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The classic Neotethyan Ankara Melange formed within the Triassic-Eocene İzmir-Ankara-Erzincan ocean ('N Neotethys'), bordered in central Anatolia by the Kırşehir and Tauride-Anatolide continental units to the south and by the discontinuous Sakarya continent to the northwest. Farther north, the separate Intra-Pontide ocean probably remained partly open until the early Cenozoic. The Neotethyan Ankara Melange developed via phases of intra-oceanic accretion (mainly pre-Aptian), initial continental accretion (i.e. Coniacian (?)), arc magmatism (Upper Cretaceous) and continent-continent collision (Maastrichtian-Early Eocene). Variably dismembered ophiolitic rocks of Early-Middle Jurassic age within the Ankara Melange formed by supra-subduction zone (SSZ) spreading above a generally northward-dipping subduction zone. Volcanic-sedimentary lithologies of Triassic-Cretaceous age represent fragments of oceanic crust including variably sized oceanic seamounts. The oceanic volcanics and sediments accreted from the downgoing plate, whereas the ophiolites represent fragments of the overriding plate. The main driver of accretion in the Ankara area was collision of a large Upper Jurassic-Lower Cretaceous oceanic seamount (probably plume related) and its capping carbonate platform, with Middle-Late Jurassic fore-arc oceanic lithosphere. Intra-oceanic arc and proximal-distal fore-arc basin units developed above the accretionary complex and within remnant Neotethyan ocean to the north during the Upper Cretaceous. After docking with the Sakarya continent, the Ankara Melange was transgressed by continental margin fore-arc and syn-collisional foreland basin sediments (Campanian-Early Eocene). Comparisons with Neotethyan melanges across Anatolia to the Caucasus indicate exceptional development in the type Ankara area. [ABSTRACT FROM AUTHOR]

The temporal distribution of enriched source components and magmatism in continental collision zones provides critical information about mantle dynamic processes in collision-related environments. This paper presents petrology, mineralogy, K-Ar ages and whole-rock major and trace elements, as well as Sr-Nd-Pb-Hf isotopic compositions of Melikler volcanism in Kars Plateau (KP) in the East Anatolia Collision Zone, NE Turkey, with the aim to understand the role of the subducting slab, the origin of magmatism and the geodynamic evolution in the collision-related environments. Our K-Ar dating results show the Melikler volcanism erupted between 5.29 and 1.7 Ma and allows us to divide it into an early (5.29–2.53 Ma) and a late (2.24–1.7 Ma) stage. Major-trace element abundances, isotopic compositions, EC(R) AFC (energy-constrained recharge, assimilation, and fractional crystallisation) and MELTS model calculations of both stages indicate that the least evolved samples were not affected by significant crustal contamination and fractional crystallisation. More evolved samples of the late stage underwent AFC processes with up to 6–9% crustal assimilation; however, those of the early stage were differentiated from a parental magma composition via AFC (up to 2–7.5% crustal assimilation) and experienced magma replenishment at pressure of 0.5 kbar; thus, both early and late stages have experienced open system conditions. The least evolved samples of both stages across the KP have arc-enriched geochemical and isotopic signatures, characterised by prevalent negative Nb–Ta anomalies and moderately radiogenic Sr, unradiogenic Nd-Hf and highly radiogenic Pb isotopic compositions. These primary melts could be derived from a depleted MORB mantle source metasomatised by sediment melt from the subducting Neotethys oceanic slab. Combined trace elemental and isotopic modelling results suggest that the least evolved samples of the early stage were formed by 2–4% melting of an amphibole-bearing garnet lherzolitic mantle source, which was metasomatised by 0.3–0.5% contribution of subducted slab component with a ratio of sediment melt/AOC (altered oceanic crust) melt about 90:10. A depleted lherzolitic mantle source containing apatite and garnet through inputs of 0.6–0.8% melts derived from the subducted oceanic slab, with 5–10% partial melting degree, could produce the least evolved samples of the late stage. Thermobarometric calculations reveal that the least evolved samples of the late stage are derived from the lithosphere-asthenosphere boundary at a depth of 77–82 km; in contrast, those of the early stage are produced from the lithosphere at a depth of 66–69 km. Literature data and the findings obtained from this study indicate that the onset of the Arabian-Eurasian collision may have occurred in the Oligocene and lithospheric dripping caused by the hard collision that occurred around the Late Miocene-Early Pliocene may produce the Melikler volcanic rocks. [ABSTRACT FROM AUTHOR]

