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The timing and mechanism of the crustal extension that caused blocks of continental crust to rift and drift northwards from the northern Gondwana margin during the Early Palaeozoic are currently debated. Here, we present new field, geochemical and U-Pb zircon data from peri-Gondwanan Central Sakarya terrane in NW Turkey to shed light on the timing and petrogenesis of extensional magmatism and subsequent passive margin development of the northern Gondwana margin. Our 1/25.000 scale mapping of a selected area (250 km2) has revealed a south-vergent thrust stack comprising three slices. The Middle Slice of the thrust stack consists of a gneiss-amphibolite complex that has a basement-cover type stratigraphy (before regional metamorphism). The basement unit consists of meta-granitoids, intruded by meta-syenite and banded amphibolites, with geochemical characteristics reflecting I&S-type, A-type and within plate alkaline/transitional-type magmatism, respectively. The cover meta-clastic sediments have amphibolite lenses with MORB and back-arc basin-type geochemistry. Meta-granitoid bodies yielded zircon U-Pb ages of 507 ± 16 Ma, 503 ± 12 Ma, and 488 ± 2.6 Ma (Late Cambrian-Early Ordovician), whereas the meta-syenites gave ages of 473.9 ± 5.7 Ma and 471.4 ± 2.5 Ma (late Early Ordovician); also, age of the banded amphibolite was dated as 473.3 ± 4 Ma. The youngest detrital zircon population in the pebbly quartzite sample within cover meta-sediments (458 ± 3 Ma) constrains the maximum depositional age to around early Late Ordovician. The late Early Ordovician bimodal magmatism, a key focus of our study, is interpreted to have formed in response to the Rheic Ocean rifting along the northern margin of Gondwana. The Late Cambrian granitic magmatism, a precursor to bimodal magmatism, can be explained by lithospheric thinning and upwelling of the asthenosphere to form anatectic silicic melts. The unconformity between the basement and cover units may represent the initiation of a new phase of extension at the N Gondwana margin that culminated in the northward drifting of the Central Sakarya and the opening of Palaeotethys, associated with back-arc basic magmatism in Late Ordovician-Silurian. [ABSTRACT FROM AUTHOR]

The carbonate rocks in the eastern part of NE Turkey are situated within the Pontide paleo-magmatic arc and are frequently in contact with granitoid formations, often hosting skarn mineralization in the region. These carbonate rocks, typically found on ridges and hillsides exhibit predominant orientations along east–west, northeast-southwest, and northwest-southeast directions. A part of limestone, named as biomicrite, metamorphosed and display a saccharoidal texture. Comprised mainly of calcite, with less secondary quartz and iron oxide minerals, these carbonate rocks are classified as Fe-poor calcio-carbonate and magnesio-carbonate, having higher CaO and LOI contents. Marble and recrystallized limestone with granoblastic texture mainly comprise of calcite, less quartz, magnetite, and hematite. Marble classification diagrams suggest calcic skarn mineralization, indicated by decreasing CaO (or CO2) and increasing MgO from limestone to marble (or skarn). Strontium contents deviate slightly from the lithosphere carbonate average, while low Rb contents, attributed to skarn metamorphism, indicate the absence of K-bearing minerals. The high Al2O3/SiO2 in the carbonate rocks can points out hydrothermal activity and carbonate disengagement can indicate to actualize at temperatures that can affect Ce and Al mobilities. The low authigenic U value, low U/Th and Ni/Co ratios in carbonate rocks have been implied that protolith constituents deposited under oxic conditions. Positive Eu anomalies in limestone and marble suggest the influence of hydrothermal fluids. Carbon and oxygen isotope values in marble are similar with those of metamorphic and skarn marbles, indicating a magmatic origin. Overall, mineralogical and geochemical analyses propose a uniform source and/or geological process for all studied marbles. [ABSTRACT FROM AUTHOR]

The Sakarya Zone (northern Turkey) is characterized by the emplacement of voluminous granitoids during the late Carboniferous. In this study, we present geological, U-Pb zircon age, elemental abundance and Sr-Nd-Pb isotopic data on two highly evolved Carboniferous granite bodies within the Early to Late Jurassic volcaniclastic rocks in the Şiran region. The largest body forms a roughly E-W trending ~30 km long and 0.5–2.5 km wide stripe the southern boundary of which is a southvergent thrust, and the other one a subcircular outcrop, ~5 by ~3 km, unconformably overlain by Lower Jurassic volcaniclastic rocks. Their emplacement ages are constrained by LA-ICP-MS U-Pb zircon dating to 310–313 ± 7 Ma (2σ, late Carboniferous). The granitic rocks consist of quartz, microperthitic K-feldspar, plagioclase, and minor biotite, and are characterized by highly evolved compositions with high concentrations of SiO2, Na2O, K2O and Ba, and low concentrations of TiO2, Fe2O3*, MgO, CaO, P2O5 and Sr. Geochemical characteristics indicate a highly fractionated high-K calc-alkaline peraluminous I-type affinity. Chondrite-normalized rare-earth element (REE) patterns are slightly fractionated, with light REEs enriched with respect to middle and heavy ones, and showing variable negative Eu anomalies. On the N-MORB-normalized multi-element variation diagrams, samples display negative anomalies of Ba, Nb, Sr, P, Zr, Eu, and Ti, and positive anomalies of K, and Pb. Initial 87Sr/86Sr and εNd values are 0.70432–0.70610 and −6 to −11, respectively, similar to other Carboniferous high-K calc-alkaline granites and mafic-ultramafic intrusions in the region. The compositional characteristics of the Şiran granites can be explained mainly by fractional crystallization involving hornblende, plagioclase, and biotite and without the involvement of significant amounts of garnet. There is no need to invoke magma mixing and/or melting of a heterogeneous source to account for the geochemical variation. We propose that the late Carboniferous granites formed by remelting of middle- to high-K calc-alkaline mafic rocks at lower crustal depths, followed by extensive fractionation at the upper crustal depths. A thorough review of data from the literature reveals that highly fractionated granites constitute a significant component of the late Carboniferous granites in the Eastern Pontides. [ABSTRACT FROM AUTHOR]

Copyright of Mugla Journal of Science & Technology is the property of Mugla Journal of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The pre-Liassic basement of the Biga Peninsula, located in the westernmost part of the Sakarya Zone, consists of metamorphic assemblages that were considered to represent different continental basements in the north and south, and the suture (ophiolitic/mélange) zone(s) between them. The Çetmi mélange, defined as between these continental fragments (the Kazdağ Massif in the south and the Çamlıca Massif in the north) was evaluated as a subduction accretionary mélange of the Intra-Pontide Ocean and it was assumed that a suture passed through this part of the peninsula. This study was carried out on the most widely distributed outcrops of the Çetmi mélange(?) on the northwest flank of the Kazdağ Massif. These units, which are named the Örenli metamorphics, are represented by a succession of low-grade metamorphic volcanic-volcaniclastic rocks and alternating metasedimentary rocks and recrystallized limestones. The tectonostratigraphically lowermost levels of the Örenli metamorphics are a blocky-chaotic assemblage, whereas the uppermost levels are a regular metavolcanic-metapelite succession, which passes upward into the Late Triassic recrystallized limestones, and is cut by very low-grade metamorphic diabase dykes of 165.81 ± 1.55 Ma age. Furthermore, metavolcanic rocks of this succession show a calc-alkaline association of Basalt-Andesite-Dacite-Rhyolite (BADR) pattern in the chemical classification diagram, which is the signature volcanic rock suite of convergent margins. In addition, all the metavolcanic rock samples show a significant enrichment in terms of incompatible elements and LIL elements and negative Nb and Ti anomalies on the MORB normalized multielement spider diagram, which indicates that these rocks characterize high-K calc-alkaline volcanism at the active continental margins. Field relationships, zircon U-Pb geochronology, and geochemical data support that these units, outcropping in the study area, represent a Triassic active continental margin, most probably a fore-arc setting, related to the Paleo-Tethyan subduction, but not the subduction mélange of the Intra-Pontide Ocean. [ABSTRACT FROM AUTHOR]

