BAYBURT TÜFLERİNİN PETROGRAFİK, PETROKİMYASAL VE PETROLOJİK ÖZELLİKLERİ: DOĞU PONTİD GÜNEY ZONU’NDA EOSEN KALKALKALEN FELSİK VOLKANİZMASI

In the Bayburt area, the tuffs named as “Bayburt tuffs” outcropping in Eocene basin aremade of two levels as bottom and upper units, interstratified with a claystone-marl interlayer. Lowerlayer contains two whereas upper one unit, and every unit show gradating from coarse towards finegrainedtuffs. Tuffs contain dominantly glass shards, pumice and crystal fragments (plagioclase, quartz,biotite, sanidine). Coarse and fine-grained levels are characterised by their crystal fragment/glass shardratio. Based on modal composition, coarse-grained level can be classified as vitric-crystal tuff and finegrainedlevel as vitric tuff. Geochemically, tuffs are rhyodacite to dacitic in composition and exhibitmedium-K calcalkaline and peraluminous characteristics. They show chemical variation trends,probably reflecting pre-eruption magmatic processes, especially crystal fractionation by volatile effect.Rare earth element patterns are spoon-like in shape, with (La/Lu)N=14-20, and pronounced Eu anomaliesindicating plagioclase fractionation. The investigated tuffs differ from the rest of Eocene volcanics in thesouthern zone by their field characteristics and acidic composition. In the tuffs, presence of very freshand angular glass shards and common crystal fragments, but lack of lithic fragments may indicatephreatomagmatic acidic volcanism in or very near to Eocene basin in the region. Furthermore,geochemical data indicate that these rocks derived from an intermediate magma source (andesiticparent).Bayburt yöresinde Eosen havzasında yüzlek veren tüfler “Bayburt tüfleri” olarak tanımlanmışolup, kiltaşı-marn ara seviyesiyle birbirinden ayrılabilen alt ve üst olmak üzere iki düzeydenoluşmaktadır. Alt birim iki üst birim ise bir seviye içermektedir. Her bir seviye iri taneliden ince tanelitüflere doğru derecelenme göstermektedir. Tüfler, başlıca cam kıymıkları, pomza ve kristal parçaları(plajiyoklas, kuvars, biyotit, sanidin) içermektedir. İri ve ince taneli seviyeler, kristal/cam oranınındeğişmesiyle belirginleşmektedir. Modal bileşimlerine göre, iri taneli seviye vitrik-kristal tüf ve incetaneli seviye ise vitrik tüf olarak tanımlanmaktadır. Jeokimyasal olarak tüfler, riyodasitik-dasitikbileşimli, orta-K’lu kalkalkalen ve peralumin karakterlidirler. Kimyasal değişimleri, püskürme öncesimagmatik olaylardan özellikle gazların etkisiyle gelişen kristal ayrımlaşmasına işaret eder. Nadir toprakelement dağılımları, (La/Lu)N=14-20 oranıyla kaşık şekilli olup, plajiyoklas ayrımlaşmasına işaret edenbelirgin negatif Eu anomalisine sahiptir. İncelenen tüfler, gerek arazi özellikleri ve gerekse asitikbileşimleri bakımından Güney Zon’daki diğer Eosen volkanitlerinden farklıdırlar. Kayaçlarda, çok tazeve köşeli cam kıymıkları ve kristal parçalarının bolluğu buna karşın litik parçaların yokluğu, tüflerinEosen havzasında veya yakınında freatomagmatik bir püskürmeyle oluştuğuna işaret etmektedir.Ayrıca, jeokimyasal veriler kayaçların, ortaç bir magmadan (andezitik ana magma) türediklerinigöstermektedir

Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harsit Pluton, Eastern Turkey

