Southern Neotethys Research Articles

Geodynamic significance of granitoid magmatism in the southeast Anatolian orogen: geochemical and geochronogical evidence from Göksun–Afşin (Kahramanmaraş, Turkey) region

In southeast Anatolia, there are number of tectonomagmatic units in the Kahramanmaras–Malatya–Elazig region that are important in understanding the geological evolution of the southeast Anatolian orogenic belt during the Late Cretaceous. These are (a) metamorphic massifs, (b) ophiolites, (c) ophiolite-related metamorphics and (d) granitoids. The granitoids (i.e. Goksun–Afsin in Kahramanmaras, Dogansehir in Malatya and Baskil in Elazig) intrude all the former units in a NE–SW trending direction. The granitoid in Goksun–Afsin (Kahramanmaras) region is mainly composed of granodioritic and granitic in composition. The granodiorite contains a number of amphibole-bearing mafic microgranular enclaves of different sizes, whereas the granite is intruded by numerous aplitic dikes. The granitoid rocks have typical calcalkaline geochemical features. The REE- and Ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, as well as biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The K–Ar geochronology of the granitoid rocks yielded ages ranging from 85.76±3.17 to 77.49±1.91 Ma. The field, geochemical and geochronological data suggest the following Late Cretaceous tectonomagmatic scenario for southeast Anatolia. The ophiolites were formed in a suprasubduction zone tectonic setting whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or late-thrusting (∼90 Ma). These units were then overthrust by the Malatya–Keban platform during the progressive elimination of the southern Neotethys. Thrusting of the Malatya–Keban platform over the ophiolites and related metamorphic rocks was followed by the intrusion of the granitoids (88–85 Ma) along the Tauride active continental margin in the southern Neotethys.

Age and Stratigraphic Relationships of Structurally Deepest Level Rocks, Oman Mountains: U/Pb SHRIMP Evidence for Late Carboniferous Neotethys Rifting

Igneous zircons in felsic schist, or metatuff, infolded with mafic schist, calcschist, and quartz mica schist of the As Sifah lower plate window, NE Oman, have yielded a U/Pb SHRIMP crystallization age of $$298\pm 3$$ Ma. The metatuff was previously considered to represent Permian bimodal volcanism, but these data indicate that the magmatism is older and suggest that Neotethys intracontinental rifting on the Oman part of the Gondwana northern margin was initiated in the Late Carboniferous. This, combined with δ13C values of calcschists indicating a predominantly pre–Late Permian age for the basal lower plate metacarbonates, suggests that passive margin carbonate ramp development occurred in the Late Carboniferous/Early Permian during Neotethys oceanic spreading and not just in the Late Permian, as previously thought. The restricted occurrence of the metatuff to the Saih Hatat lower plate, a unique lower plate stratigraphy, and the unique δ13C values of the calcschists all suggest that the lower plate was certainly distal, and possibly exotic, to the Arabian Peninsula. The felsic schist sample was entrained within an eclogite megaboudin at As Sifah. The age relationships therefore suggest that the high‐P rocks that reached pressures of up to 20 kbar and are now part of the lower plate of Gregory and coworkers were either part of a subducted Florida‐style promontory as part of the attenuated leading edge of the Arabian platform or part of a subducted microplate that was originally caught in the developing southern Neotethys ocean some 1300 km from the margin.

The Berit transect of the Tauride thrust belt, S Turkey: Late Cretaceous–Early Cenozoic accretionary/collisional processes related to closure of the Southern Neotethys

