Northern Neotethys Research Articles

Tectono-stratigraphy, formation and emplacement ages of the Beyşehir-Hoyran Nappes in the south of the Sultan Dağları (Isparta, SW Türkiye)

The Beyşehir-Hoyran Nappes (BHN), in the south of Sultan Dağları, consist of ophiolite, mélange and nappe slices of different lithologies and ages belonging to the oceanic crust and related rocks, which originated from the northern Neotethys and were thrusted southwards over the Taurus Platform. These nappes, namely the Marmaris ophiolite nappe, the Gülbahar nappe and the Domuzdağ nappe, are represented by three tectonically related nappe-slices that extend as a narrow NW-SE trending belt to the south of the Sultan Dağları. The Marmaris ophiolite nappe (Upper Cretaceous) is formed by three subunits namely the Marmaris ophiolite, the Kızılcadağ mélange and the Yenicekale metamorphics. Hornblende minerals from amphibolites of the Yenicekale metamorphic rock unit yielded a 40Ar-39Ar age of 93.9±0.34 Ma (Cenomanian-Turonian boundary). Besides, late Triassic to early Jurassic ages were obtained from the deep marine sedimentary rocks of the Gülbahar nappe based on the radiolarian assemblages. Paleontological and radiometric ages obtained from this study show that the formation of the BHN should began in the Turonian and ended in the Late Maastrichtian. The nappes, on the other hand, were emplaced over southern Sultan Dağları in the early-middle Paleocene and reached their present position as a result of late Eocene movements.

Latest Carboniferous–Early Permian Rifting of the Northern Gondwanan Margin and the Opening of the Northern Neotethys: New Evidence from the Carboniferous and Permian Foraminiferal Assemblages from the Beysehir-Hoyran Nappes, Central Taurides (Southern Turkey)

Latest Carboniferous–Early Permian Rifting of the Northern Gondwanan Margin and the Opening of the Northern Neotethys: New Evidence from the Carboniferous and Permian Foraminiferal Assemblages from the Beysehir-Hoyran Nappes, Central Taurides (Southern Turkey)

Palaeomagnetic evidence of the deformation of the Pontides during the closure of the Intra-Pontide Ocean in the early Cretaceous

SUMMARY Several models exist concerning the deformation history of the Pontides in North Anatolia during the Cretaceous period, which vary depending on the positions of the Istanbul and Sakarya zones, the consumption of the northern branches of the Neotethys ocean and the rifting of several sub-basins. Notably, the early Cretaceous tectonic history of the Pontides involved the closure of the northern Neotethys ocean (Intra-Pontide ocean), and the collision between the Istanbul and Sakarya zones, producing thrust structures along the collisional front. The lack of palaeomagnetic data providing evidence for this deformation pattern demonstrates that further investigation is required, particularly focusing on the Lower Cretaceous strata in the Pontides. Thus, this study aimed to examine samples from a total of 78 sites from the Lower–Upper Cretaceous sedimentary rocks, and Middle Eocene to Middle Miocene sedimentary and volcanic rocks. Results of this study indicated large counterclockwise rotations up to R±ΔR = −73.9°±9.1°, and small clockwise rotations of R±ΔR = 14.2°±12.2° in the Istanbul and Sakarya zones, during the Early Cretaceous and Late Cretaceous periods. These rotation patterns are accompanied by the closure of the Intra-Pontide ocean, and the collision between the Istanbul and Sakarya zones during the Early and Late Cretaceous periods. On the other hand, in the Middle Eocene, small counterclockwise rotations of R±ΔR = −6.4°±13.9° and 4.6°±12.9° along the western coastline of the Pontides indicated that the northern margin of the Pontides was stable during this period.

