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Application of The Titanium-In-Quartz Thermobarometer to Eclogites from The Biga Peninsula, NW Turkey
(Iop Publishing Ltd, 2016) Sengun, Firat; Zack, Thomas
Eclogites crop out in the Eamlica metamorphics and beneath the Eetmi melange as a tectonic slice in the Biga Peninsula in northwest Turkey. The Eamlica metamorphics occur in the westernmost part of the Biga Peninsula and are tectonically separated from the Denizgoren ophiolite in the west by the Ovacik fault. The Eetmi melange found on the southern part of the Biga Peninsula is mainly composed of various types of blocks within a detritic matrix. The high-P assemblages in eclogite consist of omphacite + garnet + epidote + glaucophane + quartz + phengite. Typical accessory minerals are rutile, zircon and sphene. Ti-in-quartz thermobarometer (TitaniQ) was applied on eclogites from the Biga Peninsula. The P-T dependencies of Ti-in-quartz solubility can be combined with P-T dependencies of Zr-in-rutile solubility to estimate pressure and temperature of crystallization. Titanium concentrations in quartz from the Eamlica metamorphics range from 0.26 to 0.91 ppm. Zirconium concentrations in rutile range from 26 to 64 ppm. However, Ti contents in quartz from the Eetmi melange vary from 0.47 to 2.19 ppm. Zr contents in rutile range between 50 and 150 ppm. Regional high-P metamorphism with peak conditions of 551 +/- 5 degrees C and 21.5 +/- 0.3 kbar in eclogite from the Eamlica region and 624 +/- 17 degrees C and 22.6 +/- 1.6 kbar in eclogite from the Eetmi region. Tiin- quartz thermobarometer gives precise and comprehensible pressure and temperature values when using the Zr-in-rutile thermobarometer, which could be an advantage over classical methods.
Early Cambrian S-type granites in the Sakarya Zone, NE Turkey: A record for transition from subduction to post-collisional extension deduced from U-Pb zircon age and Nd-Hf isotopes
(Elsevier, 2022) Karsli, Orhan; Sengun, Firat; Dokuz, Abdurrahman; Aydin, Faruk; Kandemir, Raif; Kristoffersen, Magnus; Santos, Jose Francisco
Cadomian realms have recently received much attention in the Alpine-Mediterranean orogenic belts, with discontinuous outcrops extending from the Alps to the Istanbul Zone, Menderes Massif, Taurides in Turkey and Iran as well. However, they have not been identified in the Sakarya Zone, northern Turkey to date. Here, we present, for the first time, zircon U-Pb geochronology, zircon Hf-isotopes and trace elements as well as whole-rock geochemistry and Nd-isotopes from the Karamese metagranitoid in the Yusufeli (Artvin) area, NE Turkey. The zircon U-Pb age data demonstrate that the Karamese metagranitoid intruded into the Precambrian basement units in the Early Cambrian (ca. 534-530 Ma). Zircon overgrowths in the Karamese metagranitoid interpreted as a result of metamorphic overprint yielded ages of 328 Ma. This age indicates that the Sakarya Zone experienced the Variscan metamorphic events at 328 Ma. The Early Cambrian metagranitoid shows that some rocks in the basement of the Sakarya Zone date back to Precambrian in age. The Karamese metagranitoid is an S-type granite, with high modal content of muscovite (similar to 10%). The samples show highly peraluminous [A/CNK = molar Al2O3/(CaO + K2O + Na2O) = 1.34-1.58] and medium-K calc-alkaline geochemical affinities. The Karamese metagranitoid displays low REE concentrations and a slight positive Eu anomaly and show slightly light REEs and LILEs enrichments, and HFSEs depletions. The samples have negative epsilon(Nd)(t) of -4.76 to -2.90 and epsilon(Hf) (t) of -4.75 to -1.08 values. These geochemical-isotopic characteristics reveal that the Karamase metagranitoid originated through fluid-absent muscovite dehydration melting of heterogeneous metasedimentary source rocks (mostly greywacke), with a minor input of juvenile mafic melt. We argue that the Early Paleozoic metagranitoids along the eastern Sakarya Zone is an expression of crustal thinning in the Cadomian orogenic belt in northern Gondwana, with the tectonic turnover from convergent margin to crustal extension possibly induced by break-off of Tornquist oceanic lithosphere which is a branch of Iapetus Ocean during Early Cambrian.
