The Intra-Pontide ophiolites in Northern Turkey revisited: From birth to death of a Neotethyan oceanic domain

The Anatolian peninsula is a key location to study the central portion of the Neotethys Ocean(s) and to understand how its western and eastern branches were connected. One of the lesser known branches of the Mesozoic ocean(s) is preserved in the northern ophiolite suture zone exposed in Turkey, namely, the Intra-Pontide suture zone. It is located between the Sakarya terrane and the Eurasian margin (i.e., Istanbul-Zonguldak terrane) and consists of several metamorphic and non-metamorphic units containing ophiolites produced in supra-subduction settings from the Late Triassic to the Early Cretaceous. Ophiolites preserved in the metamorphic units recorded pervasive deformations and peak metamorphic conditions ranging from blueschist to eclogite facies. In the non-metamorphic units, the complete oceanic crust sequence is preserved in tectonic units or as olistoliths in sedimentary mélanges. Geochemical, structural, metamorphic and geochronological investigations performed on ophiolite-bearing units allowed the formulation of a new geodynamic model of the entire "life" of the Intra-Pontide oceanic basin(s). The reconstruction starts with the opening of the Intra-Pontide oceanic basins during the Late Triassic between the Sakarya and Istanbul-Zonguldak continental microplates and ends with its closure caused by two different subductions events that occurred during the upper Early Jurassic and Middle Jurassic. The continental collision between the Sakarya continental microplate and the Eurasian margin developed from the upper Early Cretaceous to the Palaeocene. The presented reconstruction is an alternative model to explain the complex and articulate geodynamic evolution that characterizes the southern margin of Eurasia during the Mesozoic era. Keywords: Intra-Pontide suture zone, Central Pontides, Northern Turkey, Ophiolites, Neotethys Ocean, Geodynamic

the intra pontide suture zone in the tosya kastamonu area northern turkey

ABSTRACTWe present the first detailed geological map of the tectonic units documented in the easternmost branch of the Intra-Pontide suture (IPS) zone in the Tosya-Kastamonu area (Northern Turkey). The Main Map is at 1:50,000 scale and covers an area of about 350 km2. It derived from 1:25,000 scale classic field mapping and represents a detailed overview of the complexities documented in the IPS zone, a tectonic nappe stack originating from the closure of the Intra-Pontide Oceanic basin and the subsequent collision between the Istanbul-Zonguldak terrane and the Sakarya composite terrane. The map shows the orientations of superposed foliations, fold axes and mineral lineations on the basis of geometric cross-cutting relationships documented within the five tectonic units of the IPS zone and provides information on its present-day architecture resulting from activity of the North Anatolian Fault

The origin of the asymmetry in the Iceland hotspot along the Mid-Atlantic Ridge from continental breakup to present-day

The Iceland hotspot has profoundly influenced the creation of oceanic crust throughout the North Atlantic basin. Enigmatically, the geographic extent of the hotspot influence along the Mid-Atlantic Ridge has been asymmetric for most of the spreading history. This asymmetry is evident in crustal thickness along the present-day ridge system and anomalously shallow seafloor of ages ∼49–25 Ma created at the Reykjanes Ridge (RR), SSW of the hotspot center, compared to deeper seafloor created by the now-extinct Aegir Ridge (AR) the same distance NE of the hotspot center. The cause of this asymmetry is explored with 3-D numerical models that simulate a mantle plume interacting with the ridge system using realistic ridge geometries and spreading rates that evolve from continental breakup to present-day. The models predict plume-influence to be symmetric at continental breakup, then to rapidly contract along the ridges, resulting in widely influenced margins next to uninfluenced oceanic crust. After this initial stage, varying degrees of asymmetry along the mature ridge segments are predicted. Models in which the lithosphere is created by the stiffening of the mantle due to the extraction of water near the base of the melting zone predict a moderate amount of asymmetry; the plume expands NE along the AR ∼70–80% as far as it expands SSW along the RR. Without dehydration stiffening, the lithosphere corresponds to the near-surface, cool, thermal boundary layer; in these cases, the plume is predicted to be even more asymmetric, expanding only 40–50% as far along the AR as it does along the RR. Estimates of asymmetry and seismically measured crustal thicknesses are best explained by model predictions of an Iceland plume volume flux of ∼100–200 m^3/s, and a lithosphere controlled by a rheology in which dehydration stiffens the mantle, but to a lesser degree than simulated here. The asymmetry of influence along the present-day ridge system is predicted to be a transient configuration in which plume influence along the Reykjanes Ridge is steady, but is still widening along the Kolbeinsey Ridge, as it has been since this ridge formed at ∼25 Ma

The Arkot Dağ Mélange Central Turkey: evidences for the geodynamic evolution of the Intra-Pontide suture zone.