Ophiolitic mélanges in Anatolia represent Mesozoic subduction-accretion complexes, which are unusually poor in land-derived coarse-clastic rocks. A segment of the ophiolitic mélange in the Beynam region south of Ankara was studied. The ophiolitic mélange consists of three accretionary units (AUs), which are distinguished by lithology, structure, age and geochemistry. At the base there is a serpentinite mélange, which is overlain by a semi-intact Upper Jurassic ophiolite with boninite geochemistry. The topmost AU consists of ocean-island-like alkali basalts with seamount-derived Triassic shallow-marine limestones and Jurassic radiolarian cherts, which are stratigraphically overlain by Upper Cretaceous fore-arc turbidites. The base of the fore-arc sequence is palaeontologically and isotopically dated to the early to middle Campanian (c. 81 Ma). Detrital zircons from the fore-arc sequence indicate a Late Cretaceous (87–81 Ma) magmatic arc as a source. The formation of the subduction-accretion complex was a two-stage process. The first stage took place during the Late Jurassic – Early Cretaceous, when supra-subduction type oceanic crust was generated, and subduction accretion was intra-oceanic. In the second stage during the Late Cretaceous the subduction jumped inboard, creating an Andean-type convergent margin, and the Jurassic oceanic crust was incorporated in the subduction-accretion complex. The lack of land-derived sandstones in the ophiolitic mélange can be attributed to the intra-oceanic subduction and to the limestone deposition in the upper plate during the main phase of subduction accretion in the Late Jurassic – Early Cretaceous. [ABSTRACT FROM AUTHOR]

The Late Cretaceous accretionary complexes along the İzmir-Ankara-Erzincan (IAE) Neo-Tethyan suture zone in northern Turkey record the subduction–accretion processes of the oceanic lithosphere ranging in age from the Late Triassic to the Late Cretaceous. These accretionary complexes contain fragments of Early and Middle Jurassic metamorphic and non-metamorphic ophiolites. Here, we report new geochemical and geochronological data from the metamorphic and non-metamorphic ophiolitic rocks, which are observed in the Tekelidağ mélange (northern Sivas) of the IAE suture zone. Geochemical characteristics of these rocks point to formation in a subduction-related tectonic setting. Igneous zircons from meta-plagiogranite injected into the meta-ophiolitic rocks yielded zircon U–Pb age of 188 ± 4 Ma (2σ, Early Jurassic), and those from a non-metamorphic plagiogranite crosscutting the non-metamorphic ophiolitic rocks gave an age value of 168 ± 2 Ma (2σ, Middle Jurassic). The igneous crystallization age of the non-metamorphic plagiogranite is identical with the metamorphic age of meta-ophiolitic rocks, which has been dated as Middle Jurassic (166.7 ± 2 Ma, 2σ) by the 40Ar–39Ar method. These age data indicate that (i) the supra-subduction zone ophiolite formation lasted about 20 Ma, (ii) the supra-subduction zone ophiolite and the meta-ophiolitic rocks formed simultaneously in the Middle Jurassic, and (iii) the meta-ophiolitic rocks are remnants of the metamorphosed equivalents of the Early Jurassic supra-subduction zone oceanic crust. The supra-subduction zone ophiolite formation probably occurred over an extended period of time in the Jurassic Neo-Tethys. [ABSTRACT FROM AUTHOR]