Early Variscan magmatism along the southern margin of Laurasia: geochemical and geochronological evidence from the Biga Peninsula, NW Turkey
(Springer, 2017) Sengun, Firat; Koralay, O. Ersin
Massive, fine-grained metavolcanic rocks of the CamlA +/- ca metamorphic unit exposed in the Biga Peninsula, northwestern Anatolia, have provided new Carboniferous ages and arc-related calc-alkaline petrogenesis constraints, suggesting that the Biga Peninsula was possibly involved in the Variscan orogeny. The metavolcanic rocks are mainly composed of metalava and metatuff and have the composition of andesite. Chondrite-normalized REE patterns from these rocks are fractionated (La-N/Yb-N 2.2 to 8.9). Europium anomalies are slightly variable (Eu/Eu* = 0.6 to 0.7) and generally negative (average Eu/Eu* = 0.68). The metavolcanic rocks have a distinct negative Nb anomaly and negative Sr, Hf, Ba, and Zr anomalies. These large negative anomalies indicate crustal involvement in their derivation. Tectonic discrimination diagrams show that all metavolcanic rocks formed within a volcanic arc setting. Zircon ages (LA-ICP-MS) of two samples yield 333.5 +/- 2.7 and 334.0 +/- 4.8 Ma. These ages are interpreted to be the time of protolith crystallization. This volcanic episode in the Biga Peninsula correlates with other Variscan age and style of magmatism and, by association with a collisional event leading to the amalgamation of tectonic units during the Variscan contractional orogenic event. Carboniferous calc-alkaline magmatism in the Sakarya Zone is ascribed to arc-magmatism as a result of northward subduction of Paleo-Tethys under the Laurasian margin. Geochemical and U-Pb zircon data indicate that the Sakarya Zone is strikingly similar to that of the Armorican terranes in central Europe. The Biga Peninsula shows a connection between the Sakarya Zone and the Armorican terranes.
Geology and Tectonic Emplacement of Eclogite and Blueschists, Biga Peninsula, Northwest Turkey
(Tubitak Scientific & Technological Research Council Turkey, 2011) Sengun, Firat; Yiğitbaş, Erdinç; Tunc, Ismail Onur
The Biga Peninsula in northwestern Anatolia is a tectonic mosaic, comprising different tectonic units, representing the Sakarya Continent and oceanic assemblages of different origin and ages. The Camlica metamorphic association, a member of this orogenic mosaic in the westernmost part of the peninsula, is subdivided into three formations, from bottom to top; the Andiktasi formation, the Dedetepe formation, and the Salihler formation. Eclogite-facies metamorphic rocks occur as tectonic slices within schist-marble intercalations of the Dedetepe formation. These slices, about 2 km long and 500 m wide, include two different rock types; (i) quartz-mica schists, and (ii) metabasite lenses with eclogite/blueschist paragenesis. Foliation in the Dedetepe formation of the Camlica metamorphic association generally dips SW and strikes NW-SE around Dedetepe hill and Camlica village. In contrast, eclogite-facies metabasite slices strike NE-SW with NW-dipping foliation. The eclogite-facies metabasite lenses are typically low-temperature eclogites that may represent tectonic slices of an accretionary complex associated with a subduction zone. Blueschists were produced by retrograde metamorphism from eclogite during late stage shearing. The host rocks record only a single-stage greenschist-facies metamorphism and were juxtaposed with the eclogite-facies metamorphic rocks along ductile-semi-brittle (?) strike-slip faults aft er the eclogite-facies metamorphism and during or aft er the low-grade metamorphism of the Camlica metamorphic unit. Age constraints on the metamorphic units and the age of the common cover units suggest that this juxtaposition by strike-slip tectonics occurred between the late Cretaceous and early Eocene.