U-Pb dating of arc to post-collisional magmatic events in northwestern Anatolia: The Eocene Granitoids in NW Anatolia revisited

Northwestern Anatolia contains voluminous Cenozoic magmatic rocks which were emplaced during syn- to-post collisional stages of long-term crustal accretion and extensional stages since the late Paleocene. The Eocene to Late Miocene plutonic and volcanic rocks that are located throughout the Rhodopes, northern Aegean, and the western part of Western Anatolia show generally southward decreasing ages, coupled with an increasing crustal recycling component in their genesis. However, the early Eocene, ∼SW–NE-trending, mafic volcanic and the early Eocene, ∼NW-SE-trending, granitoid belts in the northeastern parts of Western Anatolia do not share these features. We present here new U-Pb zircon ages, whole-rock geochemical analyses, and Sr-Nd isotopic data from the early Eocene NW-SE-trending granitoid belt, together with age data from arc-related pyroclastics in the region, in an effort to resolve these uncertainties.The age data reveal that the post-collisional magmatism along the ∼ NW–SE-trending granitoid belt occurred ∼ 58–41 Ma; i.e. ∼ 30 Myr after the Pontide arc magmatism that was active from ∼ 92–74 Ma. We suggest that the ∼ SW–NE-trending mafic volcanic and the ∼ NW-SE-trending granitoid belts developed in response to break-off of two subducted slabs in the northern Neotethys. In addition, emplacement of the ∼ NW-SE trending granitoid belt may also have been influenced by a zone of weakness related to a series of NW–SE-trending dextral strike-slip shear zones lying from the Kapıdağ shear zone close to the Rhodopes in the NW to the Uludağ shear zone in the SE.

District-Scale VMS to Porphyry-Epithermal Transitions in Subduction to Postcollisional Tectonic Environments: The Artvin Au-Cu District and the Hod Gold Corridor, Eastern Pontides Belt, Turkey

Abstract Porphyry, epithermal, and volcanogenic massive sulfide (VMS) deposits can form together in the same mineral district in convergent margin environments. Their spatial association and superposition indicate evolving tectonic settings. The Artvin Au-Cu district is one of the major clusters of VMS bimodal-felsic, porphyry, and epithermal deposits in the Eastern Pontides belt in northeast Turkey. Whereas ore-forming processes, timing, and tectonic setting of VMS mineralization are well defined in Artvin, those for porphyry and epithermal mineralization remain less constrained. Our district-scale field study focused on the Hod gold corridor in the Artvin district, which is defined by the NE-trending alignment of the recent Au-Cu mineral discoveries (~205 t Au; ~0.33 Mt Cu; e.g., Hod Maden, Ardala-Salinbaş, and Taç-Çorak) that include Au-rich porphyry, highand intermediate-sulfidation epithermal, carbonate-replacement, and hybrid VMS-epithermal mineralization styles. Our new U-Pb, 40Ar/39Ar, and Re-Os geochronological results interpreted with previously compiled data show that magmatism in the Artvin district formed in the Carboniferous (358–325 Ma), Jurassic (182–174 Ma), Late Cretaceous (92–78 Ma), Eocene (51–40 Ma), and Oligocene (30 Ma). Porphyry and epithermal mineralization along the Hod gold corridor peaked in the Early (~113 Ma; Berta prospect) and Late Cretaceous (~86.5-82 Ma; e.g., Taç and Çorak deposits) and Eocene (~50 Ma; e.g., Ardala deposit), whereas VMS bimodal-felsic mineralization only formed in the Late Cretaceous (~91–85 Ma). Therefore, we interpret that the Hod gold corridor was a long-lived, deep crustal-scale structural feature along which the successive magmatic and mineralization events were emplaced. In addition, the timing of porphyry Cu-Mo mineralization can significantly (>20 Ma) postdate the crystallization age of the intrusive host rocks in the Artvin district, such as at Berta and Balcılı camp, which emphasizes the importance of dating mineralization directly to correctly attribute the tectonic setting. The distribution of Late Cretaceous mineral occurrences suggests a possible eastward temporal evolution from VMS (~91–85 Ma) to epithermal-porphyry systems (~86.5–82 Ma), transitioning from back-arc to arc settings at the onset of the Northern Neotethyan oceanic slab rollback and accompanied by increasingly elevated gold content eastwards across the Artvin district.