The geological setting of Turkey can be described as an assemblage of continental terranes separated by ophiolite-bearing suture zones that mark the areas where the PaleoTethyan and NeoTehyan oceanic basins were destroyed. In northern Turkey, one of the most important suture zones is represented by the Intra-Pontide one consisting of an east-west trending belt of deformed and/or metamorphic units located at the boundary between the Istanbul-Zonguldak terrane to the north and the Sakarya terrane to the south. These units can be regarded as issued from the Intra-Pontide domain, whose geodynamic history is still a matter of debate. Along the Akpinar-Araç-Bayramoren geotraverse, located in central Turkey, an ophiolite-bearing mélange, known as the Arkot Dağ Mélange, is well-exposed along the Intra-Pontide suture zone. The Arkot Dağ Mélange can be described as an Upper Santonian chaotic sedimentary deposit consisting of an up to 1000-m-thick succession of slide-blocks of different sizes and lithologies enclosed in a sedimentary matrix consisting of shales, coarse-grained arenites, pebbly mudstones and pebbly sandstones. The slide-blocks, from a few meters to hectometers in size, are represented by metamorphic rocks (mainly micaschists and gneisses), by ophiolites (peridotites, gabbros, IAT and BAB basalts and cherts) and by sedimentary rocks (cherts, neritic and pelagic limestone, marly limestone and ophiolite-bearing turbidites). The youngest age among the slide- blocks has been provided by the ophiolite-bearing turbidites where a late Coniacian nannofossil assemblage has been found. The cherts have provided a wide range of ages from the Middle Triassic to Late Cretaceous, whereas the fossils found in the limestone indicate Late Jurassic to Early Cretaceous ages. The matrix of the Arkot Dağ Mélange, even if unaffected by metamorphism, shows deformations represented by multiple meters-thick cataclastic shear zones at the boundaries of the mélange slices or inside them. According to its features, the source area of the Arkot Dağ Mélange was most likely a stack of continental and oceanic thrust sheets emplaced in the Late Cretaceous onto a continental margin. The data collected from the different slide-blocks suggest that the Intra-Pontide domain was characterised by an oceanic basin that opened at the latest in the Early Jurassic. The opening of the Intra-Pontide oceanic basin was followed by the development of a subduction zone with a subsequent opening of suprasubduction oceanic basin in the Middle Jurassic – Early Cretaceous. The convergence in this suprasubduction oceanic basin started at the Early/Late Cretaceous boundary by an obduction process, whereas its final closure can be regarded as Late Paleocene

Insights into the Tethyan mantle heterogeneity: Trace element evidence from the Karakaya Complex, Central Anatolia

Highlights: • Strong Nb-kick originates from metasomatized oceanic lithospheric mantle (OLM). • Metasomatized OLM is a plume-related material causing Tethyan mantle heterogeneity. • The voluminous Middle Triassic Nilüfer magmatism is linked to mantle plumes. Abstract: The Nilüfer Unit of the Karakaya Complex (northern Turkey) preserves the remnants of the voluminous Triassic Tethyan magmatism. In the Imrahor area (Ankara), the Nilüfer Unit is characterized by a megablock consisting of hydrothermally altered basalts, gabbros, and subordinate wehrlitic cumulates. These lithologies display marked positive Nb anomalies with depleted Th/La ratios and varying degrees of LREE enrichment. They can be subdivided into two groups based on Nb/Nb*, which are not related to each other via fractional crystallization or extent of partial melting. With their strong Nb-kick and broad La/Sm range, the Imrahor lithologies are more akin to FOZO (Focus Zone)- or C (common component)-type melts than EM (Enriched Mantle) and HIMU (high μ). The Zr-Nb systematics reveals that melt mixing was an essential process in the petrogenesis of these mafic rocks. Based on geochemical modeling, the trace element systematics of the İmrahor lithologies can be explained by melting metasomatized oceanic lithospheric mantle (OLM) infiltrated by very low-degree melt fractions. The metasomatized OLM may represent a recycled, plume-related material that has generated Nb-enriched melts during the Triassic Tethyan magmatism

