Izmir-Ankara Ocean Research Articles

U–Pb ages and Hf isotopic compositions of zircon from the Early Miocene Kestanbol Magmatic Complex in NW Anatolia (Turkey): Implications for crustal contribution in the post-collisional magmatism

The Tertiary post-collisional magmatic activity in NW Anatolia occurred after the Late Cretaceous to Early Tertiary collision of the Sakarya and Anatolide-Tauride blocks and the closure of the Izmir-Ankara Ocean. The magmatism resulted in coeval emplacement of granitic plutons and andesitic volcanic rocks along the Izmir-Ankara-Erzincan Suture Zone (IAESZ). The Kestanbol Magmatic Complex (KMC) on the Biga Peninsula (W of the IAESZ), is one of the representative magmatic complexes in the Sakarya Zone situated north of the IAESZ. Monzo-dioritic (syeno-diorite) plutonic rocks show close relationships with dacitic, trachyandesitic and rhyolitic rocks in space and time which are characterized by enrichment in large-ion lithophile elements (LILE) and depletion in Nb, Ta, P and Ti, interpreted as reflecting an arc-related origin.Trace element concentrations and isotope data indicate that the KMC (the Kestanbol pluton, and the Ayvacık and the Balabanlı volcanic rocks) was formed by differentiation of mantle-derived mafic melts via assimilation of ancient continental materials coupled with mineral fractionation. The zircon ages for the Kestanbol pluton and the Ayvacık volcanic rocks are 22.24 and 21.58 Ma, respectively, whereas zircon U-Pb age data suggest that the Balabanlı volcanic rocks (19.33 ± 0.30 Ma) is ~3 million years younger than the Kestanbol pluton and the Ayvacık volcanic rocks. Hf isotopes in zircon (εHf(t) ranging from −5.7 to −0.7), combined with U-Pb ages, support the hypothesis that the mantle source of the Kestanbol magmatism was severely modified by crust-derived metasomatic fluids during the previous subduction.

Preliminary results of the radiolarian-chert hosted manganese deposit within the Vezirler ophiolitic mélange (Kula-Manisa, western Turkey): constraints on the origin, paleo-redox conditions, and depositional environments

In Turkey, Late Cretaceous ophiolitic complexes and melange assemblages of the Izmir-Ankara-Erzincan Suture Zone, part of the northern branch of the Neotethys Ocean are rich in Mn-oxide deposits. These deposits are related to the red-violet radiolarian-chert blocks within the melange units. Of these, the Vezirler Melange, consisting of pelagic limestone, pillow basalt, radiolarite blocks, and highly altered serpentinite are distributed in the northern part of the Kula (Manisa) region, western Turkey. Here, the Mn-oxide deposit occurs as interlayers and, to a lesser degree in sharp contact with the radiolarian-chert-basalt-mudstone associations, and are highly folded and fractured. Based on XRD and petrographic studies, mineral paragenesis of the Mn-ores consists predominantly of braunite, pyrolusite, pysilomelane, quartz, and calcite. Geochemically, Mn-ores have high Ba (mean 10,854 ppm) and Sr (mean 4491 ppm) and low contents of Co ( 7) and low Co/Ni (< 1), Co/Zn (< 2), Y/Ho (< 41) ratios and low ΣREE (< 100) indicate that Kula Mn-ores formed in a submarine hydrothermal system. Redox-sensitive element ratios [V/(V + Ni) = 0.13–0.46, Ni/Co = 1.74–4.59)] and positive Mn*sn (0.22–0.92) indicate that the Kula Mn-ores formed in an oxic depositional environment. Furthermore, a low Lan/Ndn (1.19–3.04), Lasn/Ndsn (< 1.36); moderate Lasn/Cesn and Al/(Al + Fe) ratios; weak negative Ce/Ce* anomaly (0.58); low Ceanom values (< − 0.32); and high Sr concentrations (up to 20,178 ppm) indicate that the Kula manganese deposit formed in a high-salinity and oxygenated marine sedimentary environment with as part of a distal hydrothermal system. Radiolarians from different blocks within the Late Cretaceous melange complexes hosting the Mn-oxide deposits along Izmir-Ankara-Erzincan Suture Zone in northern Turkey yielded a wide range of ages, Middle Triassic to Late Cretaceous. Hence, the Mn-oxides could have formed at any time during that interval, when oceanic crust was generated in different tectonic settings of the Izmir-Ankara Ocean. The ophiolite was then emplaced southward onto the Menderes Platform prior to the middle Eocene.

