turkey, ophiolites, ophiolitic mélange and continental margin units were emplaced southwards onto the Arabian Margin, a promontory of North Africa in latest Cretaceous time. The south Neotethyan basin’s north margin experienced northward subduction, accretion, arc volcanism and ophiolite emplacement in Late Cretaceous time. The intervening southerly Neotethyan oceanic basin remained partly open in the Early Tertiary, finally closing by diachronous collision in Eocene-Oligocene time, followed by further convergence and overthrusting in the Miocene. The Eocene later stages of convergence were marked by renewed arc volcanism and extensive subduction accretion (e.g. Maden Complex). In the west, subduction remained active in Late Oligocene-Early Miocene time giving rise to sedimentary mélanges (olistostromes) of the Misis-Andirin Mountains (Adana region) as an accretionary wedge. By the Miocene the subduction zone accommodating Africa-Eurasia convergence had been relocated to its present position south of Cyprus. Areas behind this subduction experienced crustal extension (e.g. Antalya and Adana-Cilicia Basins) from the Late Miocene onwards. After onset of westward ‘tectonic escape’ of the Turkish Plate in the Early Pliocene, southeastern Turkey was transected by the South Anatolian Transform Fault. Strike-slip was dissipated though the Kyrenia-Misis Lineament into Cyprus. Today, southeastern Turkey records a post-collisional setting, whereas areas to the west experience incipient collision of the African and Turkish Plates.

Tectono-stratigraphy and evolution of the Mesozoic Pindos ophiolite and related units, northwestern Greece

The northwest Pindos Mountains expose Mesozoic and Tertiary thrust sheets, which include the Jurassic Pindos ophiolite, composed of ultramafic and mafic oceanic crustal rocks. The tectono-stratigraphy of these units is: (i) mainly ultramafic ophiolitic thrust sheet and basal metamorphic sole (Dramala Complex and Loumnitsa Unit); (ii) Late Cretaceous platformal limestones (Orliakas Group); (iii) dismembered intrusive and extrusive ophiolitic rocks (Aspropotamos Complex): (iv) tectonic melange and olistostromes, dominated by Triassic-Jurassic volcanic and sedimtntary rocks (Avdella Melange); (v) coherent thrust sheets of Late Jurassic–Late Cretaceous deep-water sediments (Dio Dendra Group); (vi) Early Tertiary flysch (Pindos Flysch). Immobile trace-element studies indicate that Triassic and Jurassic extrusives of the volcanic-sedimentary melange formed mainly at within plate and/or mid-ocean ridge settings. By contrast, structurally overlying ophiolitic extrusives include boninitic volcanics and island arc tholeiites, of supra-subduction zone origin. Initial ophiolite displacement (c. 165 Ma) is recorded in metamorphic sole formation, including basal peridotite mylonite, amphibolites and greenschists. The sole rocks have MORB and WPB chemical affinities. In our favoured model, the Pindos ophiolite formed above a Mid-Jurassic westerly-dipping intra-oceanic subduction zone, accompanied by accretion to form melange, followed by collision and emplacement with the Pelagonian margin. Final suturing of the Pindos ocean, however did not take place until Early Tertiary times.

Lycian melange, southwestern Turkey: An emplaced Late Cretaceous accretionary complex

The Lycian thrust belt is an important part of the Tethyan orogenic belt in the eastern Mediterranean region. It includes a unit of internally disrupted, thin-skinned thrust sheets (layered tectonic melange) and a melange rich in ophiolitic material (ophiolitic melange). The layered tectonic melange is dominated by Mesozoic distal deep-water sedimentary rocks, and the ophiolitic melange includes disrupted thrust sheets of early Mesozoic shallow-water limestone and blocks of basalt of both mid-ocean ridge and within-plate geochemical affinities. A complete record of closure of a Tethyan oceanic basin began with Late Cretaceous intraoceanic subduction, followed by latest Cretaceous trench-continental collision, and ended with mid-Tertiary continental collision, and orogenic collapse.

Neotectonic intersection of the Aegean and Cyprus tectonic arcs: extensional and strike-slip faulting in the Isparta Angle, SW Turkey