Assemblages de radiolaires, conodontes et ammonites du Trias supérieur au Jurassique inférieur du bloc de Tavuscayiri, Mélange de Mersin, Turquie: contraintes de temps pour la frontière T/J et évolution sédimentaire de la marge sud de la Néotethys du nord

Le Mélange de Mersin (au nord-ouest de la ville de Mersin) comprend une diversisté de grands blocs sédimentaires et d’écailles tectoniques d’origines paléozoïque et mésozoïque. Parmi ceux-ci, ces derniers présentent des moulages faciaux et tectonostratigraphiques des nappes de Beysehir-Hoyran (vestiges de la Néotethys du nord). Le bloc Tavuscayiri, situé au centre du Mélange de Mersin, près de la colline d’Orbuklukeli, constitue l’une de ces occurrences mésozoïques, avec une séquence pélagique continue du Trias supérieur au Jurassique inférieur. Sur la colline d’Orbuklukeli, une succession d’âges allant du Norien moyen au Toarcien a été datée avec précision. Elle commence par des assemblages de conodontes pour le Norien et le Rhétien et comprend des radiolaires pour le Rhétien supérieur. Une couche de tuf acide correspond à la limite T-J, qui passe au-dessus d’une série de calcaires à chert de plus en plus dominante, marquant un approfondissement progressif de la séquence. Les radiolaires de l’Hettangien inférieur sont peu représentés, mais un assemblage diversifié et bien conservé de radiolaires a été retrouvé de l’Hettangien moyen au Pliensbachien. Au total, quatre-vingt-cinq taxons, dont quatorze espèces nouvelles, ont été identifiés. De plus, un genre nouveau, Praeudalia Tekin, n. gen., est décrit dans la partie qui concerne le Rhétien. Le sommet de la section est représenté par des calcaires nodulaires du faciès Ammonitico rosso, comprenant une faune diversifiée d’ammonites du Toarcien. Tous les niveaux de la coupe Orbuklukeli du bloc Tavuscayiri peuvent être corrélées avec ceux décrits précédemment du groupe/formation Kayabasi, dans l’unité Bozkir et dans les unités Gülbahar/Gümüslü, des nappes lyciennes.The Mersin Mélange (northwest of Mersin city) includes a variety of large sedimentary blocks/tectonic slices of Palaeozoic and Mesozoic origins. Of these, the latter represents facial and tectonostratigraphic counterparts of the Beysehir-Hoyran Nappes (remnants of the northern Neotethys). The Tavuscayiri Block, located at the center of the mélange and close to the Orbuklukeli hill, is one of such Mesozoic occurrences, with a continuous pelagic sequence from the Upper Triassic to Lower Jurassic. At the Orbuklukeli hill, a succession of middle Norian to Toarcian age has been precisely dated, which starts with conodont assemblages for the Norian and Rhaetian and includes radiolarians for the upper Rhaetian. An acidic tuff layer corresponds to the T-J boundary, which passes above to an increasingly dominating chert-bearing limestone series, marking a gradually deepening-upward of the sequence. The early Hettangian radiolarians are poorly represented, but diverse and well-preserved radiolarians have been retrieved from the middle Hettangian to the Pliensbachian. A total of eighty-five taxa, including fourteen new species, have been determined. In addition to these, one new genus (Praeudalia Tekin, n. gen.) has been described from the Rhaetian part of the section. The top of the section is represented by nodular limestones in Ammonitico rosso facies, including a diverse Toarcian ammonite fauna. All lithologies of the Orbuklukeli section along the Tavuscayiri Block can be correlated with the previously described lithologies of the Kayabasi Group/Formation in the Bozkir Unit, and Gülbahar/Gümüslü units in the Lycian Nappes.</p

Late Triassic to Early Jurassic radiolarian, conodont and ammonite assemblages from the Tavuscayiri block, Mersin Mélange, southern Turkey: Time constraints for the T/J boundary and sedimentary evolution of the southern margin of the northern Neotethys