Geochemical and isotopic markers of the most primitive basaltic melts allow us to understand the temporal evolution of the lithospheric mantle and geodynamic processes. This paper presents the geochemical, Sr-Nd-Pb-Hf isotopic data, K Ar dating and the petrological evolution of the petrogenesis of the late Miocene-early Pliocene basaltic volcanism observed in the Baltacık-Günkoru region in the northeastern of Lake Van in Eastern Anatolia Collision Zone (EACZ). These data allow us to understand the origin of collision-related magmatism and the geodynamic processes in the late Miocene-early Pliocene in the EACZ. Geochronological age data (K Ar) indicate that basaltic volcanism erupted between ∼7.63 and 5.24 Ma. Major-incompatible trace element contents, Sr Nd isotopic compositions of the studied samples and EC-AFC (energy-constrained recharge, assimilation, and fractional crystallization), and MELTS model calculations point out that basaltic volcanism has undergone fractional crystallization but unaffected crustal contamination. Petrological models created using 87Sr/86Sr, ℇNd and ℇHf isotopic data, together with calculated primary melt compositions of basaltic lavas, indicate that the DMM-type (Depleted Morb Mantle) mantle source is metasomatized by melts rather than fluids derived from subducted oceanic lithosphere. Combined trace element and isotopic modelling results indicate that the calculated primary melts were formed by 2.5–5% melting of a metasomatised spinel-garnet lherzolitic mantle source, including amphibole and 1% residual rutile. This mantle source has been metasomatised by a 1–3% contribution of subducted slab component, with a sediment melt/AOC (altered oceanic crust) melt ratio of about 90:10. Thermobarometric calculations based on calculated primary melts compositions indicate that the lithosphere-asthenosphere boundary (LAB) is a depth of 67 ± 4 km for 7.53–5.24 Ma. Literature data and the findings obtained from this study indicate that the late Miocene to early Pliocene basaltic volcanism in the south of the EACZ) is progressed by the delamination of the mantle lithosphere. This delamination occurred in a fragmented/patched or dripping manner rather than whole-scale delamination in the 3–4 million years between ∼9 Ma and 5–6 Ma. [Display omitted] • Studied basalts erupted in the Late Miocene to Early Pliocene. • LAB under EACZ decreased from Late Miocene to Early Pliocene via delamination. • Delamination emerged fragmented/patched or dripping rather than a whole scale. [ABSTRACT FROM AUTHOR]

The Pozantı-Karsantı ophiolite is one of the well-preserved supra-subduction-zone oceanic lithosphere slices. It offers a unique opportunity to study oceanic crust formation, and to specify subduction initiation processes of the Inner Tauride ocean in the Neo-Tethyan subduction system. The Pozantı-Karsantı ophiolite is tectonically underlain by a subophiolitic metamorphic sole and mélanges. The metamorphic sole is mostly amphibolites that are enriched in light rare earth elements and large-ion lithophile elements, low εNd(t) values (+ 5.4 to + 8.3) and high 207Pb/204Pb ratios, suggesting an OIB-like geochemical affinity. Secondary ion mass spectrometry (SIMS) zircon and titanite U–Pb ages reveal a protolith age at ~ 122.2 ± 1.3 Ma and metamorphic age at 92–90 Ma for the amphibolites. Gabbro and diabase dikes intruded the metamorphic sole rocks and ophiolitic units at ~ 91 to 90 Ma. Their elemental and Sr–Nd–Pb isotopic characteristics indicate a MORB-like mantle source, different from subduction fluid-altered dikes formed at 86.9 ± 3.1 Ma. The temporal-geochemical sequence therefore suggests that the intra-oceanic subduction initiated at 91.9 ± 0.8 Ma within an older lithosphere (> 122 Ma) of the Inner Tauride ocean. Incipient subduction led to forearc (ultra-)slow-spreading seafloor with mafic dikes of 91–90 Ma. The fast switch from MORB- to SSZ-type oceanic spreading might have occurred in less than 3 Myr and marks the inception of a mature subduction zone. [ABSTRACT FROM AUTHOR]