Abstract The Isparta Angle and adjacent Antalya Bay areas constitute an important segment of the eastern Mediterranean region, located at the intersection of the southward-convex Aegean and Cyprus arcs. Some recent tectonic maps show the Isparta Angle as a NW–SE compressional lineament extending eastwards into the Kyrenia Range of northern Cyprus. However, fault data from the onshore Isparta Angle, together with offshore shallow seismic reflection data, show that the present morpho-tectonic setting is dominated by extension. The last phase of compression to affect the area studied in the Late Miocene, was accompanied by regional nappe emplacement (Lycian Nappes). Onshore, fault planes, measured from fault zones bounding both the limbs and the core of the Isparta Angle are oriented predominantly NE–SW, NW–SE and N–S. Superimposed slickenfibres show that reverse faults were succeeded, in turn, by right-lateral faults, then by normal faults. The fault phases are dated by stratigraphical and geomorphological evidence. Reverse faults date from the Late Miocene, or earlier compressional deformation, whereas the right-lateral faults mainly developed during latest Miocene–Early Pliocene. Normal faulting dominated from the Late Pliocene–Recent. An interpretation of shallow seismic reflection data shows that Antalya Bay is characterised by a NW–SE-trending asymmetrical graben system that has continued to be active. During the Late Miocene–Early Pliocene right-lateral strike-slip resulted from shear along the eastern termination of a zone of extension and rotation that characterises the western Aegean. This shear was focused in a N–S direction by inherited zones of structural weakness in the basement (Antalya Complex). The switch to NE–SW extension in the Late Pliocene–Quaternary relates to a regional change in stress direction throughout the Aegean region and was accompanied by strong uplift of the Bey Daǧlari region of the Taurus Mountains, bordering the Isparta Angle in the west. The Isparta Angle is the link between: (a) the extensional province of western Turkey bounded to the south by the actively subducting Hellenic arc; and (b) the uplifted Anatolian plateau bounded to the south by the Cyprus subduction zone. Understanding the Miocene to Recent tectonic development helps elucidate the kinematics of the region. The new structural data presented lend no support for recent suggestions that the Isparta Angle and Antalya Bay represent parts of a regional compressional zone related to plate collision.

Laser 40Ar/39Ar dating of single detrital muscovite grains from early foreland-basin sedimentary deposits in India: Implications for early Himalayan evolution

In India, the Dagshai and overlying Kasauli Formations represent the oldest exposed continental foredeep sediments eroded from the Himalayan orogen. 40Ar/39Ar dating of individual detrital white micas from these sedimentary units has provided maximum depositional ages of <28 Ma for the Dagshai Formation at one locality and <25 Ma at a second locality, whereas deposition of the Kasauli Formation occurred after 28 Ma at two localities and after 22 Ma at a third locality. This timing suggests that, in India, the start of substantial exhumation and erosion from the rising Himalayan orogen was delayed until 28 Ma.

Tectonic Development of the Eastern Mediterranean Region

The Eastern Mediterranean region is a classic area for the study of tectonic processes and settings related to the development of the Tethyan orogenic belt. The present set of research and synthesis papers by Earth scientist from countries in this region and others provides an up-to-date, interdisciplinary overview of the tectonic development of the Eastern Mediterrenean region from Precambrian to Recent. Key topics include continental rifting, ophiolite genesis and emplacement, continental collision, extensional tectonics, crustal exhumation and intraplate deformation (e.g. active faulting). Alternative tectonic reconstructions of the Tethyan orogen are presented and discussed, with important implications for other regions of the world. The book will be an essential source of information and interpretation for academic researchers (geologists and geophysicists), advanced undergraduates and also for industry professionals, including those concerned with hydrocarbons, minerals and geological hazards (e.g. earthquakes).

Tectonic significance of the Eratosthenes Seamount: a continental fragment in the process of collision with a subduction zone in the eastern Mediterranean (Ocean Drilling Program Leg 160)

Abstract One of the objectives of ODP Leg 160 in the eastern Mediterranean Sea (April–May, 1995) was concerned with the study of processes of genesis and incipient collision of an inferred crustal fragment, the Eratosthenes Seamount, with the active margin of the Eurasian plate to the north, represented by southern Cyprus. The upper part of the Eratosthenes Seamount (i.e. upper several hundred metres) was found to include both shallow- and deep-water carbonates dating back to Early Cretaceous time. Shallow-water platform carbonate deposition, similar to that of the onshore Levant continental margin to the east (i.e. part of the North African plate), was followed by submergence to bathyal depths (>1000 m) in the Late Cretaceous to Middle Eocene, punctuated by depositional and tectonic hiatuses. Tectonic uplift (approximately 1 km) was followed by shallow-water carbonate deposition in the Early Miocene. The platform was exposed during the Messinian desiccation crisis. During the Early Pliocene the platform subsided to bathyal depths associated with localised accumulation of limestone debris flows. Subsidence accelerated in the Late Pliocene–Early Pleistocene, reaching a present-day maximum depth of ca. 2500 m. Deformation of the Eratosthenes Seamount (i.e. subsidence and high-angle faulting) resulted from crustal flexure, induced by southward overthrusting of the Cyprus active margin. Tectonic subsidence of the Eratosthenes Seamount was approximately synchronous with rapid surface uplift of the over-riding plate, the Troodos Ophiolite of southern Cyprus. This uplift is explained in terms of incipient collision of an Eratosthenes continental fragment with a subduction trench, coupled with the effects of diapiric protrusion of serpentinite located within the core of the Troodos Ophiolite. The Eratosthenes drilling, thus, documented a modern analogue of subduction/collisional processes leading to accretion of continental fragments and carbonate platforms in orogenic belts.