The eastern part of the Sakarya Zone, known as the Eastern Pontides, is represented by a south-facing carbonate platform during the Late Jurassic-Early Cretaceous. The shallow marine carbonate sedimentation is masked by hemipelagic sedimentation during the Turonian to Coniacian. The Turonian-Coniacian strata are widely exposed in the Gümüşhane area. In this study, we present new microfacies and geochemical data that can provide new insights into the palaeo-oceanic conditions during the time of their deposition.These strata consist of yellow to gray, thick-bedded, graded calcarenites, calcilutite, pelagic limestone, and monogenic conglomerates. The dominant components are carbonate fragments, including dolomites and limestone, as well as allochthonous bioclasts. Volcanic rock fragments, quartz, cherts, and glauconites are also present, with their abundance varying along the section. The micritic component and planktonic fauna exhibit an increasing abundance in the upward direction, indicating a gradual deepening of the depositional environment. Hence, the analyzed samples can be interpreted as transgressive series deposited on slopes or the deep shelf basin.Furthermore, these strata exhibit distinct V/(V+Ni) and Ni/Co ratios without a notable negative Ce anomaly, suggesting relatively oxygen-reduced conditions. They also show a slight enrichment in alkali elements (Rb and Cs) and post-transition elements (Ga), and LREE, indicating intense weathering. The Ga/Rb and K/Al values further support warm and humid Cretaceous conditions. Thus, the Turonian-Coniacian strata offer valuable information about ancient environments, climate conditions, and the basin evolution of the Tethys Ocean in the Eastern Black Sea region.

Magmatic activity in the Sakarya Zone, an important segment of the Alpine orogenic belt, continues intermittently from the middle Carboniferous to Miocene. In this study, we provide geochronological and geochemical data from the Dağdibi Pluton in the eastern Sakarya Zone to present some inferences on the source region and petrogenesis of the middle Eocene magmatism. U–Pb zircon geochronology from two granodiorite samples gives middle Eocene ages of 44.75 ± 0.92 and 45.01 ± 0.59 Ma. The pluton is mainly composed of K-feldspar, plagioclase, quartz, Mg-hornblende/actinolite, Fe–Ti oxides and small amounts of biotite, and secondary chlorite and epidote. Parental magma of the intrusive rocks has a high-K calc-alkaline affinity with metaluminous character. The oxygen fugacity values vary between −18 and −17. The rocks show slightly radiogenic 87Sr/86Sr(i) (0.704845–0.705726) ratios and ϵNdi values between −0.96 and +0.52. Pb–Pb isotope ratios are typical for those of the lower continental crust. ϵHf(i) values of the zircons range from 0.14 to 10.26. The geochemical and isotopic features of the pluton point to a parental magma derived from a depleted mantle that was metasomatized by fluids during previous subduction events. The volumetric abundances of the rock types are decreased as the silica content increase, implying that the fractional crystallization is the most important process during the formation of the present compositional range of the pluton. Amphibole, plagioclase and Fe–Ti oxides are the fractionated phases while K-feldspar is largely accumulated. In the light of the data presented above, slab breakoff is regarded as the geodynamic process responsible for the formation of the Dağdibi Pluton in the middle Eocene. [ABSTRACT FROM AUTHOR]

The Almacık Block is a tectonic sliver formed during the activity of the North Anatolian Fault Zone (NAFZ). It includes two important tectonic zones of the Western Pontides (NW Anatolia): the İstanbul and the Sakarya Zones meet along a suture zone called the Intra-Pontide Suture Zone (IPSZ). The units within the İstanbul Zone are exposed in the eastern part of the Almacık Block, whereas the rocks of the Sakarya Zone are exposed in the west. In the presented study, some of the magmatic rocks have been analysed using the zircon U-Pb method: these rocks have previously been either incorrectly or not dated. The U-Pb results have shown that some of the granitic rocks in the İstanbul Zone, which intruded into the amphibolites of the Intra-Pontide Suture Zone, have a crystallization age of 559–556 Ma. A granitoid block in the Upper Cretaceous wild flysch formed over the units of the İstanbul Zone had an age of ~566 Ma. Two distinct granitoid bodies in the Sakarya Zone were dated at 404.5 ± 3.9 Ma (Early Devonian) and 161.8 ± 0.82 Ma (Late Jurassic) ages. The palaeo-exhumation evolutions of the zones were obtained using the zircon (U-Th)/He technique (ZrHe) to understand the differences in the geological evolution of the individual zones. ZrHe ages of the samples obtained from the İstanbul Zone indicate a pronounced Early Cretaceous palaeo-exhumation period. The Middle-Upper Jurassic Mudurnu Formation in the Sakarya Zone gave ZrHe ages close to its sedimentation age, which indicates that the major part of the unit was not buried too deep to open the ZrHe closure system. Unlike those the İstanbul Zone, the main ZrHe age peaks of the Sakarya Zone are ~202, 160, 98, 74, and 52 Ma. Finally, a sample of the metamorphic rocks that were assigned to the IPSZ yielded a peak age of ~63 Ma, which indicates that the final closure of the Intra-Pontide Ocean (IPO) took place during the Early Tertiary. [ABSTRACT FROM AUTHOR]

The eastern Sakarya Zone (SZ), one of the Alpine Himalayan Belt's main components, has complex Mesozoic–Cenozoic geodynamic evolution, which remains controversial. Early-Middle Jurassic volcano-sedimentary successions (Şenköy Formation) extensively outcrops in Gümüşhane region, NE Turkey. It is regarded as a critical unit to understand the Mesozoic tectonic evolution of the eastern Sakarya Zone. One of the Şenköy Formation's predominant units is sandstone succession, preserving implications for paleoenvironmental conditions and tectono-sedimentary development of Neotethys Ocean. Thus, a combined analysis of comprehensive petrography, whole-rock major, trace and rare earth element data is carried out on the sandstones, which are well constrained as late Sinemurian- Pliensbachian. The sandstones are mainly arkosic to lithic arenites in lithology showing poor textural maturities. They are mostly represented by relatively high ICV, low CIA, high K2O/Al2O3, Fe2O3+ MgO, TiO2, Th/U, pronounced negative Eu anomaly, enriched LREEs, elevated GdN/YbN, low Ce/Ce*, Ni/Co, La/V and Zr/Ti. The petrographic and geochemical characteristics imply that the sediments may have experienced relatively low chemical weathering processes and slight reworking and recycling processes with a short transport distance before deposition in the basin. Early Jurassic sandstone successions were interpreted as a transgressive series, showing a predominantly open sea environment with oxidizing paleoenvironmental conditions. The sandstone samples' paleoenvironment is likely to be located along the southern margin of the arc and the Neotethyan basin to the south. The extensional and trans-extensional tectonic regime might have played an essential role in controlling the basin's isolated-half graben and/or asymmetric geometry, leading to changes in the provenance of studied sandstone samples. Thus, the geochemical signature differences are probably associated with basement-related proximal origins and minor effects of the multi-phases petrogenesis that experienced different source to sink processes. Early Jurassic sandstones were probably derived from multi-genetic source rocks, including (i) granite and (ii) metamorphic rocks. Our new data has also indicated that other source rocks can include mafic to felsic volcanic succession. The possible provenance for granitic pluton and metamorphic rocks can be provided by the Hercynian heterogenetic crystalline basement widespread throughout the SZ. However, mafic to felsic volcanic rock source is likely to be associated with the pre-Early Jurassic nearby volcanic-arc, which is rarely recorded in the eastern SZ. The source rock signatures may imply a close genetic link with ancient magmatic-arc generation due to the southward subduction of Palaeotethys. [ABSTRACT FROM AUTHOR]