Ophiolitic fragments scattered over a wide area of Central Anatolia exhibit varying degrees of metamorphism, from unmetamorphosed to upper amphibolite facies, although geochemical similarities suggest they are all part of the Central Anatolian Ophiolite (CAO). Magmatic crystallization of oceanic crust in the CAO at ~ 91 Ma coincided with high-grade metamorphism of rocks that underlie the southern, highest grade part of the CAO, raising questions about the tectonic relationship of the ophiolite to underlying metasedimentary and plutonic rocks. New geochronology results show that the 40Ar/39Ar hornblende age of amphibolite-facies metagabbro in the high-grade metamorphic part of the CAO is ~ 87 Ma, similar to hornblende ages from amphibolite in the underlying Niğde metamorphic/plutonic massif. Biotite in a deformed quartzofeldspathic rock associated with high-grade meta-ophiolitic rocks yielded an 40Ar–39Ar age of ~ 78 Ma, similar to biotite ages from the Niğde Massif. Hornblende in gabbro from unmetamorphosed CAO yielded an older 40Ar/39Ar age of ~ 90 Ma, similar to the previously determined crystallization age of the ophiolite. These data indicate that the southern part of the ophiolite was incorporated into and therefore metamorphosed and deformed with the orogenic mid-crust now exposed in the Niğde metamorphic–plutonic complex, whereas the northern, unmetamorphosed part of the ophiolite was obducted onto the continent. This distinct difference in different parts of the ophiolite may indicate oblique collision or irregularities in the continental margin, resulting in part of the ophiolite being incorporated into the orogenic crust and subsequently exhumed and cooled with it, and another part being obducted. [ABSTRACT FROM AUTHOR]

The Beyşehir-Hoyran Nappes, including Mesozoic carbonate platform rocks, deepsea sediments, and ophiolite-related units, crop out extensively on the western limb of the Isparta Angle in the Central Taurides, Turkey. The ophiolite-related rocks are represented by variably serpentinized harzburgitic mantle tectonites, tectonically underlain by a subophiolitic metamorphic sole and mélange. The harzburgitic mantle tectonites and metamorphic sole are intruded by undeformed isolated dikes. Protoliths of the metamorphic sole are similar to within-plate alkali basalts and associated sediments. The isolated dikes were geochemically derived mainly from tholeiitic magma and, to a lesser extent, from alkaline magma. Five isolated dike samples yielded U-Pb ages ranging from 90.8 ± 1.6 Ma to 87.6 ± 2.1 Ma (zircon) and from 102.3 ± 7.4 Ma to 87.5 ± 7.9 Ma (titanite). Seven amphibolite samples yielded U-Pb age ranges of 91.1 ± 2.1-88.85 ± 1.0 Ma (zircon) and 94.0 ± 4.8-90.0 ± 9.4 Ma (titanite) and a 40Ar-39Ar age range of 93.7 ± 0.3-91.4 ± 0.4 Ma (hornblende). U-Pb and 40Ar-39Ar ages of mineral phases with different closure temperatures (~900-500 °C) from the isolated dikes and metamorphic sole rocks are almost identical and overlapping within 1σ, suggesting that both the magmatic growth of oceanic crust and formation of metamorphic sole were contemporaneous and cooled very rapidly. Hence, all the data should be interpreted as the crystallization ages of the ophiolite and metamorphic sole pair. Genesis of suprasubduction zone-type oceanic crust, genesis and exhumation of the metamorphic sole, and postmetamorphic dike emplacement within the Inner Tauride Ocean can be best explained by subduction initiation and rollback processes during the Late Cretaceous based on petrological and geochronological data obtained from the ophiolitic rocks of the Beyşehir-Hoyran Nappes. [ABSTRACT FROM AUTHOR]