We report on an integrated study of a critical segment of the Tauride thrust belt in SE Turkey (Berit area). Units related to two sutures are exposed in the northerly and southerly parts of the area studied. In the north the Upper Cretaceous Binboğa Melange reflects the closure of a northerly Mesozoic oceanic basin. In the south, contrasting units document the closure of the Southern Neotethys. In the south, the Berit (or Göksun) ophiolite formed as an incipient oceanic arc within the Southern Neotethys during the Late Cretaceous (c.90 Ma). Intercalated amphibolite–granulite facies rocks may record a dismembered metamorphic sole. An underlying meta-sedimentary/meta-volcanic unit is interpreted as accreted continental rift and oceanic seamount lithologies. The Berit ophiolite was accreted to the Tauride active continental margin to the north around 85 Ma and was then intruded by calc-alkaline granites (c.70–85 Ma). Northerly margin units were exhumed and covered by shelf-carbonate sediments during latest Cretaceous–Early Cenozoic time. Northward subduction during the mid-Cenozoic (c.45 Ma) resulted in back-arc extension along the Tauride active margin and subduction-influenced volcanism, possibly controlled by slab roll-back. During Oligocene–Early Miocene time the Southern Neotethys closed and the Tauride active margin was telescoped to create the present south-vergent thrust stack. This was accompanied by mass wasting of the advancing allochthon to form sub-aqueous frontal olistostromes. The Arabian platform was over-ridden by Mid-Miocene time, followed by left-lateral strike-slip along the East Anatolian Fault zone, as Anatolia began to escape westwards towards the Aegean Sea.

Whole-rock and mineral chemistry of cumulates from the Kızıldağ (Hatay) ophiolite (Turkey): clues for multiple magma generation during crustal accretion in the southern Neotethyan ocean

AbstractThe late Cretaceous Kızıldağ ophiolite forms one of the best exposures of oceanic lithospheric remnants of southern Neotethys to the north of the Arabian promontory in Turkey. The ultramafic to mafic cumulate rocks, displaying variable thickness (ranging from 165 to 700 m), are ductiley deformed, possibly in response to syn-magmatic extension during sea-floor spreading and characterized by wehrlite, olivine gabbro, olivine gabbronorite and gabbro. The gabbroic cumulates have an intrusive contact with the wehrlitic cumulates in some places. The crystallization order of the cumulus and intercumulus phases is olivine (Fo86–77)± chromian spinel, clinopyroxene (Mg#92–76), plagio-clase(An95–83), orthopyroxene(Mg#87–79). The olivine, clinopyroxene, orthopyroxene and plagioclase in ultramafic and mafic cumulate rocks seem to have similar compositional range. This suggests that these rocks cannot represent a simple crystal line of descent. Instead the overlapping ranges in mineral compositions in different rock types suggest multiple magma generation during crustal accretion for the Kızıldağ ophiolite. The presence of high Mg# of olivine, clinopyroxene, orthopyroxene, and the absence of Ca-rich plagioclase as an early fractionating phase co-precipitating with forsteritic olivine, suggest that the Kızıldağ plutonic suite is not likely to have originated in a mid-ocean ridge environment. Instead the whole-rock and mineral chemistry of the cumulates indicates their derivation from an island arc tholeiitic (IAT) magma. All the evidence indicates that the Kızıldağ ophiolite formed along a slow-spreading centre in a fore-arc region of a suprasubduction zone tectonic setting.

Facies and palaeogeographic evidence for the Miocene evolution of the Isparta Angle in its regional eastern Mediterranean context

We summarise facies evidence for four Miocene Basins (Lycian, Aksu, Köprü and Manavgat) within the Isparta Angle. Facies patterns are plotted on six palaegeographic maps restored to their pre-late Miocene setting. These maps are used to help infer the various controls on deposition. Facies trends and structural features suggest that the individual basins were kinematically linked within the overall African–Eurasia convergence zone. The Miocene Basins represent a classic example of how related basins may develop within an evolving orogen subject to variable controls through time. The dominant control was tectonic although autocyclic sedimentary processes (e.g., reef growth), and both relative and eustatic sea-level change played a significant role. From the palaeogeographic reconstructions and the tectonic context of the Isparta Angle, we infer that during the early Miocene, the westerly Lycian basin and the neighbouring Aksu basin experienced flexural subsidence related to southeastward thrusting of the Lycian Nappes. More distal effects of the forebulge may have caused uplift around the Aksu and Köprü basins initiating N–S half-grabens bounded by master faults on the eastern side of each basin. Later, the eastern basins of the Isparta Angle were influenced by regional northward subduction and inferred slab retreat within a remnant of the Southern Neotethys located within the Mediterranean Sea at the intersection of the south Aegean and Cyprus arcs.