We present elemental and Sr-Nd-Pb isotopic data for the magmatic suite (similar to 79 Ma) of the Harsit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO(2) = 59.43-76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO(2) = 54.95-56.32 wt%), and exhibits low Mg# (<46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb)(n) = 2.40-12.44] and display weak Eu anomalies (Eu/Eu* = 0.30-0.76). The rocks are characterized by enrichment of LILE and depletion of HFSE. The Harsit host rocks have weak concave-upward REE patterns, suggesting that amphibole and garnet played a significant role in their generation during magma segregation. The host rocks and their enclaves are isotopically indistinguishable. Sr-Nd isotopic data for all of the samples display I(Sr) = 0.70676-0.70708, epsilon(Nd)(79 Ma) = -4.4 to -3.3, with T(DM) = 1.09-1.36 Ga. The lead isotopic ratios are ((206)Pb/(204)pb) = 18.79-18.87, ((207)Pb/(204)Pb) = 15.59-15.61 and ((208)Pb/(204)Pb) = 38.71-38.83. These geochemical data rule out pure crustal-derived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir-Ankara-Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr-Nd isotope modeling shows that the generation of these magmas involved similar to 65-75% of the lower crustal-derived melt and similar to 25-35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar-Ar plateau age on hornblende, combined with regional studies, imply that the Harsit pluton formed in a subduction setting and that the back-arc extensional period started by least similar to 79 Ma in the Eastern Pontides.Geochemistry & GeophysicsMineralogySCI(E)33ARTICLE4467-48716

Postcollisional transition from subduction- to intraplate-type magmatism in the eastern Sakarya zone, Turkey: Indicators of northern Neotethyan slab breakoff

WOS: 000483604100012Postcollisional magmatism in the eastern Sakarya zone was recorded by voluminous basic volcanism and repeated plutonism during the early Cenozoic. the temporal and geochemical evolution of these magmatic rocks is important for understanding the possible geodynamic history of the Sakarya zone. Here, we investigated three representative plutons lying between the towns of Camlihemsin (Rize) and Ispir (Erzurum), Turkey. These are largely composed of medium-K gabbroic diorites (Marselavat Pluton), shoshonitic monzonites (Gullubag Pluton), and high-K granites (Ayder Pluton). We present whole-rock geochemistry, Ar-40/Ar-39 geochronology, and Sr, Nd, and Pb isotope analyses from the plutons to constrain the timing of variations in magmatism and source characteristics, and we provide a new approach to the proposed geodynamic models, which are still heavily debated. the Ar-40/Ar-39 geochronology reveals a cooling sequence from ca. 45 Ma for the Marselavat Pluton through ca. 41 Ma for the Giilliibag Pluton to ca. 40 Ma for the Ayder Pluton. Whole-rock geochemistry and Sr, Nd, Pb isotopes suggest that crustal contamination was not an important factor affecting magma compositions. Although there was no arc-related tectonic setting in the region during the middle Eocene, the Marselavat Pluton shows some subduction affinities, such as moderately negative Nb and Ta anomalies, and slightly positive Pb anomalies. These signatures were possibly inherited from a depleted mantle source that was modified by hydrous fluids released from the oceanic slab during Late Cretaceous subduction. Geochemical traces of the earlier subduction become uncertain in the Gullubag samples. They display ocean-island basalt-like multi-element profiles and Nb/Ta, Ce/Pb, and La/Ba ratios. All these point to a mantle source in which earlier subduction signatures were hybridized by the addition of asthenospheric melts. Melting of calc-alkaline crustal material, probably emplaced during the first phase of middle Eocene magmatism (Marselavat), led to the formation of granitic plutonism (Ayder Pluton). Our data in conjunction with early Eocene adakite-like rocks show that melt generation, as in the given sequence, was most probably triggered by breakoff of the northern Neotethyan oceanic slab, similar to 13 m.y. after the early Maastrichtian collision between the Sakarya zone and Anatolide-Tauride block, and continued until the end of the middle Eocene. A shallow-marine transgression occurred contemporaneously with the middle Eocene magmatism throughout the Sakarya zone. An extension in this magnitude seems unlikely to be the result of orogenic collapse processes only. the main cause of this extension was most probably related to the northward subduction of the southern Neotethys Ocean beneath the Anatolide-Tauride block. the result is a volumetrically larger amount of middle Eocene magmatism than that expected in response to slab breakoff.Karadeniz Technical University (BAP Project)Karadeniz Technical University [2007.118.002.2]; Karadeniz Technical UniversityKaradeniz Technical University [FBA-2015-5314]A. Dokuz acknowledges financial support through a grant from Karadeniz Technical University (BAP Project no. 2007.118.002.2) awarded to A. Dokuz, and also benefited from another grant (BAP Project no. FBA-2015-5314) from Karadeniz Technical University awarded to F. Aydin. Frank C. Ramos (New Mexico State University) conducted Sr, Nd, and Pb isotope analyses, and Robert Duncan (Oregon State University) assisted with 40Ar/39Ar ages. We are very grateful to Aral Okay and Yann Rolland for their extremely careful and constructive reviews, which improved the quality of the paper significantly. We thank Associate Editor Erdin Bozkurt and Editor-in-Chief Brad S. Singer for their insightful editorial comments and suggestions. Caner Akyel is also thanked for his assistance during the fieldwork