Facies analysis and depositional model for the Oxfordian Hanifa Formation, Central Saudi Arabia

The Jurassic was a time for major global changes in climate, tectonics, and oceanography, reflected in the southern Neo-Tethys Ocean by a distinct transition from carbonate-poor to carbonate-dominated sedimentation. To better constrain the effect of this turning point in the Late Jurassic, key outcrops of Oxfordian deposits of the Arabian Plate were investigated through detailed sedimentologic analysis. High-resolution (centimeter-scale) description and analysis of eight outcropping sections with a cumulative thickness of 461 m through the Oxfordian Hanifa Formation along a N–S 535 km-long transect in central Saudi Arabia are used to develop a comprehensive conceptual depositional evolution through time. Nine sedimentary lithofacies are interpreted and grouped into four facies associations. These associations include: I) outer-ramp association (FA1), II) mid-ramp association (FA2), III) inner-ramp grainy-facies association (FA3), and VI) inner-ramp reefal association (FA4). The lithofacies succession distinguishes two depositional phases, a middle Oxfordian homoclinal ramp (Phase 1) that corresponds to the Hawtah Member, and a late Oxfordian reef-bearing carbonate ramp (Phase 2) that corresponds to the Ulayyah Member. After being restricted to the high latitudes in the northern Neo-Tethys during early and middle Oxfordian ages, the carbonate ramp evolution within the Hanifa Formation reflects the expansion of scleractinian coral reefs over the southern Neo-Tethys passive margin in the late Oxfordian. However, the distribution of the corals in the Arabian Plate is mainly controlled by water salinity and siliciclastic input; they are absent northward due to hypersalinity and southward due to siliciclastic input. Furthermore, the differential subsidence and the resulting uneven topography, in addition to the eustatic sea level variation during the Oxfordian age, controls the distribution of different depositional styles over the Arabian Plate (homoclinal ramp, distally-steepened ramp, rimed shelf, and intrashelf basin).

Mineralogy and PGE geochemistry of chromitites and peridotites of the sapat complex in the indus suture zone, northern Pakistan: implications for magmatic processes in the supra-subduction zone

ABSTRACT The Sapat Complex in Northern Pakistan contains remnants of the northern Neo-Tethys Ocean, presently exposed along the Indus Suture Zone. The mantle peridotites of the Sapat Complex include harzburgites, dunites, and subordinate lherzolites. Harzburgites are the dominant peridotite variety over dunites. The dunites are hosted by harzburgites and occur exclusively as ‘envelopes’ surrounding chromitite pods. The podiform chromitites show disseminated, banded, and massive textures. Chromitites exhibit variable Cr# [Cr/(Cr + Al)] and Mg# [Mg/(Mg + Fe2+)], which range from 0.76 to 0.77, and from 0.64 to 0.66, respectively, while TiO2 contents are <0.2 wt.%. These features perhaps reflect crystallization of the chromian spinel from a boninitic magma. Similarly, chromian spinel in peridotites manifest a wide range of Cr# and Mg#, from 0.49 to 0.83 and 0.41 to 0.57, respectively, and are characterized by very low TiO2 values, averaging at 0.1 wt.%. Chromian spinel of chromitites and peridotites of the Sapat Complex have also very low Fe3+# (<0.01), which indicate their crystallization under low oxygen fugacities. The platinum group elements (PGE) distributions show high (Os + Ir + Ru)/(Rh + Pt + Pd), very low Pd/Ir values, and are defined by a prominently fractionated chondritic normalized PGE pattern, hence, this deposit is a typical example of an ophiolitic chromitite. The studied peridotites are highly depleted in PGE compared to chondritic values. The PdN/IrN values, averaging to 1.5 in dunites are unfractionated, while PGE spidergrams of harzburgites and lherzolites depict minor positive slopes, a minor positive Ru anomaly, and have average PdN/IrN values of 2.3 and 2.4, respectively. Furthermore, the harzburgites, dunites, and lherzolites display generally flat chondritic and primitive mantle normalized PGE patterns, and therefore, are nearly identical to highly depleted mantle peridotites. The mineralogical and PGE geochemical imprints of Sapat Complex chromitites and peridotites establish a strong affinity to supra-subduction zone ophiolites. Moreover, calculated parental melts of the chromitites and various geochemical discrimination diagrams elucidate that the chromitites were derived from boninitic magma produced by melting of depleted mantle peridotites in an oceanic arc, characterized by low oxygen fugacity, similar to a supra-subduction zone tectonic setting. This research highlights the use of mineralogy and geochemical compositions of chromitites and peridotites to reveal deep magmatic processes in a supra-subduction zone environment.