Testing models of Late Palaeozoic–Early Mesozoic orogeny in Western Turkey: support for an evolving open-Tethys model

Field evidence from north–south transects tests three tectonic models for Tethys in Western Turkey for when a Late Palaeozoic ocean was closing and an Early Mesozoic ocean opening. In Model 1, a Palaeozoic ocean subducted southwards, rifting continental fragments from Gondwana and opening a Triassic Neo-Tethys to the south. Closure and collision occurred by latest Triassic time. In Model 2, a wide Palaeozoic Tethys subducted northwards with an active Eurasian margin and a passive Gondwana margin. The northern Gondwana margin rifted in the Triassic; fragments either remained nearby (Taurides) or drifted northwards (e.g. Karakaya) attached to a north-subducting plate. New oceanic crust replaced Palaeo-Tethys with Neotethys and back-arc marginal basins opened along the south Eurasian margin (e.g. Küre). In Model 3, a Palaeozoic ocean also subducted northwards opening wide marginal basins. A wide Southern Neotethys opened along the Gondwana margin. Rifted Eurasian (Anatolides) and Gondwana (Taurides) fragments collided in mid-Tethys by latest Triassic time. Field evidence from the Pontides supports north-dipping subduction models (Model 2 or 3 above). Key features are a south-vergent, HP–LT accretionary prism, magmatic arc and back-arc basin system bordering the Eurasian margin. Also, evidence from the Tauride Mountains favours Model 2 over Model 3. Critically, the Anatolides and Taurides appear to have a common history and were unlikely to have been located on opposite sides of Tethys, as in Model 3.

The Late Cretaceous palaeolatitude of the Neotethyan spreading axis in the eastern Mediterranean region

A compilation of available palaeomagnetic data from the Troodos (Cyprus) and Baër–Bassit (Syria) ophiolitic terranes of the eastern Mediterranean Tethyan orogenic belt is presented. The ophiolites represent fragments of oceanic lithosphere generated at a Neotethyan spreading axis in the Late Cretaceous, although debate continues over the tectonic setting of this spreading axis and its position within the eastern Mediterranean palaeogeography. Two types of model reconstructions have been proposed: Type 1—the ophiolites formed in a southerly Neotethyan basin by spreading above an oceanic subduction zone. The Baër–Bassit ophiolite was then emplaced a relatively short distance (tens of kilometers) southwards on to the Arabian continental margin, leaving the Troodos ophiolite isolated in an intra-oceanic setting to the west; and Type 2—the ophiolites formed in a northerly Neotethyan basin by spreading at a ‘normal’ oceanic ridge, with subsequent large-scale thrusting (hundreds of kilometers) to the south of emplaced ophiolites over microcontinental fragments to reach their present positions. Palaeomagnetic determination of the palaeolatitude of the Neotethyan spreading axis is, therefore, of considerable interest.Previous palaeomagnetic analyses have demonstrated the presence of significant, and in some cases extreme, relative tectonic rotations of a variety of origins in both ophiolites. To allow palaeomagnetic data from these rotated units to be combined, an inclination-only formulation of the palaeomagnetic tilt test is employed. This provides unequivocal evidence that both ophiolites retain pre-deformational remanent magnetizations, which are interpreted as original ocean-floor magnetizations acquired close to the time of crustal formation in the Late Cretaceous. The mean inclinations of 37.0±2.6° for the Troodos terrane and 41.1±3.4° for the Baër–Bassit terrane indicate respective palaeolatitudes for the spreading axes of 20.6°N±1.8° and 23.6°N±2.5°, consistent with a Late Cretaceous position between the Arabian and Eurasian margins. These data, together with a well-defined palaeolatitude of 25.5°N±4.5° for the eastern Pontides previously reported in the literature, provide constraints which must be incorporated in any successful tectonic reconstruction of the eastern Mediterranean Tethys. The implications of these constraints for Type 1 and 2 models are discussed using a series of plate tectonic cross-sections constructed along a line extending northwards from the Arabian continental margin. In the absence of palaeomagnetic data from Late Cretaceous rocks of the eastern Taurides, however, it is presently impossible to use these palaeolatitudinal constraints to resolve the root zone debate on a purely palaeomagnetic basis. Solutions which satisfy the constraints may be found for both types of model reconstruction. Additional, published field-based geological considerations, however, strongly support models in which the Troodos and Baër–Bassit (and other southerly) ophiolites were generated in a southern Neotethyan basin, rather than those involving generation in a northerly basin and subsequent large-scale thrust displacement to the south.