Zircon Lu-Hf isotope systematics and U-Pb geochronology, whole-rock Sr-Nd isotopes and geochemistry of the early Jurassic Gokcedere pluton, Sakarya Zone-NE Turkey: a magmatic response to roll-back of the Paleo-Tethyan oceanic lithosphere

KANDEMIR, RAIF/0000-0002-0344-9159WOS: 000403544100007The early Mesozoic was a critical era for the geodynamic evolution of the Sakarya Zone as transition from accretion to collision events in the region. However, its complex evolutionary history is still debated. To address this issue, we present new in situ zircon U-Pb ages and Lu-Hf isotope data, whole-rock Sr-Nd isotopes, and mineral chemistry and geochemistry data of plutonic rocks to better understand the magmatic processes. the Gokcedere pluton is mainly composed of gabbro and gabbroic diorite. LA-ICP-MS zircon U-Pb dating reveals that the pluton was emplaced in the early Jurassic (177 Ma). These gabbros and gabbroic diorites are characterized by relatively low SiO2 content of 47.09 to 57.15 wt% and high Mg# values varying from 46 to 75. the samples belong to the calc-alkaline series and exhibit a metaluminous I-type character. Moreover, they are slightly enriched in large ion lithophile elements (Rb, Ba, Th and K) and light rare earth elements and depleted in high field strength elements (Nb and Ti). Gabbroic rocks of the pluton have a depleted Sr-Nd isotopic composition, including low initial Sr-87/Sr-86 ranging from 0.705124 to 0.705599, relatively high epsilon(Nd) (t) values varying from 0.1 to 3.5 and single-stage Nd model ages (T-DM1 = 0.65-0.95 Ga). in situ zircon analyses show that the rocks have variable and positive epsilon(Hf) (t) values (4.6 to 13.5) and single-stage Hf model ages (T-DM1 = 0.30 to 0.65 Ga). Both the geochemical signature and Sr-Nd-Hf isotopic composition of the gabbroic rocks reveal that the magma of the studied rocks was formed by the partial melting of a depleted mantle wedge metasomatized by slab-derived fluids. the influence of slab fluids is mirrored by their trace-element characteristics. Trace-element modeling suggests that the primary magma was generated by a low and variable degree of partial melting (similar to 5-15%) of a depleted and young lithospheric mantle wedge consisting of phlogopite-and spinel-bearing lherzolite. Heat to melt the mantle material was supplied by the ascendance of a hot asthenosphere triggered by the roll-back of the Paleo-Tethyan oceanic lithosphere. the rising melts were accompanied by fractional crystallization and encountered no or minor crustal contamination en route to the surface. Taking into account these geochemical data and integrating them with regional geological evidence, we propose a slab roll-back model; this model suggests that the Gokcedere gabbroic pluton originated in a back-arc extensional environment associated with the southward subduction of the Paleo-Tethyan oceanic lithosphere during the early Jurassic period. Such an extensional event led to the opening of the northern branch of the Neotethys as a back-arc basin. Consequently, we conclude that the gabbroic pluton was related to intensive extensional tectonic events, which peaked during the early Jurassic in response to the roll-back of Paleo-Tethyan oceanic slab in the final stage of oceanic closure.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112Y103]This research was financially supported by Grant # 112Y103 from the Scientific and Technological Research Council of Turkey (TUBITAK). Faruk Aydin, Ibrahim Uysal, Yilmaz Demir and Mehdi Ilhan are thanked for their assistance in field and lab works. We would like to thank to E. Yalcin Ersoy for the geo-chemical modeling of the trace-element data. We gratefully acknowledge on English editing efforts of the manuscript by Jacqueline O'Neill Ozcelik. Special thanks to three anonymous reviewers whose comments improved this paper significantly. Further thanks are owed to Gordon Moore for his editorial effort and constructive comments