Chronology of subduction and collision along the İzmir-Ankara suture in Western Anatolia: records from the Central Sakarya Basin

ABSTRACTWestern Anatolia is a complex assemblage of terranes, including the Sakarya Terrane and the Tauride-Anatolide Platform that collided during the late Cretaceous and Palaeogene (80–25 Ma) after the closure of the Izmir-Ankara Ocean. Determining the precise timing at which this ocean closed is particularly important to test kinematic reconstructions and geodynamic models of the Mediterranean region, and the chronology of suturing and its mechanisms remain controversial. Here, we document the Cretaceous-Eocene sedimentary history of the Central Sakarya Basin, along the northern margin of the Neotethys Ocean, via various approaches including biostratigraphy, geochronology, and sedimentology. Two high-resolution sections from the Central Sakarya Basin show that pelagic carbonate sedimentation shifted to rapid siliciclastic deposition in the early Campanian (~ 79.6 Ma), interpreted to be a result of the build-up of the accretionary prism at the southern margin of the Sakarya Terrane. Rapid onset of deltaic progradation and an increase in accumulation rates in the late Danian (~ 61 Ma), as well as a local angular unconformity are attributed to the onset of collision between the Sakarya Terrane and the Tauride-Anatolide Platform. Thus, our results indicate that though deformation of the subduction margin in Western Anatolia started as early as the Campanian, the closure of the İzmir-Ankara Ocean was only achieved by the early Palaeocene.

Radiolarian biochronology of upper Anisian to upper Ladinian (Middle Triassic) blocks and tectonic slices of volcano-sedimentary successions in the Mersin Mélange, southern Turkey: New insights for the evolution of Neotethys

The Mersin Ophiolitic Complex located in southern Turkey comprises two main structural units; the Mersin Mélange, and a well-developed ophiolite succession with its metamorphic sole. The Mersin Mélange is a sedimentary complex including blocks and tectonic slices of oceanic litosphere and continental crust in different sizes. Based on different fossil groups (Radiolaria, Conodonta, Foraminifera and Ammonoidea), the age of these blocks ranges from Early Carboniferous to early Late Cretaceous. Detailed fieldwork in the central part of the Mersin Mélange resulted in identification of a number of peculiar blocks of thick basaltic pillow-and massive lava sequences alternating with pelagic-clastic sediments and radiolarian cherts. The oldest ages obtained from the radiolarian assemblages from the pelagic sediments transitional to the volcano-sedimentary succession in some blocks are middle to late Late Anisian. These pelagic sediments are overlain by thick sandstones of latest Anisian to middle Early Ladinian age. In some blocks, sandstones are overlain by clastic and pelagic sediments with lower Upper to middle Upper Ladinian radiolarian fauna. Considering the litho- and biostratigraphical data from Middle Triassic successions in several blocks in the Mersin Mélange, it is concluded that they correspond mainly to the blocks/slices of the Beysehir-Hoyran Nappes, which were originated from the southern margin of the Neotethyan Izmir-Ankara Ocean. As the pre-Upper Anisian basic volcanics are geochemically evaluated as back-arc basalts, this new age finding suggest that a segment of the Izmir-Ankara branch of the Neotethys was already open prior to Middle Triassic and was the site of intraoceanic subduction.