• Mersin peridotites show significantly depleted nature. • Peridotites indicate metasomatic interaction with boninitic melts. • Chromitites derived from boninitic melts. • Composition of laurite inclusions indicate low fS 2 conditions. • Subduction initiation formed island arc tholeiites and boninites. The Mersin ophiolite of the Central Taurides in southern Turkey represents an incomplete section of ocean lithosphere consisting from bottom to top of chromitite-bearing mantle peridotites, cumulate dunites, clinopyroxenites, and gabbros with rare pillow lavas covered by bathypelagic sedimentary rocks. The tectonized peridotites are harzburgites with minor dunites. They are strongly melt-depleted peridotites, comprising chromian spinel (Cr-spinel) with medium to high Cr-numbers (Cr#) [100 × Cr/(Cr + Al) = 48–82] and low Al 2 O 3 concentrations (0.05–2.2 wt%). They display concave chondrite-normalized rare earth element (REE) patterns, which we interpret as evidence for their refertilization by boninitic melts in a mantle wedge. Geochemical evidence suggests that the parental magmas of the high-Cr podiform chromitites (Cr# Sp = 71–83) were of boninitic composition. The chromitites host a platinum-group mineral (PGM) assemblage of laurite [Ru# = 64.0–90.7] and Os-Ir alloys, indicating crystallization within a range of low f S 2 conditions (log f S 2 ∼ −2 to −1.3) and a T max of ∼1200 °C. Mineral compositions and geochemical data of the basalts show tholeiitic to alkali compositions. The tholeiites show mildly light REE depleted patterns and high Th/Yb and La/Nb ratios indicate the presence of a sediment component, implying a subduction-related origin. Petrogenetic modeling indicates that the tholeiitic basalts resulted from 20% melting of a spinel-bearing asthenospheric mantle. The initial ε Nd values of 7.2 and 4.9 for two tholeiite samples indicate depleted asthenosphere and more enriched mantle sources probably due to the input of older sediment. A comparison with the data of other ophiolite complexes from southern Turkey suggests subduction-overprinted mantle sources as seen in immature island arcs. The trace element patterns of the alkali basalts are similar to OIB implying an origin unrelated to that of the ophiolite assemblage. The composition of the OIB can be modeled by mixing of magmas from low-degree (1–2%) melting of garnet-bearing lherzolite (GLS) with melt fractions from a spinel-bearing lherzolite (SLS) at variable proportions (GLS/SLS = 7/10–1/10). We propose the following tectono-magmatic model for the petrogenetic evolution of the Mersin ophiolite: i) oceanic ridge spreading generated MORB type magmas (not observed in our sample collection), (ii) melting of deep mantle sources beneath MORB type crust generated OIB-like basalts in Neo-Tethyan oceanic basin, (iii) subduction initiation and formation of an infant forearc basin formed island arc tholeiites and boninites. [ABSTRACT FROM AUTHOR]

Chromite, ultramafic and mafic rocks from Eldivan, Yapraklı, Ayli Dağ, Küre, Elekdağ and Kızılırmak in northern Turkey have been studied to determine their mineral and whole-rock geochemical, and Re-Os isotope geochemical characteristics. Most of the studied peridotites display depleted but commonly V-shaped chondrite-normalized rare-earth element (REE) patterns while some peridotites as well as pyroxenites from all areas exhibit light REE depleted patterns. Olivine (forsterite 82 to 92 mol%) and spinel (chromium number 13 to 63) in the studied peridotites exhibit a wide range of compositions. Compositions of spinels suggest that peridotites from Eldivan, Ayli Dağ and Küre experienced relatively large degrees of partial melting (~ 15 and 19 wt%), whereas those of the Kızılırmak area most likely reflect lower melting degrees (~ 4–6 wt%). Whole-rock and mineral chemical data indicate that the ultramafic rocks are similar to abyssal and supra-subduction zone peridotites. The ultramafic rocks of the investigated areas exhibit a wide range of 187Re/188Os (0.12 to 6.6) and measured 187Os/188Os (0.122–1.14), while the basaltic rocks from Küre, Eldivan and Kızılırmak areas have high 187Re/188Os (128–562) and measured 187Os/188Os (0.724–1.943). On the other hand, chromite from Eldivan, Elekdağ and Kızılırmak show high Os contents (21.81–44.04 ppb) and low 187Re/188Os (0.015–0.818) and 187Os/188Os (0.122–0.133). Re-Os model ages (TChur) for all analyzed samples yielded scattered ages ranging from Jurassic to Proterozoic. Overall, geochemical data are interpreted to reflect different degrees of partial melting, melt – rock interactions and metasomatic effects that produced a heterogeneous mantle in a supra-subduction setting. [ABSTRACT FROM AUTHOR]