Tekin, Kagan, Krystyn, Leopold, Okuyucu, Cengiz, Bedi, Yavuz, Sayit, Kaan (2020): Late Triassic to Early Jurassic radiolarian, conodont and ammonite assemblages from the Tavuscayiri block, Mersin Mélange, southern Turkey: Time constraints for the T/J boundary and sedimentary evolution of the southern margin of the northern Neotethys. Geodiversitas 42 (27): 493-537, DOI: 10.5252/geodiversitas2020v42a2

Geological setting and geochemical signatures of the mafic rocks from the Intra-Pontide suture zone: implications for the geodynamic reconstruction of the Mesozoic Neotethys.

A number of suture zones exist in Turkey, which is believed to represent the closure of Paleo and NeoTethyan oceanic basins. Regarding the development of the latter oceanic entity, namely Neotethys, the geodynamic evolution of the Intra-Pontide branch, the northernmost one of a number of oceanic basins remains enigmatic. The Intra-Pontide Suture Zone (IPSZ) in Northwest Turkey includes several tectonic units most of which are characterized by the occurrence of mafic rocks with distinct geochemical signatures. In this paper, the mafic rocks collected from four of these units (the Domuz Dağ Unit, the Saka Unit, the Daday Unit and the Arkot Dağ Mèlange) have been studied in detail along two selected transects. The Domuz Dağ Unit is characterized by amphibolites, micaschists and marbles, which have been overprinted by low-grade metamorphism.The Saka Unit is in turn represented by an assemblage of slices of amphibolites, marbles and micaschists metamorphosed under upper amphibolite facies metamorphic conditions in the Late Jurassic time. In these units, the amphibolites and their retrograded counterparts display E-MORB-, OIB- BABB- and IAT-type signatures. The Daday Unit is characterized by metasedimentary and metamafic rocks metamorphosed under blueschist to sub-greenschist facies conditions. The metamafic rocks comprise actinolite-bearing schists and Na-amphibole-bearing varieties possibly derived from basaltic and gabbroic protoliths. They have a wide range of chemical compositions, displaying N-MORB-, E-MORB-, OIB- BABB- and IAT-type signatures. The Arkot Dağ Mèlange consists of a Late Santonian assemblage of slide-blocks mainly represented by basaltic lithologies showing affinities ranging from N-MORB- and IAT- to BABB-type magmas. The geochemical signature of the studied mafic rocks indicates that the tectonic units documented along the two studied transects of the Intra-Pontide Suture Zone have been derived from a supra-subduction zone. This hypothesis corroborates the available data collected from the Aylı Dağ Ophiolite Unit cropping out in the westernmost studied transect. This finding can provide new insights for the reconstruction of the geodynamic history of the Intra-Pontide domain

Pb and Hf isotope variations along the Southeast Indian Ridge and the dynamic distribution of MORB source domains in the upper mantle

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Geological and geochemical evidence for a Late Cretaceous continental arc in the Central Pontides, northern Turkey

In the Central Pontides (Northern Turkey), south of Tosya, a tectonic unit consisting of not-metamorphic volcanic rocks and overlying sedimentary succession is exposed inside a fault-bounded elongated block. It is restrained within a wide shear zone, where the Intra-Pontide suture zone, the Sakarya terrane and the Izmir-Ankara-Erzincan suture zone are juxtaposed as result of strike-slip activity of the North Anatolian shear zone. The volcanic rocks are mainly basalts and basaltic andesites (with their pyroclastic equivalents) associated with a volcaniclastic formation made up of breccias and sandstones that are stratigraphically overlain by a Marly-calcareous turbidite formation. The calcareous nannofossil biostratigraphy points to a late Santonian-middle Campanian age (CC17-CC21 Zones) for the sedimentary succession. The geochemistry of the volcanic rocks reveals an active continental margin setting as evidenced by the enrichment in Th and LREE over HFSE, and the Nb-enriched nature of these lavas relative to N-MORB. As highlighted by the performed arenite petrography, the occurrence of continent-derived clastics in the sedimentary succession supports the hypothesis of a continental arc-derived volcanic succession. Alternative geodynamic reconstructions are proposed, where this tectonic unit could represent a slice derived from the northern continental margin of the Intra- Pontide or Izmir-Ankara-Erzincan oceanic basins