Subduction-related late carboniferous to early permian magmatism in the eastern pontides, the Camlik and Casurluk plutons: insights from geochemistry, whole-rock Sr-Nd and in situ zircon Lu-Hf isotopes, and U-Pb geochronology

KANDEMIR, RAIF/0000-0002-0344-9159WOS: 000390724200007Late Carboniferous to early Permian granitoid rocks represent a volumetrically minor component of the Eastern Pontide lithosphere, but they preserve useful information about the region's tectonomagmatic history. the Casurluk and Camlik plutons primarily consist of gabbro, gabbroic diorite, diorite, monzogabbro, monzodiorite and monzonite, which intrude early to middle Carboniferous granitic basement rocks in the region. in this study, we use in situ zircon U-Pb ages and Lu-Hf isotopic values, whole-rock Sr-Nd isotopic values, and mineral chemistry and geochemistry of these plutons to determine petrogenesis and crustal evolution; we also discuss geodynamic implications. LA-ICP-MS zircon U-Pb dating of magmatic zircons from the rocks suggests that the plutons were emplaced during the late Carboniferous to early Permian (302 Ma). the metaluminous and I-type intrusive rocks belong to the high-K calc-alkaline series. in addition, they are relatively enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs); they are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs), such as Nb and Ti. All of the samples have homogeneous initial I-Sr values (0.70675 to 0.70792) and low epsilon(Nd) (t) values (-5.1 to -3.3). Zircons from the rocks of both plutons have uniform negative to slightly positive epsilon(Hf) (t) values (-3.5 to 1.4) and old Hf two-stage model ages (1323 to 1548 Ma), implying that they have the same source, as well as suggesting the involvement of old enriched litho spheric mantle materials during their magma genesis. These results, combined with the epsilon(Hf) (t) values and two stage model ages, demonstrate that the primary magmas were derived from partial melting of old lithospheric mantle material metasomatized by subduction-related fluids. Considering other regional geological data from the Sakarya Zone where these plutons formed, we conclude that late Carboniferous to early Permian magmatism in the area involved the partial melting of a phlogopite- and spinel-bearing lherzolite under an extensional regime in a subduction-related setting. Such an extension event would have caused hot asthenospheric upwelling and was likely triggered by back-arc rifting during subduction of the Paleo-Tethyan oceanic slab. Thus, the magmas are likely subduction-related products, implying that southward subduction of Paleo-Tethys oceanic lithosphere in the region began during the late Carboniferous to early Permian. (C) 2016 Elsevier B.V. All rights reserved.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112Y103]We thank to Faruk Aydin, Ibrahim Uysal and Yilmaz Demir for their assistances in field and lab works. This study was financially supported by a grant # 112Y103 from the Scientific and Technological Research Council of Turkey (TUBITAK). Special thanks go to E. Yalcin Ersoy for the geochemical modeling. We are very grateful to Jacqueline O'Neill Ozcelik for her English editing of the manuscript

Silurian to Early Devonian arc magmatism in the western Sakarya Zone (NW Turkey), with inference to the closure of the Rheic Ocean

WOS: 000558896300026The 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.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [119Y079]We appreciate the Scientific and Technological Research Council of Turkey (TUBITAK) that financially supported this study by a project with grant #119Y079. We thank Mehdi Ilhan and Emrah Yildiz for their efforts during the zircon separations and field works. We also thank Prof. Dr. Michael Roden for his editorial handling, and two anonymous reviewers for their constructive comments

Geochemistry, Re-Os isotopes and highly siderophile element abundances in the Eastern Pontide peridotites (NE Turkey): Multiple episodes of melt extraction-depletion, melt-rock interaction and fertilization of the Rheic Ocean mantle