The Misis–Andırın Complex: a Mid-Tertiary melange related to late-stage subduction of the Southern Neotethys in S Turkey

The Mid-Tertiary (Mid-Eocene to earliest Miocene) Misis–Andırın Complex documents tectonic-sedimentary processes affecting the northerly, active margin of the South Tethys (Neotethys) in the easternmost Mediterranean region. Each of three orogenic segments, Misis (in the SW), Andırın (central) and Engizek (in the NE) represent parts of an originally continuous active continental margin. A structurally lower Volcanic-Sedimentary Unit includes Late Cretaceous arc-related extrusives and their Lower Tertiary pelagic cover. This unit is interpreted as an Early Tertiary remnant of the Mesozoic South Tethys. The overlying melange unit is dominated by tectonically brecciated blocks (>100 m across) of Mesozoic neritic limestone that were derived from the Tauride carbonate platform to the north, together with accreted ophiolitic material. The melange matrix comprises polymict debris flows, high- to low-density turbidites and minor hemipelagic sediments.The Misis–Andırın Complex is interpreted as an accretionary prism related to the latest stages of northward subduction of the South Tethys and diachronous continental collision of the Tauride (Eurasian) and Arabian (African) plates during Mid-Eocene to earliest Miocene time. Slivers of Upper Cretaceous oceanic crust and its Early Tertiary pelagic cover were accreted, while blocks of Mesozoic platform carbonates slid from the overriding plate. Tectonic mixing and sedimentary recycling took place within a trench. Subduction culminated in large-scale collapse of the overriding (northern) margin and foundering of vast blocks of neritic carbonate into the trench. A possible cause was rapid roll back of dense downgoing Mesozoic oceanic crust, such that the accretionary wedge taper was extended leading to gravity collapse. Melange formation was terminated by underthrusting of the Arabian plate from the south during earliest Miocene time.Collision was diachronous. In the east (Engizek Range and SE Anatolia) collision generated a Lower Miocene flexural basin infilled with turbidites and a flexural bulge to the south. Miocene turbiditic sediments also covered the former accretionary prism. Further west (Misis Range) the easternmost Mediterranean remained in a pre-collisional setting with northward underthrusting (incipient subduction) along the Cyprus arc. The Lower Miocene basins to the north (Misis and Adana) indicate an extensional (to transtensional) setting. The NE–SW linking segment (Andırın) probably originated as a Mesozoic palaeogeographic offset of the Tauride margin. This was reactivated by strike-slip (and transtension) during Later Tertiary diachronous collision. Related to on-going plate convergence the former accretionary wedge (upper plate) was thrust over the Lower Miocene turbiditic basins in Mid–Late Miocene time. The Plio-Quaternary was dominated by left-lateral strike-slip along the East Anatolian transform fault and also along fault strands cutting the Misis–Andırın Complex.

Extreme tectonic rotations within an eastern Mediterranean ophiolite (Baër–Bassit, Syria)

Palaeomagnetic results from 27 sites at five localities within the dismembered Baër–Bassit ophiolite of northern Syria are presented. The ophiolite forms part of a series of thrust sheets emplaced over Mesozoic carbonates of the Arabian platform in the middle Maastrichtian. A positive inclination-only area-wide tilt test applied to four locality mean remanences and positive fold and reversal tests from palaeohorizontal units (pillow lavas, lava flows) within one of these localities indicate that the ophiolite preserves pre-deformation magnetisations. Variable directions of remanence between localities demonstrate that the ophiolite has experienced extreme relative anticlockwise rotations on a kilometric scale. Within the most extensively sampled ophiolite massif (Bassit sheet) there is a progressive increase in rotation from north to south. The southernmost units at the lowest structural level in the imbricate thrust stack record the highest rotation (exceeding 200°). Although tectonic rotation during imbricate thrusting has been reported in a number of orogenic belts, the pattern of rotations in the Bassit sheet is difficult to explain by differential thrust sheet rotation. Instead, regional comparisons with the Hatay ophiolite of southern Turkey and the Troodos ophiolite of Cyprus suggest that a significant component of rotation may be ascribed to intraoceanic deformation of a coherent region of oceanic crust within the southern Neotethyan basin prior to ophiolite emplacement. The partially rotated Baër–Bassit ophiolite was then emplaced and structurally dismembered by thrust faulting. During the Late Tertiary the ophiolitic units were further rotated during the initiation and development of a major sinistral strike-slip fault zone, linking the Cyprus subduction zone to the Dead Sea Transform system. The extreme rotations observed in the study are therefore of composite origin, and reflect the complex development of structural fabrics within the ophiolite.