Nummulites assemblages, biofabrics and sedimentary structures: The anatomy and depositional model of an extended Eocene (Bartonian) nummulitic accumulation from the Transylvanian Basin (NW Romania)

Extensive high-resolution palaeontological, stratigraphic and sedimentological data offer a new and comprehensive view of the genesis and evolution of the most extended Eocene nummulitic accumulation in the northern Neotethyan realm. The preserved Bartonian (SBZ 17) Nummulites assemblages consist of large, granulate Nummulites perforatus and/or small, radiate Nummulites beaumonti . The assemblages differ in taxonomic content and/or in the relative abundance of test type (A- versus B-forms): Assemblage 1 is dominated by N. beaumonti A-forms, N. perforatus A-forms are sporadic, while B-forms are rare or missing; Assemblage 2 consists of N. perforatus A- and B-forms; and Assemblage 3 consists essentially of N. perforatus A- and B-forms with only rare N. beaumonti A- and B-forms. These assemblages are interpreted as autochthonous and autochthonous to para-autochthonous, deposited on a low-angle inner shelf. Their distribution in space and time reflects the interplay between the palaeoenvironment and the ability of N. perforatus and N. beaumonti to colonize new habitats. Thus the genesis and development of the studied nummulitic accumulations mirrors the ecological preferences of the two Nummulites species, the relative sea-level, the sediment supply and possibly the climate history. The shelf around the storm wave base was first colonized by N. beaumonti and rare N. perforatus, then the mass nummulitic accumulation was formed by the accumulation of N. perforatus tests between the storm wave base and the fair weather wave base. The accumulation of abundant N. perforatus and rare N. beaumonti around the fair weather wave base occurred in the last phase. • Detailed description of a unique Eocene nummulitic accumulation. • Distribution of the assemblages are related to the relative sea-level changes. • Composition of the Nummulites assemblages are linked to the ecological preferences. • Development of the nummulitic accumulation is the result of biotic and abiotic factors.

Environmental significance of trace fossil assemblages in a tide‒wave-dominated shallow-marine carbonate system (Lower Cretaceous), northern Neo-Tethys margin, Kopet-Dagh Basin, Iran

Environmental significance of trace fossil assemblages in a tide‒wave-dominated shallow-marine carbonate system (Lower Cretaceous), northern Neo-Tethys margin, Kopet-Dagh Basin, Iran

New evidence for Late Cretaceous plume-related seamounts in the Middle East sector of the Neo-Tethys: Constraints from geochemistry, petrology, and mineral chemistry of the magmatic rocks from the western Durkan Complex (Makran Accretionary Prism, SE Iran)

The Durkan Complex in the Makran Accretionary Prism (SE Iran) has been interpreted either as a continental margin succession or a Late Cretaceous tectonically disrupted seamount chain. New whole rock and clinopyroxene chemical data for basaltic and metabasaltic rocks of the Durkan Complex allow us to distinguish two main rock groups: a) rocks showing transitional chemical affinity (Group 1) and compositions resembling those of plume-type mid-oceanic ridge basalts; b) rocks with within-plate oceanic island basalt (OIB) compositions showing a clear alkaline affinity (Group 2). Based on whole rock REE contents and clinopyroxene chemistry, alkaline rocks can be further subdivided in two sub-groups, namely, the Group 2a and 2b. Compared to Group 2a, Group 2b rocks show a more pronounced alkaline nature marked by higher whole rock La/Yb and Sm/Dy ratios and higher TiO2 and Na2O contents in clinopyroxenes. Trace element and REE petrogenetic models show that the Durkan basaltic rocks were generated from the partial melting of depleted sub-oceanic mantle source that was metasomatized by OIB-type chemical components in a within-plate oceanic setting. The chemical differences in the three rock groups are related to different combinations of partial melting degree, depths of melting, and various extent of enrichment of the mantle sources by OIB-type chemical components, which are related, in turn, to a Late Cretaceous mantle plume activity in the northern Neo-Tethys realm. We suggest that the Durkan Complex formed in a seamount setting and that its different volcano-sedimentary successions record different stages of seamount formation.