In situ Rb-Sr dating of K-bearing minerals from the orogenic Akcaabat gold deposit in the Menderes Massif, Western Anatolia, Turkey
(Pergamon-Elsevier Science Ltd, 2019) Sengun, Firat; Erlandsson, Viktor Bertrandsson; Hogmalm, Johan; Zack, Thomas
The Akcaabat gold deposit is mainly composed of massive arsenopyrite veins in strongly foliated augen gneisses of the tine Sub-massif in western Turkey. K-bearing minerals from orogenic gold veins were dated by the in situ Rb-Sr method in order to determine the formation age of the Akcaabat gold deposit. Textural relationships between the vein minerals suggest that arsenopyrite, K-feldspar, quartz, and muscovite formed in one paragenetic stage. Native gold, native bismuth, scorodite, and galena were introduced in a later paragenetic stage. The isochron derived from K-feldspar and muscovite occurring in the veins yielded 31.3 +/- 4.7 Ma. In situ Rb-Sr dating of the same assemblage (K-feldspar and muscovite) in the host rock gave an isochron age of 40.8 +/- 3.8 Ma, 10 Ma older than the vein ages, and corresponding to peak metamorphism of the regional main Menderes metamorphism during the Alpine-Himalayan orogenic event. Biotite from the host rock gave an isochron age of 28.1 +/- 2.2 Ma and probably reflects the cooling age. Homogenization temperatures from fluid inclusions in quartz show that quartz formed at 280-390 degrees C but has a dominant mode in the 350-360 degrees C temperature interval. The age of vein formation was successfully distinguished from the age of the Alpine-Himalayan orogenic event associated with main Menderes metamorphism. This study demonstrates that in situ Rb-Sr isotopic study can be applied to resolve absolute dating of orogenic deposits in metamorphic complexes.
Melting of the juvenile lower crust in a far-field response to roll-back of the southern Neotethyan oceanic lithosphere: the Oligocene adakitic dacites, NE Turkey
(Elsevier, 2020) Karsli, Orhan; Caran, Semsettin; Coban, Hakan; Sengun, Firat; Tekkanat, Osman; Andersen, Tom
Late Cenozoic tectono-thermal events and associated magmatism in the Sakarya Zone (SZ) are still contested. Although documented in the western part of the SZ, thus far, no magmatic activity has been identified in the eastern part of the Oligocene SZ. Here, we report a newly identified Oligocene magmatism to interpret the genesis with tectonic setting and gain new insight into the geological evolution of the eastern SZ. We present extensive geochemical, bulk-rock Sr-Nd and zircon Hf isotope, and zircon U-Pb chronological analyses for the Tepebasi dacites in the Artvin area, NE Turkey. Zircon UPb dating analyses revealed a dacite formation age of similar to 29.8 +/- 0.3 Ma. Geochemically, with a K2O/Na2O ratio of 0.5 to 0.6, they are composed of rocks of a medium-K calc-alkaline adakitic affinity. The samples are further characterized by low Y (6-7 ppm), and high Sr (362-588 ppm) and Sr/Y ratios (58-98), with low Mg# (41-45) values, demonstrating a close affinity with the crustal source of adakitic rocks. They have slightly radiogenic isotope concentrations (Sr-87/Sr-86(t) = 0.70460-0.70544, epsilon(Nd)(t) = +1.7 to +2.0), and single-stage Nd model ages of T-DM1 = 0.61-0.63 Ga, as well as uniform and positive epsilon(Hf) (t) of 8.2-10.5, with young Hf depleted mantle ages (T-DM1 = 0.31-0.41 Ga). These isotopic features, in combination with the geochemical signature, preclude a mantle origin. Instead, they most likely originated from a juvenile mafic lower crustal material by low degree partial melting (<%5) rather than through partial fusion of a subducting slab or thickened lower crust. Trace element modeling reveals that the mafic juvenile lower crust is composed of <10% garnet-bearing amphibolite. Furthermore, trace element compositions imply that adakitic melts formed in an extensional setting without delamination of a thick mafic lower continental crust. We conclude that the Oligocene adakitic magmatism originated in an intracontinental setting, which was subjected to far-field extensional forces induced by roll-back of south Neotethyan oceanic lithosphere just before its detachment in the collision zone. We believe that hot asthenospheric upwelling due to the far-field extension induced by the roll-back of the southern branch of the Neotethyan oceanic lithosphere triggered adakitic magmatism. The heat induced by the upwelling of the asthenosphere likely led to the heat-fluxed melting of juvenile mafic crustal material in such an extensional tectonic setting during the Oligocene epoch in the eastern SZ. (C) 2020 Elsevier B.V. All rights reserved.