Investigating the seismic properties of natural lawsonite (Lws)-bearing blueschist and eclogite is particularly important for constraining the seismic interpretation of subducting oceanic crust based on seismological observations. To achieve this end, we analyzed in detail the mineral fabrics and seismic properties of foliated Lws-blueschist and Lws-eclogites from Sivrihisar Massif in Turkey. In both blueschists and eclogites, the lawsonite fabric is characterized by three different patterns: [0 0 1] axes aligning sub-normal to foliation, and [0 1 0] axes aligning sub-parallel to lineation (normal type); [0 0 1] axes aligning sub-parallel to lineation, and [1 0 0] axes aligning sub-normal to foliation with a girdle sub-normal to lineation (abnormal type); and [0 0 1] axes aligning both sub-normal to foliation and sub-parallel to lineation, [0 1 0] axes aligning sub-parallel to lineation, and [1 0 0] axes aligning sub-normal to foliation (transitional pattern). In contrast, glaucophane and omphacite mostly present consistent axial fabrics with the [0 0 1] axes aligning to lineation. These mineral fabrics produce whole-rock seismic anisotropies with similar patterns. However, the variations in seismic anisotropies are mainly controlled by the rock type, to a lesser extent are determined by the lawsonite fabric type, and to only a small extent are affected by mineral fabric strength. Despite the constructive abnormal-type lawsonite fabric on whole-rock seismic anisotropies, because of their weaker mineral fabric strength (or deformation degree), the abnormal-type Lws-blueschist still exhibit comparatively lower seismic anisotropies than those normal-type Lws-blueschist from other localities. Based on the calculated seismic anisotropies and velocities, we estimated that when oceanic crust transforms from Lws-blueschist to Lws-eclogite with increasing subduction depth, (1) P-wave and max. S-wave polarization anisotropies reduce about 70% and 40%, respectively; and (2) variations of Vp and Vs contrasts relative to mantle peridotites are about −7% to −3% and −8% to −6%, respectively. These results corroborate the important roles of Lws-bearing blueschist and eclogite in interpreting the existence and gradual weakening of low-velocity layers in subducting oceanic crust, during the subduction process. [ABSTRACT FROM AUTHOR]

The Carboniferous compressional deformation of the Arabian Plate has been causally linked with the Hercynian orogeny. However, this epeirogenic movement occurred far from the Arabian plate. Instead, the Gondwana-directed subduction of the Paleo-Tethys oceanic crust may be the controlling factor of the Carboniferous structural development of southeast Turkey (the northern Arabian Plate). The tectonic activity resulted in uplift and widespread erosion of a large area and produced granitic intrusions, metamorphism, folding, and faulting. The compressional event was intermitted by theback-arc spreading of the Neo-Tethys Ocean (Middle Permian-Triassic) that occurred because of the detachment of the Cimmerian supercontinent from the Gondwana margin. The spreading of the Neo-Tethys caused the Arabian Plate to be subjected to extensional tectonism. The tectonic overprints of these epeirogenic events on the structural fabric of southeast Turkey have not been studied in detail. Innovations in subsurface imaging techniques, wireline logs, and sufficient-quality data enable the depiction of the traces of the Carboniferous compression and the subsequent Permian–Triassic regional extension. This study explores the structural remnants of the Carboniferous compression and the Permian–Triassic extension in southeast Turkey and their impact on the Paleozoic petroleum system. In conclusion, the Carboniferous, SW- and EW-oriented compressional forces led to major uplift, inversion, and substantive erosion in southeast Turkey. The regional uplift confined the Silurian-sourced oil exploration activities to a narrower area due to the denudation of the Silurian units towards the Carboniferous Arches. Subsequently, the opening of the Neo-Tethys yielded en-echelon NW and WNW-trending horsts and grabens bounded on both sides by normal faults, resulting in the northeastward thickening of the syn-rift units. The horst structures allow hydrocarbon accumulation in the Ordovician Bedinan Formation sandstones tectonically juxtaposed with the Silurian source rock. [Display omitted] • The mid-Carboniferous compression caused the development of "arch-basin" geometry in southeast Turkey. • The mid-Carboniferous compression confined the Silurian source rock into the narrower area. • The spreading of the Neo-Tethys Ocean resulted in NE-SW-oriented stretching in SE Turkey. • The horst blocks attributed to the Middle Permian–Triassic extension host significant amount of oil. [ABSTRACT FROM AUTHOR]