Origin, petrogenesis and geodynamic implications of the early Eocene Altınpınar adakitic andesites in the eastern Sakarya Zone, northeastern Turkey

Early Cenozoic magmatism in the eastern Sakarya Zone (NE Turkey) provides an important constraint on the regional tectono-magmatic evolution of the region. Early Eocene syn-collisional adakitic rocks are observed as small stocks with outcropping areas commonly less than 10 km2. This study presents petrography, whole-rock geochemistry and Sr-Nd-Pb isotope data, as well as in-situ 40Ar/39Ar age constraints on one of these adakitic andesites in the Altınpınar area of Gümüşhane, and discusses source region, petrological processes and geodynamic setting prevailed during their genesis. Andesites commonly show microlitic porphyric and vitrophyric porphyric textures, and include significant amounts of mafic microgranular enclaves (MMEs). Plagioclase, hornblende, Fe-Ti oxides and minor pyroxene are the main mineral phases. In-situ 40Ar-39Ar amphibole dating constrains the cooling age of andesites into a time span from 52.8 ± 1.3–48.8 ± 1.9 Ma. Andesites are medium to high-K calc-alkaline and display most of the signatures typical of those of the adakites. They are characterized by moderate MgO (1.7–4.1 wt%), low Y (9−14 ppm), Yb (0.9–1.5 ppm), and HREE and high Sr (325−964 ppm) contents, and high Sr/Y (36–76) ratios. 87Sr/86Sr(t) (0.704948−0.705100) and 143Nd/144Nd(t) (0.512588−0.512628) ratios are in the isotopic range of the adakites. All these geochemical and isotopic data suggest that the parental magma of adakitic andesites has been produced by partial melting of oceanic basalts under amphibole-eclogite facies conditions during the breakoff of the northern Neotethyan oceanic slab.

Geochemistry and U-Pb ages from the Kösdağ Metavolcanics in the southern Central Pontides (Turkey): Complementary data for early Late Cretaceous island arc development in the Northern Neotethys

The Kosdag Metavolcanics (KMs) in the southern Central Pontides are exposed between the Izmir-Ankara-Erzincan Suture Belt in the south and the Sakarya Composite Terrane in the north. They comprise an approximately 40-km-long tectonic unit, bounded by the splays of the North Anatolian Transform Fault in the north and the Kizilca Thrust in the south. The basement of the unit mainly consists of metabasalts, metaandesites, and metarhyolites, with well-developed blastomylonitic textures, which are interlayered by recrystallized pelagic limestone and chert. Late Cretaceous pelagic limestones of the Dikmen Formation disconformably overlie the basement. Geochemically, the KMs exhibit enrichment in Th and La relative to Nb (and Ti), indicating subduction-related magmatic signatures. The KMs are subdivided into two main types, as Type 1 and Type 2, based on their relative Zr-Hf enrichment/depletion features. All of the members of the KMs have a subalkaline nature (Nb/Y - 0.08-0.19 for Type 1; Nb/Y = 0.05-0.13 for Type 2) and display a calc-alkaline affinity. The high Zr/Nb (38.1-52.9 for Type 1, 21.8-41.2 for Type 2), low Zr/Y (4.07-5.25 for Type 1, 1.58-2.44 for Type 2), and Nb/Y (0.08-0.14 for Type 1,0.05-0.10 for Type 2) signatures of the KMs indicate that they have derived from a depleted source, which has been modified by a subduction component. The laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon ages of the metarhyolite samples ranged between 94.64 +/- 0.77 Ma and 113.2 +/- 2.3 Ma, suggesting the presence of an intraoceanic subduction zone during the early Late Cretaceous within the Izmir-Ankara-Erzincan branch of the Neotethys Ocean in the Central Pontides.

The closure of the Vardar Ocean (the western domain of the northern Neotethys) from the early Middle Jurassic to the Paleocene time, based on the surface geology of eastern Pelagonia and the Vardar zone, biostratigraphy, and seismic-tomographic images of the mantle below the Central Hellenides.