Dilek, Yildirim/0000-0003-2387-9575; Uysal, Ibrahim/0000-0001-7607-2893; Meisel, Thomas Cameron/0000-0001-5572-3212; KANDEMIR, RAIF/0000-0002-0344-9159WOS: 000348620100010We report on the structure, geochemistry, Re-Os isotopes and relative abundances of highly siderophile elements (HSEs) of the Paleozoic peridotite-basalt occurrences in the Eastern Pontide belt of northeastern Turkey. These peridotites and the associated basaltic rocks are the remnants of the Rheic oceanic lithosphere, incorporated into the Eurasian continental margin during the Variscan (Hercynian) orogeny. the peridotites display a complex record of multiple magmatic, metasomatic and metamorphic events in different tectonic settings during the evolution of the Rheic upper mantle. the Beycam harzburgite (BH) contains low Al2O3 (0.51-1.88 anhydrous wt.%) and high MgO (4135-4234 wt.%) contents, and its bulk-rock trace element compositions are less than 10% of the primitive upper mantle (PUM) values. the platinum, Pd and Re contents of the Beycam harzburgite are highly depleted, whereas its Os, It, and Ru contents are slightly enriched relative to the PUM values. Its Pd and Re contents that are higher than those of the fertile Pulur Iherzolite (PL) to the south and the absence of an isochronous relationship between its Os-187/Os-188 and Re-187/Os-188 show that the trace element distribution and the isotope ratios of the Beycam harzburgite were significantly modified after the first melt-extraction episode. the first melt extraction occurred beneath the Rheic mid-ocean ridge spreading center, whereas the second melt extraction occurred in a mantle wedge above a Rheic subduction zone. the primary magmatic phases of the Pulur lherzolite show the geochemical characteristics typical for fertile lherzolite, formed in the early stages of oceanic lithosphere generation subsequent to the continental break up. the Pulur Iherzolite also contains a secondary magmatic phase in the form of networks of dinopyroxene veins and channels, which are interpreted as an evidence for solid state melt-rock reactions between the Iherzolite and a percolating basaltic melt above a subduction zone. This dinopyroxene addition resulted in the formation of variable concentrations of Al2O3 (2.47-433 wt.%) and MgO (29.76-40.10 wt.%) in the lherzolite. the rhenium, Pd and Pt concentrations of the Pulur lherzolite are depleted relative to the PUM values, whereas the Os, Ir and Ru concentrations are in the range of the PUM values as commonly observed in peridotites with a melt depletion history. the high suprachondritic Os-187/Os-188 is however, inconsistent with a simple melt depletion history, and can be explained by the addition of radiogenic Os-bearing sulfide phases into the lherzolite as a result of melt-rock reactions. Basaltic rocks with an island arc tholeiitic composition from the Beycam area represent the partial melting product of the moderately depleted Beycam harzburgite and the basaltic parental melt from which the dinopyroxene precipitated. the covariation between the Re-187/Os-188 and Os-187/Os-188 of these basaltic rocks defines an isochron age of 377 +/- 8 Ma (late Devonian). the combined structural, geochemical and isotope data indicate a prolonged history of multiple episodes of melt extraction-depletion, and melt-rock interaction and fertilization of the mantle lithosphere of the Rheic Ocean. (C) 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.Mineral Research and Exploration Institute of Turkey (MTA)Ministry of Energy & Natural Resources - Turkey; Miami University; TUBITAK, TurkeyTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK)Our work in the Eastern Pontides has been supported by research grants from TUBITAK, Turkey. Y Dilek acknowledges the support by the Mineral Research and Exploration Institute of Turkey (MTA) and Miami University (through his Distinguished Professor discretionary funds) for his fieldwork in NE Turkey. Constructive and thorough reviews by J. Brendan Murphy, Mei-Fu Zhou and Jingsui Yang helped us improve the science and organization of the paper, and are gratefully acknowledged. We thank the Gondwana Research Editor-in-Chief, Professor Santosh, and the Special Issue Guest Editors for their editorial handling of the manuscript

Tracking the timing of Neotethyan oceanic slab break-off: Geochronology and geochemistry of the quartz diorite porphyries, NE Turkey