Radiolarian assemblages of Middle and Late Jurassic to early Late Cretaceous (Cenomanian) ages from an olistolith record pelagic deposition within the Bornova Flysch Zone in western Turkey

Abstract The Bornova Flysch Zone (BFZ) in NW Anatolia comprises several olistoliths or tectonic slivers, representing various parts of the Izmir-Ankara ocean. Radiolarian assemblages extracted from one of the olistoliths of the BFZ, cropping out along the Sögütlü section, to the NE Manisa city, were studied in detail. The lowermost part of the section contains latest Bajocian – early Callovian radiolarian taxa, followed by radiolarian assemblages indicating Late Jurassic to early Late Cretaceous (Cenomanian) ages. Previous studies reveal that the Izmir-Ankara oceanic basin was initially opened during late Ladinian – early Carnian. The new radiolarian data obtained from this olistolith reveals that relatively condensed, and possibly more or less continuous, pelagic sedimentation took place during the late Middle Jurassic to early Late Cretaceous in a non-volcanic oceanic basin closer to the Tauride-Anatolide platform margin.

Oceanization of the northern Neotethys: Geochemical evidence from ophiolitic melange basalts within the İzmir–Ankara suture belt, NW Turkey

The remnants of the Neotethyan Izmir–Ankara Ocean, the main branch of Neotethys in the eastern Mediterranean are represented by the Dagküplü Melange Complex in Central Sakarya, NW Turkey. It comprises several blocks or tectonic slices of pillow lavas, some of which include mudstones and radiolarian cherts as intra-pillow-fillings or interlayers. In the Igdecik area, a huge basaltic block has been studied in detail. Geochemical data reveal three distinct basalt types separated by sheared contacts. The first of these groups is an enriched mid-oceanic ridge basalt (E-MORB) type which is enriched in the most incompatible trace elements relative to normal MORB (N-NORB) in addition to having heavy rare earth elements (HREE) depletion, suggesting the influence of residual garnet in their mantle source region. The second is back-arc basin basalt (BABB) type with relatively depleted trace element compositions with respect to N-MORB together with a negative Nb anomaly, suggesting generation above an intra-oceanic subduction zone where partial melts are derived from a depleted (MORB-like) mantle. The final group is island-arc tholeiite (IAT) type, displaying the most depleted trace element abundances among the studied groups in addition to marked Nb depletion, reflecting intra-oceanic supra-subduction zone (SSZ) signatures similar to the BABB-type but requiring a depleted mantle source which has experienced a previous melt extraction. Combined with a previously ascribed Late Triassic age of Tekin et al. (2002) (221 Ma, Late Carnian; based on the radiolarian fauna found in a chert layer alternating with mudstones), the associated basalts with E-MORB-type geochemical signatures, suggest formation of oceanic crust as early as Late Carnian. This age is the oldest thus far obtained from the basalts of the Izmir–Ankara Ocean. This new data provides constraints on tectonic models for the opening the Izmir–Ankara Ocean and its relationship to other branches of the Neotethyan ocean in the Eastern Mediterranean area.

Late Middle Jurassic (Late Bathonian-early Callovian) radiolarian cherts from the Neotethyan Bornova flysch zone, Spil Mountains, Western Turkey

Alternating radiolarian cherts and mudstones associated with basaltic lavas occur in a olistolith within the Late Cretaceous Bornova Flysch in W Anatolia. Cherts yielded diverse and moderately preserved, Nassellaria-dominated radiolarian faunas of late Bathonian-early Callovian age. Associated volcanic rocks are geochemically classified as remnants of oceanic seamounts. This is so far the first late Middle Jurassic age from the crust of the Neotethyan Izmir-Ankara Ocean in W Anatolia, and suggests that its spreading started earlier. Similar ages were reported from the Vardar and Meliata-Hallstadt Tethyan oceanic branches in Greece and Serbia, which also opened in Late Triassic but closed earlier.