MIDDLE PERMIAN (MIDIAN) FORAMINIFERAL ASSEMBLAGES FROM THE BATAIN PLAIN (EASTERN OMAN): THEIR SIGNIFICANCE TO NEOTETHYAN PALEOGEOGRAPHY

Research Article| April 01, 2002 MIDDLE PERMIAN (MIDIAN) FORAMINIFERAL ASSEMBLAGES FROM THE BATAIN PLAIN (EASTERN OMAN): THEIR SIGNIFICANCE TO NEOTETHYAN PALEOGEOGRAPHY Daniel Vachard; Daniel Vachard 1 Université des Sciences et Technologies de Lille, U.F.R. des Sciences de la Terre, UPRESA 8014 du CNRS, Laboratoire de Paléontologie du Paléozoïque, F-59655 Villeneuve d’Ascq Cedex, France. E-mail: Daniel.Vachard@univ-lille1.fr Search for other works by this author on: GSW Google Scholar Marc Hauser; Marc Hauser 2 Mineralogisch-petrographisches Institut und Geologisches Institut, Universität Bern, Baltzerstrasse 1, 3012 Bern, Switzerland. E-mail: hauser@mpi.unibe.ch Search for other works by this author on: GSW Google Scholar Rossana Martini; Rossana Martini 3 Département de Géologie et Paléontologie, 13 rue des Maraîchers, CH-1211 Genève, Switzerland. E-mail: Rossana.Martini@terre.unige.ch Search for other works by this author on: GSW Google Scholar Louisette Zaninetti; Louisette Zaninetti 3 Département de Géologie et Paléontologie, 13 rue des Maraîchers, CH-1211 Genève, Switzerland. E-mail: Rossana.Martini@terre.unige.ch Search for other works by this author on: GSW Google Scholar Albert Matter; Albert Matter 2 Mineralogisch-petrographisches Institut und Geologisches Institut, Universität Bern, Baltzerstrasse 1, 3012 Bern, Switzerland. E-mail: hauser@mpi.unibe.ch Search for other works by this author on: GSW Google Scholar Tjerk Peters Tjerk Peters 2 Mineralogisch-petrographisches Institut und Geologisches Institut, Universität Bern, Baltzerstrasse 1, 3012 Bern, Switzerland. E-mail: hauser@mpi.unibe.ch Search for other works by this author on: GSW Google Scholar Author and Article Information Daniel Vachard 1 Université des Sciences et Technologies de Lille, U.F.R. des Sciences de la Terre, UPRESA 8014 du CNRS, Laboratoire de Paléontologie du Paléozoïque, F-59655 Villeneuve d’Ascq Cedex, France. E-mail: Daniel.Vachard@univ-lille1.fr Marc Hauser 2 Mineralogisch-petrographisches Institut und Geologisches Institut, Universität Bern, Baltzerstrasse 1, 3012 Bern, Switzerland. E-mail: hauser@mpi.unibe.ch Rossana Martini 3 Département de Géologie et Paléontologie, 13 rue des Maraîchers, CH-1211 Genève, Switzerland. E-mail: Rossana.Martini@terre.unige.ch Louisette Zaninetti 3 Département de Géologie et Paléontologie, 13 rue des Maraîchers, CH-1211 Genève, Switzerland. E-mail: Rossana.Martini@terre.unige.ch Albert Matter 2 Mineralogisch-petrographisches Institut und Geologisches Institut, Universität Bern, Baltzerstrasse 1, 3012 Bern, Switzerland. E-mail: hauser@mpi.unibe.ch Tjerk Peters 2 Mineralogisch-petrographisches Institut und Geologisches Institut, Universität Bern, Baltzerstrasse 1, 3012 Bern, Switzerland. E-mail: hauser@mpi.unibe.ch Publisher: Cushman Foundation for Foraminiferal Research Received: 27 Jul 2001 Accepted: 17 Aug 2001 First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 © 2002 Journal of Foraminiferal Research Journal of Foraminiferal Research (2002) 32 (2): 155–172. https://doi.org/10.2113/0320155 Article history Received: 27 Jul 2001 Accepted: 17 Aug 2001 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Daniel Vachard, Marc Hauser, Rossana Martini, Louisette Zaninetti, Albert Matter, Tjerk Peters; MIDDLE PERMIAN (MIDIAN) FORAMINIFERAL ASSEMBLAGES FROM THE BATAIN PLAIN (EASTERN OMAN): THEIR SIGNIFICANCE TO NEOTETHYAN PALEOGEOGRAPHY. Journal of Foraminiferal Research 2002;; 32 (2): 155–172. doi: https://doi.org/10.2113/0320155 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract Exceptionally rich Permian fusulinid assemblages, varying in age from Yakhtashian to Dzhulfian, were found in reworked limestone blocks from conglomerates of the Aseelah Unit, recently defined in the Batain Plain and dated possibly as Upper Triassic. This paper only deals with the Middle Permian, Midian (= Capitanian) microfaunas from the conglomerates.The Aseelah Unit is found associated with the Triassic Sal Formation, tectonically overlying the Qarari Unit, and is dated as Middle to Late Permian based on ammonoid assemblages and conodonts. The boulders of the Aseelah Unit are composed of exclusively Permian skeletal limestones in a sandy matrix; the limestones were deposited on a shallow marine shelf environment from the southern Neotethys. The Qarari Unit is interpreted as a hemipelagic series deposited on the distal slope of the Arabian carbonate platform.The Midian foraminifers from the Batain Plain are similar to some assemblages of Transcaucasia, of the Abadeh area (Iran), of SW Turkey (Taurus Mountains), and some, especially the Neoschwagerinidae, exhibit affinities with microfaunas of the eastern Tethys terranes of Japan. However, similar Neoschwagerinid assemblages were not found in any significant area of the Arabian Peninsula (Oman Mountains, Huqf-Haushi area, and Khuff area). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structure, petrology and seafloor spreading tectonics of the Kizildag Ophiolite, Turkey