New U–Pb zircon data from the Kurtoğlu Massif (eastern Sakarya Zone, Turkey) reveal a Cadomian back-arc basin, evolving to closure of the Rheic Ocean. A host metapsammite from the lower tectonic slice of the massif yielded detrital zircon ages ranging from Neoarchean (2.73 Ga) to late Neoproterozoic with a major population between 610 and 553 Ma and a peak at 592 Ma, implying that the basement of the Sakarya Zone has a Cadomian affinity. This metasedimentary sequence was intruded by an orthogneiss in the early Ordovician (481 Ma) probably during the opening of the Rheic Ocean. Zircon grains from the overlying metasedimentary sample yielded concordant ages spreading throughout the Mesoproterozoic (1608–1032 Ma) and early Paleozoic (516–351 Ma), suggesting that they were deposited in the Rheic Ocean likely prior to its final closure. The muscovite metagranite, emplaced into the host rocks of the Kurtoğlu Massif at 388 Ma, formed probably during northward closure of the Rheic Ocean. Zircon grains of a metasiltstone from the upper tectonic slice of the massif, represented mainly by phyllites, yielded similar age spectra to that of the host metapsammite of the lower tectonic slice. Such phyllites in the Pulur Massif ⁓ 35 km to the southeast display a close association with the ophiolitic complexes of the Rheic Ocean. This relationship together with the age spectra mentioned above suggests that sedimentation was on a place away from the Paleozoic igneous sources, in an analogous position to the southern passive margin of the Rheic Ocean. [ABSTRACT FROM AUTHOR]

[Display omitted] • A unique Oligocene dyke swarm is defined in the eastern Sakarya Zone, NE Turkey. • Oligocene magmatism sourced by partial melting of metasomatized lithospheric mantle. • Asthenospheric upwelling triggered by delamination of lower crust. • Dyke compositions record fractional crystallization and crustal assimilation. During the Cenozoic, the eastern Sakarya Zone, northeastern Turkey, has witnessed voluminous Eocene and subsidiary Miocene magmatism. By contrast, except in one previous study, Oligocene magmatism has not been reported. Here, we present new data about an Oligocene dyke swarm from the Artvin district in the easternmost part of the Sakarya Zone. Our study improves our understanding of the Oligocene magmatic and geodynamic evolution of the central Tethyan orogenic belt. The Oligocene dykes consist of two distinct rock types: quartz-bearing trachytic and adakitic trachyandesite/andesite, dated at 31.0 ± 0.2 Ma and 31.1 ± 0.2 Ma to 29.2 ± 0.3 Ma by U-Pb zircon geochronology, respectively. Geochemical analysis reveals enrichment in LREE and MREE for quartz-bearing trachytic dykes, whereas adakitic trachyandesite/andesite dykes show depletion in MREE and HREE. Radiogenic isotopic ratios (87Sr/86Sr (i) and 143Nd/144Nd (i)) and trace element data suggest that the source of Oligocene magmatism was linked to low degree (≈10–15 %) partial melting of a metasomatised lithospheric mantle previously enriched by slab-derived melts and fluids. During the magma ascent in the crust, parental magmas of the trachyandesite/andesite dykes have assimilated crustal rocks and undergone fractional crystallization dominated by amphibole. By contrast, quartz-bearing trachytic dykes have recorded plagioclase fractionation. Local extension, in conjunction with continuous foundering of delaminated thickened lower crust beneath the eastern Sakarya Zone, which likely triggered asthenospheric mantle upwelling and resulted in sporadic Oligocene magmatism. Our study highlights the distinct tectonic and magmatic setting of the rare Oligocene magmatism in the eastern Sakarya Zone compared to Oligocene magmatism in the Tauride-Anatolide and South Armenian blocks. [ABSTRACT FROM AUTHOR]

The Hellenic subduction system governs the entire Aegean region through the creation of a migrating magmatic arc that has existed since the beginning of the Early Cenozoic. The Karadağ Pluton is situated in the NW part of Turkey and represents one of the distinct snapshots of this subduction system during the Late Oligocene-Early Miocene Period.iod. It consists of 2 major lithological units, based on their petrographic and geochemical features, comprising: 1) main plutonic facies (SiO2 < 70 wt.%) that are dominated by hornblende- and biotite-bearing monzogranite, quartz monzonite, and granodiorite, and 2) late-stage more felsic facies (SiO2 > 70 wt.%) that are represented by cordierite-free and cordierite-bearing leucogranites. Zircon U-Pb laser ablation inductively-coupled plasma mass spectrometry and K-Ar dating revealed crystallization and cooling ages of 23.9 ± 0.5 Ma and 20.2 ± 0.9 Ma for the main plutonic bodies, and 22.0 ± 1.1 Ma for the leucogranite facies, respectively. The pluton had a high-K calc-alkaline affinity and exhibited a metaluminous to peraluminous (aluminum saturation index of <1.1), and displayed an I-type character. It was enriched with large ion lithophile elements and light rare earth elements, and it was depleted of high field strength elements with negative Eu anomalies. In the tectonic setting discrimination diagrams, all of the granite samples fell into the volcanic arc granite and syn-collisional granite fields. The initial Sr-Nd isotope data of the pluton were compatible with an enriched mantle source. Petrographic and geochemical features indicated that it has been affected by multiple magma evolution processes, such as fractional crystallization, magma mixing, and assimilation. Moreover, the pluton displayed source heterogeneities and peritectic mineral entrainment, such as the coexistence of K-feldspar and cordierite, which could be interpreted as incongruent melting of the crust in the fluid-present system. The petrological and geochemical data suggested that the Karadağ Pluton formed by the mixing of mantle-derived mafic and crustal-derived felsic magmas at shallow crustal levels, mainly derived by the partial melting events related to the northward subduction of the Hellenic slab beneath the Sakarya Zone. [ABSTRACT FROM AUTHOR]

The Gönen granitoid is exposed in the western Sakarya Zone and is overlain unconformably by a Jurassic succession. The medium to coarse-grained Gönen 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 Gönen 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 Gönen granitoid. Magmatic zircons have negative ?Hf(t) values (-3.2 to -8.3), indicating that the granitoid magma was derived from the recycling of ancient crustal materials. TDM 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 Gönen granitoid. [ABSTRACT FROM AUTHOR]

Copyright of Türkiye Jeoloji Bülteni is the property of TMMOB JEOLOJI MUHENDISLERI ODASI and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

The Ekmekçi granodiorite porphyry is a unit in the E-W trending, postcollisional Eocene magmatic rocks of northern Anatolia. It occurs as a relatively small stock, but represents a link between plutonic and volcanic rocks. This Early Eocene granodiorite porphyry intruded into the Upper Triassic rocks of the Karakaya complex in the Sakarya Zone. In this study we present geochemical and zircon U-Pb LA-ICP-MS age data to contribute to understanding the Early Tertiary postcollisional tectonic setting of NW Anatolia. The granodiorite porphyry includes plagioclase, quartz, hornblende, K-feldspar, biotite, and minor zircon, apatite, sphene, and opaque minerals. The stock displays medium-K calc-alkaline I-type and metaluminous affinity. Similar to other Eocene magmatic rocks, it displays characteristic features of subduction-related magmatism, such as enrichment in large-ion lithophile elements relative to highfield strength elements and enrichment of light rare earth elements relative to heavy rare earth elements with a lack of significant Eu anomalies. They are characterized by homogeneous initial Sr and Nd isotopic compositions of 0.7044-0.7049 and 0.51255-0.51260, respectively. Zircon U-Pb data indicate that the Ekmekçi granodiorite porphyry was emplaced at 5.1 ± 1 Ma (2s Ypresian). Geochemically, the Ekmekçi granodiorite porphyry is similar to mafic volcanic rocks rather than the plutonic rocks of the same age. It was emplaced to the north of the İzmir-Ankara-Erzincan Suture (northern plutonic belt of NW Anatolia) and can be correlated with southern plutons such as Orhaneli, Topuk, Tepeldağ, Gürgenyayla, and Sivrihisar in the Anatolide-Tauride block in terms of age. [ABSTRACT FROM AUTHOR]