Comment on “207Pb–206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the Central Anatolian crust, Turkey” – Boztug, D., Tichomirowa, M. & Bombach, K., 2007, JAES 31, 71–86

A continent-oceanic island arc collision model was proposed as a new geodynamic scenario for the evolution of the Cretaceous Central Anatolian granitoids in the Central Anatolian crystalline complex (CACC) by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb–206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust, Turkey. Journal of Asian Earth Sciences 31, 71–86]. The key aspects of this model include an intra-oceanic subduction in the Neotethyan Izmir-Ankara Ocean, formation of an island arc and its subsequent collision with the northern margin of the Tauride–Anatolide Platform. The identical scenario was initially proposed by Göncüoglu et al. (1992) [Göncüoglu, M.C., Erler, A., Toprak, V., Yalınız, K., Olgun, E., Rojay, B., 1992. Geology of the western Central Anatolian Massif, Part II: Central Areas. TPAO Report No: 3155, 76 p] . Moreover, the weighted mean values of the reported 207Pb–206Pb single-zircon evaporation ages by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb–206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust: Turkey. Journal of Asian Earth Sciences 31, 71–86] from A-type granitoids in the CACC seem to be miscalculated and contrast with the field data.

GEOCHEMISTRY, TECTONO-MAGMATIC DISCRIMINATION AND RADIOLARIAN AGES OF BASIC EXTRUSIVES WITHIN THE IZMIR-ANKARA SUTURE BELT (NW TURKEY): TIME CONSTRAINTS FOR THE NEOTETHYAN EVOLUTION

The Dagkuplu Melange in the Central Sakarya Valley represents the northernmost outcrops of the Izmir-Ankara Suture Belt in northwest Anatolia. In addition to blocks and slivers of serpentinite, gabbro, blueschist, neritic and pelagic limestones, it includes blocks of basic volcanic rocks associated with radiolarian cherts, pelagic carbonates and mudstones. The preliminary geochemical data revealed the existence of a variety of basaltic rocks with magma types ranging in composition of MORB, IAT, OIB and CAB, in the melange. The age of the radiolarian assemblage from a tectonic block of chert-mudstone alternation associated with OIB-type basalts within the melange is assigned to early Berriasian - early Hauterivian, based on the co-occurrence of radiolarian taxa as Angulobracchia sp. cf. A. (?) portmanni, Godia nodocentrum, Pantanellium masirahense, Thanarla brouweri, Pseudoeucyrtis hanni, Svinitzium mizutanii, Mirifusus dianae s.l., Tethysetta boesii. Another block of chert-mudstone alternation associated with MORB-type basalts includes the following Cenomanian radiolarian fauna: Thanarla pulchra, Novixitus mclaughlini, Pseudodictyomitra pseudomacrocephala, Pseudodictyomitra tiara, Stichomitra communis. New findings from the Central Sakarya area combined with previous data of the authors reveal that the Izmir-Ankara Ocean started to open already in the Late Triassic. The formation of OIB-type intra-plate seamounts within the Izmir-Ankara Ocean began in late Bathonian and persisted until early Aptian. The the intra-oceanic subduction and the generation of supra-subduction-type volcanism started in early Santonian and the spreading-ridge of the Izmir-Ankara Ocean plate was not subducted until the Cenomanian.

First evidence of Late Carnian radiolarians from the Izmir–Ankara suture complex, central Sakarya, Turkey: implications for the opening age of the Izmir–Ankara branch of Neo-Tethys

Within the Late Cretaceous mélange complex of the Izmir–Ankara suture zone in central Sakarya area, north-western Turkey, a megablock with radiolarian cherts associated with basaltic pillow lavas has been dated by radiolarians. The studied radiolarian assemblage and conodonts yielded an early Late Carnian age. This age is the oldest obtained from the chert blocks all along the suture belt and has important implications for the rifting/opening age of the Izmir–Ankara branch of the Tethys ocean in north-western Turkey. Based on this new data, it is concluded that during the Late Triassic the Izmir–Ankara seaway was connected to the other Tethyan oceanic branches and deep enough to provide chert sedimentation and exchange radiolarians with the main open oceans. It is further suggested that the long-lasting misinterpretation of a Liassic rifting/opening of the Izmir–Ankara ocean should be revised.