Petrography, geochemistry, and provenance of Jurassic sandstones from the Sakarya Zone, NW Turkey
(Tubitak Scientific & Technological Research Council Turkey, 2019) Sengun, Firat; Koralay, Osman Ersin
The Jurassic sandstones exposed in the western part of the Sakarya Zone are yellowish to brown, moderate to well sorted, medium to coarse-grained, grain-supported, and cemented by calcareous and minor silica. Sandstones are mainly classified as litharenite, subarkose, and arkose according to the relative proportions of quartz, feldspar and rock fragments, and major element ratios. On the SiO2 variation diagram, Na2O and K2O show slight positive correlations, which could reflect abundance of sodic plagioclase and K-feldspar with quartz within high Si-content sandstones. Sandstones generally exhibit slight LREE enrichment with respect to HREEs. The REE plots are characteristic for sedimentary rocks derived from the upper continental crust. Combining the results of several provenance discrimination diagrams, elemental ratios (Th/Sc, Zr/Sc, La/Th), and REE contents in sandstones, they reveal that the sandstones originated from intermediate to felsic source rocks. Accordingly, the probable source of the Jurassic sandstones is the crystalline basement of the Sakarya Zone consisting of Devonian, Carboniferous, and Permian granitoids, and high-grade metamorphic basement rocks. The Jurassic sandstones mostly have characteristic features of passive continental margin basins. It can be noted that the sandstones may have been deposited in a marginal basin that began to open in Early Jurassic time. CIA and CIW values for the Jurassic sandstones suggest that the source area was subject to low to moderate chemical weathering under semihumid to semiarid climatic conditions.
Provenance of detrital rutiles from the Jurassic sandstones in the Central Sakarya Zone, NW Turkey: U-Pb ages and trace element geochemistry
(Elsevier Gmbh, 2020) Sengun, Firat; Zack, Thomas; Dunkl, Istvan
This provenance study focuses on detrital rutile grains from Jurassic sandstones of the Bayirkoy Formation in the central Sakarya Zone. Cr and Nb concentrations of detrital rutile grains in the Jurassic sandstones vary from 18 to 6855 mu g/g and 70-13440 mu g/g, respectively. Source area discrimination based on the Cr-Nb concentrations shows that 79 % of the detrital rutile grains originated from metapelitic and 21 % from metamafic rocks. The calculated rutile formation temperatures vary from 471 to 798 degrees C with an average temperature of 635 degrees C at P=10 kbar. Zr-in-rutile thermometer gives overlapping temperatures for all detrital rutile grains from both the metapelitic and metamafic sources. This demonstrates that most of the detrital rutiles sourced from metapelitic and metamafic rocks underwent similar metamorphic conditions and have similar metamorphic history. The U-Pb rutile dating yielded ages for the detrital rutiles in the time range of 346 to 319 Ma, which gives the age of metamorphism for the potential source rocks. Trace element compositions, Zr-in-rutile thermometer and U-Pb rutile geochronology show that detrital rutile grains were predominantly derived from early Carboniferous rocks that underwent metamorphism in amphibolite-facies conditions. Amphibolite-facies rocks of the Saricakaya Massif in the central Sakarya Zone seem to be the primary source lithologies for the detrital rutiles in the Jurassic Bayirkoy Formation as it comprises previously-mentioned source lithologies and has a close geographic position to the area studied. Carboniferous Variscan metamorphism was followed by emplacement of numerous post-collisional granitoids in the central Sakarya Zone.
Rutile geochemistry and thermometry of eclogites and associated garnet-mica schists in the Biga Peninsula, NW Turkey
(Elsevier Gmbh, 2017) Sengun, Firat; Zack, Thomas; Topuz, Gultekin
In northwest Turkey, high-pressure metamorphic rocks occur as exotic blocks within the cetmi m lange located on the south of the Biga Peninsula. Rutile chemistry and rutile thermometry obtained from the eclogite and associated garnet-mica schist in the cetmi m lange indicate significant trace element behaviour of subducted oceanic crust and source-rock lithology of detrital rutiles. Cr and Nb contents in detrital rutile from garnet-mica schist vary from 355 to 1026 pzig and 323 and 3319 g/g, respectively. According to the Cr-Nb discrimination diagram, the results show that 85% of the detrital rutiles derived from metapelitic and 15% from metamafic rocks. Temperatures calculated for detrital rutiles and rutiles in eclogite range from 540 degrees C to 624 degrees C with an average of 586 degrees C and 611 degrees C to 659 degrees C with an average of 630 degrees C at P = 2.3 GPa, respectively. The calculated formation temperatures suggest that detrital rutiles are derived from amphibolite- and eclogite-facies metamorphic rocks. Amphibolite-facies rocks of the Kazdag Massif could be the primary source rocks for the rutiles in the garnet-mica schist from the cetmi m lange. Nb/Ta ratios of metapelitic and metamafic rutiles fall between 7-24 and 11-25, respectively. Nb/Ta characteristics in detrital rutiles may reflect a change in source-rock lithology. However, Nb/Ta ratios of rutiles in eclogite vary from 9 to 22. The rutile grains from eclogites are dominated by subchondritic Nb/Ta ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration. (C) 2017 Elsevier GmbH. All rights reserved.