Abstract The Kizildag ophiolite in southern Turkey is a remnant of the Neo-Tethyan oceanic crust and displays well-preserved magmatic and tectonic structures of seafloor spreading origin. The ophiolite consists of two structurally distinct massifs that are separated by the NW-striking high-angle Tahtaköprü fault. The main massif to the west contains a serpentinized peridotite core adjoined on the southeast by the normal fault-bounded plutonic sequence and sheeted dyke complex in a structural graben. The dyke-gabbro boundary within this graben is in places faulted along a low-angle detachment surface and is locally marked by a transition zone with mutual intrusive relations between the dykes and isotropic gabbros and plagiogranites. This igneous boundary contains numerous proto-dyke intrusions marking a well-preserved root zone of the sheeted dyke complex and may represent the roof of a fossil magma chamber. Mineralized oceanic faults within the dyke complex form two major subsets. Dyke-parallel normal faults form horst and graben structures and locally flatten with depth acquiring a listric geometry. Dyke-perpendicular faults display steep dips and subhorizontal slickenside lineations, suggesting their oblique- to strike-slip nature. The graben structure containing the plutonic sequence and the sheeted dyke complex is analogous to those documented in the Troodos ophiolite and may similarly represent a fossil spreading axis. The second massif east of the Tahtaköprü fault consists mainly of serpentinized peridotites directly overlain by lava flows, rotated dyke blocks, and gabbros. Sulfide mineralization along some fault planes in the extrusive rocks indicates that hydrothermal systems were associated and operated synchronously with magmatic and tectonic extensional processes. Stratigraphic relations and the structural architecture in this massif suggest that the Kizildag oceanic crust underwent crustal denudation and unroofing of the upper mantle as a result of tectonic extension at a spreading centre. The Tahtaköprü fault separating the two massifs is an accommodation zone that permitted differential movements between the adjacent ridge segments during generation of the Neo-Tethyan oceanic lithosphere. The general structure of the ophiolite suggests its evolution via seafloor spreading and an asymmetric simple shear extension along a slow-spreading centre. The sheeted dykes and pillow lavas have relatively high SiO 2 and Al 2 O 3 and low FeO and TiO 2 concentrations and show limited FeO and TiO 2 enrichments with decreasing MgO contents. These compositional properties differ markedly from typical tholeiitic suites from the ocean floor and arc settings, but correspond closely to those documented from the sheeted dyke complex and the lower volcanic suite of the Troodos ophiolite. The major element compositions suggest low pressure and high degree of melting from a depleted mantle source. The trace element concentrations are markedly depleted in both high-field strength and rare-earth elements and relatively enriched in largeion-lithophile elements compared to normal MORB. It is inferred that the Kizildag ophiolite formed in a tectonic setting where melting occurred at relatively low pressures within the stability field of spinel and proceeded to high melt fractions possibly by progressive depletion and melt removal. A limited positive correlation between the extent of melting and light rare-earth enrichment can be related to infiltration by fluids or melts derived from a more fertile source or possibly a subducting slab fragment. Comparison of the structure and petrology of the Troodos and Kizildag ophiolites and the regional geology suggest their evolution along a seafloor spreading system within the Southern Neo-Tethys. Spreading probably occurred in short segments and resulted in development of the Cretaceous Neo-Tethyan seaway as a marginal basin between the Tauride platform in the north and Afro-Arabia in the south.