The timing of major tectonic events and the driving mechanisms for magma generation during Late Cenozoic convergence and collision between Arabia and Eurasia still remain unknown. The Sakarya Zone (SZ) in northern Turkey is a critical member of this collisional assemblage. In the easternmost part of the SZ, we have recognized a Late Miocene volcanic suite termed the Çağirankaya volcanics which displays characteristic post-collisional geochemical features. Here, we report a new data set of zircon U Pb ages, whole-rock major and trace element, as well as Sr Nd isotope analyses for dacite and andesite samples from the Çağirankaya volcanics. Zircon U Pb ages for a selected dacitic lava sample average 5.16 ± 0.11 Ma (mean square of weighted deviates, MSWD = 0.45, n = 35), confirming a late Miocene age of this volcanic episode. The high-K calc-alkaline andesites and dacites exhibit an adakite-like geochemical signature, and are characterized by high Sr (424 to 552 ppm), Sr/Y ratios (31–43), and low Mg# (42 to 46) values, along with low Y (12–14 ppm) and heavy rare earth element (HREE) concentrations, that resemble those in adakites formed by partial melting of hot oceanic slab during subduction. Isotopic compositions are near bulk Earth (87Sr/86Sr(t) = 0.70482 to 0.70489, ε Nd (t) = +1.08 to +1.33), which rules out a solely asthenospheric origin. Elevated Nb/Ta (14 to 17) and K 2 O/Na 2 O (0.6–1.0) imply a juvenile mafic lower crustal source composed of ~20% garnet-bearing amphibolite. Geochemical modeling suggests that adakite-like parental melts were generated in the absence of subduction and without large-scale delamination of lower continental crust. Instead, our findings suggest that Late Miocene adakite-like volcanic rocks in the SZ formed in a post-collisional intra-continental setting, which experienced far-field extension after the subducted slab of the southern Neotethyan branch became detached in the collision zone. Asthenospheric upwelling and underplating of basaltic magma provided the heat for partial melting of lower crustal amphibolite, forming minor amounts of adakite-like melts in the SZ. • The Çağirankaya volcanics erupted in Late Miocene in the Sakarya Zone. • They exhibit adakite-like geochemical signature. • All characteristics suggest that they were derived from a juvenile lower crust. • Upwelling of hot asthenosphere due to far-field forces caused partial melting. • Adakitic melt do not require contemporaneous subduction of a hot oceanic slab. [ABSTRACT FROM AUTHOR]

Abstract The Early Jurassic in the Sakarya Zone, Turkey, was dominated by basic magmatism. The products of this magmatic episode are found as basaltic lavas and pyroclastic rocks in the Şenköy Formation, which was deposited in an extensional basin, or as intrusives cutting Variscan crystalline basement rocks. The Olur (Erzurum) region in the easternmost part of the Sakarya Zone is one of the few locations where contemporaneous acidic rocks crop out, exposed in an area of ~50 km2. The acidic rocks in the eastern Sakarya Zone consist of dacitic lavas, rare pyroclastic rocks, and very rare pebble dikes. Porphyries and trondhjemites are their intrusive equivalents and crop out as dikes and small stocks within the underlying Variscan basement. These Early Jurassic rocks have modal K-feldspar contents of <10% and are trondhjemitic in character. Laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of zircons from two samples yielded formation ages for these rocks of 185.3 ± 1.0 and 184.1 ± 1.1 Ma (±2σ). Geochemically, the rocks are strongly peraluminous and display a medium- to low-K affinity and sodic compositions (K 2 O/Na 2 O = 0.03–0.49). Enrichment in large-ion lithophile elements and depletion in Nb, Ta, P, and Ti are regarded as signatures of a subduction-related setting. Moderately radiogenic I Sr ratios (0.70508–0.70877) and depleted mantle-like Ɛ Nd (t) values (−0.6 to +3.0) and Pb(t) isotopes suggest that the acidic rocks were derived from juvenile lower crust. Geochemical and isotope data imply that the partial melting of juvenile mafic lithologies of the lower crust produced K-poor tonalitic melts that later fractionated to trondhjemitic melts while ascending to the surface. Considering the available data, we suggest that the Early Jurassic bimodal magmatic rocks of the eastern Sakarya Zone were formed in a back-arc setting during the southward subduction of the Paleotethys oceanic lithosphere. These rocks are a prime example of the formation of shallow subduction products following Late Triassic ridge subduction. Highlights • The Early Jurassic dacitic rocks have peraluminous composition and low-K affinity • Partial melting of tholeiitic granulites produced tonalitic melt • Tonalitic magma fractionated to trondhjemitic magma • The trondhjemitic magma extruded to surface at around 185 Ma • A shallow southward subduction is envisaged [ABSTRACT FROM AUTHOR]

Gölbaşı (Ankara) güneybatısında birbiri ile tektonik ilişkili iki farklı istif yer alır. Yapısal olarak altta yer alan düşük dereceli metamorfik istif fillat, metabazit, kristalize kireçtaşı, şist ve kuvars porfir damarları ile temsil edilir. Üstte ise Erken Karbonifer-Geç Permiyen yaşlı neritik ve pelajik karbonatlar ile bunlar üzerinde uyumsuzlukla yer alan Geç Permiyen yaşlı kırıntılı ve karbonatlar vardır. Yapısal olarak üstte yer alan neritik karbonatlardan alınan örneklerde Erken Karbonifer (Vizeyen-Serpuhoviyen) ile Orta Karbonifer (Başkiriyen-Moskoviyen) yaşı saptanmıştır. Sığ fasiyesteki bu karbonatlar Orta Karbonifer-Permiyen yaşta radyolaryalı pelajik çökellerle üzerlenir. En üstteki neritik karbonatlardan elde edilen fosiller ile de Kubergandiyen-Murgabiyen yaşı saptanmıştır. Bu Permo-Karbonifer istifi üzerinde kırıntılı ve karbonatlardan oluşan bir istif uyumsuzlukla yer alır. Tabanda yer alan çakıltaşları ve kumtaşları bol kuvars, karbonat taneli ve daha az oranda metamorfik kayaç parçaları içerir ve üstte doğru orta kalın tabakalı dolomitik kireçtaşı ve kireçtaşlarına geçer. Sığ denizel ortamda çökelen bu karbonatlarda Murgabiyen-Doraşamiyen yaşı saptanmıştır. Geç Paleozoyik yaşlı karbonat temelin Erken- Orta Karbonifer’de neritik, Orta Karbonifer-Permiyen’de pelajik, Kubergandiyen- Murgabiyen’de yine neritik ortamda çökeldiği, bir deformasyon döneminden sonra kuzeydeki Variskan temele eklemlendiği ve Geç Permiyen transgresyonu ile de yeni bir karbonat çökeliminin başladığı ve sonuçta Üst Karakaya Kompleksi içinde yer alan egzotik blokların bir bölümünün bu temelden türediği önerilmiştir.