The Kazdağı Massif was previously considered as the metamorphic basement of the Sakarya Zone, a microcontinental fragment in NW Anatolia. Our new field mapping, geochemical investigations, and radiometric dating lead to a re-evaluation of previous suggested models of the massif. The Kazdağı metamorphic succession is subdivided into two major units separated by a pronounced unconformity. The lower unit (the Tozlu metaophiolite) is a typical oceanic crust assemblage consisting of ultramafic rocks and cumulate gabbros. It is unconformably overlain by a thick platform sequence of the upper group (the Sarıkız unit). The basement ophiolites and overlying platform strata were subjected to a single stage of high-temperature metamorphism under progressive compression during the Alpine orogeny, accompanied by migmatitic metagranite emplacement. Radiometric age data obtained from the Kazdağı metamorphic succession reveal a wide range of ages. Metagranites of the Kazdağı metamorphic succession define a U–Pb discordia upper intercept age of ca. 230 Ma and a lower intercept age of 24.8 ± 4.6 Ma. This younger age agrees with207Pb/206Pb single-zircon evaporation ages of 28.2 ± 4.1 to 26 ± 5.6 Ma. Moreover, a lower intercept age of 28 ± 10 Ma from a leucocratic metagranite supports the Alpine ages of the massif within error limits. Reconnaissance detrital zircon ages constrain a wide range of possible transport and deposition ages of the metasediments in the Sarıkız unit from ca. 120 to 420 Ma. Following high-temperature metamorphism and metagranite emplacement, the Kazdağı sequence was internally imbricated by Alpine compression, and the lowermost Tozlu ophiolite thrust southward onto the Sarıkız unit. Field mapping, internal stratigraphy, and new radiometric age data show that the Sarıkız unit is the metamorphic equivalent of the Mesozoic platform succession of the Sakarya Zone. The underlying metaophiolites are remnants of the Palaeo tethys Ocean, which closed during the early Alpine orogeny. After strong deformation attending nappe emplacement, the unmetamorphosed Miocene Evciler and Kavlaklar granites intruded the tectonic packages of the Kazdağı Massif. During Pleistocene time, the Kazdağı Massif was elevated by EW trending high-angle normal faults dipping to Edremit Gulf, and attained its present structural and topographic position. Tectonic imbrication, erosion and younger E–W-trending faulting were the main cause of the exhumation of the massif. [ABSTRACT FROM AUTHOR]

Abstract: The ophiolites of Amasia in the northwestern part of the Sevan–Akera suture zone (Lesser Caucasus, NW Armenia) correspond to a well-preserved example of a major obduction of oceanic lithosphere over the South Armenian continental block. Our mapping evidenced a series of (1) un-metamorphosed gabbroic oceanic crust, (2) serpentinites and a greenschist grade tectonic melange composed of deformed pillow-basalts, radiolarites and cherts, and (3) a basal slice of garnet amphibolites bearing similar compositional features as the ophiolite. These units are sliced and deformed by post-Eocene thrusting related to the shortening of the suture zone after the collision of the South Armenian Block with Eurasia. 40Ar/39Ar dating on gabbro amphiboles yielded ages of 169.0±4.6 to 175.8±3.9Ma. This age and geochemical composition of ophiolite rocks are similar to those of other ophiolite outcrops in Armenia and NE Turkey. Structural and geochemical analyses undertaken on the garnet amphibolites suggest it to represent the obducted ophiolite metamorphic sole. All these data are in agreement with the presence of a unique ophiolite nappe at the scale of NE Turkey–Armenia originating from a Jurassic intra-oceanic back-arc basin, obducted onto the Armenian–Taurides–Anatolides microblocks in the early Late Cretaceous (c. 90Ma). [Copyright &y& Elsevier]