Seismic tomographic images of the mantle below the Hellenides indicate that the Vardar Ocean probably had a composite width of over 3000 km. From surface geology we know that this ocean was initially located between two passive margins: Pelagonian Adria in the west and Serbo-Macedonian-Eurasia in the east. Pelagonia was covered by a carbonate platform that accumulated, during Late Triassic to Early Cretaceous time, where highly diversified carbonate sedimentary environments evolved and reacted to the adjacent, converging Vardar Ocean plate. We conceive that on the east side of the Vardar Ocean, a Cretaceous carbonate platform evolved from the Aptian to the Maastrichtian time in the forearc basin of the Vardar supra-subduction volcanic arc complex. The closure of the Vardar Ocean occurred in one episode of ophiolite obduction and in two episodes of intra-oceanic subduction. 1. During the Middle Jurassic time a 1200-km slab of west Vardar lithosphere subducted beneath the supra-subduction, 'Eohellenic', arc, while a 200-km-wide slab obducted onto Pelagonia between the Callovian and Valanginian times. 2. During the Late Jurassic through to the Cretaceous time a 1700-km-wide slab subducted beneath the evolving east Vardar-zone arc-complex. Pelagonia, the trailing edge of the subducting east-Vardar Ocean slab, crashed and underthrust the Vardar arc complex during the Paleocene time and ultimately crashed with Serbo-Macedonia. Since the late Early Jurassic time, the Hellenides have moved about 3000 km toward the northeast while the Atlantic Ocean spread.

Age determination of the Oligocene Qom Formation and interpretation of palaeoenvironments in the Qom back-arc basin (northern Neotethys) using benthic foraminifera

Age determination of the Oligocene Qom Formation and interpretation of palaeoenvironments in the Qom back-arc basin (northern Neotethys) using benthic foraminifera

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

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.

At the crossroads of the Lesser Caucasus and the Eastern Pontides: Late Cretaceous to early Eocene magmatic and geodynamic evolution of the Bolnisi district, Georgia

The Bolnisi district is a distinct tectonic zone of the Lesser Caucasus, which is considered to represent the eastern extremity of the Turkish Eastern Pontides. Late Cretaceous, low-K, calc-alkaline to high-K rhyolite of the Mashavera and Gasandami Suites is the predominant rock type of the district, and is accompanied by subsidiary dacite, and rare high-alumina basalt and trachyandesite of the Tandzia Suite. The Mashavera and Gasandami rhyolite and dacite have yielded U-Pb LA-ICP-MS and TIMS zircon ages between 87.14 ± 0.16 and 81.64 ± 0.94 Ma, which are in line with the Coniacan-Santonian ages of radiolarian fauna of the Mashavera Suite. The felsic rocks of the Mashavera and Gasandami Suites were deposited during a ~6.6 m.y.-long silicic magmatic flare-up event, which together with the Tandzia Suite mafic rocks, documents Late Cretaceous bimodal magmatism in an extensional tectonic setting. Trace element data indicate that high Y-Zr, low- to high-silica rhyolite and dacite, and low Y-Zr high-silica rhyolite have been erupted, respectively, from coeval deep and shallow crustal reservoirs. The rocks of the bimodal magmatic event are overlain by high-K volcanic rocks of the Campanian Shorsholeti Suite, which have been erupted during slab roll-back and steepening, from magmas produced by deep melting of a metasomatised mantle. Eocene postcollisional felsic intrusions crosscut the Late Cretaceous rock.The Coniacian to early Campanian bimodal magmatism, and the subsequent high-K magmatism of the Bolnisi district are contemporaneous and share geochemical characteristics with the Late Cretaceous magmatism of the Eastern Pontides. It documents the existence of a Late Cretaceous regional silicic magmatic province, and subsequent high-K magmatism during slab steepening. This regional magmatic evolution coincided with the opening of the Black Sea and the Adjara-Trialeti basins. This evolution was coeval with the wanning stages of northern Neotethyan subduction, after a ~40 m.y.-long magmatic lull along the southern Eurasian convergent margin. Early Eocene adakite-like magmatism affected both the Bolnisi district and the Eastern Pontides, demonstrating a common postcollisional magmatic evolution.

Carnian (Upper Triassic) Lavas and Tuffites from the Mersin Mélange: Evidence for Intraoceanic Arc Rifting in the Northern Neotethys

AbstractIn Anatolia, the northern branch of Neotethys is represented by Izmir-Ankara-Erzincan (IAE) Ocean, whose fragments and associated continental entities are preserved in the IAE Suture. Howev...