Abstract Biostratigraphy of Santonian-Danian calcareous nannofossils and planktonic foraminifera was studied in Göynük village and close surroundings located in northwest Turkey. Calcareous nannofossil and planktonic foraminifera assemblages from this time interval were investigated in detail in seven stratigraphic sections measured in the Değirmenözü Member, Yenipazar Formation and Seben Formation. The UC12 zone in the Santonian, UC13 zone, UC14a-bTP and UC15a-b-c-dTP subzones in the Campanian and UC20a-b-c-dTP subzones in the Maastrichtian were defined with nannofossil species assemblages. Planktonic foraminifera assemblages determined included Dicarinella asymetrica Total Range Zone (TRZ) from the Santonian, Globotruncanita elevata Partial-range Zone and Globotruncana ventricosa Partial-range Zone from the Campanian and Racemiguembelina fructicosa Partial-range Zone and Pseudoguembelina hariaensis Partial-range Zone from the Maastrichtian. There was a significant reduction in nannofossil species at the Cretaceous-Paleogene (K-Pg) boundary with dominance of Braarudosphaera bigelowii, Thoracosphaera sp. and Markalius inversus species and increased abundance of biserial planktonic foraminifera species. Just above this boundary in the Danian NP1 and NP2 nannofossil zones and Parvularugoglobigerina eugubina Taxon-range Zone, Parasubbotina pseudobulloides Partial-range Subzone (P1a) , S. triloculinoides Lowest Occurrence Subzone (P1b), and G. compressa/Praemurica uncinata Lowest Occurrence Subzone (P1c) were identified from planktonic foraminifera. Highlights • Detailed nannofossil and planktonic foraminifera biostratigraphy was studied for the Değirmenözü Member, Yenipazar Formation and Seben Formation. • Seven nannofossil zones and nine planktonic foraminifera zones from the Santonian to the Danian. At the K-Pg boundary, Braarudosphaera bigelowii, Thoracosphaera sp. and Markalius inversus nannofossils are dominantly observed with biserial and smalldimension planktonic foraminifera species common. [ABSTRACT FROM AUTHOR]

Alkaline volcanics exposed at similar stratigraphic levels in Upper Cretaceous at Bayburt, Amasya-Gümüşhacıköy and Ankara-Kalecik locations along the southern boundary of the Sakarya Zone provide macroscopically two different lithologies which are containing large pyroxene porphyries and large analcimized leucite porphyries. These rocks formed as a result of the low-grade partial melting of the metasomatized phlogopite-rich mantle rocks, which resulted in the step subduction angle of the aged oceanic crust before the collision. In the course of following their cases, in the middle / shallow depths of the crust, in the magma chambers they underwent differentiation and reached two different lithologies. [ABSTRACT FROM AUTHOR]

The study was performed in central-northern Anatolia (from Ankara to Amasya) to investigate the relationships of the Sakarya Zone units and the Izmir–Ankara–Erzincan suture (IAES) melange. It reveals that all the Sakarya Zone units are metamorphic and three main tectonostratigraphic units have been distinguished for the first time: the BAA (metasiliciclastic rocks capped by metacarbonates and varicoloured phyllite), the BKC (poly-metamorphic garnet-bearing micaschist and metabasite with a well-preserved relict HP–LT amphibole in a low-amphibolitic to greenschist-facies framework) and the AMC (meta-arkose passing vertically to carbonate–phyllitic alternations and, then, to a thick succession of prevailing acidic to intermediate–basic metavolcanites and volcanic-rich metasediments). The BAA and AMC, whose metamorphic frameworks are of Cimmerian age, underlie the Mesozoic carbonate cover sequences (e.g. t2-3, j3–k1) that often show tectonic detachments and slicing. The piling up of the BAA above the HP–LT BKC can be correlated to the tectonic superposition of two similar units (i.e. the Cimmerian Çangaldağ Complex and the Alpine Middle–Upper Cretaceous Domuzdağ Complex, respectively) defined by previous authors in other sectors of the Central Pontides front. The ophiolitic melange generally underlies the Sakarya Zone, but locally (e.g. SE of Amasya) tectonically rests above the latter, probably owing to back-thrusting that occurred during the Tertiary syn-collisional shortenings and the later strike-slip tectonics. We hypothesize that, also in these areas, the Sakarya Zone–IAES consists of a complex tectonic stack of different units, belonging to different palaeogeographic domains and orogenic events (Cimmerian versus Alpine orogenies), but originated within a single long-lived (since Late Triassic to Paleocene/Eocene times), prograding subduction–accretion system in front of the Laurasian continent. [ABSTRACT FROM AUTHOR]

Massive, fine-grained metavolcanic rocks of the Çamlıca 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/Yb ~ 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. [ABSTRACT FROM AUTHOR]

The eastern Blacksea magmatic arc (EBMA) in the eastern Sakarya Zone (ESZ) provides an excellent opportunity to investigate birth of an extensional intra-arc and back-arc settings in the Late Cretaceous over the Early Cretaceous northern passive margin of the Neotethys Ocean. Volcano-stratigraphy clearly shows that the Late Cretaceous volcanic activity of the EBMA occurred in two major phases. Bimodality, characterized by mafic/basaltic rocks at the base and felsic/silicic types on top of it, is a typical feature of the lower (LVS) and upper (UVS) volcanic successions in the Giresun region of the ESZ. U Pb and Ar Ar ages support the volcanic succession as two-stage (LVS: ca. 92–85 and UVS: ca. 83–67 Ma) bimodal volcanism. Both the volcanic successions are represented by similar rock types consisting of tholeiitic to calc-alkaline basalt-basaltic andesites and calc-alkaline to shoshonitic dacite-rhyolites. Basaltic (M1- and M2-series) and felsic/silicic (F1- and F2-series) samples of the LVS and UVS have an arc-like signature with enriched large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs). Also, the felsic/silicic samples of the F1- and F2-series show prominent negative Sr and Eu anomalies (Eu/Eu* = 0.4 to 0.9), suggesting that plagioclase fractionation played a key role on the evolution of both felsic series. Bimodal rock series in two phases have a wide range of 87Sr/86Sr (i) (0.7048–0.7075) and 143Nd/144Nd (i) (0.5123–0.5127) ratios with variable ɛNd (i) values of −3.8 to +3.0. 206Pb/204Pb (i) , 207Pb/204Pb (i) and 208Pb/204Pb (i) isotope ratios of the Giresun volcanic rocks vary in the range of 17.97–18.52, 15.55–15.65 and 37.53–38.56, respectively. Geochemical and isotopic data suggest that the parental magma of the M1-basaltic rocks were probably derived from a shallow (spinel-bearing) mantle metasomatized by slab/sediment-derived fluids. In contrast, the M2-basalts seem to have been originated from a deeper mantle source (spinel-garnet transition zone) enriched by slab/sediment-derived fluids and hydrous melts (bulk sediment) metasomatism with some contributions of lower/upper crustal materials. The least evolved basaltic samples in two phases are consistent with moderate (∼10–15%) to high degree (∼20–30%) partial melting of the metasomatized mantle. The silicic melts of the F1- and F2-rocks series, on the other hand, were likely derived from melting of lower crustal materials consisting of meta-basalts/andesites and lesser amount of meta-sediments. Subsequently, these melts experienced FC ± AFC and mixing processes during their ascent and emplacement to generate high-silica (rhyolitic) melts. Our data, combined with previous studies, suggest that two-stage bimodal volcanic rocks of the Late Cretaceous in the ESZ were formed in the transition from an extensional continental intra-arc to a back-arc setting during the northward subduction of the northern branch of Neotethys Ocean. [Display omitted] • Late Cretaceous two-stage (92–85 and 83–67 Ma) bimodal volcanism in the ESZ. • Bimodality is characterized by basaltic and dacitic-rhyolitic rocks in both stages. • Basaltic rocks were derived from mantle metasomatized by slab/sediment fluids±melts. • Dacite-rhyolites were originated from the melting of a heterogeneous crustal source. • Two-stage bimodal volcanism formed in an extensional arc/back-arc setting. [ABSTRACT FROM AUTHOR]