Silurian to Early Devonian arc magmatism in the western Sakarya Zone (NW Turkey), with inference to the closure of the Rheic Ocean
(Elsevier, 2020) Karsli, Orhan; Sengun, Firat; Dokuz, Abdurrahman; Kandemir, Raif; Aydin, Faruk; Andersen, Tom
The Rheic Ocean is the most significant Paleozoic ocean that detached peri-Gondwana terranes from the northern Gondwana margin throughout the closure of the Iapetus Ocean. The suture of the Rheic Ocean spreads from Mexico to the Middle East, and the timing of its final closure is well-documented by the rocks formed in the Variscan-Alleghanian-Ouachita orogeny which led to the formation of the supercontinent Pangaea. However, as robust paleomagnetic and quantitative data are mostly lacking, the onset and evolution of the subduction of the Rheic Ocean are highly speculative, and they require further confirmation. Recently, the well-preserved metagranitoids along the western Sakarya Zone (SZ) in Anatolia have been identified, and they provide new data that improve our knowledge on the evolution of the Early Paleozoic Rheic Ocean along the northern Gondwana. Here, we present new geochronological, in situ zircon Hf isotope, and whole-rock geochemical analyses of these metagranitoids from the western SZ to enhance our understanding of the subduction processes of the Rheic Ocean. IA-ICP-MS zircon U-Pb dating demonstrated that the Boziiyuk and Borcak metagranitoids from the western SZ were emplaced during the Silurian to Early Devonian (431 +/- 2.7 to 403 +/- 3.5 Ma). The both granitoids have medium- to high-K. calc-alkaline magmatic character, and exhibit peraluminous to slightly metaluminous geochemical signature. They show a typical arc pattern in terms of trace elements and have a uniform, moderate negative epsilon(Hf) (t) of -3.2 to -9.7, with Mesoproterozoic Hf depleted mantle model ages (T-DM1 = 12 to 1.4 Ga). The geochemical and isotopic characteristics are not consistent with those of depleted mantle melts and melts derived from the crustal rocks in an intracontinental environment. Instead, the parental magma is likely generated from the partial melting of a homogeneous and enriched mantle wedge source. We propose that the Silurian to Early Devonian arc-related magmatism is associated with a northward subduction episode of the Rheic Oceanic lithosphere beneath the peri-Gondwana terranes. Hence, we consider that the opening of Paleotethys Ocean formed in a back-arc basin of subduction in Andean style to the north rather than a continental rift to the south in response to south-directed and short-lived supra-subduction zone (SSZ)-type subduction during the Silurian to Early Devonian. (C) 2020 Elsevier B.V. All rights reserved.
The geochemistry, origin and tectonic setting of the Tozlu metaophiolite in the Kazdağ Massif (Biga Peninsula, NW Anatolia)
(Slovak Acad Sciences Geological Inst, 2023) Sengun, Firat; Hasozbek, Altug; Dogan-Kulahci, Gullu Deniz
The Tozlu metaophiolite is composed predominantly of metagabbro, banded amphibolite, metadunite, and serpentinite, which are exposed in the Kazdag Massif located in the northwestern part of Turkey. The geochemistry (major, trace, and rare earth elements) and petrography of the Tozlu metaophiolite in the Kazdag Massif provided significant knowledge about protolith, petrogenesis, source characteristics and tectonic setting in northwest Turkey. Trace element geochemistry, Ti/Y (29.95-296.92 ppm) and Nb/Y (0.01-0.17 ppm) ratios suggest that metaophiolitic rocks were derived from a tholeiitic magma and igneous protolith of basaltic composition. The immobile trace element tectono-magmatic discrimination diagrams define a mid-ocean ridge basalt (MORB) to volcanic arc (IAT) affinity for the Tozlu metaophiolite. The metaophiolitic rocks demonstrate flat rare earth element (REE) patterns and enrichment of large ion lithophile elements (LILEs; i.e., Rb, Ba, Th), as well as depletion of high field strength elements (HFSEs; i.e., Nb, Th, Ti, Hf). N-MORB characteristics of the Tozlu metaophiolite on a multi-element diagram suggest that the protolith of metaophiolitic rocks generated in a subduction-related setting. The tholeiitic metaophiolitic rocks resulted from the metamorphism of an island arc-type basaltic protolith and display subduction zone components according to the Th/Yb and Ta/Yb ratios. The Tozlu metaophiolite with MORB/IAT affinity witness for supra-subduction zone originated in island arc/back-arc settings.