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

Lawsonite is an abundant hydrous mineral in subducted oceanic crust and sediments and is an important carrier of water (∼11.5 wt%) and trace elements (REE, U, Th, Sr, Pb) into the mantle. Despite its widespread stability at the high-pressure/low-temperature conditions of subduction, it is rarely preserved in the geologic record, particularly in eclogite. Therefore, scarce fresh lawsonite eclogites in which the composition of lawsonite can be directly determined are important geochemical archives of fluid-mediated processes during subduction. Of particular interest are lawsonite-rich veins and layers that may represent former fluid pathways or metasomatic zones and that therefore may record element mobility related to fluid-rock interaction during subduction and/or incipient exhumation. In the Sivrihisar (Turkey) subduction complex, lawsonite-rich veins and layers comprised of ∼30–50 % lawsonite occur at pod margins where lawsonite eclogite has been partially transformed to lawsonite blueschist. To understand the petrogenesis of these lawsonite-rich assemblages, we conducted a petrographic and geochemical study of a representative lawsonite-rich layer at the margin of a meter-scale lawsonite eclogite pod. Bulk rock and mineral major and trace element analyses were conducted along a transect consisting of the lawsonite-rich layer (Lws + Grt + Ph), its glaucophane-rich margin (Gln + Grt + Lws + Ph + Rt), and the lawsonite eclogite host at varying distances from the layer (∼1–2 cm away and >10 cm away). The bulk-rock composition of the lawsonite eclogite indicates a basaltic protolith that experienced interactions with (meta-)sedimentary rocks before or during the crystallization of high-pressure phases such as garnet and rutile. Integrated major and trace element composition and zoning in high-pressure phases indicate that the lawsonite-rich layer and its associated glaucophane-rich margin likely formed at or near peak eclogite-facies conditions (2.2–2.4 GPa, 520 °C) as a result of fluid-mediated processes that scavenged Al 2 O 3 , MnO, Y, Th, HFSE, and REE from the eclogite immediately adjacent to the vein (∼1–2 cm away). Mass balance calculations also suggest the addition of LILE and transition metals (Ni, Cr, Zn) to the lithologic layers at the pod margin; these elements were likely supplied from an external source, such as serpentinites and/or sediments, both of which occur interspersed with mafic rocks in the Sivrihisar complex. Fluid-rock interaction may have also driven changes in fO 2 , as omphacite, glaucophane, lawsonite, and phengite from the pod margin record core-to-rim increases in Fe3+. These changes in bulk composition preferentially stabilized glaucophane-rich (blueschist) and LREE- and LILE-enriched lawsonite-rich assemblages at the pod margin. [ABSTRACT FROM AUTHOR]

• Excessive crustal thickening in central Pontides was revealed by gravity analysis. • A crustal thickness decreases (S to N) represents a transition from continental to oceanic crust. • A crustal thickening (E to W) can be explained by indentation of the Kırşehir Block into the Pontides. The Turkish Pontide orogenic belt belongs to the former Eurasian margin, which is the result of two major successive processes of the closure of the Tethyan oceans: subduction followed by collision. This almost E-W trending large mountain range shows an arc-shaped geometric structure in the northern Turkey. According to previous studies based on geological and paleomagnetic data, oroclinal deformation was proposed as a result of the geodynamic evolution due to the Africa-Eurasia convergence in the region. The aim of study is to determine how this important evolution is expressed in the lithosphere beneath the region by gravity modelling. A Bouguer gravity anomaly map was constructed and from this a gravity model is presented that reveals the general crustal structure underneath the northern Turkey. The results present a significant crustal thickness change that occurs in the N-S and as well as in the E-W directions. From S to N, a significant sharp crustal thickness decrease (~20 km) was found, while from E to W the crustal thickness beneath the Pontides increases by approximately 7 km. While an average thickness of 37 km was calculated in the East, it reached a maximum value of ~44 km in the West. Although the reason for the increase in crustal thickness from north to south is logical in terms of the geodynamic evolution, the increase from east to west is probably caused by the nature of the continental collision. The most plausible explanation is an (oblique) NW indentation of the Kırşehir Block into the Pontides. [ABSTRACT FROM AUTHOR]