Abstract: The lowest structural levels of the İstanbul Zone are exposed in the Sünnice Massif, north of Bolu. They comprise the greenschist-facies Ediacaran calc-alkaline bimodal Yellice metavolcanics, which are intruded by the Dirgine granitoid. Amphibolite-facies mafic and subordinate ultramafic rocks of the Çele mafic complex, hitherto termed the Çele meta-ophiolite, include hornblende gneisses of island arc meta-tholeiitic and transitional to calc-alkaline metagabbroic compositions, and were previously thought to be part of the İstanbul Zone basement. Together with minor serpentinized troctolite and harzburgite lenses, they are exposed in a broadly antiformal structure beneath the Yellice metavolcanics. Although these rocks structurally underlie, and, on account of their higher metamorphic grade, were previously thought to be older than the Ediacaran–Cambrian rocks of the İstanbul Zone basement, their oldest isotopic dates are Permian, indicating that they are instead much younger than the overlying rocks, from which they must be divided by an (inferred) İstanbul Zone basal thrust. Instead, these mafic rocks may be linked to the Almacık Complex, and hence interpreted as the underthrust crustal base to a Permo–Triassic active continental margin attached to the Gondwana-derived Sakarya Zone now located south of the İstanbul Zone. Triassic and Jurassic metamorphic ages record compressional events marking a Cimmerian event closing the Palaeotethys Ocean. [Copyright &y& Elsevier]

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The Biga Peninsula, in the north-western part of Western Anatolia, is part of the Sakarya Zone of the Western Pontides and the tectonically overlying Ezine group. The basement rocks are intruded by the early Miocene Kestanbol Pluton and early to middle Miocene calc-alkaline to shoshonitic-ultrapotassic volcanic successions related to postcollisional continental extension. The Kestanbol Pluton mainly comprises monzonite and granodiorite and is cut by shoshonitic-ultrapotassic tephriphonolite dykes. 40Ar-39Ar ages of biotite (21.22 ± 0.09 Ma) and leucite (22.21 ± 0.07 Ma) crystals indicate that tephriphonolite dyke emplacement was coeval with the intrusion of the Kestanbol Pluton during the early Miocene (21.5 ± 1.6, 22.8 ± 0.2 Ma). The geochemical features of the tephriphonolite dykes suggest a phlogopite-bearing mantle source which may originate from a previously metasomatised subcontinental lithospheric mantle source. This mantle source shows the imprints of carbonate-reach oceanic sediment recycling and crustal material contamination processes, which evolved during northward subduction and closure of the northern branch of the Neo-Tethys Ocean beneath the Sakarya zone during the late Cretaceous to Eocene. [ABSTRACT FROM AUTHOR]

Abstract: A unique example of isotopically-dated Devonian metagranitoid (the Çamlık metagranite; ) crops out in the Biga Peninsula, NW Turkey, although its contact relationships with the country rocks and geodynamic setting have remained to be enigmatic so far. Our field work, however, has shown that a number of metagranitoid bodies similar to the Çamlık metagranite intruded the country rocks and developed contact metamorphic zones, consisting of andalusite and calcsilicate hornfelses, garnet–epidote and diopsite–wollastonite skarns. The country rocks of these metagranitoids are made up of regionally metamorphosed metaclastic successions with subordinate metacarbonate–metachert–metabasites (the Kalabak formation), intercalated with tectonic slices of meta-serpentinites. The metagranitoids and the Kalabak formation are collectively termed here the Havran Unit which forms a NE–SW trending, 20km wide and 80km long belt in the Biga Peninsula. The Havran Unit is unconformably overlain by the Late Triassic shallow marine sediments and is in tectonic contact with the Permo-Triassic Karakaya Complex, interpreted as the Palaeotethyan subduction–accretion complex. U–Pb SHRIMP-II and LA–ICP–MS dating of the zircons from four individual plutons yielded crystallization ages ranging from 389.1±2.6 to 401.5±4.8Ma (i.e. Early to Middle Devonian). Based on their geochemical characteristics, the metagranitoids are divided into two groups named the Çamlık and Yolindi metagranitoids. Both granitoids display distinct subduction signature and plot in the volcanic arc granite and post-collisional granite fields on tectonic discrimination diagrams. 87Sr/86Sr( T ) values of these intrusions vary between 0.707367 and 0.715588 while their 143Nd/144Nd( T ) values range from 0.51166 to 0.51187. Very low values of εNd( T ) (from −5.3 to −9.1) imply that the Lower to Mid-Devonian metagranitoids in the Havran Unit might have been generated by partial melting of lower continental crust, probably driven by a major magma underplating event. Delamination and/or slab-breakoff models are considered to be the most plausible mechanisms for the genesis of these metagranitoids. The data obtained in this study has shown for the first time the widespread existence of Devonian and older basement in NW Turkey. Regional geological correlations imply that this basement may be an exotic terrane in the Sakarya Zone, emplaced during the Late Triassic, prior to its amalgamation with the Palaeotethyan Karakaya Complex. [Copyright &y& Elsevier]

High-pressure and ultrahigh-pressure metamorphic rocks crop out widely in the northern Aegean. In many instances their ages and tectonic setting are poorly constrained. Here we report newly discovered high-pressure rocks of continental crustal origin and of Late Cretaceous age southwest of the Marmara Sea. They occur at the contact between the Rhodope-Strandja Zone in the north and the Sakarya Zone in the south. The Kemer Metamorphic Complex is composed mainly of mica schist, calcschist and marble with minor metabasite and serpentinite. The mica schists contain garnet, phengite (3.30-3.44 c.p.f.u), (±) paragonite, albite, epidote, calcite, chlorite and titanite. The high-pressure metamorphic origin of the mica schists is shown by the high silica contents of the white micas and by glaucophane inclusions in garnet. In the metabasites the mineral assemblage is garnet, barroisite, epidote, albite, titanite, quartz, phengite and chlorite; no evidence is let for the former presence of high-pressure minerals. Metamorphic conditions are constrained by mineral equilibria: a 560-640°C temperature at a minimum pressure of 10 kbar. The metamorphism is dated at 64-84 Ma by the Rb-Sr phengite-whole rock method. The Kemer Metamorphic Complex is in tectonic contact with an accretionary ophiolitic mélange consisting of limestone, basalt, serpentinite, greywacke, radiolarian chert and metabasite. Some of the metabasites in the mélange contain Na-amphibole and lawsonite, indicating a subduction origin. The ages of the limestone blocks in the mélange range from Late Triassic to Late Cretaceous and that of the radiolarite blocks from Middle Jurassic to Early Cretaceous, indicating an oceanic domain dating back to Late Triassic at least. The Kemer Metamorphic Complex and the Çetmi Mélange are intruded by a granodiorite of Early Eocene (52 Ma) age and are unconformably covered by a Late Eocene volcano-sedimentary succession. The lithology of the Kemer Metamorphic Complex resembles a continental margin rather than an oceanic accretionary complex. This and the presence of a Late Cretaceous magmatic arc in the north (Sredna-Gora-Pontide) suggest that the Kemer metamorphic rocks were initially deposited on the northern passive margin of the Sakarya Zone, which was subducted under the Rhodope-Strandja continental domain. [ABSTRACT FROM AUTHOR]