KARSTIC RESERVOIRS OF THE MID‐CRETACEOUS MARDIN GROUP, SE TURKEY: Tectonic and Eustatic Controls on their Genesis, Distribution and Preservation

The mid‐Cretaceous Mardin Group is the main producing reservoir interval in the oilfields of SE Turkey. During the mid‐Cretaceous, deposition of lime mudstones and bioclastic limestones took place on a carbonate platform. Repeated tectonic uplift occurred locally throughout this time, during the early stages of the closure of the southern Neotethys. The interplay of eustatic transgressions and regressions with local tectonic uplift controlled deposition and diagenesis, the latter including major secondary porosity development during dolomitization and karstification. Minor shortening and uplift in the Late Cretaceous and Palaeogene created structural traps and may also have enhanced fracture porosity. Major thin‐skinned thrust tectonics breached many reservoirs in the late Miocene. Surface anticlines which formed during the Miocene have attracted most of the exploration drilling to date, but may be the sites of the most intense breaching of the reservoirs. The distribution of the best potential reservoirs is not necessarily linked to the positions of Miocene anticlines.

PALAEOZOIC TECTONIC HISTORY OF SE TURKEY

A review of published data for the Palaeozoic of SE Turkey, together with facies distribution and palaeo‐fault maps derived from regional field data, are used to interpret the Palaeozoic tectonic history of the region.Intracratonic rifting events in the Early Cambrian and the Early Ordovician led to syn‐rift deposition within fault‐bounded basins. Marine transgressions across the region in the mid‐Cambrian and mid‐to‐Late Ordovician were probably influenced by regional thermal subsidence after each rifting event, in addition to (glacio‐)eustatic mechanisms. Marine transgressions in the Early Silurian and Early Carboniferous are thought to have been entirely eustatic in origin.Poorly‐constrained, Late Palaeozoic facies variations across the region can be related to uplift during the Caledonian and Hercynian orogenic episodes. Widespread tilting and erosion before the Cretaceous, which has removed much of the Late Palaeozoic record from this region, resulted from uplift at the edges of a major rift system which was initiated during the Triassic‐to‐Jurassic opening of the Southern Neotethys.

Interactions of Tethyan blocks and evolution of Asian fold belts

Two segments of the Tethys ocean, the northern Palaeo-Tethys and the southern Neo-Tethys, were distinct in that the opening of the latter in Late Palaeozoic-Early Mesozoic times coincided with (or caused) the closing of the former. Continental blocks formed by rifting of the major plates of China and India interacted with each other and with major cratonic blocks, and produced the Asian and the southeast Asian fold belts. Central Iran, Tibet and Shan-west Malay were parts of the greater Gondwanic Indo-Arabian plate, and these rifted away to create the Neo-Tethys. These together with other blocks of the Palaeo-Tethys reduce the width of the Tethys ocean as originally conceived. The episodic Asiatic orogenies relate to progressive southward and southwestward migration of the subduction and the collision zones. The resultant fold belts, except for the unique Himalayan belt which is a reworked microcontinent, can generally be compared in geological and tectonic development from southeast Asia to west-central Asia.