TitaniQ Thermometer and Trace Element Composition of Rutile in Meta-Ophiolitic Rocks From the Kazdag Massif, Biga Peninsula
(Tmmob Jeoloji Muhendisleri Odasi, 2016) Sengun, Firat
Ophiolitic meta-gabbros are exposed on the Kazdag Massif located in the southern part of the Biga Peninsula. Trace element composition of rutile and quartz was determined for metagabbros from the Kazdag Massif by LA-ICP-MS. The Zr content of both matrix rutiles and rutile inclusions in garnet range from 176 to 428 ppm (average 335 ppm). Rutile grains usually have a homogeneous Zr distribution. The rutile grains from studied samples in the Kazdag Massif are dominated by subchondritic Nb/Ta (11-23) and Zr/Hf ratios (20-33). Nb/Ta and Zr/Hf show positive correlation, which is probably produced by silicate fractionation. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents. The core of rutile grains are generally characterized by low Nb/Ta ratios of 17-18 whereas the rims exhibit relatively high Nb/Ta ratios of 19-23. Trace element analyses in rutile suggest that these rutile grains were grown from metamorphic fluids. Ti-in-quartz can be used as a thermobarometer when used in combination with Zr-in-rutile thermometer. P-T conditions of ophiolitic meta-gabbros were calculated by Ti content of quartz and Zr content of rutile, which are in equilibrium with each other. Ti contents of quartz are ranging between 28 and 42 ppm (average 36 ppm). A P-T estimate can be obtained from the intersection of the Ti-in-quartz isopleths with the Zr-in-rutile isopleths, which yield similar to 660 degrees C and 10 kbar. The P-T conditions of meta-ophiolitic rocks suggest that they occur as a different separate higher-pressure tectonic slice in the Kazdag Massif. Amphibolite-facies metamorphism resulted from northward subduction of the Izmir-Ankara branch of the Neo-Tethyan Ocean under the Sakarya Zone. Metamorphism was followed by internal imbrication of the Kazdag Massif resulting from southerly directed compression during the collision.
Trace element composition of rutile and Zr-in-rutile thermometry in meta-ophiolitic rocks from the Kazdag Massif, NW Turkey
(Springer Wien, 2016) Sengun, Firat; Zack, Thomas
In northwest Turkey, ophiolitic meta-gabbros are exposed on the Kazdag Massif located in the southern part of the Biga Peninsula. Trace element composition of rutile and Zr-in-rutile temperatures were determined for meta-gabbros from the Kazdag Massif. The Zr content of all rutiles range from 176 to 428 ppm and rutile grains usually have a homogeneous Zr distribution. The rutile grains from studied samples in the Kazdag Massif are dominated by subchondritic Nb/Ta (11-19) and Zr/Hf ratios (20-33). Nb/Ta and Zr/Hf show positive correlation, which is probably produced by silicate fractionation. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents. The core of rutile grains are generally characterized by low Nb/Ta ratios of 17-18 whereas the rims exhibit relatively high Nb/Ta ratios of 19-23. Trace element analyses in rutile suggest that these rutile grains were grown from metamorphic fluids. The P-T conditions of meta-gabbros were estimated by both Fe-Mg exchange and Zr-in-rutile thermometers, as well as by the Grt-Hb-Plg-Q geothermobarometer. The temperature range of 639 to 662 A degrees C calculated at 9 kbar using the Zr-in-rutile thermometer is comparable with temperature estimates of the Fe-Mg exchange thermometer, which records amphibolite-facies metamorphism of intermediate P-T conditions. The P-T conditions of meta-ophiolitic rocks suggest that they occur as a different separate higher-pressure tectonic slice in the Kazdag metamorphic sequence. Amphibolite-facies metamorphism resulted from northward subduction of the A degrees zmir-Ankara branch of the Neo-Tethyan Ocean under the Sakarya Zone. Metamorphism was followed by internal imbrication of the Kazdag metamorphic sequence resulting from southerly directed compression during the collision.