Abstract: The boundary between the Gondwana and Laurussia, or a terrane separated from it, is traced by a suture recording the closure of the Rheic ocean in the Pulur, Beyçam and Kurtoğlu areas of the eastern Sakarya Zone of Turkey. Pulur lherzolite has a lower Cr# [100Cr/(Cr+Al)=5−37] of the spinel and slightly enriched flat medium-heavy rare earth element (M-HREE) whole-rock pattern typical for those of the fertile abyssal-type lherzolite. By contrast, the Beyçam harzburgite displays the mineralogical and geochemical features of a moderately depleted residue at a supra subduction zone (SSZ). Some of spinels from the Beyçam peridotites show TiO2 contents (0.15–0.48wt.%) identical to a later interaction with a melt of island-arc tholeiite (IAT) composition. Meta-basalt from the Beyçam area is the representative of such a melt and displays the whole-rock M-HREE pattern of a complementary product of the Beyçam harzburgite. Data presented in this study support the primarily northward directed closure of the Rheic ocean, but suggest that the Variscan basement in the eastern part of the Sakarya Zone consists of mantle peridotites formed in a south-vergent SSZ. This dual polarity of subduction in the Rheic ocean, at least in the second half of its closure, is also favored by the geological structure and lithological diversity of the Variscan rocks. These are: (1) spatial distribution of the peridotites, e.g., SSZ-type harzburgites to the north and abyssal-type lherzolites to the south, (2) lack of high-pressure metamorphic rocks, (3) decrease in the degree of Variscan metamorphism toward the north, and (4) emplacement of Variscan syn-collisional magmatism into the low grade metamorphic rocks to the north. Paleotethys was the other ocean of the region created in the Late Paleozoic. Northward subduction of the Rheic ocean from Early Devonian to Early Carboniferous appears to be the most plausible mechanism responsible for the opening of Paleotethys. In this scenario the Paleotethys is envisaged as a back-arc basin opened to the north in the wake of separated terranes from Laurussia. Onset of trench-Rheic mid-ocean ridge collision in the Early Devonian along the northern margin of Laurussia has been proposed to account for the initiation of SSZ-type subduction to the south. The short duration of this subduction appears insufficient to open a fully developed back-arc basin to the south because the elimination of Rheic mid-ocean ridge to the north accelerated the oceanic closure. [Copyright &y& Elsevier]

Abstract: The Lower to Middle Jurassic Mudurnu formation of the Sakarya Zone (Northern Turkey) was deposited in an extensional basin. This unit crops out along the southern Pontide range and consists of marine sedimentary rocks including debris flows, lignite-bearing clastic rocks and Ammonitico Rosso horizons alternating with mafic and felsic volcanic and volcaniclastic rocks. Magmatic rocks of the Mudurnu formation comprise two compositionally different groups; 1) a mafic group including diabase–microgabbro–basaltic lavas and their pyroclastic equivalents, and 2) a felsic group including granite porphyries and felsic pyroclastic rocks. All the magmatic members of the Mudurnu formation are subalkaline and display a calc-alkaline affinity. They are bimodal, with a significant silica gap between the mafic and felsic members with the exception of a few samples. These magmatic rocks display enrichment in LILE and depletion in Nb, Ta, P and Ti, implying a subduction-related magmatic signature. Melting modelling for the mafic rocks indicates that they originated possibly from subcontinental lithospheric mantle (SCLM) composed of spinel lherzolite. εNd(i) values (+1.5 to +4.3) imply that the mafic volcanic and hypabyssal rocks were possibly derived from a time-integrated LREE-depleted mantle source. The initial Sr and Nd isotope values, and εNd(i) of the felsic hypabyssal rocks are comparable to the mafic ones. The isotope data point to a genetic relationship between the felsic and mafic members. Results obtained from the geochemical modelling of incompatible versus compatible trace elements show that the felsic rocks were derived from the mafic melts by fractional crystallization (FC) process. In the light of their regional geological setting and these geochemical characteristics, we propose that the magmatic rocks of the Mudurnu formation formed in an extensional basin situated on an active and/or just ended subduction zone during the Jurassic period. The Mudurnu formation is a good example of extensional magmatism derived from a depleted mantle source that displayed subduction signatures and that was modified by fluids from a long-lived subduction event. [Copyright &y& Elsevier]

High-pressure low-temperature metamorphic sediments of the Phyllite–Quartzite unit sensu stricto and the Talea Ori group are investigated in the field, microstructurally and by U–Pb dating of detrital zircons to shed light on their palaeogeographic origin. Zircon age spectra with ages >450 Ma of the Phyllite–Quartzite unit sensu stricto indicate a palaeogeographic origin at the northern margin of East Gondwana. In contrast, the lower stratigraphic, siliciclastic formations of the Talea Ori group show a high number of well-rounded Cambrian to Early Carboniferous aged zircons and a Neoproterozoic zircon age spectrum with East Gondwana affinity. Based on the comparison of zircon age data, a possible distal sediment source is the Sakarya Zone at the southern active margin of Eurasia. To reconcile the zircon data with the geological observations we propose different alternative models, or a combination of these, including sediment transport from the Sakarya Zone and/or a westerly source towards the northern margin of Gondwana as well as terrane-displacement of the Sakarya Zone. Also, a palaeogeographic origin of the Talea Ori group at the southern active margin of Eurasia cannot be excluded. This alternative, however, would not be consistent with the usually assumed association of the Talea Ori group with the Plattenkalk unit characterized by a palaeogeographic origin at the northern margin of Gondwana. [ABSTRACT FROM AUTHOR]

In the Pulur complex (Sakarya Zone, Eastern Pontides, Turkey) a low-grade tectonometamorphic unit (Doğankavak) is exposed in three tectonic windows beneath a complex medium-pressure high-temperature metamorphic unit of late Carboniferous age. The thrust plane between both units is transgressively covered by Liassic conglomerates. The Doğankavak unit comprises a sequence of metabasites with MORB-type chemical compositions and phyllites, with subordinate calcareous phyllites, marbles, quarzofeldspathic schists and metacherts. This sequence is interpreted as a former accretionary complex related to the consumption of the Palaeotethys. Mineral parageneses in the metabasites allow for the distinction of two domains with slightly different peak metamorphic conditions, i.e. 375–425 °C/0.5–0.8 GPa (greenschist facies) and 400–470 °C/0.6–1.1 GPa (albite-epidote amphibolite facies). The age of metamorphism is constrained at ~ 260 Ma (early Late Permian) by two Rb-Sr mineral-whole rock ages (hornblende, phengite) and one 40Ar/39Ar single step total fusion age (phengite). In conjunction with previous data on other accretionary complexes in the Sakarya zone in Northern Turkey, the data presented in this study suggest a continuous subduction of the Palaeotethys at least from Early/Late Permian to Late Triassic and a discontinuous preservation of accretion complexes in both space and time. [ABSTRACT FROM AUTHOR]