Palaeogene stratigraphy and chronology of the western Sivas Basin, central Anatolia (Turkey): Tectono‐sedimentary evolution of a well‐preserved basin along the northern Neotethys suture zone

AbstractThe Sivas Basin overlaps the northern Neotethys suture zone in central Anatolia (Turkey) and contains a ca. 12‐km thick succession of Cenozoic strata that provides an exceptional record of major tectonic transitions from subduction to continental assembly and tectonic escape. Consensus regarding the tectonic and palaeogeographic evolution of this segment of the Arabia‐Eurasia collision zone has been hindered by uncertainty in the tectonic setting of the early (Palaeogene) Sivas Basin, which has been variably interpreted as a remnant ocean, forearc, foreland, wedge‐top or intracontinental extensional basin. Here we integrate new geologic mapping (&gt;5,000 km2), stratigraphy, facies analysis and U‐Pb geochronology from the western Sivas Basin to produce a detailed time‐stratigraphic framework and a refined Palaeogene tectono‐sedimentary model for the Sivas Basin. Earliest marine sedimentation occurred during the Maastrichtian‐Palaeocene in a remnant ocean setting due to incomplete closure of the northern Neotethys Ocean. Rapid accumulation of &gt;2 km of basin floor turbidites during the middle to late Eocene reflect a transition to a foreland setting. A major late Eocene unconformity (ca. 38–34 Ma) coincides with the initiation of the north‐vergent southern Sivas fold‐thrust belt, which inverted and structurally partitioned the basin into a southern wedge‐top and a northern evaporitic foreland basin; the entire basin was dominantly nonmarine after this unconformity. Published palaeomagnetic data integrated with a newly discovered tuff dated at 31.9 Ma reveal that the 2.8‐km thick Altinyayla Formation was deposited from ca. 34 to 26 Ma in an unconfined braided fluvial system. Close stratigraphic correlations between the western, central and northern Sivas Basin suggest that the entire basin evolved from a remnant ocean to peripheral retro‐foreland basin during the middle to late Eocene, and finally a fragmented foreland basin since the Oligocene. This general evolution may be a characteristic of such sedimentary basins formed on suture zones across Anatolia and in other collisional orogens globally.

Stratigraphic record of Eponides Montfort 1808 (benthic Foraminifera) through the Paleocene carbonates of the northern Neotethys margin

In the former northern Neotethys margin where Paleocene shallow-water limestone successions crop out (Austria, Turkey and Iran), morphotypes closely resembling Eponides have been recognized. These foraminifers are lamellar-perforated, with a trochospirally arranged set of trapezoidal chambers.We have tested their generic identification through a detailed architectural analysis of thin sections of carbonate rocks in which Eponides-like specimens have abundantly been recovered. This study shows the occurrence of bipartitor, arched septa and a pseudoumbilicus formed by the fusion of ventral ends of chambers. These features allow us to identify the specimens as Eponides, although the specific attribution has not been attempted. The evolutionary pattern displayed by the Late Cretaceous and Cenozoic Eponides and phylogenetically-related allies is briefly discussed.

Biostratigraphy of Lower Permian foraminiferal assemblages from platform-slope carbonate blocks within the Mersin Mélange, southern Turkey: Paleogeographical implications

The Mersin Mélange (MM) as a part of the Mersin Ophiolitic Complex in southern Turkey is a sedimentary complex including blocks and tectonic slices within a Late Cretaceous matrix. Two blocks (Keven and Cingeypinari) within the MM originated from the northern branch of Neotethys (Izmir-Ankara-Erzincan Ocean) and have been studied in detail using foraminiferal assemblages to correlate them with coeval successions in the Taurides and to approach the Early Permian evolution of the northern branch of the Neotethys. The Keven block includes mainly slope deposits (poorly-sorted carbonate breccia and fossiliferous calcarenite) and dated as late Asselian-Sakmarian, whereas the Cingeypinari block consists of platform deposits (fossiliferous platform carbonate and quartz sandstone alternation) assigned to the Sakmarian-early Artinskian. These Early Permian Cingeypinari and Keven blocks from the Beysehir-Hoyran Nappes are biostratigraphically well correlated to the northerly originated Hadim nappe and its equivalents in the Tauride Belt. Considering recent studies on the Mersin Mélange, a possible mantle plume existed during the Late Carboniferous-Early Permian time interval along the northern Gondwanan margin. This event led to the opening of the northern Neotethys and deposition of the pelagic “Karincali” sequence with volcanic material in the basinal conditions. The data presented suggest that the Keven block relates to the slope and the Cingeypinari block to platform conditions deposited as a lateral equivalent of the Karincali sequences during the Early Permian.