Tracking the timing of Neotethyan oceanic slab break-off: Geochronology and geochemistry of the quartz diorite porphyries, NE Turkey
(Pergamon-Elsevier Science Ltd, 2020) Karsli, Orhan; Dokuz, Abdurrahman; Aydin, Faruk; Uysal, Ibrahim; Sengun, Firat; Kandemir, Raif; Santos, Jose Francisco
The initiation of the break-off of the northern branch of the Neotethyan oceanic lithosphere is an important but poorly understood event in the geology of the Sakarya Zone (SZ) in northeastern Turkey. Although it is wellknown that Latest Cretaceous intrusives (-70 Ma) and early Eocene adakitic magmatic rocks are present in the eastern SZ, the outcrops of the early Eocene non-adakitic rocks are very limited, and their tectono-magmatic evolution has not been studied. We describe a small outcrop of non-adakitic quartz diorite porphyry in the Kov area of the Gumushane region in northeastern Turkey. The genesis of these porphyries is significant in evaluating the syn-to post-collision-related magmatism. The LA-ICP-MS zircon U-Pb dating revealed that the Kov quartz diorite porphyries (KQDP) formed at ca. 50 Ma, coeval with adakitic rocks, and-20 Myr later than the slab rollback-related intrusive rocks. The KQDPs are calc-alkaline in composition and enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), with significant negative anomalies of Nb, Ta, and Ti but positive anomalies of Th, U, and Pb. Isotopic compositions of the samples show limited range of variation and slight enrichment of 87Sr/86Sr(t) (0.70489 to 0.70555), epsilon Nd(t) (-1.4 to -1.2) with TDM of 1.11 to 1.61 Ga. Pb isotopic ratios of the samples point to an enriched mantle source. They were likely crystallized from the melt that originated from an EM2-type spinel-facies subcontinental lithospheric mantle (SCLM), followed by the fractionation with insignificant crustal assimilation. The SCLM was metasomatically enriched, and the metasomatic agent was likely H2O-rich fluids rather than sediments released from subducting oceanic crust during the Late Cretaceous closure of the Neotethyan oceanic lithosphere. In conjunction with the geological background and previous data, we propose that the generation of the KQDPs resulted from a slab break-off event that caused ascending or infiltration of hot asthenosphere, triggering mantle melting. Such sporadic occurrences of the KQDPs, with coeval adakitic rocks in the SZ, are likely associated with the onset of extensional tectonics due to the earlier stage of slab break-off along the region during the early Eocene period.
U-Pb zircon geochronology of northern metamorphic massifs in the Biga Peninsula (NW Anatolia-Turkey): new data and a new approach to understand the tectonostratigraphy of the region
(Taylor & Francis Ltd, 2012) Tunc, Ismail Onur; Yiğitbaş, Erdinç; Sengun, Firat; Wazeck, Jana; Hofmann, Mandy; Linnemann, Ulf
Metamorphic massifs of the Biga Peninsula can be divided into two approximately ENE-WSW-trending belts. It is believed that these two belts represent two different tectonic zones separated by a NE-trending Alpine ophiolitic suture. The Sakarya Zone lies to the S-SE of this Alpine suture, and consists of the Kazdag metamorphic complex which is tectonically overlain by the Permo-Triassic Karakaya Complex. The metamorphic rocks, as an Alpine edifice located N-NW of the suture, have been assigned to the Rhodope and Serbo-Macedonian massifs of Bulgaria and Greece. The northern metamorphic belt is represented by the Karadag Massif in the west, which has been evaluated as a different unit from the others, the Karabiga Massif in the east and the Camlica Massif between them. All three massifs are mapped in detail in light of previous studies and LA-ICP-MS U-Pb zircon dating was applied to stratigraphically compare them. Contrary to previous studies, our data indicate that the basement metamorphic associations in these three areas show similar characteristics concerning their stratigraphical and lithological aspects and also spatial distribution of their outcrops. U-Pb LA-ICP-MS dating of zircons from the three individual metamorphic massifs yielded the following data: maximum sedimentation ages of the protolith of mica schists in the range of 559 +/- 17 to 582 +/- 30 Ma; crystallisation age of the protolith of metavolcanic rocks of 577 +/- 20 Ma; and crystallisation age of the protolith of eclogites at 565 +/- 9 Ma. These ages clearly show that the metamorphic units of the northern massifs are comparable to each other. Also, the U-Pb zircon concordia diagrams from these three metamorphic massifs show remarkably similar patterns. In addition to the similar maximum sedimentation ages for all mica schists with crystallisation ages of the protoliths of the metabasic rocks, there are two major complex tectono-thermal overprints (episodic lead loss events), at c. 330-300 Ma (Variscan?) and c. 100-10 Ma (Alpine and late Alpine?), respectively. Field mapping and analytical data indicate that the basement rocks of the northern massifs in the Biga Peninsula have a correlative Late Ediacaran to Early Cambrian stratigraphic range. In part, Permian strata unconformably overlie basement rocks in the Karadag Massif. Both tectono-thermal events are demonstrated by coeval episodic lead loss of many zircons in all samples from all areas. Finally, the results of this research do not support an Alpine suture between the two metamorphic belts of the Biga Peninsula. Therefore, the geological evolution of the region might require reevaluation.