[Display omitted] • Paleomagnetic results from the Marmara region were reported since the Late Cretaceous. • Middle Eocene-Oligocene sedimentary rocks show counterclockwise rotation of 27°. • The Thrace Basin, İstanbul Zone and the Sakarya Zone were considered as a stable area. • Deformation was found to be associated with the westwards movement of the Anatolian plate. The Marmara region (northwestern Turkey) is located along the Alpine-Himalayan orogenic belt, and consists of tectonic fragments of the İstanbul Zone, the Rhodope Strandja Massif, the Sakarya Zone and the Thrace basin. The Middle Eocene-Lower Miocene sedimentary rocks of the Thrace Basin covers a large area over the Rhodope Strandja Massif. It has been reported that the İstanbul Zone began to migrate southward, away from the Moesia Platform, along the dextral Western Black Sea Fault to the west and the sinistral Western Crimean Fault to the east, post the opening of the Western Black Sea in the Late Cretaceous. The İstanbul Zone and the Sakarya Zone collided after the closure of the Intra-Pontide Ocean in the Early Eocene. In this study, the Upper Cretaceous–Oligocene sedimentary and volcanic rocks, sampled from 90 sites in the Marmara region, were used to examine the deformation history of the Marmara region since Late Cretaceous. Our palaeomagnetic data showed counterclockwise rotation of R ± ΔR = 33.2° ± 9.8° and R ± ΔR = 28.5° ± 6.8° in the Sakarya Zone, for periods of Late Cretaceous and Middle Eocene-Oligocene, respectively. Similar rotations were detected from the Middle Eocene to Oligocene rocks in the Thrace Basin and the İstanbul Zone. Our results indicate that the tectonic entities in this region were underwent a post-Oligocene counterclockwise rotation of ca. 27° due to the westwards movement of the Anatolian plate, regardless of fault affected block deformation. [ABSTRACT FROM AUTHOR]

This provenance study focuses on detrital rutile grains from Jurassic sandstones of the Bayırköy Formation in the central Sakarya Zone. Cr and Nb concentrations of detrital rutile grains in the Jurassic sandstones vary from 18 to 6855 μg/g and 70–13440 μg/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 ℃ with an average temperature of 635 ℃ 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 Sarıcakaya Massif in the central Sakarya Zone seem to be the primary source lithologies for the detrital rutiles in the Jurassic Bayırköy 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. [ABSTRACT FROM AUTHOR]

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 Tepebaşı dacites in the Artvin area, NE Turkey. Zircon U Pb dating analyses revealed a dacite formation age of ~29.8 ± 0.3 Ma. Geochemically, with a K 2 O/Na 2 O 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 (87Sr/86Sr(t) = 0.70460–0.70544, ε 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 ε 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. Unlabelled Image • The Tepebaşı dacite erupted in Oligocene in the Sakarya Zone. • The samples show adakite-like geochemical affinity. • All the findings imply that the dacites originated from a juvenile lower crust. • Heat source is upwelling asthenosphere due to extensional far-field forces. • The melt generation do not require contemporaneous subduction or thickened crust. [ABSTRACT FROM AUTHOR]

• The Early Eocene porphyries are I-type metaluminous in composition. • These porphyries were derived from an enriched mantle domain. • Infiltration of asthenosphere due to slab break-off event triggered partial melting. • The porphyries represent an early stage of extensional tectonic in the Sakarya Zone. 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 well-known 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 Gümüşhane 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 roll-back-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), ε Nd (t) (−1.4 to −1.2) with T DM 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 H 2 O-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. [ABSTRACT FROM AUTHOR]

• Late Cretaceous volcanism of the ESZ erupted in two successive stages. • The successive stages are characterized by mafic and felsic volcanic rocks. • Mafic rocks of both stages were derived from underplated basaltic melts. • Composition of the felsic rocks was controlled by MASH and crustal processes. • Volcanism took place during northward subduction of the northern Neotethys Ocean. The Late Cretaceous Artvin volcanic rocks (LCAVs) from the eastern Sakarya zone (ESZ) of NE Turkey are composed of mafic/basaltic (S1-Çatak and S2-Çağlayan) and felsic/acidic (S1-Kızılkaya and S2-Tirebolu) rock types that occurred in two successive stages: (i) first stage (S1: Turonian–Early Santonian) and (ii) second stage (S2: Late Santonian–Campanian). Clinopyroxene thermobarometric results point that the S2-Çağlayan basaltic rocks have crystallised at higher temperatures and under deeper crustal conditions than those of the S1-Çatak basaltic rocks. The LCAVs show a wide compositional spectrum, ranging from tholeiite to calc-alkaline/shoshonite and are typically represented by a geochemical composition resembling subduction-related arc rocks although the 87Sr/86Sr (i) (0.7044–0.7071) and ɛNd (i) values (−0.63 to + 3.47) as well as 206Pb/204Pb (i) (18.07–18.56), 207Pb/204Pb (i) (15.57–15.62) and 208Pb/204Pb (i) (37.12–38.55) ratios show very limited variation. The parent magmas of the S1-Çatak and S2-Çağlayan mafic volcanic rocks were derived from underplated basaltic melts that originated by partial melting of metasomatised spinel lherzolite and spinel-garnet lherzolite, respectively. It is proposed that the compositions of the S1-Kızılkaya (mainly dacitic) and S2-Tirebolu (rhyolitic to trachytic) felsic rocks were particularly controlled by metasomatised mantle–crust interaction and MASH zone + shallow crustal fractionation processes. Our data, together with data from previous studies, suggest that the S1- and S2-mafic and felsic rocks of the LCAVs (~95–75 Ma) are the products of two-stage volcanic event that took place during the northward subduction of the northern Neotethys Ocean (NNO). [ABSTRACT FROM AUTHOR]

The Sakarya Zone (northern Turkey) is a Gondwana-derived continental block accreted to northern Laurussia during the Carboniferous, and is regarded as the eastward extension of Armorica. Timing of its detachment from the northern margin of Gondwana, thus opening of the Paleo-Tethys, is poorly known. Here, we report on metagranite and amphibolite with Silurian igneous crystallization ages from the Early Carboniferous high-temperature/middle to low-pressure amphibolite-facies metamorphic rocks of the Sarıcakaya Massif within the Sakarya Zone (NW Turkey). The metagranite-amphibolite complex is exposed mainly along the southern margin of the Sarıcakaya Massif over an area of ca. 12 km by 1.5 km. The metagranite contains preserved domains of porphyric texture, indicative of derivation from a former granite porphyry. The amphibolite is devoid of any relict igneous texture. Both the metagranite and amphibolite are crosscut by late up to 50 cm thick felsic veins. Uranium-Pb dating on igneous zircons from both metagranite and amphibolite yielded Silurian ages of ca. 419 ± 6 to 434 ± 7 Ma (2σ), and on those from a felsic vein an age of 319 ± 5 Ma (2σ) (Late Carboniferous). Geochemically, amphibolite displays anorogenic transitional tholeiitic to alkaline signatures. Initial εHf values of the igneous zircons from both metagranite and amphibolite show a large variation with medial values of −16 to −9 and + 3 to +6, respectively. Thus, the protoliths of amphibolite were derived from melts of depleted mantle, and those of the metagranite, on the other hand, from melts of reworked crustal material. We suggest that the Silurian anorogenic magmatism is related to a rifting event at the northern margin of Gondwana leading to the detachment of the Sakarya Zone and hence placing an age on the initial opening of the Paleo-Tethys. This interpretation is based on (i) the presence of Late Silurian to Devonian deep-sea sedimentary blocks in the Paleo-Tethyan accretionary complexes, and (ii) the resemblance of the U Pb age spectra of detrital zircons in the metaclastic sequence of the Sarıcakaya Massif to those of Cambro-Ordovician sandstones in Jordan (Gondwana), and (iii) the local occurrence of anorogenic A-type granites of Late Ordovician-Silurian age in the Anatolide-Tauride Block, a continental block which rifted from Gondwana during the Early Triassic. Wholly anorogenic nature of the Late Ordovician to Silurian igneous rocks in the Sarıcakaya Massif and reported in literature does not support the opening of the Paleo-Tethys as back-arc ocean, as suggested in most paleogeographic reconstructions. • Metagranite and amphibolite in the Sarıcakaya Massif have Silurian crystallization ages. • Amphibolites display anorogenic tholeiitic to alkaline signature. • Protoliths of the amphibolite were derived from the heterogeneous mantle. • Protolith of the metagranite was derived from crustal melts. • Silurian magmatism is probably related to the opening of Paleo-Tethys. [ABSTRACT FROM AUTHOR]