Santos, Jose Francisco/0000-0003-4997-8264; UYSAL, IBRAHIM/0000-0001-7607-2893WOS: 000564255300002The 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.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [108Y200]; Portuguese Foundation for Science and TechnologyPortuguese Foundation for Science and Technology [UID/GEO/04035/2013]The authors acknowledge the fund from the Scientific and Technological Research Council of Turkey (TUBITAK) with grant #108Y200. Dr. Bin Chen is thanked for carrying out of the lead isotope analyses. We appreciate the fund by the Portuguese Foundation for Science and Technology for the Sr-Nd isotopic analyses which were implemented at the University of Aveiro, with a project Geobiotec (UID/GEO/04035/2013). This work benefited from the constructive comments by Dr. Milan Kohut and two anonymous reviewers as well as the advices from Editor-in-Chief Prof. Dr. Mei-Fu Zhou

Late Jurassic Magmatism and Stratigraphy in the Eastern Sakarya Zone, Turkey: Evidence for the Slab Breakoff of Paleotethyan Oceanic Lithosphere

KANDEMIR, RAIF/0000-0002-0344-9159WOS: 000392384000001Middle-Late Jurassic Cimmerian events in Turkey have been actively discussed in the past three decades, but proposed tectonic models associated with magmatism, metamorphism, and stratigraphic features remain controversial. To address this issue, Upper Jurassic mafic lavas are investigated at three locations (Alucra, Gumushane, and Olur) in the eastern Sakarya Zone, northeastern Turkey. These lavas are submarine and form planar flows parallel with the bedding plane in the Upper Jurassic carbonate sequence near the base or just below in the clastic sedimentary rocks. the basaltic lavas show calc-alkaline features and possess Nb-Ta values and Nb/U, Nb/La, and Ce/Pb ratios that are greater than those of island arc basalts. Multielement patterns are almost hump shaped, similar to ocean island basalts, which experience Pb depletion and weak negative Nb-Ta, Zr-Hf, and Ti anomalies. the low initial (Sr-87/Sr-86) ratios (0.70372-0.70554), positive initial epsilon(Nd) values (+2.7 to +4.4), and initial Pb isotope ratios that plot between mid-ocean-ridge and ocean island basalts are consistent with a melt derived from subcontinental lithospheric mantle, metasomatized by earlier fluids from subducted sediments and plume materials from the asthenosphere. Moderate Dy/Yb ratios with an average value of 1.8 imply partial melting in the spinel-garnet transition zone at depths of similar to 70-100 km. Slab breakoff is suggested as a geodynamic mechanism that accounts for these geochemical signatures. This inference is also favored by stratigraphic and sedimentologic evidence from the Upper Jurassic-Lower Cretaceous sedimentary rocks, which is consistent with short-lived vertical (epirogenic) movements in the region. Lower-Middle Jurassic sequences are transgressive, suggesting that subduction-related extension opened a backarc basin (Neotethys) in the south of the Sakarya Zone. Upper Jurassic-Lower Cretaceous carbonates point tectonically to tranquility during carbonate deposition in the Neotethys Ocean, which seems to have been achieved by complete closure of the Paleotethys in the north. About 15-20 m.yr. later (Kimmeridgian), after first carbonate deposition, intraplate-typemafic lavas ascended up to the shelf surface of the Neotethys. This was followed by formation of disconformity surfaces and then accumulation of coarse clastic sediments. All this points to a short-lived epirogenic movement that we ascribe to the breakoff of the southward-subducting Paleotethyan oceanic lithosphere in the Late Jurassic.Research Foundation of Karadeniz Technical University [2007.118.002.2, 2009.112-005-2]This research was supported by the Research Foundation of Karadeniz Technical University (2007.118.002.2and2009.112-005-2). E. Reitter is thanked for his help during the Sr-Nd-Pb isotope analyses. We wish to thank the reviewer, D. van Hinsbergen, and Editor D. Rowley, who provided many comments that improved the manuscript. We also wish to remember the sixth author of this essay, Ahmet Sami Derman, who died on May 18, 2012. He enabled us to become aware of the mafic rocks in this study during the fieldwork for his project on the Upper Jurassic-Lower Cretaceous carbonates of the Eastern Pontides