Zircon U-Pb age and Hf isotopic composition of the Carboniferous Gonen granitoid in the western Sakarya Zone of Turkey
(Tubitak Scientific & Technological Research Council Turkey, 2020) Sengun, Firat; Koralay, Osman Ersin; Kristoffersen, Magnus
The Gonen granitoid is exposed in the western Sakarya Zone and is overlain unconformably by a Jurassic succession. The medium to coarse-grained Gonen granitoid has mineral assemblage of K-feldspar, plagioclase, quartz, muscovite, and biotite. Accessory phases are apatite and zircon. In this study, zircon U-Pb age is combined with Lu-Hf isotopes, which are presented to reveal the magma source and possible petrogenetic processes that took place during the formation of the parental magma for the Gillen granitoid. U-Pb dating of magmatic zircons yielded a concordia age of 336.3 +/- 2.9 Ma referring to the early Carboniferous crystallization age of the GOnen granitoid. Magmatic zircons have negative epsilon(HT)(t) values (-3.2 to -8.3), indicating that the granitoid magma was derived from the recycling of ancient crustal materials. T-DM model ages vary in the range of 1489-1811 Ma, indicating that the crustal material involved during the early Carboniferous partial melting could be extracted from the mantle or added to the basement of the Sakarya Zone in the Mesoproterozoic/Paleoproterozoic times. Geochronological and Lu-Hf findings point to a collisional setting rather than ongoing subduction during the formation of the early Carboniferous Gonen granitoid.
Zr-in-rutile thermometry of eclogites from the Karakaya Complex in NW Turkey: Implications for rutile growth during subduction zone metamorphism
(Elsevier Gmbh, 2017) Sengun, Firat
Eclogites occur as a tectonic slice within a metabasite-phyllite-marble unit of the Karakaya Complex in northwest Turkey. The high-pressure mineral assemblage in eclogite is mainly composed of garnet + omphacite + glaucophane + epidote + quartz. Trace element characteristics of rutile and Zr-in-rutile temperatures were determined for eclogites from the Karakaya Complex. Core-rim analyses of rutile grains yield remarkable trace element zoning with lower contents of Zr, Nb and Ta in the core than in the rim. The variations in Zr, Nb and Ta can be ascribed to growth zoning rather than diffusion effects. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents, which could be ascribed to the effect of metamorphic dehydration in subduction zones on rutile Nb/Ta differentiation. The rutile grains from eclogites in the Karakaya Complex are dominated by subchondritic Nb/Ta and Zr/Hf ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration. The Zr contents of all rutile grains range between 81 and 160 ppm with an average of 123 ppm. The Zr-in-rutile thermometry yields temperatures of 559-604 degrees C with an average temperature of 585 degrees C for eclogites from the Karakaya Complex. This average temperature suggests growth temperature of rutile before peak pressure during the subduction. However, some rutile grains have higher Zr contents in the outermost rims compared to the core. Zr-in-rutile temperatures of the rims are about 20 degrees C higher than those of the cores. This suggests that the outermost rims would have grown from a distinct fluid at higher temperatures than that of the cores. Moreover, Zr contents and calculated temperatures in both inclusion rutile and matrix rutile from eclogites are identical, which suggests that eclogites within the Karakaya Complex belong to the same tectonic slice and underwent similar metamorphic evolution. (C) 2017 Elsevier GmbH. All rights reserved.

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